Recent acquisitions in the global technical textiles sector include the purchaseof Jackson Products by Kimberly-Clark and the takeover of JKT by MölnlyckeHealth Care. Also, ConvaTec has sold its Unomedical Wound Care and Ophthalmicsbusiness to Aspen Surgical Products Holding. In business news, Ahlstrom has temporarily laid off workers with the aim ofreducing production in line with current demand. A Kuwaiti government unit haspurchased a number of LifeShirt Personnel Management Systems from RAE Systems tomonitor first responders. Lenzing has hiked its fibre prices while alsoannouncing management changes in its Nonwoven Fibers business, and Polymer GroupInc (PGI) has made plans to close its manufacturing plant in North Little Rock,Arkansas, USA. Technology Marketing Inc (TMI) has set up an agreement with Zyvex PerformanceMaterials (ZPM) to distribute the latter's Epovex and Arovex carbonnanotube-based products, and TenCate Protective Fabrics has won an order fromPropper International for its Defender M fabric. Texas Tech University andEnercon Industries, a supplier of plasma treating systems, have joined forces todevelop plasma technology for nonwovens and technical textiles, and the USmilitary has awarded contracts to Solar Integrated Technologies for the supplyand installation of integrated photovoltaic (BIPV) roofing systems for buildingsat US military bases. In investment news, a state-of-the-art fabric laboratoryhas been opened at Texas Tech University to develop protective products. Elmarcoand Oerlikon Neumag have made plans to deliver new nano fiber nonwovensmanufacturing lines to Russia while Fiberweb has made plans to invest in newmelt blown capacity at its facility in Biesheim, France. Freudenberg has openeda plant in the UK for making activated carbon adsorptive products while NonwovenSolutions has invested in a medical graven needle punched nonwovens line.Polymer Group Inc (PGI) has completed the installation of a new line in Mexico,and Sanitars has started up a third hydro entanglement line at its plant inItaly. In the meantime, P2i has opened an office and appointed a regional salesmanager in the USA to increase its business in the country. Recently formed joint ventures include a partnership between FiberVisions andTel Rad Cuyo (TRC) to produce and sell polypropylene fibres in South America.Fiberweb ad Fitesa have established a 50/50 joint venture to supply hygienefabrics in the Americas, and ZPM has teamed up with PolyOne Corporation todevelop carbon nanotube-filled polymer materials. In market news, global consumption of hygiene absorbent products grew to 386 bnunits in 2008, and the Indian government has been advised to focus on more areasin technical textiles.
Source : www.researchandmarkets.com
jeudi 29 octobre 2009
lundi 17 août 2009
Nonwovens For Medical Applications
Innovations in the growing nonwoven medical textiles sector include new products aimed at infection prevention.
Janet Bealer Rodie, Managing Editor
N onwoven textiles play a significant role in the medical sector. The product range includes surgical gowns, masks and other wearable products; surgical drapes, pads; dressings; filtration materials; and implantable textiles such as tissue scaffolds for rebuilding internal organs, among other products. By far, most nonwoven products used outside the body are disposable, single-use articles that have the advantage of not requiring sterilization or cleaning for reuse. However, there are some that can be reused to provide the required function over a limited period of time. In North America, disposable nonwoven medical apparel products alone represent a market totaling nearly $1.46 billion, according to the Association of the Nonwoven Fabrics Industry (INDA), Cary, N.C.; and the market is growing by approximately 1 to 2 percent annually. Globally, the medical nonwoven disposables market is forecast to grow to $12 billion annually by 2010, according to market research firm Global Industry Analysts Inc., San Jose, Calif. Products used inside the body may provide a basis for cells to grow and regenerate tissue — for example, a ligament that has been destroyed or damaged that can be regenerated using a bioabsorbable material that eventually becomes indistinguishable from the ligament itself. Manufacturing processes used to make these medical nonwovens include needlepunch; hydroentangling; spunbond, meltblown and a combination of the two; and thermal bonding. Bicomponent splittable or fibrillated fibers, nanotechnology and fiber modification also play important roles in some recent developments, a number of them involving filtration and barrier technologies. “Nanofibers are becoming very popular for medical textiles used to filter viruses and bacteria,” said Jeff Haggard, vice president of technology at West Melbourne, Fla.-based Hills Inc., a developer of man-made fiber technology and machinery. Hills has been a pioneer in the development of bicomponent fibers as well as meltblown and spunbond technologies and their applications, and it offers meltblown technology that can produce fibers in the range between 25 and 400 nanometers (nm), with an average size of 250 nm. A Collaborative Development Collaborations between research institutes and private industry have yielded numerous important developments in the nonwoven medical textile field. As one example, Pathogen Removal and Diagnostic Technologies Inc. (PRDT), a joint venture between ProMetic BioSciences Ltd., England, and the American Red Cross, Washington, has developed a filter to remove prion protein from red blood cell concentrate. Prions are responsible for degenerative brain diseases such as mad cow disease and other such diseases, including its human cousin and the target of this filter, variant Creutzfeld-Jakob disease. The filter, marketed in the United Kingdom by France-based MacoPharma S.A. under the brand name P-CAPT™, comprises a target-specific affinity resin sandwiched between nonwoven membranes using a calendering process. The membrane development was carried out through a collaboration with the Nonwovens Cooperative Research Center (NCRC) at North Carolina State University (NCSU). The effort brought together prion experts at the University of Maryland, and chemical engineers involved in bioseparations and NCRC nonwovens staff and engineers at NCSU.
Janet Bealer Rodie, Managing Editor
N onwoven textiles play a significant role in the medical sector. The product range includes surgical gowns, masks and other wearable products; surgical drapes, pads; dressings; filtration materials; and implantable textiles such as tissue scaffolds for rebuilding internal organs, among other products. By far, most nonwoven products used outside the body are disposable, single-use articles that have the advantage of not requiring sterilization or cleaning for reuse. However, there are some that can be reused to provide the required function over a limited period of time. In North America, disposable nonwoven medical apparel products alone represent a market totaling nearly $1.46 billion, according to the Association of the Nonwoven Fabrics Industry (INDA), Cary, N.C.; and the market is growing by approximately 1 to 2 percent annually. Globally, the medical nonwoven disposables market is forecast to grow to $12 billion annually by 2010, according to market research firm Global Industry Analysts Inc., San Jose, Calif. Products used inside the body may provide a basis for cells to grow and regenerate tissue — for example, a ligament that has been destroyed or damaged that can be regenerated using a bioabsorbable material that eventually becomes indistinguishable from the ligament itself. Manufacturing processes used to make these medical nonwovens include needlepunch; hydroentangling; spunbond, meltblown and a combination of the two; and thermal bonding. Bicomponent splittable or fibrillated fibers, nanotechnology and fiber modification also play important roles in some recent developments, a number of them involving filtration and barrier technologies. “Nanofibers are becoming very popular for medical textiles used to filter viruses and bacteria,” said Jeff Haggard, vice president of technology at West Melbourne, Fla.-based Hills Inc., a developer of man-made fiber technology and machinery. Hills has been a pioneer in the development of bicomponent fibers as well as meltblown and spunbond technologies and their applications, and it offers meltblown technology that can produce fibers in the range between 25 and 400 nanometers (nm), with an average size of 250 nm. A Collaborative Development Collaborations between research institutes and private industry have yielded numerous important developments in the nonwoven medical textile field. As one example, Pathogen Removal and Diagnostic Technologies Inc. (PRDT), a joint venture between ProMetic BioSciences Ltd., England, and the American Red Cross, Washington, has developed a filter to remove prion protein from red blood cell concentrate. Prions are responsible for degenerative brain diseases such as mad cow disease and other such diseases, including its human cousin and the target of this filter, variant Creutzfeld-Jakob disease. The filter, marketed in the United Kingdom by France-based MacoPharma S.A. under the brand name P-CAPT™, comprises a target-specific affinity resin sandwiched between nonwoven membranes using a calendering process. The membrane development was carried out through a collaboration with the Nonwovens Cooperative Research Center (NCRC) at North Carolina State University (NCSU). The effort brought together prion experts at the University of Maryland, and chemical engineers involved in bioseparations and NCRC nonwovens staff and engineers at NCSU.
