Biodegradable Silicon-Containing Elastomers for Tissue Engineering Scaffolds and Shape Memory Polymers
Commonly used thermoplastic biodegradable polymers are generally brittle and lack appreciable elasticity at physiological temperature and thereby fail to mimic the elastic nature of many human soft tissues such as blood vessels. Thus, there is a need for biomaterials which exhibit elasticity. Biodegradable elastomers are promising candidates whose elasticity more closely parallels that of soft tissues. In this research, we developed hybrid biodegradable elastomers comprised of organic and inorganic polymer components in a block copolymer system: poly(e-caprolactone) (PCL) and poly(dimethylsiloxane) (PDMS), respectively. A block structure maintains the distinct properties of the PCL and PDMS components. These elastomers may be useful for the tissue engineering of soft tissues as well as for shape memory polymer (SMP) devices. Tri-block macromers of the form PCLn-block-PDMSm-block-PCLn were developed to permit systematic variations to key features including: PDMS block length, PCL block length, PDMS:PCL ratio, and crosslink density. The macromer was capped with acrylating groups (AcO) to permit their photochemical cure to form elastomers. Thus, a series of biodegradable elastomers were prepared by photocrosslinking a series of macromers in which the PCL blocks varied (n = 5, 10, 20, 30, and 40) and the PDMS block was maintained (m = 37). All elastomers displayed hydrophobic surface properties and high thermal stability. These elastomers demonstrated systematic tuning of mechanical properties as a function of PCL block length or crosslink density. Notable was strains at break as high as 814% making them suitable for elastomeric bioapplications. Elastomers with a critical PCL block length (n = 30 or 40) exhibited shape memory properties. Shape memory polymers based on an organic-inorganic, photocurable silicon-containing polymer system is a first of its kind. This SMP demonstrated strain fixity of 100% and strain recovery near 100% after the third thermomechanical cycle. Transition from temporary to permanent shape was quite rapid (2 sec) and at temperatures near body temperature (60 degrees C). Lastly, porous analogues of the biodegradable elastomers were created using a novel porogen - salt leaching technique. Resulting porous elastomers were designed for tissue engineering scaffolds or shape memory foams.