Simultaneous formation and mineralization of star-P(EO-stat-PO) hydrogels

- Hydrogel mineralization with nano-HA was achieved by adding alpha-tricalcium phosphate to a star-P(EO-stat-PO) gel
- Strength improvement by the factor of 30 was demonstrated in comparison to simply adding unreactive filler particles
- Mineral loads of up to 75% hydroxyapatite were obtained with mechanical properties similar to those of cancellous bone

Natural bone is an organic-inorganic composite of highly ordered collagen fibrils and ~ 60-70% nanocrystalline hydroxyapatite (HA) crystals resulting in a high fracture resistance for various mechanical loading situations. This study aimed to synthesize highly mineralized hydrogels to mimic the mechanical properties of cancellous bone. A six armed star molecule functionalized with isocyanate groups as reactive termini (NCO-sP(EO-stat-PO)) was used to build up a hydrogel matrix, which was then subsequently mineralized with hydroxyapatite nanocrystals following the hydrolysis of incorporated α-tricalcium phosphate particles. The advantage of this dual setting approach in comparison to simply adding unreactive filler particles to the hydrogel was demonstrated to be a strength improvement by the factor of 30. After 1-28 d setting, the mechanical properties of a composite with 30 wt% NCO-sP(EO-stat-PO) such as elasticity (5.3-1.4%), compression strength (11-23 MPa) and E-modulus (211-811 MPa) were found to be similar to the properties of cancellous bone.