2, ATSP Innovations, Champaign, Illinois, United States
3, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
4, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Development of porous materials consisting of polymer host matrix enriched with bioactive ceramic particles to initiate cellular organism reproduction while maintaining mechanical reliability in vivo is a long-standing challenge for permanent bone substitutes. Aromatic thermosetting copolyester (ATSP), introduced in the late 1990s, utilizes low cost, easily processable and highly crosslinkable oligomers to develop a high-performance polymer system. The crosslinked morphology of ATSP formed by aromatic polyester backbone interconnected via covalent oxygen bonds enables strong physical properties and outstanding chemical inertness. We recently introduced ATSP nanocomposites for which near-homogenous distribution and good incorporation of nanofillers contribute to significantly enhanced physical properties. As well, a prior biocompatibility study on ATSP morphology demonstrates direct-contact cytotoxicity test results that fibroblasts remain healthy and adhered on ATSP specimens following an incubation period. In addition, having strong adhesive bonding with metals, significant specific impact energy absorption capacity, and promising tribological properties, ATSP bionanocomposites are hence strong candidates for various orthopedic implant applications. Here, we demonstrate hydroxyapatite bioceramic particles (HAs) reinforced aromatic thermosetting copolyester matrix bionanocomposite, within the scope of providing an insight into interfacial interaction and coupling mechanisms between the HAs and ATSP matrix. The ATSP bionanocomposite is fabricated through solid-state mixing a matching set of precursor oligomers with HA particles. During endothermic condensation polymerization reaction, the constituent oligomers form a mechanochemically robust crosslinked aromatic backbone while incorporating the HAs into a self-generated cellular structure. We initially discuss the physicochemical effects induced by the HAs on the thermal polymerization reaction. Morphological analysis demonstrates near-homogenous distributions of the HAs within both precursor oligomer domain and nanocomposite matrix. Mechanical characterization shows a crack-arresting mechanism induced by the HAs which promotes a deformation-tolerant morphology with relatively enhanced material toughness. Chain relaxation dynamics in the glass transition regime are altered by segmental confinement of the polymer network instigated by the HAs. Chemical spectroscopy of the backbone chain configuration shows the formation of a covalent interfacial coupling between the HAs and ATSP matrix. A follow-up study will focus on systematical biocompatibility analysis of the ATSP matrix and ATSP bionanocomposites in various biological environments. This work may also initiate further characterization efforts on intermolecular interactions between the bioceramic particles and biocompatible polymer systems toward developing advanced synthetic bone morphologies.