The P-CAPT™ filter for removing prion protein from red blood cell concentrate comprises a target-specific affinity resin sandwiched between nonwoven membranes. Photo and schematic courtesy of MacoPharma S.A. Disease Prevention: Multiple-Use Protection Current warnings of a swine flu (H1N1) pandemic must be providing a boon to nonwoven face mask and respirator sales, as people around the world have been shown wearing the masks in an effort to avoid inhaling the virus or spreading possible infection to others. The US Department of Health and Human Services has established a website, http://www.flu.gov/, to provide information about H1N1, avian flu (H5N1) and pandemic flu in general. The website includes a page with information and guidance provided by the Centers for Disease Control and Prevention and the Occupational Safety and Health Administration about the use of masks and respirators to protect against infection. Numerous other websites offered by health organizations and governments around the world also provide relevant information. Mask manufacturers reportedly are escalating their operations to meet the increased demand. “ We’ve gotten some big orders in several countries and are ramping up production,” said John Dolan, CEO, Carey International Ltd., a Westerly, R.I.-based worldwide distributor of a new, multiple-use respirator mask made with a needlepunched, four-ply fabric comprising two outer layers featuring Agion® silver/copper zeolite compounds permanently embedded into the fiber and two inner filtration layers to prevent microbial or other particle penetration. The outer layers have been shown to kill Streptococcus pyogenes, methicillin-resistant Staphylococcus aureus and other bacteria; and inactivate H1N1, H5N1, the common cold and other viruses. The filtration layers comply with National Institute of Occupational Safety and Health N95 and N99 standards. The N99 mask — certified according to European Respiratory Protection Standard EN149:2001 FFP3 level to have 99-percent-or-greater particle filtration effcacy, and also approved by Canadian regulatory agencies — is currently available outside the United States. It has been shown in trials to be effective for at least 28 days, compared with eight to 12 hours effective use for standard single-use masks; and the cost per day of use of the mask is about one-tenth of the cost of a single-use mask. Bill Hurst, director of business development at Wakefield, Mass.-based Agion, said the silver and copper work synergistically to provide faster antimicrobial action than silver alone. “ The ionic exchange between the copper and the sulfur that makes up the bacterium cell membrane helps compromise that membrane,” he said. Conclusion Products such as the P-CAPT blood filter and the N99 respirator mask are but two innovations being offered in the growing nonwoven medical textile market. New fiber and processing technologies as well as collaborative, multidisciplinary efforts will contribute to ongoing product development and further market growth.
BARRIER FABRICS OF SPUNBOND SPECIALTY
The first recorded use of fibers being used in medicine was mentioned in the "Surgical Papyrus" nearly 4000 years ago. The description is of the use of stitches to repair wounds. Of course, it is quite likely that hand-woven cloth or spider webs were used even earlier to stop bleeding. In the "Susanta Sambita" of Indian literature, written approximately 2500 years ago, a variety of suture materials are mentioned including horsehair, leather strips, cotton, animal sinews, and fibrous tree bark.
Today it is unlikely that any man-made fibers exist that have not at some time been considered for use in the medical field. Hospital rooms are floored, curtained, and furnished with similar materials to those in our homes. The staff needs uniforms and patients need clothing. Thus, the largest use of fibers in the medical industry is for items which do not differ significantly in the chemical type or physical specifications for those in our domestic surroundings. For many of these applications, spunbond fabrics are preferred because of their low cost which allows one time use and thus minimizes sterilization procedures.
Non-Wovens
When I first started speaking at this seminar approximately seven years ago, I knew of very little activity directed towards development of special fibers for the areas of medical textiles where spunbond and non-woven fabrics are widely used. Since these textiles are not generally thought to come into contact with body fluids and are generally inexpensive, it did not seem likely that research in this area would make economical sense. Today that has certainly changed in the area of barrier fabrics. With the rapid increase in blood borne diseases such as Hepatitis C, the need to provide medical workers with inexpensive protective garments that provide a barrier to fluids such as water, blood, and alcohol has become critical.
To meet these needs, work is being done in many areas. In some cases special coatings and/or films are being added to fibers and fabrics. In other cases, ingredients are added directly into polymer being used to make the fibers. Melt blown, low denier fibers are being layered in the middle of spunbonds. Bicomponent fibers are also being used in the production of spunbonds and other non-wovens. In other non-wovens, splittable fibers are being used that results in fibers of 0.2 dpf after splitting in a hydroentanglement process. With bicomponent technology it is also feasible to put extremely expensive additives in a polymer sheath on a sheath/core fiber to give the desired surface properties required without the high cost that would be incurred if the additive was included throughout the fiber.
The major technologies used to manufacture non-woven fabric materials are:
Hydroentangling or needling
Carded Thermal bonding
Spunbonding
Meltblowing
All of these processes are used to make non-woven fabrics that compete in the medical marketplace.
Thermal bonded fabrics are generally made by carding staple fiber into a wide web that is then compressed and bonded with heat (Fig. 1). The basic fiber can be made from polypropylene, polyester, or other fibers including bicomponent fibers. When homopolymer fibers are used, thermal bonding can be achieved by adding a low melting material into the web which promotes the bonds or by selective melting of small areas of the sheet which can be seen on the resulting pattern in the material. When bicomponent fibers are used, only the lower melting polymer is used to make the bonds. The most common bicomponent fibers used today for this application are 50/50 sheath/core PP/PET fibers.
Hydroentangled and needled non-woven fabrics are also produced from a carded web of fibers (Fig. 2). However, in these processes the bonding or consolidation of the fiber web into a sheet is accomplished by entangling the fibers by needle punching or water jets (hydroentangling). In the case of hydroentangling, water jets are used for the needling process. A scrim or backing can also be used. The backing may be another non-woven product, a paper product, or even a woven fabric. In the product made in this fashion, the backing material is what generally determines the barrier properties.
Spunbond processes (Fig. 3) are direct from polymer to sheet process with high mass production per production unit that results in very low commercial costs. They are often combined with melt blowing (Fig. 4) to give improved barrier and cover properties with very low fabric weights. Coatings, fibers, and other additives can be applied in secondary processes. The fiber produced in spinning can be either homopolymer or bicomponent. Fiber diameters are often as low as 20 microns for the spunbond process and as low as 2 microns for the meltblown process.
Techniques to Improve Barrier Properties
The "Holy Grail" of barrier fabrics for medical applications would be a low cost non-woven material that is breathable, sterilizable, flexible, and extremely resistant to blood and viral penetration. The following is a discussion of techniques being considered to produce such a fabric.
Increased basis weight
Coatings and films
Lower denier fibers
Meltblown layers
Bicomponent fibers
Sheath/core
Additives
Splittable
The easiest way to increase the barrier properties of a non-woven fabric is to increase the basis weight. In reality this may have little effect on the barrier properties but will definitely have a major effect on the cost and comfort of the fabric or garment. A better approach is to use a more hydrophobic fiber to make the fabric. Another approach is to increase the bonding; however, this will reduce the flexibility of the fabric and can give the garment a stiff, "boardy" feel. For example, Tyvek has excellent barrier properties but is extremely inflexible even in thin sheets.
A similar approach is to add coatings or even bond a film to the non-woven fabric. A continuous film or coating will obviously give excellent barrier properties, but like a heavily bonded fabric, will be stiff and boardy. Generally, a coated fabric will not breathe since normal films are not breathable, but breathable films are being developed. A better approach is to use a coating that is hydrophobic to change the surface tension of the fabric to resist the penetration of water and also fill the pores of the fabric to decrease the size of the openings available for penetration.
Another approach is to lower the denier or size of the fibers used to make the non-woven fabric. This decreases the size of the openings in the fabric assuming the same basis weight and also increases the surface area of the fibers. If the fiber or the coating on them is hydrophobic, this can result in a great improvement in the barrier properties. Although there is some increase in cost with the use of smaller diameter fibers, the major obstacle to going to lower denier fibers in thermal bonded non-wovens has generally been their unavailability due to fiber spinning complications and increased difficulties in carding or web forming of low denier fibers.
