Exploration of solvent casting for designing engineered microstructures for biomedical and functional applications

In this paper, we report the synthesis and characterization of composites of bioplastics (Poly-lactic Acid (PLA), Polyhydroxyalkaonate (PHA), and PLA-PHA blends) filled with dried grains with solubles (DDGS) and hydroxyapatite (HAP) by using a solvent casting process. Detailed microstructural, thermal, and mechanical characterization is presented in the text. At low concentrations of HAP (5-10 vol%) and DDGS (5-31 vol%) additions, the bioplastic films had mechanical integrity, but the ultimate tensile strength (UTS) decreased after the addition of DDGS and HAP reinforcements due to poor adhesion between the bioplastics and fillers. In the intermediate concentration, pre-pregnated chips of DDGS (31-51 vol%)-bioplastics and HAP (30-50 vol%)-bioplastics with dichloromethane (DCM) were partially dried and then hot-pressed to produce bulk samples (HPC-process). The addition of bioplastics improved the plasticity of DDGS-bioplastics composites. The HAP-bioplastics composites showed polymer dependent response, for example the ultimate compressive strength (UCS) of 50%HAP-PLA, and 30%HAP-PLA were 77.6 +/- 10.2 and 97.7 +/- 5.9 MPa, respectively which are comparable to bone. The DDGS additions increased the hydrophilicity of PLA, PHA, and PLA-PHA blend. For comparison, HAP increased the hydrophilicity of PHA and PLA-PHA blends. At higher concentration (bioplastics with 70 vol% HAP additions), the films converted into microencapsulated HAP particles with bioplastics by a simple milling process thus eliminating the need for emulsions and/or surfactants during the microencapsulation process.