Soy- and casein-based membranes are newly proposed materials disclosing a combination of properties that might allow for their use in a range of biomedical applications. Two of the most promising applications are drug delivery carrier systems and wound dressing membranes. As for all newly proposed biomaterials, a cytotoxic scanning must be performed as a preliminary step in the process of the determination of the compatibility with biological systems (biocompatibility). In this study, the cytotoxicity of both soy- and casein-based protein biomaterials has been evaluated and correlated with the materials degradation behavior. It was possible to show, through morphological and biochemical tests that these natural origin materials do not exert any cytotoxic effect over cells, and in some cases can in fact enhance cell proliferation. The different treatments to which the membranes were subjected during their processing (that include crosslinking with glyoxal and tannic acid, and physical modification by thermal treatment) seemed to have a clear effect both on the materials mechanical properties and on their in vitro biological behavior.

This work reports on the development and characterization of novel meltable polymers and composites based on casein and soybean proteins. The effects of inert (Al(2)O(3)) and bioactive (tricalcium phosphate) ceramic reinforcements over the mechanical performance, water absorption, and bioactivity behavior of the injection-molded thermoplastics were examined. It was possible to obtain materials and composites with a range of mechanical properties, which might allow for their application in the biomedical field. The incorporation of tricalcium phosphate into the soybean thermoplastic decreased its mechanical properties but lead to the nucleation of a bioactive calcium-phosphate film on their surface when immersed in a simulated body fluid solution. When compounded with 1% of a zirconate coupling agent, the nucleation and growth of the bioactive films on the surface of the referred to composites was accelerated. The materials degradation was studied for ageing periods up to 60 days in an isotonic saline solution. Both water uptake and weight loss were monitored as a function of the immersion time. After 1 month of immersion, the materials showed signal of chemical degradation, presenting weight losses up to 30%. However, further improvement on the mechanical performance and the enhancement of the hydrolytic stability of those materials will be highly necessary for applications in the biomedical field.

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Novel double-layer delivery devices based on soy protein derived materials were designed and produced using an innovative two material co-injection moulding technique. It was demonstrated that the viscosity ratio between core and skin layer materials played an important role in the formation of the interfacial shape, namely the skin thickness and uniformity of the bi-materials. The adequate selection of the materials used and the optimisation of the respective processing conditions enabled an accurate control of the relative thickness of the layers of the device. The preliminary results confirmed the potential of these systems to achieve a controlled drug delivery.

The aim of this study was to develop new soy protein drug delivery matrix systems by melt-processing techniques, namely, extrusion and injection moulding. The soy matrix systems with an encapsulated drug (theophylline, TH) were previously compounded by extrusion performed at two different pH values, (i) pH 4 (SIpDtp) and (ii) pH 7 (SIDtp), and further injection-moulded into a desired shape. During the extrusion process the matrixes SIDtp were also cross-linked with glyoxal (0.6X-SIDtp) and reinforced with a bioactive filler, hydroxylapatite (SI-HADtp). The obtained mouldings were used to study the drug-release mechanisms from the plastic soy-TH matrixes. In an isotonic saline solution (ISS) buffered at pH 5.0 (200 mM acetate buffer), the resulting release kinetics could be described using the Fick's second law of diffusion. Because the diffusion coefficients were found to be constant and the boundary conditions to be stationary, these systems are drug-diffusion controlled. Conversely, the dominant phenomena in an isotonic saline solution buffered at pH 7.4 (200 mM Tris/HCl buffer) are more complex. In fact, because of the higher polymer solubility, the resulting matrix is time-variant. So, the drug release is affected by swelling, drug diffusion, and polymer dissolution, being faster when compared to ISS-200 mM acetate buffer, pH 5.0. The changes in the formulation composition affecting the correspondent release rates were also investigated. At pH 7.4, increasing the cross-linking degree of the polymer matrix (via reaction with glyoxal or heat treatment) or decreasing the net charge (extruding at pH near its isoelectric point) led to lower release rates. The incorporation of ceramic filler caused the opposite effect. Because of the low solubility of the matrix at pH 5.0, no significant variations were detected with variations in the selected formulations. These systems, based on a nonstandard protein-based material, seem to be very promising to be used as carriers for drug delivery.