3D printable PCL-<i>b</i>-P(MMA-<i>co</i>-TMSPMA)/silica hybrids using a PCL RAFT agent

Inorganic/organic hybrid biomaterials have the potential to combine the benefits of bioactive glasses, such as bone bonding and osteogenesis, with the ability to withstand cyclic loading. Here, we report on silica/poly(ε-caprolactone-methacrylate) hybrids, using hydroxy monofunctional-PCL as a reversible addition-fragmentation chain transfer (RAFT) agent, for controlled polymerization of PCL-<i>b</i>-P(methyl methacrylate-<i>co</i>-3-(trimethoxysilyl)propyl methacrylate), PCL-<i>b</i>-P(MMA-<i>co</i>-TMSPMA), block copolymers by a combination of ring opening polymerization (ROP) and RAFT polymerization techniques. The new polymer was used for the preparation of hybrids <i>via</i> the sol-gel method, with TMSPMA providing covalent bonds between the silica and PCL-<i>b</i>-P(MMA-<i>co</i>-TMSPMA). The effect of the ratio of CL/silane containing units on the mechanical properties of the hybrids was investigated. The compositions that yielded optimal mechanical properties in bulk form (yield stress 39.3 MPa to 52.9 MPa at a strain of 4-6%) were developed into "inks" for 3D printing porous biodegradable scaffolds for biomedical applications by direct writing. Degradation tests of scaffolds in phosphate buffered saline (PBS) over the course of 180 days showed ∼30% degradation of PCL. The mechanical properties of scaffolds with pore channels of 234-380 μm reduced yield strength to 5.2-7.4 MPa, but yield strain remained at ∼4%. <i>In vitro</i> studies indicated biocompatibility, in terms of exposure of human bone marrow stem cells (hBMCs) to the dissolution products of the scaffolds.