Kimberly-Clark had good commercial success with the development of SMS fabrics (Fig. 5). These fabrics have a layer of meltblown fibers sandwiched between two layers of spunbond fabric. The meltblown fibers have a fiber diameter of approximately 2 microns and provide an excellent barrier layer while still leaving the fabric breathable. The major disadvantage to the approach is the cost of the equipment required to produce the fabric and due to the low throughput limitation of the meltblown process.
When this technology is combined with bicomponent spinning, even more enhanced properties can be obtained. For example, a 30/70 sheath/core PE/PP fiber (Fig. 7) can be spun with low denier to give improved softness as well as good barrier properties and cover in very low basis weight fabrics. Because of the low amount of polymers in the sheath, additives such as polytetrafluoride products can be used to improve water penetration properties without a major increase in cost. Also because the PE has a low melting temperature, the process can be run at high processing speeds even with a high mass rate of product per unit length. Bicomponent structures of radiation stable polymers (such as PET & PE in the sheath of a core/sheath structure) are being developed into medical fabrics.
In another bicomponent approach, a splittable fiber such as a segmented pie (Fig. 8) can be provided as a staple fiber, carded, and then hydroentangled. The fibers split apart during the hydroentangling process give a soft, highly pliable fabric with excellent barrier properties. In the near future it is expected that this process will also be combined with spunbond fabrics to improve the cost even further for throwaway, light weight fabrics with excellent barrier properties.
Source : John Hagewood, Ph.D., P.E.
Today it is unlikely that any man-made fibers exist that have not at some time been considered for use in the medical field. Hospital rooms are floored, curtained, and furnished with similar materials to those in our homes. The staff needs uniforms and patients need clothing. Thus, the largest use of fibers in the medical industry is for items which do not differ significantly in the chemical type or physical specifications for those in our domestic surroundings. For many of these applications, spunbond fabrics are preferred because of their low cost which allows one time use and thus minimizes sterilization procedures.
Non-Wovens
When I first started speaking at this seminar approximately seven years ago, I knew of very little activity directed towards development of special fibers for the areas of medical textiles where spunbond and non-woven fabrics are widely used. Since these textiles are not generally thought to come into contact with body fluids and are generally inexpensive, it did not seem likely that research in this area would make economical sense. Today that has certainly changed in the area of barrier fabrics. With the rapid increase in blood borne diseases such as Hepatitis C, the need to provide medical workers with inexpensive protective garments that provide a barrier to fluids such as water, blood, and alcohol has become critical.
To meet these needs, work is being done in many areas. In some cases special coatings and/or films are being added to fibers and fabrics. In other cases, ingredients are added directly into polymer being used to make the fibers. Melt blown, low denier fibers are being layered in the middle of spunbonds. Bicomponent fibers are also being used in the production of spunbonds and other non-wovens. In other non-wovens, splittable fibers are being used that results in fibers of 0.2 dpf after splitting in a hydroentanglement process. With bicomponent technology it is also feasible to put extremely expensive additives in a polymer sheath on a sheath/core fiber to give the desired surface properties required without the high cost that would be incurred if the additive was included throughout the fiber.
The major technologies used to manufacture non-woven fabric materials are:
Hydroentangling or needling
Carded Thermal bonding
Spunbonding
Meltblowing
All of these processes are used to make non-woven fabrics that compete in the medical marketplace.
Thermal bonded fabrics are generally made by carding staple fiber into a wide web that is then compressed and bonded with heat (Fig. 1). The basic fiber can be made from polypropylene, polyester, or other fibers including bicomponent fibers. When homopolymer fibers are used, thermal bonding can be achieved by adding a low melting material into the web which promotes the bonds or by selective melting of small areas of the sheet which can be seen on the resulting pattern in the material. When bicomponent fibers are used, only the lower melting polymer is used to make the bonds. The most common bicomponent fibers used today for this application are 50/50 sheath/core PP/PET fibers.
Hydroentangled and needled non-woven fabrics are also produced from a carded web of fibers (Fig. 2). However, in these processes the bonding or consolidation of the fiber web into a sheet is accomplished by entangling the fibers by needle punching or water jets (hydroentangling). In the case of hydroentangling, water jets are used for the needling process. A scrim or backing can also be used. The backing may be another non-woven product, a paper product, or even a woven fabric. In the product made in this fashion, the backing material is what generally determines the barrier properties.
Spunbond processes (Fig. 3) are direct from polymer to sheet process with high mass production per production unit that results in very low commercial costs. They are often combined with melt blowing (Fig. 4) to give improved barrier and cover properties with very low fabric weights. Coatings, fibers, and other additives can be applied in secondary processes. The fiber produced in spinning can be either homopolymer or bicomponent. Fiber diameters are often as low as 20 microns for the spunbond process and as low as 2 microns for the meltblown process.
Techniques to Improve Barrier Properties
The "Holy Grail" of barrier fabrics for medical applications would be a low cost non-woven material that is breathable, sterilizable, flexible, and extremely resistant to blood and viral penetration. The following is a discussion of techniques being considered to produce such a fabric.
Increased basis weight
Coatings and films
Lower denier fibers
Meltblown layers
Bicomponent fibers
Sheath/core
Additives
Splittable
The easiest way to increase the barrier properties of a non-woven fabric is to increase the basis weight. In reality this may have little effect on the barrier properties but will definitely have a major effect on the cost and comfort of the fabric or garment. A better approach is to use a more hydrophobic fiber to make the fabric. Another approach is to increase the bonding; however, this will reduce the flexibility of the fabric and can give the garment a stiff, "boardy" feel. For example, Tyvek has excellent barrier properties but is extremely inflexible even in thin sheets.
A similar approach is to add coatings or even bond a film to the non-woven fabric. A continuous film or coating will obviously give excellent barrier properties, but like a heavily bonded fabric, will be stiff and boardy. Generally, a coated fabric will not breathe since normal films are not breathable, but breathable films are being developed. A better approach is to use a coating that is hydrophobic to change the surface tension of the fabric to resist the penetration of water and also fill the pores of the fabric to decrease the size of the openings available for penetration.
Another approach is to lower the denier or size of the fibers used to make the non-woven fabric. This decreases the size of the openings in the fabric assuming the same basis weight and also increases the surface area of the fibers. If the fiber or the coating on them is hydrophobic, this can result in a great improvement in the barrier properties. Although there is some increase in cost with the use of smaller diameter fibers, the major obstacle to going to lower denier fibers in thermal bonded non-wovens has generally been their unavailability due to fiber spinning complications and increased difficulties in carding or web forming of low denier fibers.
Kimberly-Clark had good commercial success with the development of SMS fabrics (Fig. 5). These fabrics have a layer of meltblown fibers sandwiched between two layers of spunbond fabric. The meltblown fibers have a fiber diameter of approximately 2 microns and provide an excellent barrier layer while still leaving the fabric breathable. The major disadvantage to the approach is the cost of the equipment required to produce the fabric and due to the low throughput limitation of the meltblown process.
When this technology is combined with bicomponent spinning, even more enhanced properties can be obtained. For example, a 30/70 sheath/core PE/PP fiber (Fig. 7) can be spun with low denier to give improved softness as well as good barrier properties and cover in very low basis weight fabrics. Because of the low amount of polymers in the sheath, additives such as polytetrafluoride products can be used to improve water penetration properties without a major increase in cost. Also because the PE has a low melting temperature, the process can be run at high processing speeds even with a high mass rate of product per unit length. Bicomponent structures of radiation stable polymers (such as PET & PE in the sheath of a core/sheath structure) are being developed into medical fabrics.
In another bicomponent approach, a splittable fiber such as a segmented pie (Fig. 8) can be provided as a staple fiber, carded, and then hydroentangled. The fibers split apart during the hydroentangling process give a soft, highly pliable fabric with excellent barrier properties. In the near future it is expected that this process will also be combined with spunbond fabrics to improve the cost even further for throwaway, light weight fabrics with excellent barrier properties.
