Crosslinking protein-based materials

ProLastin polymers are a family of protein-based materials w hose resorption rate in vivo can be controlled by adjusting the sequence and not just the composition of the polymer (Cappello et al, 1995). These adjustments can be made so as to cause little change in the formulation characteristics of the materials, their physical forms, or their mechanical properties. They have good mechanical integrity with no need for chemical crosslinking. They degrade by enzymatic proteolysis and are presumed to resorb by surface erosion. Their breakdowm products are peptides or amino acids w hich are electroneutral at physiological pH and cause no undue inflammation or tissue response. 

Up until the 1960s, milk protein-based materials were used for making glossy record album covers, buttons and decorative items. Labels for some cheeses are still made with crosslinked casein. The film-forming properties of casein and whey proteins were investigated with the aim of developing edible films and coatings [91, 92]. Caseins... 

The mechanical properties of protein-based materials closely depend on the plasticizer content, temperature and ambient relative humidity (16,34,35). At constant temperature and composition, an increase in relative humidity leads to a major change in the material properties, with a sharp drop in mechanical strength and a concomitant sharp rise in distortion. These modifications occur when the Tg of the material is surpassed (Figure 1). These variations can be reduced by implementing crosslinking treatments (physical or chemical) or using high cellulose or mineral loads (22). 

Elastin-mimetic protein polymers have been fabricated into elastic networks primarily via y-radiation-induced, radical crosslinking of the material in the coacervate state [10]. Although effective, this method cannot produce polymers gels of defined molecular architecture, i.e., specific crosslink position and density, due to the lack of chemoselectivity in radical reactions. In addition, the ionizing radiation employed in this technique can cause material damage, and the reproducibility of specimen preparations may vary between different batches of material. In contrast, the e-amino groups of the lysine residues in polymers based on Lys-25 can be chemically crosslinked under controllable conditions into synthetic protein networks (vide infra). Elastic networks based on Lys-25 should contain crosslinks at well-defined position and density, determined by the sequence of the repeat, in the limit of complete substitution of the amino groups. 

Chem. Descrip. Hydroxymethyl dioxoazabicyclooctane CAS 6542-37-6 EINECS/ELINCS 229-457-6 Uses Crosslinking agent for resorcinol phenol-formaldehyde or protein-based resin systems, paints/coatings, adhesives, and inks raw material for synthesis... 

Hydroxymethyl dioxoazabicyclooctane CAS 6542-37-6 EINECS/ELINCS 229-457-6 Synonyms 7-Hydroxymethyl-1,5-dioxo-3-aza-bicyclooctane 1H,3H,5H-Oxazolo [3,4-c] oxazole-7a(7H)-methanol Oxazolo [3,4-c] oxazol-7a-yl-methanol Ciassification Heterocyclic organic compd. Empihcai CeHnNOs Properties M.w. 145.16 Toxicoiogy Irritant TSCA listed Uses Antimicrobial in cosmetics crosslinking agent for resorcinol phenol-formaldehyde or protein-based resin systems raw material for synthesis for paints, coatings, adhesives, and inks... 

In addition, caseinate-based films were crosslinked with formaldehyde (HCHO). The occurrence of covalent bridges between protein chains allows water-insoluble three-dimensional network to be achieved. The crossHnking was combined with plasticizing to produce caseinate films with improved mechanical properties and water resistance which are able to replace synthetic films and to overcome protein film deficiencies. Nevertheless, in spite of crosslinked protein material being water insoluble, it was also shown that during water immersion, plasticizer exuded out of the film, even for highly crosslinked samples. 

Wheat gluten is another protein from plants, which was intensively studied for its material applications. Wheat processing requires the presence of plasticizers such as glycerol or water to disrupt disulfide bonds. To control the formation of a crosslinked network, cysteine, formaldehyde or glutaraldehyde can be added. This contributes also to an improvement in moisture sensitivity and in elongation at break. On the other hand, the wheat gluten fibres have better properties compared to other protein-based bio products for biomedical applications. 

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