Chemical characterization of a degradable polymeric bone adhesive containing hydrolysable fillers and interpretation of anomalous mechanical properties

An experimental, light-curable, degradable polyester-based bone adhesive reinforced with phosphate glass particles ((P2O5)0.45(CaO)x(Na2O)0.55−x, x = 0.3 or 0.4 mol) or calcium phosphate (monocalcium phosphate/β-tricalcium phosphate (MCPM/β-TCP)) has been characterized. Early water sorption (8 wt.% at 1 week) by the unfilled set adhesive catalysed subsequent bulk degradation (4 wt.% at 2 weeks) and substantial decline in both elastic and storage moduli. Addition of phosphate glass fillers substantially enhanced this water sorption, catalysed greater bulk mass loss (40–50 and 52–55 wt.%, respectively) but enabled generation of a microporous scaffold within 2 weeks. The high levels of acidic polymer degradation products (38–50 wt.% of original polymer) were advantageously buffered by the filler, which initially released primarily sodium trimetaphosphate (P3O93-). Calcium phosphate addition raised polymer water sorption to a lesser extent (16 wt.%) and promoted intermediate early bulk mass loss (12 wt.%) but simultaneous anomalous increase in modulus. This was attributed to MCPM reacting with absorbed water and β-TCP to form more homogeneously dispersed brushite (CaHPO4) throughout the polymer. Between 2 and 10 weeks, linear erosion of both polymer (0.5 wt.% week−1) and composites (0.7–1.2 wt.% week−1) occurred, with all fillers providing long-term buffer action through calcium and orthophosphate (PO43-) release. In conclusion, both fillers can raise degradation of bone adhesives whilst simultaneously providing the buffering action and ions required for new bone formation. Through control of water sorption catalysed filler reactions, porous structures for cell support or substantially stiffer materials may be generated.