HB physical properties. Comparison

HB physical properties. Comparison of the measured dry and the- oretical solid densities of HAPCL and HAPLGA fibers (the weight for a given volume if all space was filled: 90 wt % HA and 10 wt % polymer) revealed that HAPCL and HAPLGA fibers are about 50% porous (Fig. 4A and Supplementary Materials and Methods) (55). Once saturated with water, the density increases by 0.5 g/cm3, indicating that the porosity is open and accessible. This accessible porosity is a vital characteristic for promoting nutrient diffusion, cell migration and viability, and tissue in- tegration. These microstructural characteristics also impart hydrophili- city and high liquid absorbency (Fig. 4B) to the HB, which is ideal for enhanced cell, bioactive factors, and nutrient infiltration. In contrast to other 3D-printed HA composite systems, which do not exhibit signifi- cant absorbance of fluids, the surfaces of HAPCL and HAPLGA are dominated by exposed HA (Fig. 4, C and D), as indicated by the dark red coloring after Alizarin Red S calcium-specific staining, a property dis- tinct from that of HA-containing hot-melt printed scaffolds (Fig. 4E), trisolvent (1:1 HA/PLGA by weight) printed scaffolds (Fig. 4F), and even human allograft bone (Fig. 4G), which has less CaP at the surface.