Alimentary 'green' proteins as electrospun scaffolds for skin regenerative engineering.

As a potential alternative to currently available skin substitutes and wound dressings, we explored the use of bioactive scaffolds made of plant-derived proteins. We hypothesized that 'green' materials, derived from renewable and biodegradable natural sources, may confer bioactive properties to enhance wound healing and tissue regeneration. We optimized and characterized fibrous scaffolds electrospun from soy protein isolate (SPI) with addition of 0.05% poly(ethylene oxide) (PEO) dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol, and from corn zein dissolved in glacial acetic acid. Fibrous mats electrospun from either of these plant proteins remained intact without further cross-linking, possessing a skin-like pliability. Soy-derived scaffolds supported the adhesion and proliferation of cultured primary human dermal fibroblasts. Using targeted PCR arrays and qPCR validation, we found similar gene expression profiles of fibroblasts cultured for 2 and 24 h on SPI substrates and on collagen type I at both time points. On both substrates there was a pronounced time-dependent upregulation of several genes related to ECM deposition remodelling, including MMP-10, MMP-1, collagen VII, integrin-α2 and laminin-ß3, indicating that both plant- and animal-derived materials induce similar responses from the cells after initial adhesion, degrading substrate proteins and depositing extracellular matrix in a 'normal' remodelling process. These results suggest that 'green' proteins, such as soy and zein, are promising as a platform for organotypic skin equivalent culture, as well as implantable scaffolds for skin regeneration. Future studies will determine specific mechanisms of their interaction with skin cells and their efficacy in wound-healing applications.

Electrospun fibers from wheat protein: investigation of the interplay between molecular structure and the fluid dynamics of the electrospinning process.

In the present work, we demonstrate the ability to electrospin wheat gluten, a polydisperse plant protein polymer that is currently available at roughly 0.50 dollars/lb. A variety of electrospinning experiments were carried out with wheat gluten from two sources, at different solution concentrations, and with native and denatured wheat gluten to illustrate the interplay between protein structure and the fluid dynamics of the electrospinning process. The presence of both cylindrical and flat fibers was observed in the nonwoven mats, which were characterized using both polarized optical microscopy and field emission scanning electron microscopy. Retardance images obtained by polarized optical microscopy exhibited evidence of molecular orientation at the surface of the fibers. We believe that fiber formation by electrospinning is a result of both chain entanglements and the presence of reversible junctions in the protein, in particular, the breaking and re-forming of disulfide bonds that occur via a thiol/disulfide interchange reaction. The presence of the highest molecular weight glutenin polymer chains in the wheat protein appeared to be responsible for the lower threshold concentration for fiber formation, relative to that of a lower molecular weight fraction of wheat protein devoid of the high molecular weight glutenin component. Denaturation of the wheat protein, however, clearly disrupted this delicate balance of properties in the experimental regimes we investigated, as electrospun fibers from the denatured state were not observed.

Designing new materials from wheat protein.

We recently discovered that wheat gluten could be formed into a tough, plasticlike substance when thiol-terminated, star-branched molecules are incorporated directly into the protein structure. This discovery offers the exciting possibility of developing biodegradable high-performance engineering plastics and composites from renewable resources that are competitive with their synthetic counterparts. Wheat gluten powder is available at a cost of less than dollars 0.5/lb, so if processing costs can be controlled, an inexpensive alternative to synthetic polymers may be possible. In the present work, we demonstrate the ability to toughen an otherwise brittle protein-based material by increasing the yield stress and strain-to-failure, without compromising stiffness. Water absorption results suggest that the cross-link density of the polymer is increased by the presence of the thiol-terminated, star-branched additive in the protein. Size-exclusion high performance liquid chromatography data of molded tri-thiol-modified gluten are consistent with that of a polymer that has been further cross-linked when compared directly with unmodified gluten, handled under identical conditions. Remarkably, the mechanical properties of our gluten formulations stored in ambient conditions were found to improve with time.

Interpreting the signal from a localized fluorescence sensor: a study by angle-resolved XPS and dynamic SIMS.

Angle-resolved X-ray photoelectron spectroscopy (XPS) and dynamic secondary ion mass spectroscopy (DSIMS) experiments were conducted to assess the interactions between a diamine curing agent and a glycidoxysilane-modified glass substrate. This effort was motivated by earlier work, in which a fluorescent probe localized in dilute quantities in the silane layer was used to track the penetration of the resin into the silane layer, as well as the resin cure. XPS and DSIMS experiments were performed on the silane layers immersed only in the resin hardener, providing more detailed information about the concentration profile and structural reorganization within the silane layer due specifically to hardener penetration. Dynamic SIMS spectra reveal the presence of hardener in the layer, as indicated by the strong CN- signal throughout the silane layer thickness. The XPS results indicate the presence of an amine gradient within the top 10 nm of the silane coating, with less amine penetration deeper into the silane layer. The XPS data also suggest some level of anisotropy in the molecular structure of the diamine/glycidoxysilane coating, as revealed by the differences in the relative atomic concentrations and peak positions of the C1s components at two different take-off angles.

Dewetting of unreacted epoxy/amine mixtures on silica.

We employ a direct method, time-of-flight secondary ion mass spectroscopy (ToF-SIMS), to determine experimentally the chemical compositions of the wetted and dewetted regions of an uncured epoxy thin film. Determining the composition of the dewetted region indicated the presence of a very thin sublayer of resin in what was thought to be a region devoid of resin. The capability of ToF-SIMS to probe small 65 x 65 microm(2) areas of the surface has permitted us to directly compare the SIMS spectra of the wetted and dewetted regions to the survey spectra of the reactants. This may indicate the strength of resin/silica interactions, which determine interface formation and properties.