Effect of Molecular Weight and Functionality on Acrylated Poly(caprolactone) for Stereolithography and Biomedical Applications

Degradable polymers are integral components in many biomedical polymer applications. The ability of these materials to decompose in situ has become a critical component for tissue engineering, allowing scaffolds to guide cell and tissue growth while facilitating gradual regeneration of native tissue. The objective of this work is to understand the role of prepolymer molecular weight and functionality of photocurable poly(caprolactone) (PCL) in determining reaction kinetics, mechanical properties, polymer degradation, biocompatibility, and suitability for stereolithography. PCL, a degradable polymer used in a number of biomedical applications, was functionalized with acrylate groups to enable photopolymerization and three-dimensional printing via stereolithography. PCL prepolymers with different molecular weights and functionalities were studied to understand the role of molecular structure in reaction kinetics, mechanical properties, and degradation rates. The mechanical properties of photocured PCL were dependent on cross-link density and directly related to the molecular weight and functionality of the prepolymers. High-molecular weight, low-functionality PCLDA prepolymers exhibited a lower modulus and a higher strain at break, while low-molecular weight, high-functionality PCLTA prepolymers exhibited a lower strain at break and a higher modulus. Additionally, degradation profiles of cross-linked PCL followed a similar trend, with low cross-link density leading to degradation times up to 2.5 times shorter than those of more highly cross-linked polymers. Furthermore, photopolymerized PCL showed biocompatibility both in vitro and in vivo, causing no observed detrimental effects on seeded murine-induced pluripotent stem cells or when implanted into pig retinas. Finally, the ability to create three-dimensional PCL structures is shown by fabrication of simple structures using digital light projection stereolithography. Low-molecular weight, high-functionality PCLTA prepolymers printed objects with feature sizes near the hardware resolution limit of 50 μm. This work lays the foundation for future work in fabricating microscale PCL structures for a wide range of tissue regeneration applications.