Assembly of hydroxy apatite: beta tricalcium phosphate: Calcium sulfate bone engineering scaffolds

Scope and Method of Study. Directed assembly and characterization of composite Hydroxyapatite/betaTri-CalciumPhosphate/Calcium Sulfate (HA/betaTCP/CaS) scaffolds with designed pore distribution for controlled solubility. Concentrated aqueous colloidal gel ink for extrusion-based direct writing was formulated with commercial HA and betaTCP powders blended with, ammonium poly(acrylate) (dispersant), hydroxypropylmethylcellulose (viscosifier), and Polyethyleneimine (flocculant). Prior to ink formulation, HA and betaTCP powders were calcined, milled, dried and characterized by X-ray diffraction. Mixtures of HA:betaTCP in volumetric ratios of 15:85, 35:65, and 60:40 were formulated as inks. Rice starch was formulated as ink and mixtures ceramic: rice starch blended in volumetric ratios of 85:15, 75:25, and 50:50 were produced. Disk samples (O11mm x 3mm thick) with an internal lattice structure of 250mum rods spaced by 250 mum or 500 mum in a periodic, open pore network were printed and sintered at 1100, 1125, 1150, 1175, and 1200oC for 4 hours. The control set for each composition and pore structure had empty pores while the two test groups were filled with 2.4% Chitosan gel or Calcium Sulfate (CaS). The scaffolds were immersed in simulated body fluid and weight loss was measured by gravimetric analysis on a three day frequency.;Findings and Conclusions. The assembled three-dimensional, binary HA/betaTCP structures can be sintered successfully and have both phases present in the final product. The scaffolds dissolve faster with higher betaTCP content and CaS filled scaffolds show dissolution behavior dominated by surface erosion of the filler phase. Micro-porosity induced by porogens does not accelerate the dissolution in vitro. In contrast, chitosan filled samples showed minimal weight loss, attributed to shielding of the betaTCP from SBF by the conformal and relatively stable chitosan hydrogel. Designer porous HA-betaTCP scaffolds may also include controlled solubility behavior by controlling HA: betaTCP ratio and selecting soluble pore filler. CaS may be used as a sacrificial pore filler to retard scaffold dissolution by 75 days, whereas chitosan hydrogel may persist as filler for longer periods.