Source : John Hagewood, Ph.D., P.E.
lundi 10 août 2009
Nonwovens technologies for medical implants
NON WOVEN TECHNOLOGIES FOR MEDICAL IMPLANTS
Martin Dauner
Institut für Textil- und Verfahrenstechnik
Denkendorf, Germany
Introduction
The 20th century may be regarded as the century of endoprostheses. In preceding times only few people were treated with tissue replacements or even supporting structures inside the body. The application of “biomaterials” was almost limited to sutures, wound dressings and crunches. In some cases gold and ivory have been used for teeth and bone substitutes. In the late 19th, but mainly in the 20th century treatment of completely failed organs became possible by more or less self sufficient artificial implants. These implants require an integration to the surrounding tissue at the interface but take over the function of the replaced organ fully. As examples
endoprostheses like hip or knee prostheses may be mentioned which transfer the applied load passively mimicking geometrically and mechanically the replaced structure. Besides the general demand on the biocompatibility the requirements on these prostheses are appropriate shape, stiffness and strength. Active implants like pacemakers are even more depart from the original organ as they function by electronic or biochemical ways. More or less inert materials like stainless steel and titanium, ceramics and high performance polymers have been introduced successfully as biomaterials. Despite the high degree of function and reliability one has reached today with these implants, there are a wide areas in which artificial organs cannot replace sufficiently the biological tissue.
At the end of the 20th century a new strategy for tissue replacement has been invented called tissue engineering where the rebuilding of the biological organs is promoted actively or passively with the aid of artificial “interactive” devices.
As an early approach the vascular prostheses, made of a porous knitted or woven tube, act as an scaffold for sometimes vascularised connective and scar tissue which penetrates the textile. Clotting blood makes the vessel tight and build the so called neointima as a quite fair substitute for the endothelium. Today one tries to promote the replacement of an injured tissue or organ by a new but identical tissue. Now the implants have to act as a housing and a scaffold rather than a self sufficient artificial organ. The bodies own cells are the main actor. For this application the “weak” textiles, preferably nonwovens, perform best by providing just space. Now resorbable
polymers and ceramics are favorite materials, but in distinct cases non degradable polymers are required.
Where the replacement of tissues by endoprostheses failed, now in the 21th century new cartilage, skin and endocrine organs become realizable by tissue engineering with the help of nonwovens.
2. Nonwoven technology
The applications of nonwovens are characterized usually by their high porosity, large fiber surfaces and the absorbance capability for other substances. Regarding implants the following fields are covered by nonwovens:
· nonwovens as drug carrier or delivery system;
· the use of the (semi-) permeability of nonwovens: patches for defect covering or wound dressing
· nonwovens as scaffolds for tissue engineering.
What makes nonwovens suitable for tissue engineering? Cells need a well defined space as information how to organize themselves. Few as possible foreign material should claim this space. The cells shall arrange themselves in this space but most of them should not attach flat to any surface. Naturally they are generating such a space as the “extracellular matrix” which mainly consists of collagen. This extracellular collagen matrix prepared for scanning electron microscopy presents itself as a nonwoven structure.
For temporarily or long term substitution of the extracellular matrix high voluminous nonwovens are used. They are characterized by a high to very high porosity up to 98 %, i.e. only 2% polymer per volume. The pore size varies depending on the process and the processing parameters from 0,1 μm to 100 μm or even larger. The fiber size is about 1 to 15 μm, to low for flat cell adherence. The strength of these nonwovens is limited but usually sufficent for handling and mechanical stimulation. Their elasticity may be low to high depending on the used polymer, the fiber fineness and the processing.
Various processes for the manufacturing of nonwovens are known. Often the standard processes are to be modified for the specific need of implants. One mainfactor is the size of the device. Commercial nonwoven processes have high output rates. For example a typical melt blow equipment of 4 m width and 4000 capillaries extrude 400 kg polymer per hour. We havedeveloped an one capillary melt blow tool for implants. Its production rate is 120 g/h.
2.1 Staple fiber nonwoven process
The staple fiber nonwoven process is the conventional process which is known from nonwovens of natural fibers as wool and cotton. For internal medical applications man made fibers are used. Polymers are melt or solution spun to filaments which are stretched to high orientation. The filaments are cut to staple fibers of 20 to 80 mm length, carded, crosslapped and finally strengthened. For implant applications where high volume nonwovens are required, calendering as well as chemical or thermobonding are less suitable because they reduce the porosity. We prefer a needling process which interlace the fibers by barbed needles. This process is possible with flat sheets as well as with tubes.
For fiber stretching as well as for the carding usually spinning preparations are required which are not easily extracted from the final nonwoven. Thus we are washing the fibers after cutting. The use of non toxic spinning preparation is obligatory anyway. At the card we use an electrostatic discharging which allows the production at limited speed without spinning preparation.
The stable fiber nonwoven process is an expensive and time consuming process with many production steps. As a special feature it offers to mix materials so as degradable with non degradable or different degradable polymers with graded degradation times.
2.2 Spunbonding process
To avoid the use of spinning preparations we have introduced a spunbonding process with online needling. Usually spunbonded nonwovens are strengthened by calendering or melting adhesives and solved bonding agents respectively. These processing aids reduce the porosity, change the surface properties of the nonwoven and impair the biocompatibility.
In the spunbonding process polymer is spun to filaments which are stretched online by an draw off jet and laid on a conveyor belt which delivers the nonwoven to the needling machine. If required cold calendering may provide the light nonwoven with some strength for the needle punching.
Flat high porous nonwovens can be produced very economically. Spinning preparations are not required. Any fiber forming thermoplastic polymer may be used; crystalline polymers are preferred.
Using degradable polymers like polyglycolic acid or polylactides we have found that they may shrink dramatically when they are brought into physiological environment in vitro or in vivo, i.e. 37°C in watery solution. This could be shown to be due to a depression of the glass transition of the polymers below 37°C. Shrinkage means not only reduction in size but more important a change in porosity and pore sizes. We are actually up to investigate the spinning parameters to eliminate this shrinkage.
2.3 Melt blown process
The melt blown process is the most simple way to produce nonwovens. A molten polymer is delivered through capillaries like at the filament spinning. A high speed hot air stream is pulling out the polymer from the capillaries which forms fine fibrils by that way. The fibrils are delivered to a support system by the air stream. They stick together due to residual heat and motion energy generating at once the almost finished nonwoven.
The melt blown system is unique to form complex shaped implants like tubular prostheses or even an auricle. For tubular prostheses the fibrils are wound on an rotating mandril. The auricle is formed on an accordingly shaped matrix which is to be moved by a 6 axes system to have an even distribution and orientation of fibrils.
All fiber forming polymers but especially elastomeric materials like polyurethanes can be processed. But as the orientation and crystallinity of the polymer molecules are generated only partially, shrinkage may occur as with the spunbonding process.
2.4 Solution spraying process
The solution spraying process have been developed mainly for small scale medical applications as the large amount of solvents is a limitation under economical and ecological views.
The process resembles the melt blown process. The solved polymer is delivered through a capillary and pulled out by an air stream which evaporates the solvent by vacuum produced bythe jet injection effect. Fibrils are formed which stick together by residual solvent. The processing can be performed at ambient temperature.
The process has been developed for tubular prostheses but is extended now to flat sheets. It could be shown that amorphous and elastomeric polymers are best suitable for this process. But in any case they must be soluble in any reasonable solvent.
The size of the fibrils is about 1 μm and lower; the nonwoven is comparably tight with pore sizes of 0,1 μm to 10 μm and a porosity of 70 – 90%.
2.5 Wet laid nonwoven
One of the conventional nonwoven processes, the wet laid process, is rarely used for medical devices.
Fibers are dispersed and isolated in a liquid, usually water. A conveyor belt takes the randomly oriented fibers off the liquid. The fibers are dried and bound usually thermally or chemically. This process may be used to produce nonwoven scaffolds from natural polymers.
3 Materials
General requirement on materials for implants is their biocompatibility which is to be determined for each application. Thermoplastic or soluble polymers can be processed to nonwovens. They are to be chosen depending on the intended application and the process. The spunbonded and the stable fiber process require crystalline polymers to avoid shrinkage during sterilization and at use. Solution spraying works best with amorphous polymers because residual solvent sticks in the amorphous phases and glue the fibrils together. Elastomeric polymers are preferably processed by melt blown or solution spraying.
