Supercritical CO2 Foaming of Thermoplastic Materials Derived from Sorghum and Maize: Proof of Concept Use in Mammalian Cell Culture Applications

Background: Foams are high porosity and low density materials. In nature, they are a common architecture. Some of their relevant technological applications include heat and sound insulation, lightweight materials, and tissue engineering scaffolds. Foams derived from natural polymers are particularly attractive for tissue culture due to their biodegradability and bio-compatibility. Here, the foaming potential of an extensive list of materials was assayed, including slabs elaborated from whole flour, the starch component only, or the protein fraction only of sorghum or maize seeds.

Methodology/Principal findings: We used supercritical CO₂ to produce foams from thermoplasticized sorghum and maize derived materials. Polyethylene-glycol, sorbitol/glycerol, or urea/formamide were used as plasticizers. We report expansion ratios, porosities, average pore sizes, pore morphologies, and pore size distributions for these materials. High porosity foams were obtained from zein thermoplasticized with polyethylene glycol, and from starch thermoplasticized with urea/formamide. Zein foams had a higher porosity than starch foams (88% and 85%, respectively), and a narrower and more evenly distributed pore size distribution. Starch foams exhibited a wider span of pore sizes and a larger average pore size than zein (208.84 vs. 55.43 μm², respectively). In proof of concept cell culture experiments, Chinese Hamster Ovary (CHO) cells and four different prostate cancer cell lines (PC3, LNCaP, 22RV1, and DU145) proliferated on zein foams.

Conclusions/Significance: We conducted screening and proof-of-concept experiments on the fabrication of foams from cereal-based bio-plastics. We propose the strain at break of the materials to be foamed (as calculated from stress vs. strain rate curves) as a key indicator of foamability. Some of the produced foams exhibit attractive properties (average pore size, pore size distribution, and porosity) for cell culture applications; we were able to establish and sustain mammalian cell cultures on zein foams for extended time periods.