Yiqi Yang

Cytocompatible cross-linking of electrospun zein fibers for the development of water-stable tissue engineering scaffolds.

This paper reports a new method of cross-linking electrospun zein fibers using citric acid as a non-toxic cross-linker to enhance the water stability and cytocompatibility of zein fibers for tissue engineering and other medical applications. The electrospun structure has many advantages over other types of structures and protein-based biomaterials possess unique properties preferred for tissue engineering and other medical applications. However, ultrafine fiber matrices developed from proteins have poor mechanical properties and morphological stability in the aqueous environments required for medical applications. Efforts have been made to improve the water stability of electrospun protein scaffolds using cross-linking and other approaches, but the current methods have major limitations, such as cytotoxicity and low efficiency. In this research electrospun zein fibers were cross-linked with citric acid without using any toxic catalysts. The stability of the cross-linked fibers in phosphate-buffered saline and their ability to support the attachment, spreading and proliferation of mouse fibroblast cells were studied. The cross-linked electrospun fibers retained their ultrafine fibrous structure even after immersion in PBS at 37 degrees C for up to 15 days. Citric acid cross-linked electrospun zein scaffolds showed better attachment, spreading and proliferation of fibroblast cells than uncross-linked electrospun zein fibers, cross-linked zein films and electrospun polylactide fibers.

Potential of plant proteins for medical applications

Various natural and synthetic polymers are being explored to develop biomaterials for tissue engineering and drug delivery. Although proteins are preferable over carbohydrates and synthetic polymers, biomaterials developed from proteins lack the mechanical properties and/or biocompatibilities required for medical applications. Plant proteins are widely available, have low potential to be immunogenic and can be made into fibers, films, hydrogels and micro- and nano-particles for medical applications. Studies, mostly with zein, have demonstrated the potential of using plant proteins for tissue engineering and drug delivery. Although other plant proteins such as wheat gluten and soyproteins have also shown biocompatibility using in vitro studies, fabricating biomaterials such as nano-fibers and nano-particles from soy and wheat proteins offers considerable challenges.

Properties and potential applications of natural cellulose fibers from the bark of cotton stalks

Natural cellulose fibers have been obtained from the bark of cotton stalks and the fibers have been used to develop composites. Cotton stalks are rich in cellulose and account for up to 3 times the quantity of cotton fiber produced per acre. Currently, cotton stalks have limited use and are mostly burned on the ground. Natural cellulose fibers obtained from cotton stalks are composed of approximately 79% cellulose and 13.7% lignin. The fibers have breaking tenacity of 2.9 g per denier and breaking elongation of 3% and modulus of 144 g per denier, between that of cotton and linen. Polypropylene composites reinforced with cotton stalk fibers have flexural, tensile and impact resistance properties similar to jute fiber reinforced polypropylene composites. Utilizing cotton stalks as a source for natural cellulose fibers provides an opportunity to increase the income from cotton crops and make cotton crops more competitive to the biofuel crops.

Formaldehyde-free zein fiber—preparation and investigation

A novel dry-spinning method for the preparation of zein fiber without using formaldehyde is presented. The fiber thus obtained had good stability to boiling aqueous acetic acid solution with breaking tenacity and elongation of 1.0 g/d and 30%, respectively. Citric acid and butanetetracarboxylic acid were used as nonformaldehyde crosslinking agents for the preparation of zein fiber successfully. Using polycarboxylic acids have advantages such as no toxicity and low sensitivity to the variation of processing conditions over formaldehyde containing stabilizers. The effects of crosslinking before and after stretching on improvement of fiber properties were discussed. Fiber morphological structure was also examined by means of wide angle x-ray diffraction and sonic velocity.

Novel 3D Electrospun Scaffolds with Fibers Oriented Randomly and Evenly in Three Dimensions to Closely Mimic the Unique Architectures of Extracellular Matrices in Soft Tissues: Fabrication and Mechanism Study

In this work, novel electrospun scaffolds with fibers oriented randomly and evenly in three dimensions (3D) including in the thickness direction were developed based on the principle of electrostatic repulsion. This unique structure is different from most electrospun scaffolds with fibers oriented mainly in one direction. The structure of novel 3D scaffolds could more closely mimic the 3D randomly oriented fibrous architectures in many native extracellular matrices (ECMs). The cell culture results of this study indicated that, instead of becoming flattened cells when cultured in conventional electrospun scaffolds, the cells cultured on novel 3D scaffolds could develop into stereoscopic topographies, which highly simulated in vivo 3D cellular morphologies and are believed to be of vital importance for cells to function and differentiate appropriately. Also, due to the randomly oriented fibrous structure, improvement of nearly 5 times in cell proliferation could be observed when comparing our 3D scaffolds with 2D counterparts after 7 days of cell culture, while most currently reported 3D scaffolds only showed 1.5- to 2.5-fold improvement for the similar comparison. One mechanism of this fabrication process has also been proposed and showed that the rapid delivery of electrons on the fibers was the crucial factor for formation of 3D architectures.