3.1 Non resorbable polymers
Polyethyleneterephthalate (PET) and polypropylene (PP) are the most used polymers in the melt spinning processes as for technical applications. High elastic structures are produced from segmented thermoplastic polyurethanes both by melt blown and by solution spraying.
3.2 Resorbable polymers
A great progress has been made with the synthesis of resorbable polymers first for suture materials.
Resorbable materials can dissolve from the body - or even from the in-vitro cell culture - when a new functional tissue has grown. Preferably the hydrolysable polyesters of the a-hydroxycarbonic acids are used: polyglycolic acid (PGA) and polylactic acid (PLA) and also a number of copolymers. All these polymers are melt processable but polyglycolic acid should not be processed by solution spraying.
The degradation rate (loss of strength) of these polymers range from 2 weeks (PGA)
to over 52 weeks (P-L-LA). Typically the resorption – the complete loss of mass – takes three more times. The long degradation time of the poly-L-lactic acid (P-L-LA) can be reduced by g-irradiation as it is used for sterilization.
3.3 Shrinkage
Shrinkage turned out to be an important problem of nonwovens for implants namely with resorbable polymers. Shrinkage reduces the porosity and the pore size and it changes the dimensions which must be avoided for shaped implants.
In the body environment the glass transition of these resorbable polymers is depressed to about the body temperature due to water uptake. Shrinkage is related to the amorphous phases in a polymeric material and to residual stresses, which are produced by the fiber spinning. It happens at heating above the glass transition because secondary intermolecular bonds become weak. It does not occur at crystalline materials when the binding forces in the crystalline phases are sufficiently strong. That means, shrinkage can not be avoided for amorphous polymers if they are under internal stresses; fully oriented (highly crystalline) yarns do not shrink; the
shrinkage can be avoided for pre-oriented yarns by thermal treatment.
With the high oriented yarns used for staple fiber nonwovens shrinkage can be fully avoided. In the solution spraying process the low orientation of the polymer molecules and their possible complete relaxation during the processing allows the production of nonwovens free of shrinkage.
Nonwovens by the spunbonding process may show important shrinkage depending on the polymer and the process parameters. While with poly-L-lactide we succeeded to avoid the shrinkage by high orientation and crystallisation during the process; with polyglycolide up to 50 % shrinkage occurs. Additional thermal treatment is required to stabilize the nonwoven; yet it changes the nonwoven structure as well.
Melt blown nonwovens of resorbable polymers show the most dramatic shrinkage. Some copolymers shrink already during processing. The thermal treatment of complex shaped prostheses is rather complicated, sometimes impossible. So, hard work is still required to learn more about the shrinkage effect and how to avoid it.
4 Applications
Nonwovens may be used as implants at any application where the healing and rebuilding of the bodies own tissue shall be promoted. The process to be chosen depends on the application and the required way of interaction. The application of nonwovens range from patches from polyurethane for dura mater replacement which are produced by solution spraying and vascular prostheses as well from polyurethane by solution spraying over hemostyptic nonwovens from resorbable polymers to scaffolds for tissue engineering. Examples of the latter most fascinating field shall be given more in detail:
4.1 Tracheal prostheses
Tracheal prostheses were produced first by the solution spraying technology. The tubular nonwoven was reinforced by integrated horse-shoe shaped clasps according to the cartilage clasps of the natural trachea. The pore size on the outer surface allowed the ingrowth not only of tissue but of small blood vessels. The surface in the lumen had a porosity lower than 0,1 μm in order to avoid the penetration of bacteria from the contaminated breathing air.
In the 1990 the strategy was changed to a biohybrid tracheal prosthesis which shall have the natural layer of ciliated cells on the lumen surface. Bacteria tightness is no longer required. For hybridisation the prosthesis will be implanted in a well vascularized area of the patient’s body. After ingrowth of tissue which is to cover the inner surface of the prosthesis, in-vitro cultivated ciliated epithelial cells are injected into the lumen where they seed on the inner surface. As soon as the cells have fixed themselves the prosthesis will be put in situ to replace the damaged tracheal segment.
For this application larger pore sizes are necessary to allow the complete penetration of body tissue. These pore sizes of about 150 μm could not be produced accordingly by solution spraying process. Thus the modified melt blowing process has been developed.
4.2 Cartilage repair: scaffolds for in-vitro hybridisation
In cell cultures cells grow only as a monolayer on the surface of the culture dish. If they are adapted to grow in the 3rd dimension they still lack of information of the intended shape and size for the transplant. The nonwoven offers this information besides a large (fiber) surface.
Today resorbable nonwoven scaffolds are mainly processed by staple fiber process which offer a high pore volume, fine fibers and no shrinkage. The needle punching assures the required strength. A sufficient number of cartilage cells is brought into the nonwoven structure, where they attach to the fibers and start to produce collagen and other components of the extracellular matrix. Specific articular cartilage can be preferably generated by additional mechanical stimulation. When the new cartilage is formed the polymer should resorb prior to the implantation of the cartilage.
A scaffold for the auricle shall be formed by melt blowing. Yet here the problem of shrinkage still limitates the use of resorbable polymers.
4.3 Biohybrid liver assist device
The liver has some ability to recover. At acute liver failure a temporary assist device bridges the time for recovery or the time to get a liver transplant. The purification of blood at the renal dialysis is accomplished extracorporally only by technical means.
The more demanding tasks of the liver in blood purification, protein synthesis and other metabolic activities can not be simulated by artificial techniques. Here an extracorporal system was designed using liver cells which undertake the elimination and/or conjugation of metabolites.
In a dialysator housing a melt blow polyurethane nonwoven containing polypropylene capillaries is arranged. Hepatocytes will be cultivated in the nonwoven. Through the PP capillaries the hepatocytes are provided with oxygen. The blood flow is directed through the nonwoven passing the liver cells. The liver cells metabolize toxic substances of the blood. The blood will be delivered back purified to the patient’s body.
Martin Dauner
Institut für Textil- und Verfahrenstechnik
Denkendorf, Germany
Introduction
The 20th century may be regarded as the century of endoprostheses. In preceding times only few people were treated with tissue replacements or even supporting structures inside the body. The application of “biomaterials” was almost limited to sutures, wound dressings and crunches. In some cases gold and ivory have been used for teeth and bone substitutes. In the late 19th, but mainly in the 20th century treatment of completely failed organs became possible by more or less self sufficient artificial implants. These implants require an integration to the surrounding tissue at the interface but take over the function of the replaced organ fully. As examples
endoprostheses like hip or knee prostheses may be mentioned which transfer the applied load passively mimicking geometrically and mechanically the replaced structure. Besides the general demand on the biocompatibility the requirements on these prostheses are appropriate shape, stiffness and strength. Active implants like pacemakers are even more depart from the original organ as they function by electronic or biochemical ways. More or less inert materials like stainless steel and titanium, ceramics and high performance polymers have been introduced successfully as biomaterials. Despite the high degree of function and reliability one has reached today with these implants, there are a wide areas in which artificial organs cannot replace sufficiently the biological tissue.
At the end of the 20th century a new strategy for tissue replacement has been invented called tissue engineering where the rebuilding of the biological organs is promoted actively or passively with the aid of artificial “interactive” devices.
As an early approach the vascular prostheses, made of a porous knitted or woven tube, act as an scaffold for sometimes vascularised connective and scar tissue which penetrates the textile. Clotting blood makes the vessel tight and build the so called neointima as a quite fair substitute for the endothelium. Today one tries to promote the replacement of an injured tissue or organ by a new but identical tissue. Now the implants have to act as a housing and a scaffold rather than a self sufficient artificial organ. The bodies own cells are the main actor. For this application the “weak” textiles, preferably nonwovens, perform best by providing just space. Now resorbable
polymers and ceramics are favorite materials, but in distinct cases non degradable polymers are required.
Where the replacement of tissues by endoprostheses failed, now in the 21th century new cartilage, skin and endocrine organs become realizable by tissue engineering with the help of nonwovens.
