Choosing the proper materials for medical devices in development means balancing safety, efficacy, and cost.
For devices coming into contact with living systems, biocompatibility is the key feature of component materials, and often choosing a known (and approved) material with a demonstrated biocompatibility profile is preferable so that designers can concentrate on the functionality of a device for the specific task at hand—e.g., engineering challenges, device performance, therapeutic efficacy, and so on.
But innovative materials can provide opportunities to optimize device performance, supplement biocompatibility, and/or decrease development costs. This blog will discuss some recent innovative materials and their possible therapeutic applications. See also our previous blog, “Advances in Medical Device Materials. Part 1: Polycarbonate Resins.”
Synthetic Collagen Fibers
Collagen, the most copious structural protein in mammals, is a key component of connective tissues such as skin, tendons, and cartilages. It is a triple helix protein, has a unique amino acid sequence, and has unusually high hydroxyproline content. Bovine and porcine collagen have been implanted clinically for decades and are well tolerated without any serious immune response.
The fast-growing understanding of the extracellular matrix (ECM) and improvements in the generation of synthetic matrix components indicates that synthetic collagen fibers offer compelling benefits over conventional polymers for soft tissue repair and replacement. New discoveries on mimicking self-assembly of collagen proteins and new ways to formulate synthetic collagen bring us closer to developing better methods of creating synthetic tissues and repairing our own tissues after injury.
Researchers at Rice University, for example (see Jalan et al, Sarkar et al), have been studying synthetic collagen fibers and how mimetic peptides can self-assemble into helices in an offset fashion that creates sticky ends. This allows them to aggregate into fibers or gels that may be used in cosmetic and reconstructive medicine.
Researchers from the Lawrence Berkeley National Laboratory and the University of California–San Diego (see Yang et al), in collaboration with the U.S. Department of Energy, have uncovered the unique properties of skin that make it resistant to damage. The authors viewed the effects of stress on collagen and made the first direct observations of collagen fibrils and fibers rotating, straightening, stretching, and sliding in the direction of the applied stress in order to reduce the load and prevent tearing. In a Berkeley Lab press release interview, the researchers claim that this new understanding can be applied to improving artificial skin or to the development of materials for flexible electronics.
A new formulation of aligned coating based on a collagen/alginate multilayer film has been developed and studied by researchers at the French Institute of Health and Medical Research (see Chaubaroux et al). Data from microscopic assessments show that cells align with the collagen fibrils of the coating. This can be useful in providing a scaffolding for tissue regeneration following injuries.
Trimethylene Carbonate (TMC)/Lactide/Glycolide Polymers
Biomaterials that are both strong and resorbable are useful in implants and surgical meshes. A Swedish company has created a surgical mesh from two different degradable polymers that provides tissue support for 6 to 9 months. The first polymer, made of trimethylene carbonate (TMC), lactide, and glycolide, is a quick-dissolving fiber that offers support for 2 months before degrading. The second, longer-lasting polymer is a blend of TMC and lactide that is more elastic, maintains support for 6-9 months, and degrades completely in 3 years. The fiber is now in use for hernia repair, abdominal wall reconstruction, and breast surgery.
A terpolymer, a polymer made up of three distinct monomers, was developed using lactide, TMC, and glycolide (PLAA-TMC-GA terpolymer) by researchers at Qingdao University of Science and Technology in China (see Shen at al) for possible use as a bioresorbable cardiovascular stent. The terpolymer was compared to other available polymers to test their in vitro compatibilities using various assays relevant to stent safety (MTT assay, hemolytic test, dynamic clotting time, platelet adhesion, platelet activation, protein adsorption, plasma recalcification time, and release of cytokines). The terpolymer performed well and may prove beneficial for use in patients requiring cardiovascular stents.
Material Characterization Testing Challenges
The new materials mentioned above provide exciting opportunities to produce devices and products with custom design and qualities. However, these new materials also pose significant challenges when it comes to ISO 10993-18-based material characterization testing. For instance, the biodegradable terpolymers may be prone to degradation due to hydrolysis and/or cross-esterification during extraction conditions. Therefore careful attention must be paid during selection of appropriate extraction solvents and extraction conditions. NAMSA has excellent resources, expertise, and experience in extractable and leachable screening of such materials and can provide excellent service and guidance for such testing needs.
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Chaubaroux C, Perrin-Schmitt F, Senger B, et al. Cell alignment driven by mechanically induced collagen fiber alignment in collagen/alginate coatings. Tissue Eng Part C Methods. 2015 Mar 17 [Epub ahead of print].
ISO Standards 11.100.20: Biological evaluation of medical devices [Standards catalog]. Available at:http://www.iso.org/iso/home/store/catalogue_ics/catalogue_ics_browse.htm?ICS1=11&ICS2=100&ICS3=20&.
Jalan AA, Jochim KA, Hartgerink JD, Rational design of a non-canonical “sticky-ended” collagen triple helix. J Am Chem Soc. 2014;136:7535-8.
Sarkar B, O’Leary LE, Hartgerink JD. Self-assembly of fiber-forming collagen mimetic peptides controlled by triple-helical nucleation. J Am Chem Soc. 2014;136:14417-24.
Shen X, Su F, Dong J, et al. In vitro biocompatibility evaluation of bioresorbable copolymers prepared from l-lactide, 1, 3-trimethylene carbonate, and glycolide for cardiovascular applications. J Biomater Sci Polym Ed. 2015;26:497-514.
TIGR® resorbable matrix [U.S. product information]. Novus Scientific, Inc. Available at: http://www.tigrmatrix.com/us/tigr-matrix.
Yang W, Sherman VR, Gludovatz B, et al. On the tear resistance of skin. Nat Commun. 2015;6:6649.
Yarris L. Skin tough: study at Berkeley Lab’s Advanced Light Source shows why skin is resistant to tearing [press release]. Available at:http://newscenter.lbl.gov/2015/03/31/skin-tough/.