In this seminar, polymer network architecture is shown to be leveraged to achieve biomaterial functionality in two applications: self-fitting shape memory scaffolds (to treat irregular bone defects) and synthetic cartilage.
Shape memory polymer (SMP) scaffolds were prepared having the capacity to conformally “self-fit” into and eventually heal irregular bone defects. Initially, porous scaffolds were prepared via photocrosslinking of poly(ε-caprolactone) (PCL) diacrylate using a solvent casting/particulate leaching (SCPL) method employing a fused salt template. Following exposure to warm saline at T > Ttrans (Ttrans = Tm of PCL), the scaffold became malleable and could be pressed into an irregular model defect. Subsequent cooling caused the scaffold to lock in its temporary shape within the defect. To tune mechanical and degradation properties, SMPs are formed as semi-interpenetrating networks (semi-IPNs) comprised of a cross-linked PCL-DA network and thermoplastic poly(L-lactic acid) (PLLA). Most recently, siloxane segments were incorporated into PCL networks to establish innate bioactivity.
Hydrogels are desirable candidates for cartilage replacement due to their high water content and lubricity but are limited in their mechanical properties. We evaluated a double network (DN) hydrogel composed of a poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) 1st network and a poly(N-isopropylacrylamide-co-acrylamide) [P(NIPAAm-co-AAm)] 2nd network. These PNIPAAm-based DNs demonstrated remarkably high compressive strength (~25 MPa) while maintaining a cartilage-like modulus (~1 MPa) and hydration (~80%). By directly comparing to healthy cartilage (porcine), we confirmed that these hydrogels were not only able to parallel the strength, modulus and hydration of native articular cartilage but also exhibited a 50% lower coefficient of friction.
Melissa Grunlan is a Professor of Biomedical Engineering at Texas A&M University (TAMU) and Holder of the Charles H. and Bettye Barclay Professorship in Engineering, TAMU Presidential Impact Fellow, and TAMU Chancellor EDGES Fellow. She holds courtesy appointments in the Department of Materials Science & Engineering and the Department of Chemistry. Prof. Grunlan obtained a B.S. in Chemistry and M.S. in Polymers in Coatings from North Dakota State University and a Ph.D. in Chemistry from the University of Southern California. Her work is focused on the development of synthetic polymeric biomaterials for implanted medical devices and for regenerative engineering. She is a Fellow of the American Chemical Society (ACS) and the American Institute for Medical and Biological Engineering (AIMBE).