2. Nonwoven technology
The applications of nonwovens are characterized usually by their high porosity, large fiber surfaces and the absorbance capability for other substances. Regarding implants the following fields are covered by nonwovens:
· nonwovens as drug carrier or delivery system;
· the use of the (semi-) permeability of nonwovens: patches for defect covering or wound dressing
· nonwovens as scaffolds for tissue engineering.
What makes nonwovens suitable for tissue engineering? Cells need a well defined space as information how to organize themselves. Few as possible foreign material should claim this space. The cells shall arrange themselves in this space but most of them should not attach flat to any surface. Naturally they are generating such a space as the “extracellular matrix” which mainly consists of collagen. This extracellular collagen matrix prepared for scanning electron microscopy presents itself as a nonwoven structure.
For temporarily or long term substitution of the extracellular matrix high voluminous nonwovens are used. They are characterized by a high to very high porosity up to 98 %, i.e. only 2% polymer per volume. The pore size varies depending on the process and the processing parameters from 0,1 μm to 100 μm or even larger. The fiber size is about 1 to 15 μm, to low for flat cell adherence. The strength of these nonwovens is limited but usually sufficent for handling and mechanical stimulation. Their elasticity may be low to high depending on the used polymer, the fiber fineness and the processing.
Various processes for the manufacturing of nonwovens are known. Often the standard processes are to be modified for the specific need of implants. One mainfactor is the size of the device. Commercial nonwoven processes have high output rates. For example a typical melt blow equipment of 4 m width and 4000 capillaries extrude 400 kg polymer per hour. We havedeveloped an one capillary melt blow tool for implants. Its production rate is 120 g/h.
2.1 Staple fiber nonwoven process
The staple fiber nonwoven process is the conventional process which is known from nonwovens of natural fibers as wool and cotton. For internal medical applications man made fibers are used. Polymers are melt or solution spun to filaments which are stretched to high orientation. The filaments are cut to staple fibers of 20 to 80 mm length, carded, crosslapped and finally strengthened. For implant applications where high volume nonwovens are required, calendering as well as chemical or thermobonding are less suitable because they reduce the porosity. We prefer a needling process which interlace the fibers by barbed needles. This process is possible with flat sheets as well as with tubes.
For fiber stretching as well as for the carding usually spinning preparations are required which are not easily extracted from the final nonwoven. Thus we are washing the fibers after cutting. The use of non toxic spinning preparation is obligatory anyway. At the card we use an electrostatic discharging which allows the production at limited speed without spinning preparation.
The stable fiber nonwoven process is an expensive and time consuming process with many production steps. As a special feature it offers to mix materials so as degradable with non degradable or different degradable polymers with graded degradation times.
2.2 Spunbonding process
To avoid the use of spinning preparations we have introduced a spunbonding process with online needling. Usually spunbonded nonwovens are strengthened by calendering or melting adhesives and solved bonding agents respectively. These processing aids reduce the porosity, change the surface properties of the nonwoven and impair the biocompatibility.
In the spunbonding process polymer is spun to filaments which are stretched online by an draw off jet and laid on a conveyor belt which delivers the nonwoven to the needling machine. If required cold calendering may provide the light nonwoven with some strength for the needle punching.
Flat high porous nonwovens can be produced very economically. Spinning preparations are not required. Any fiber forming thermoplastic polymer may be used; crystalline polymers are preferred.
Using degradable polymers like polyglycolic acid or polylactides we have found that they may shrink dramatically when they are brought into physiological environment in vitro or in vivo, i.e. 37°C in watery solution. This could be shown to be due to a depression of the glass transition of the polymers below 37°C. Shrinkage means not only reduction in size but more important a change in porosity and pore sizes. We are actually up to investigate the spinning parameters to eliminate this shrinkage.
2.3 Melt blown process
The melt blown process is the most simple way to produce nonwovens. A molten polymer is delivered through capillaries like at the filament spinning. A high speed hot air stream is pulling out the polymer from the capillaries which forms fine fibrils by that way. The fibrils are delivered to a support system by the air stream. They stick together due to residual heat and motion energy generating at once the almost finished nonwoven.
The melt blown system is unique to form complex shaped implants like tubular prostheses or even an auricle. For tubular prostheses the fibrils are wound on an rotating mandril. The auricle is formed on an accordingly shaped matrix which is to be moved by a 6 axes system to have an even distribution and orientation of fibrils.
All fiber forming polymers but especially elastomeric materials like polyurethanes can be processed. But as the orientation and crystallinity of the polymer molecules are generated only partially, shrinkage may occur as with the spunbonding process.
2.4 Solution spraying process
The solution spraying process have been developed mainly for small scale medical applications as the large amount of solvents is a limitation under economical and ecological views.
The process resembles the melt blown process. The solved polymer is delivered through a capillary and pulled out by an air stream which evaporates the solvent by vacuum produced bythe jet injection effect. Fibrils are formed which stick together by residual solvent. The processing can be performed at ambient temperature.
The process has been developed for tubular prostheses but is extended now to flat sheets. It could be shown that amorphous and elastomeric polymers are best suitable for this process. But in any case they must be soluble in any reasonable solvent.
The size of the fibrils is about 1 μm and lower; the nonwoven is comparably tight with pore sizes of 0,1 μm to 10 μm and a porosity of 70 – 90%.
2.5 Wet laid nonwoven
One of the conventional nonwoven processes, the wet laid process, is rarely used for medical devices.
Fibers are dispersed and isolated in a liquid, usually water. A conveyor belt takes the randomly oriented fibers off the liquid. The fibers are dried and bound usually thermally or chemically. This process may be used to produce nonwoven scaffolds from natural polymers.
3 Materials
General requirement on materials for implants is their biocompatibility which is to be determined for each application. Thermoplastic or soluble polymers can be processed to nonwovens. They are to be chosen depending on the intended application and the process. The spunbonded and the stable fiber process require crystalline polymers to avoid shrinkage during sterilization and at use. Solution spraying works best with amorphous polymers because residual solvent sticks in the amorphous phases and glue the fibrils together. Elastomeric polymers are preferably processed by melt blown or solution spraying.
3.1 Non resorbable polymers
Polyethyleneterephthalate (PET) and polypropylene (PP) are the most used polymers in the melt spinning processes as for technical applications. High elastic structures are produced from segmented thermoplastic polyurethanes both by melt blown and by solution spraying.
3.2 Resorbable polymers
A great progress has been made with the synthesis of resorbable polymers first for suture materials.
Resorbable materials can dissolve from the body - or even from the in-vitro cell culture - when a new functional tissue has grown. Preferably the hydrolysable polyesters of the a-hydroxycarbonic acids are used: polyglycolic acid (PGA) and polylactic acid (PLA) and also a number of copolymers. All these polymers are melt processable but polyglycolic acid should not be processed by solution spraying.
The degradation rate (loss of strength) of these polymers range from 2 weeks (PGA)
to over 52 weeks (P-L-LA). Typically the resorption – the complete loss of mass – takes three more times. The long degradation time of the poly-L-lactic acid (P-L-LA) can be reduced by g-irradiation as it is used for sterilization.
3.3 Shrinkage
Shrinkage turned out to be an important problem of nonwovens for implants namely with resorbable polymers. Shrinkage reduces the porosity and the pore size and it changes the dimensions which must be avoided for shaped implants.
In the body environment the glass transition of these resorbable polymers is depressed to about the body temperature due to water uptake. Shrinkage is related to the amorphous phases in a polymeric material and to residual stresses, which are produced by the fiber spinning. It happens at heating above the glass transition because secondary intermolecular bonds become weak. It does not occur at crystalline materials when the binding forces in the crystalline phases are sufficiently strong. That means, shrinkage can not be avoided for amorphous polymers if they are under internal stresses; fully oriented (highly crystalline) yarns do not shrink; the
shrinkage can be avoided for pre-oriented yarns by thermal treatment.
With the high oriented yarns used for staple fiber nonwovens shrinkage can be fully avoided. In the solution spraying process the low orientation of the polymer molecules and their possible complete relaxation during the processing allows the production of nonwovens free of shrinkage.