Gut size changes in relation to variable food quality and body size in grasshoppers

Despite their short life span, insect herbivores such as grasshoppers can manipulate their gut in response to changes in food quality and body size, as previously documented in mammals and birds. Diet dilution greatly influenced the survival, development, weight gain and the proportional allocation to gut dry weight relative to body dry weight (G/B) of Melanoplus differentialis (Orthoptera: Acrididae). When diet quality increased from 1% N (total nitrogen) to 5% N, M. differentialis survived better, developed faster and gained more weight. However, increased gut size contributed to the ability to compensate for reduced food quality so that M. differentialis was able to survive equally well and develop equally fast on 3% N diets compared with individuals fed on 5% N diets

Lightweight composites from long wheat straw and polypropylene web.

Whole and split wheat straws (WS) with length up to 10 cm have been used with polypropylene (PP) webs to make lightweight composites with properties superior to jute-PP composites with the same density. The effect of WS concentration, WS length, and split configuration (half, quarter, and mechanically split) on flexural and tensile properties of the composites has been investigated. The sound absorption properties of composites from whole straw and split straw have been studied. Compared with whole WS-PP composites, mechanically split WS-PP composites have 69% higher flexural strength, 39% higher modulus of elasticity, 18% higher impact resistance properties, 69% higher tensile strength and 26% higher Youngs modulus. Compared with jute-PP composites, mechanically split WS-PP composites have 114% higher flexural strength, 38% higher modulus of elasticity, 10% higher tensile strength, 140% higher Youngs modulus, better sound absorption properties and 50% lower impact resistance.

Graft Polymerization of Native Chicken Feathers for Thermoplastic Applications

Inexpensive and biodegradable thermoplastics were developed through graft polymerization of native chicken feather with methyl acrylate as a potential substitute for petroleum products. Poultry feathers are available in large quantities at a low price. However, natural chicken feathers have poor thermoplasticity, cannot be used to develop thermoplastic products, have very limited industrial applications, and are often considered as solid wastes. In this research, the effects of graft polymerization conditions, such as molar ratio of NaHSO(3) to K(2)S(2)O(8), initiator and monomer concentrations, pH, temperature and time of polymerization, on grafting parameters, that is, the conversion of monomer to polymer, grafting percentage, and grafting efficiency were evaluated. Methyl acrylate was found to be successfully grafted onto functional groups on the surfaces of the chicken feathers, and optimal graft polymerization conditions were also obtained. The feather-g-poly(methyl acrylate) developed showed good thermoplasticity, and feather films had substantially higher tensile properties than soy protein isolate and starch acetate films.

Hollow nanoparticles from zein for potential medical applications

Hollow nanoparticles from corn storage protein zein, with average diameters as small as 65 nm and capable of loading a large amount of drug and penetrating into the cell cytoplasm, have been developed for potential drug delivery applications. As an important protein co-product of corn-based ethanol, zein is biocompatible and has been proved to be useful for medical applications through in vitro and in vivo evaluations. Zein can overcome the limitations of inorganic or metal nanoparticles that tend to accumulate in the organs and tissues and is therefore preferable for drug delivery applications. However, it has been observed that only small proteins and peptides are able to penetrate into cells and zein with a molecular weight of 14–44 kDa may not be able to enter into the cells. In this research, hollow zein nanoparticles have been developed and the potential of the hollow zein nanoparticles to load drugs and enter the cell cytoplasm was investigated. Hollow zein nanoparticles developed in this research were capable of loading as high as 369 mg g−1 of the drug metformin at an equilibrium concentration of 3 g L−1. Metformin in hollow zein nanoparticles showed a more sustained and controlled release profile than that in solid zein nanoparticles. Hollow zein nanoparticles were found to be able to enter the fibroblast cells 1 hour after incubation. The biocompatibility, nano-scale diameters, potential for loading a large amount of drugs and the ability to penetrate into cells make hollow zein nanoparticles ideal candidates for carrying various payloads for intracellular drug delivery.

Alkali-catalyzed low temperature wet crosslinking of plant proteins using carboxylic acids.

We report the development of a new method of alkali‐catalyzed low temperature wet crosslinking of plant proteins to improve their breaking tenacity without using high temperatures or phosphorus‐containing catalysts used in conventional poly(carboxylic acid) crosslinking of cellulose and proteins. Carboxylic acids are preferred over aldehyde‐containing crosslinkers for crosslinking proteins and cellulose because of their low toxicity and cost and ability to improve the desired properties of the materials. However, current knowledge in carboxylic acid crosslinking of proteins and cellulose requires the use of carboxylic acids with at least three carboxylic groups, toxic phosphorous‐containing catalysts and curing at high temperatures (150–185°C). The use of high temperatures and low pH in conventional carboxylic acid crosslinking has been reported to cause substantial strength loss and/or undesired changes in the properties of the crosslinked materials. In this research, gliadin, soyprotein, and zein fibers have been crosslinked with malic acid, citric acid, and butanetetracarboxylic acid to improve the tenacity of the fibers without using high temperatures and phosphorus‐containing catalysts. The new method of wet crosslinking using carboxylic acids containing two or more carboxylic groups will be useful to crosslink proteins for various industrial applications.