Chemobrionic structures in tissue engineering: self-assembling calcium phosphate tubes as cellular scaffolds

A diverse range of complex patterns and mineralised hierarchical microstructures can be derived from chemobrionic systems, with formation driven by complex reaction-diffusion mechanisms far from thermodynamic equilibrium. In these experiments, self-assembling calcium phosphate tubes are generated using hydrogels made with 1 M calcium solutions layered with solutions of dibasic sodium phosphate over a range of concentrations between 0.2-1 M. Self-assembling structures prepared using 0.8 M dibasic sodium phosphate solutions were selected to assess cell-material interactions. Candidate chemobrionic scaffolds were characterised by micro-X-Ray fluorescence (μ-XRF) spectroscopy, Raman spectroscopy, powder X-ray diffraction (XRD), helium pycnometry and scanning electron microscopy (SEM). As prepared tubes were formed from non-stoichiometric hydroxyapatite (HA, Ca_10-x(PO₄)_6-x(HPO₄)_x(OH)_2-x (0 ≤x≤ 1)), which was confirmed as calcium deficient hydroxyapatite (CDHA, Ca₉(PO₄)₅HPO₄OH). Thermal treatment of tubes in air at 650 °C for 4 h converted the structures to beta tricalcium phosphate (β-TCP, β-Ca₃(PO₄)₂). The potential of these scaffolds to support the attachment of bone marrow derived mesenchymal stem cells (BMSCs) was investigated for the first time, and we demonstrate cell attachment and elongation on the fabricated tubular structures.