Nonwovens by the spunbonding process may show important shrinkage depending on the polymer and the process parameters. While with poly-L-lactide we succeeded to avoid the shrinkage by high orientation and crystallisation during the process; with polyglycolide up to 50 % shrinkage occurs. Additional thermal treatment is required to stabilize the nonwoven; yet it changes the nonwoven structure as well.
Melt blown nonwovens of resorbable polymers show the most dramatic shrinkage. Some copolymers shrink already during processing. The thermal treatment of complex shaped prostheses is rather complicated, sometimes impossible. So, hard work is still required to learn more about the shrinkage effect and how to avoid it.
4 Applications
Nonwovens may be used as implants at any application where the healing and rebuilding of the bodies own tissue shall be promoted. The process to be chosen depends on the application and the required way of interaction. The application of nonwovens range from patches from polyurethane for dura mater replacement which are produced by solution spraying and vascular prostheses as well from polyurethane by solution spraying over hemostyptic nonwovens from resorbable polymers to scaffolds for tissue engineering. Examples of the latter most fascinating field shall be given more in detail:
4.1 Tracheal prostheses
Tracheal prostheses were produced first by the solution spraying technology. The tubular nonwoven was reinforced by integrated horse-shoe shaped clasps according to the cartilage clasps of the natural trachea. The pore size on the outer surface allowed the ingrowth not only of tissue but of small blood vessels. The surface in the lumen had a porosity lower than 0,1 μm in order to avoid the penetration of bacteria from the contaminated breathing air.
In the 1990 the strategy was changed to a biohybrid tracheal prosthesis which shall have the natural layer of ciliated cells on the lumen surface. Bacteria tightness is no longer required. For hybridisation the prosthesis will be implanted in a well vascularized area of the patient’s body. After ingrowth of tissue which is to cover the inner surface of the prosthesis, in-vitro cultivated ciliated epithelial cells are injected into the lumen where they seed on the inner surface. As soon as the cells have fixed themselves the prosthesis will be put in situ to replace the damaged tracheal segment.
For this application larger pore sizes are necessary to allow the complete penetration of body tissue. These pore sizes of about 150 μm could not be produced accordingly by solution spraying process. Thus the modified melt blowing process has been developed.
4.2 Cartilage repair: scaffolds for in-vitro hybridisation
In cell cultures cells grow only as a monolayer on the surface of the culture dish. If they are adapted to grow in the 3rd dimension they still lack of information of the intended shape and size for the transplant. The nonwoven offers this information besides a large (fiber) surface.
Today resorbable nonwoven scaffolds are mainly processed by staple fiber process which offer a high pore volume, fine fibers and no shrinkage. The needle punching assures the required strength. A sufficient number of cartilage cells is brought into the nonwoven structure, where they attach to the fibers and start to produce collagen and other components of the extracellular matrix. Specific articular cartilage can be preferably generated by additional mechanical stimulation. When the new cartilage is formed the polymer should resorb prior to the implantation of the cartilage.
A scaffold for the auricle shall be formed by melt blowing. Yet here the problem of shrinkage still limitates the use of resorbable polymers.
4.3 Biohybrid liver assist device
The liver has some ability to recover. At acute liver failure a temporary assist device bridges the time for recovery or the time to get a liver transplant. The purification of blood at the renal dialysis is accomplished extracorporally only by technical means.
The more demanding tasks of the liver in blood purification, protein synthesis and other metabolic activities can not be simulated by artificial techniques. Here an extracorporal system was designed using liver cells which undertake the elimination and/or conjugation of metabolites.
In a dialysator housing a melt blow polyurethane nonwoven containing polypropylene capillaries is arranged. Hepatocytes will be cultivated in the nonwoven. Through the PP capillaries the hepatocytes are provided with oxygen. The blood flow is directed through the nonwoven passing the liver cells. The liver cells metabolize toxic substances of the blood. The blood will be delivered back purified to the patient’s body.
Spunbonding lines: Type overview
There are three different types of spunbonding lines: one, two and three beam systems, differing in working speed and total throughput.
Single beam spundbond line
For production speeds up to 250 m/min
For production speeds up to 250 m/min
Double beam spunbond line
For production speeds up to 450 m/min
For production speeds up to 450 m/min
Three beam spunbond line
For production speeds up to 800 m/min
For production speeds up to 800 m/min
The spunbonding process is the most economic way of making nonwoven materials from a polymer in one step. Endless filaments in combination with a uniform discharge guarantee low grammage whilst retaining strength.
mardi 21 juillet 2009
Un blog à découvrir d'urgence...
[...07/20/2009Oerlikon Textile up for sale http://blog.nonwovenslive.com/
Oerlikon Textile – the world’s largest manufacturer of textile machinery and nonwovens equipment – is up for sale, just two years after being purchased and changing its name from Saurer.Vice-president for Oerlikon Textile Corporate Communications André Wissenberg confirmed that the Swiss group is seeking new ownership in order to concentrate on its smaller, but potentially more lucrative, divisions. These produce machinery for making thin-film silicon solar modules and coatings and industrial vacuum systems...]
vendredi 19 juin 2009
lundi 15 juin 2009
Elaboration de non tissés à base de fibres d’alfa
Résumé
Une étude a été réalisée pour produire un non tissé à base de fibres d’alfa. Ce non tissé a été
utilisé comme renfort pour remplacer des étoffes à base de fibres de verre et de carbone
habituellement utilisées pour ces applications et qui ont un coût très élevé influençant le coût
final du produit fini.
Une étude a été réalisée pour produire un non tissé à base de fibres d’alfa. Ce non tissé a été
utilisé comme renfort pour remplacer des étoffes à base de fibres de verre et de carbone
habituellement utilisées pour ces applications et qui ont un coût très élevé influençant le coût
final du produit fini.
Introduction
Les fibres végétales sont des matériaux biodégradables et légers. Ces caractéristiques leur
donnent la possibilité d’être utilisées comme couche de renfort dans les structures composites.
Le coton est la fibre végétale la plus utilisée dans le monde. D’autres fibres végétales telles
que le lin et le chanvre trouvent aussi des applications dans les domaines textiles et
paratextiles. Les fluctuations dans le prix du pétrole et de ces dérivés ont encouragé beaucoup
d’industriels à revaloriser les fibres naturelles locales.
L’alfa (fig.1) est une plante abondante en Tunisie utilisée comme pâte papetière avec une
valeur ajoutée faible.
Dans cette étude, nous proposons de réaliser des non tissés à partir de ces fibres pour pouvoir
les utiliser comme couche de renfort pour des emboîtures
La récolte d’alfa
En Tunisie, l’alfa se trouve surtout dans les régions de Kasserine, Sidi Bouzid, Gafsa et
Kairouan. La longueur de la plante peut atteindre de 50 à 80 cm, quant au diamètre de la fibre,
il varie de 1 à 2 mm. Sa cueillette est organisée annuellement par campagnes de 6 mois (de
septembre à février) Après une récolte manuelle, la plante est transformée en balle.
La séparation chimique
Pour éliminer la lignine (substance qui relient les fibres et rend la structure rigide) et pour
donner une certaine blancheur à la fibre, une séparation chimique a été appliquée aux feuilles
d’alfa en utilisant la soude et l’eau de javel à ébullition.
Cette étape a été réalisée au Laboratoire de Recherche en Biomécanique et Biomatériaux
Orthopédiques (LRBBO) de l’Institut Nationale d’Orthopédie M. T. Kassab
Les fibres végétales sont des matériaux biodégradables et légers. Ces caractéristiques leur
donnent la possibilité d’être utilisées comme couche de renfort dans les structures composites.
Le coton est la fibre végétale la plus utilisée dans le monde. D’autres fibres végétales telles
que le lin et le chanvre trouvent aussi des applications dans les domaines textiles et
paratextiles. Les fluctuations dans le prix du pétrole et de ces dérivés ont encouragé beaucoup
d’industriels à revaloriser les fibres naturelles locales.
L’alfa (fig.1) est une plante abondante en Tunisie utilisée comme pâte papetière avec une
valeur ajoutée faible.
