(215d) Poly(Diol Citrate) Nanocomposites with Enhanced Mechanical Properties

Biodegradable elastomeric polymers have recently received attention for their potential use in the engineering of soft tissues that exhibit elastic properties. To that end, we have developed a novel family of biodegradable elastomeric polymers referred to as poly(diol citrates). Because of the wide range of mechanical properties of tissues within the body, it is desirable to increase the range of strength and stiffness while maintaining elasticity to further enhance the versatility of these materials. To increase the range of mechanical properties that can be achieved with poly(diol citrates), copolymeric nanocomposite materials were synthesized and characterized. It was hypothesized that incorporation of a nanoscale phase into the poly(diol citrate) elastomer could greatly increase the mechanical properties of scaffolds thereof. Since poly(diol citrates) were designed for tissue engineering, the materials used to reinforce the composite were chosen from biodegradable and biocompatible polymers commonly used in tissue engineering. Two methods were used to create biodegradable nanocomposites: (A) poly(1,10-decanediol citrate) (PDC) reinforced with up to 10% poly(L-lactic acid) (PLLA) nanofibers, (B) PDC reinforced with up to 10% (w/w) nanoparticles of poly(lactic-co-glycolic acid) (PLGA). Solid films and tissue engineering scaffolds reinforced with PLLA nanofibers showed an increase in mechanical properties with increasing PLLA concentration. Increases in tensile strength of 150% were seen with a 10% nanofiber concentration. Concurrently, for the 10% nanofiber concentration, Young's modulus increased over 1000% compared to the control without PLLA reinforcement. For the tissue engineering scaffolds, the compressive modulus increased over 900% compared to the PDC control and without the permanent deformation associated with PLLA controls. The addition of the non-elastic PLLA nanofiber phase increased the elongation at break from 200% for the control to 300% for the 10% nanocomposite. In addition, the materials could still be elongated over twice their original length before rupture and without significant permanent plastic deformation. Nanocomposites fabricated with PLGA nanoparticles also showed an increase in mechanical properties with increasing nanoparticle concentration. For a 10% PLGA-PDC nanoparticle composite, the modulus and tensile strength increased by 116% and 40%, respectively over the control while the elongation at break decreased from 372% to 190%. To our knowledge, this is the first report of nanocomposite materials where the macro and nano phases were completely made from biodegradable and biocompatible synthetic co-polymers.