Latent Oxidative Polymerization of Catecholamines as Potential Cross-linkers for Biocompatible and Multifunctional Biopolymer Scaffolds.

Electrospinning of naturally occurring biopolymers for biological applications requires postspinning cross-linking for endurance in protease-rich microenvironments and prevention of rapid dissolution. The most commonly used cross-linkers often generate cytotoxic byproducts, which necessitate high concentrations or time-consuming procedures. Herein, we report the addition of "safe" catecholamine cross-linkers to collagen or gelatin dope solutions followed by electrospinning yielded junction-containing nanofibrous mats. Subsequent in situ oxidative polymerization of the catecholamines increased the density of soldered junctions and maintained the porous nanofiber architecture. This protocol imparted photoluminescence to the biopolymers, a smooth noncytotoxic coating, and good mechanical/structural stability in aqueous solutions. The utility of our approach was demonstrated by the preparation of durable antimicrobial wound dressings and mineralized osteoconductive scaffolds via peptide antibiotics and calcium chloride (CaCl2) incorporation into the dope solutions. The mineralized composite mats consist of amorphous calcium carbonate that enhanced the osteoblasts cell proliferation, differentiation, and expression of important osteogenic marker proteins. In proof-of-concept experiments, antibiotic-loaded mats displayed superior antimicrobial properties relative to silver (Ag)-based dressings, and accelerated wound healing in a porcine deep dermal burn injury model.

Interaction of gelatin with polyenes modulates antifungal activity and biocompatibility of electrospun fiber mats.

Topical application of antifungals does not have predictable or well-controlled release characteristics and requires reapplication to achieve therapeutic local concentration in a reasonable time period. In this article, the efficacy of five different US Food and Drug Administration-approved antifungal-loaded (amphotericin B, natamycin, terbinafine, fluconazole, and itraconazole) electrospun gelatin fiber mats were compared. Morphological studies show that incorporation of polyenes resulted in a two-fold increase in fiber diameter and the mats inhibit the growth of yeasts and filamentous fungal pathogens. Terbinafine-loaded mats were effective against three filamentous fungal species. Among the two azole antifungals compared, the itraconazole-loaded mat was potent against Aspergillus strains. However, activity loss was observed for fluconazole-loaded mats against all of the test organisms. The polyene-loaded mats displayed rapid candidacidal activities as well. Biophysical and rheological measurements indicate strong interactions between polyene antifungals and gelatin matrix. As a result, the polyenes stabilized the triple helical conformation of gelatin and the presence of gelatin decreased the hemolytic activity of polyenes. The polyene-loaded fiber mats were noncytotoxic to primary human corneal and sclera fibroblasts. The reduction of toxicity with complete retention of activity of the polyene antifungal-loaded gelatin fiber mats can provide new opportunities in the management of superficial skin infections.

Synthetic multivalent antifungal peptides effective against fungi.

Taking advantage of the cluster effect observed in multivalent peptides, this work describes antifungal activity and possible mechanism of action of tetravalent peptide (B4010) which carries 4 copies of the sequence RGRKVVRR through a branched lysine core. B4010 displayed better antifungal properties than natamycin and amphotericin B. The peptide retained significant activity in the presence of monovalent/divalent cations, trypsin and serum and tear fluid. Moreover, B4010 is non-haemolytic and non-toxic to mice by intraperitoneal (200 mg/kg) or intravenous (100 mg/kg) routes. S. cerevisiae mutant strains with altered membrane sterol structures and composition showed hyper senstivity to B4010. The peptide had no affinity for cell wall polysaccharides and caused rapid dissipation of membrane potential and release of vital ions and ATP when treated with C. albicans. We demonstrate that additives which alter the membrane potential or membrane rigidity protect C. albicans from B4010-induced lethality. Calcein release assay and molecular dynamics simulations showed that the peptide preferentially binds to mixed bilayer containing ergosterol over phophotidylcholine-cholesterol bilayers. The studies further suggested that the first arginine is important for mediating peptide-bilayer interactions. Replacing the first arginine led to a 2-4 fold decrease in antifungal activities and reduced membrane disruption properties. The combined in silico and in vitro approach should facilitate rational design of new tetravalent antifungal peptides.