Introduction: The development of future biomaterials faces the hurdle of tissue compliance mismatch for tissue regenerative applications.. While neat poly(glycerol sebacate) (PGS) has garnered attention in the area of regenerative medicine due to its tough mechanical properties, certain tissues require less stiffness and more elasticity. Based on our analysis of PGS/PLA copolymers (PGSLA), we hypothesize that the physical properties of PGSLA will provide a better match to the compliance of softer tissues.
Materials and Methods: PGS was synthesized via a polycondensation reaction between glycerol and sebacic acid. A reactor was charged with equimolar amounts of glycerol and sebacic acid, and 3 molar equivalents of water. The reactor was heated to 130°C under N2 flow and stirred until the sebacic acid melted. The temperature was then set to 120°C and held under N2 flow for 24 hrs, then under vacuum (~10 Torr) for 24 hrs.
PLA was synthesized via a polycondensation reaction of L-(+)-lactic acid. A reactor was charged with L-(+)-lactic acid and dehydrated at 150°C with stirring, first under N2 flow for 18 hrs, then vacuum at 97 Torr for 2 hrs, then at 30 Torr for 4 hrs.
PGSLA was synthesized via polycondensation of PGS and PLA. A reactor was charged with PGS and PLA in a 90%/10% (w/w) ratio and placed under vacuum (~10 Torr) with stirring at 120°C for 20 hrs.
The PGSLA resin was characterized by gel permeation chromatography (GPC) and oscillatory rheometry. The PGSLA resin was cast into ~2mm films and thermoset at 120°C and ~10 Torr for 72 hrs. The resulting films were cut into dog bone samples and the tensile mechanical properties were measured.
Results and Discussion: GPC chromatograms (Fig. 1) of PGSLA illustrate equivalent Mw values (~15000 Da) yet higher Mw/Mn values (8.4) than PGS (7.3), indicating a more randomly crosslinked polymer.
Rheometry measurements (Fig. 2) of PGSLA show morphological differences compared to PGS. Amplitude sweeps performed at 25°C show PGSLA storage (G') and loss (G") moduli magnitude are lower indicating a less stiff material, yet the yield strain is greater (6.1%) compared to PGS (~0.8%) indicating a more elastic material.
Tensile mechanical results of thermoset samples show PGSLA being less stiff and more elastic compared to PGS. The tensile modulus is lower (1.4 MPa vs 3.9 MPa) and strain at break is greater (27% vs 19%).
Conclusions: Polymerization of PGS with PLA has yielded a PGSLA copolymer that is less stiff and more elastic than neat PGS. The PLA fraction provides an available crosslinking agent to create a more random polymer network. These characteristics will provide better tissue compliance to soft tissues. Additionally, stiffness and elasticity could be further adjusted by increasing or decreasing the reaction time or weight fraction of PLA.