Dans cette étude, nous proposons de réaliser des non tissés à partir de ces fibres pour pouvoir
les utiliser comme couche de renfort pour des emboîtures
La récolte d’alfa
En Tunisie, l’alfa se trouve surtout dans les régions de Kasserine, Sidi Bouzid, Gafsa et
Kairouan. La longueur de la plante peut atteindre de 50 à 80 cm, quant au diamètre de la fibre,
il varie de 1 à 2 mm. Sa cueillette est organisée annuellement par campagnes de 6 mois (de
septembre à février) Après une récolte manuelle, la plante est transformée en balle.
La séparation chimique
Pour éliminer la lignine (substance qui relient les fibres et rend la structure rigide) et pour
donner une certaine blancheur à la fibre, une séparation chimique a été appliquée aux feuilles
d’alfa en utilisant la soude et l’eau de javel à ébullition.
Cette étape a été réalisée au Laboratoire de Recherche en Biomécanique et Biomatériaux
Orthopédiques (LRBBO) de l’Institut Nationale d’Orthopédie M. T. Kassab
La séparation mécanique
Pour obtenir des fibres de longueur textile permettant d’obtenir un non tissé, une séparation
chimique a été faite moyennant l’analyseur SCHIRLEY.
Les essais ont été réalisés à l’unité de recherche textile de l’ISET de Ksar Hellal
La fabrication des non tissés
Pour la fabrication des non tissés, la voie sèche a été choisie. Le principe consiste à ouvrir la
matière et la mélanger et par la suite de passer à une carde type laine suivie d’un nappeur.
Par la suite différentes techniques de consolidation ont été appliqués telles que l’aiguilletage,
le thermoliage et l’hydroliage pour donner la résistance nécessaire à la structure. Comme il
n’était pas possible de produire un article 100% alfa (faible cohésion), d’autres fibres telles
que la laine et le propylène ont été ajoutées en petite proportion.
La fabrication des différents non tissé a été réalisée dans le Centre Européen des Non Tissés
CENT en France.
Conclusion
Une valorisation de la fibre d’alfa (habituellement utilisée comme pâte dans la technique
papetière) dans le domaine du textile médical a été réalisée. Après une transformation
chimique et mécanique, les fibres ont été transformées en structures non tissées. Ces étoffes
ont été utilisées comme renfort dans le domaine orthopédique. Des travaux sont en cours pour
améliorer le processus de transformation de la fibre d’alfa.
Source : Ben Hassen Mohamed (benrayen@yahoo.fr)
Pour obtenir des fibres de longueur textile permettant d’obtenir un non tissé, une séparation
chimique a été faite moyennant l’analyseur SCHIRLEY.
Les essais ont été réalisés à l’unité de recherche textile de l’ISET de Ksar Hellal
La fabrication des non tissés
Pour la fabrication des non tissés, la voie sèche a été choisie. Le principe consiste à ouvrir la
matière et la mélanger et par la suite de passer à une carde type laine suivie d’un nappeur.
Par la suite différentes techniques de consolidation ont été appliqués telles que l’aiguilletage,
le thermoliage et l’hydroliage pour donner la résistance nécessaire à la structure. Comme il
n’était pas possible de produire un article 100% alfa (faible cohésion), d’autres fibres telles
que la laine et le propylène ont été ajoutées en petite proportion.
La fabrication des différents non tissé a été réalisée dans le Centre Européen des Non Tissés
CENT en France.
Conclusion
Une valorisation de la fibre d’alfa (habituellement utilisée comme pâte dans la technique
papetière) dans le domaine du textile médical a été réalisée. Après une transformation
chimique et mécanique, les fibres ont été transformées en structures non tissées. Ces étoffes
ont été utilisées comme renfort dans le domaine orthopédique. Des travaux sont en cours pour
améliorer le processus de transformation de la fibre d’alfa.
Source : Ben Hassen Mohamed (benrayen@yahoo.fr)
dimanche 14 juin 2009
La consolidation thermique (Thermal Bonding)
On utilise la propriété de thermo-plasticité et de thermo-fixation de certaines fibres synthétiques qui peuvent créer une adhésion sous des conditions de température adaptées.
Ces fibres peuvent constituer le voile initial ou être introduites dès la constitution du voile. Dans ce dernier cas elles ont souvent une température de fusion plus basse.
La chaleur nécessaire pour la thermo-fixation peut être apportée par :
un four à air chaud ;
une sécherie classique par contact avec des cylindres sécheurs ;
une calandre chauffée ;
un système d’ondes haute fréquence générant de l’énergie provoquant le ramollissement et la fusion des fibres.
Photo 1 : Coupe d'un non tissé en cellulose (pâte fluff) et polyoléfine thermoscelable pour produit absorbant, obtenu par voie sèche (air dry) et consolidé thermiquement
Photo 2 : Surface d'un non tissé à base synthétique pour serviette à usage unique, consolidé par calandrage à chaud (à picots)
Photo 3 : Surface d'un non tissé obtenu par voie fondue et consolidé par thermofusion (face B)
Photo 4 : Surface d'un non tissé obtenu par voie fondue et consolidé par thermofusion (face A)
Ces fibres peuvent constituer le voile initial ou être introduites dès la constitution du voile. Dans ce dernier cas elles ont souvent une température de fusion plus basse.
La chaleur nécessaire pour la thermo-fixation peut être apportée par :
un four à air chaud ;
une sécherie classique par contact avec des cylindres sécheurs ;
une calandre chauffée ;
un système d’ondes haute fréquence générant de l’énergie provoquant le ramollissement et la fusion des fibres.
Photo 1 : Coupe d'un non tissé en cellulose (pâte fluff) et polyoléfine thermoscelable pour produit absorbant, obtenu par voie sèche (air dry) et consolidé thermiquement
Photo 2 : Surface d'un non tissé à base synthétique pour serviette à usage unique, consolidé par calandrage à chaud (à picots)
Photo 3 : Surface d'un non tissé obtenu par voie fondue et consolidé par thermofusion (face B)
Photo 4 : Surface d'un non tissé obtenu par voie fondue et consolidé par thermofusion (face A)
mardi 9 juin 2009
Qu’est ce que le non tissé ?
Feuille manufacturée, constituée de voile ou de nappe de fibres orientées directionnellement ou au hasard, liées par friction et/ou cohésion et:ou adhésion à l'exclusion du papier et des produits obtenus par tissage, tricotage, tuftage, couturage incorporant des fils ou filaments de liage ou feutrés par foulage humide qu'ils soient ou non aiguilletés.
Les méthodes de base pour la réalisation du voile sont au nombre de quatre :
- La voie textile ou voie sèche :
Procédé de réalisation de non-tissé par voie textile
(cardage nappage ou aérodynamique) - La voie papetière ou voie humide :
Procédé de formation de voile par voie papetière - La voie fondue
Procédé de formation de voile par fusion de polymère sous forme de
filaments - Les techniques spécifiques (souvent combinaison des premières).
1) La voie fondue :
•Cette technologie regroupe : spunbonded, meltblown ainsi que la réalisation de films microporeux ( flash spinning). Elle fait appel aux techniques d'extrusion associées à des systèmes de formation simultanée de l'étoffe nontissée.
•Selon les techniques employées l'obtention de propriétés intéressantes est obtenue :
•ténacité forte pour les spunbonds,
•douceur due à la finesse des fibres et poids par m² faible pour les meltblowns, homogénéité des propriétés pour les films.
•Les produits multicouches voie fondue ( SMS, SMMS, ...)
2) Les techniques combinées
•Combinaison des différents systèmes, association des surfaces non-tissées et d'autres étoffes, composites, ... Les assemblages sont réalisés par :
•Laminage
•Techniques de consolidation qui réaliseront l'assemblage des différentes feuilles.
3) La consolidation
•La consolidation ou liage des non-tissés :
•Opération d'assemblage des fibres ou films par des procédés mécaniques, chimiques, ou physiques (chaleur et pression).
•Le degré de liage sera déterminant pour l'étoffe en termes de ténacité, porosité, flexibilité et densité (épaisseur et volume).
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