Use of natural coralline biomaterials as reinforcing and gas-forming agent for developing novel hybrid biomatrices: Microarchitectural and mechanical studies

This paper describes the first attempt in fabrication of three-dimensional macroporous composites of chitosan and natural coralline material with pore sizes of 300-400 μm, exceeding the upper pore size limit of 250 μm obtained with freeze-dried chitosan-based scaffolds. Natural coral particulates of less than 20 μm, which is mainly composed of calcium carbonate (CaCO ₃), was simultaneously used as reinforcing phase and gas-forming agent to obtain a structure with large pores and improved mechanical and biological properties. The reaction between the coralline material and the acidic chitosan polymer solvent, which produced carbon dioxide, was rapidly stopped by the subsequent thermally induced phase separation technique, leaving coralline particulates in the polymeric structure. Scaffolds containing five different proportions of coralline material (0, 25, 50, 75, and 100 wt%) were investigated. The coralline-chitosan weight ratio was studied for its effects on the physical properties of the scaffolds. The relation between scaffold microarchitecture and mechanical properties was assessed with scanning electron microscope (SEM), along with micro-CT imaging and compression testing. The scaffolds were used in bone marrow cell culturing experiments to assess the effect of composition on cell behavior through cell-material interaction and morphological observation by SEM. Higher coralline concentration increased the pore wall thickness and favored large pore formation. Varying the coralline particulate to chitosan polymer ratio from 0 to 75 wt% increased the average pore size from 80 μm to 400 μm while the porosity decreased from 91% to 78%. The compressive modulus was improved proportionally with the coralline content, and the 75 wt% composites had a significantly higher modulus than other chitosan-based scaffold groups. More cells were observed on scaffolds with higher coralline content. The cell culture experiments indicated that the scaffolds containing coralline material might have a high cell affinity, since it allowed fast cell attachment and spreading.