Silk fibroin hydrogels
Hydrogels are three-dimensional polymer networks which are physically durable to swelling in aqueous solutions but do not dissolve in these solutions. Hydrogel biomaterials provide important options for the delivery of cells and cytokines. Silk fibroin hydrogels have been prepared from aqueous silk fibroin solution and are formed from? β-sheet structures [55, 56]. The pH of the silk fibroin solution impacted the rate of solution gelation. Gelation of a 3% solution was obtained in two days at pH 3–4, compared with eight days as required from a solution with pH 5–12 [56]. Other factors important in gelation included silk polymer concentration and Ca++ [55]. An increase in silk fibroin concentration, increase in temperature, decrease in pH, and an increase in Ca++ concentration decreased the time of silk fibroin gelation. Hydrogel pore size was controllable based on silk fibroin concentration and temperature [55].
Supplementation of silk solutions with poloxamer 407 (a nonionic surfactant) induced gelation; however, additional poloxamer reversed the sol-gel transition [57]. Semi-interpenetrating polymer networks (SIPNs) formed by mixing poloxamer 407 and silk fibroin solution increased the mechanical properties of the hydrogel [58]. A hydrogel blend of silk fibroin and gelatin showed a temperature dependent helix coil transition of the gelatin that impacted the rheological and mechanical properties of the gel. Composition and temperature dependent properties of gelatin-silk fibroin hydrogels were examined for drug delivery purposes [59, 60]. The release of benfotiamide for oral delivery was dependent upon the concentration of fibroin in silk fibroin-glycerol hydrogels [61]. The hydrolysis of trichlormethiazide in silk fibroin hydrogels prepared in various monosaccharides (ribose, fructose, glucose, and mannose) was dependent upon the number of hydroxyl groups on the various monosaccharide molecules [62].
Osteoblasts-like cells that attached when cultured on 2% (w/v) silk fibroin hydrogels showed adherence and biocompatibility [13]. Addition of 30% glycerol to the hydrogel increased the proliferation of the cells [13]. Silk fibroin hydrogels injected in critical-sized femur defects in rabbits resulted in greater trabecular bone volume and thickness, significantly higher mineral and rate of bone formation when compared to poly(D,L lactide-glycolide) [63].
Hydrogels combining the properties of silk and elastin were formed to generate biomaterials called silk-elastin-like protein polymers (SELPs). The water content in SELP hydrogels could be managed by time of gelation and concentration of polymer, while the properties were not affected by pH, ionic strength, or temperature [64, 65]. SELP hydrogels have been employed for the release of small molecules like theophylline, vitamin B12, and cytochrome c [65]. SELP hydrogels were also used for the controlled release of DNA. Size, conformation, and concentration of DNA determined release rates of DNA from SELP hydrogels. The transfection efficiency was 1–3 orders higher than DNA delivered without hydrogel [66].
Silk fibroin hydrogelsHydrogels are three-dimensional polymer networks which are physically durable to swelling in aqueous solutions but do not dissolve in these solutions. Hydrogel biomaterials provide important options for the delivery of cells and cytokines. Silk fibroin hydrogels have been prepared from aqueous silk fibroin solution and are formed from? β-sheet structures [55, 56]. The pH of the silk fibroin solution impacted the rate of solution gelation. Gelation of a 3% solution was obtained in two days at pH 3–4, compared with eight days as required from a solution with pH 5–12 [56]. Other factors important in gelation included silk polymer concentration and Ca++ [55]. An increase in silk fibroin concentration, increase in temperature, decrease in pH, and an increase in Ca++ concentration decreased the time of silk fibroin gelation. Hydrogel pore size was controllable based on silk fibroin concentration and temperature [55].Supplementation of silk solutions with poloxamer 407 (a nonionic surfactant) induced gelation; however, additional poloxamer reversed the sol-gel transition [57]. Semi-interpenetrating polymer networks (SIPNs) formed by mixing poloxamer 407 and silk fibroin solution increased the mechanical properties of the hydrogel [58]. A hydrogel blend of silk fibroin and gelatin showed a temperature dependent helix coil transition of the gelatin that impacted the rheological and mechanical properties of the gel. Composition and temperature dependent properties of gelatin-silk fibroin hydrogels were examined for drug delivery purposes [59, 60]. The release of benfotiamide for oral delivery was dependent upon the concentration of fibroin in silk fibroin-glycerol hydrogels [61]. The hydrolysis of trichlormethiazide in silk fibroin hydrogels prepared in various monosaccharides (ribose, fructose, glucose, and mannose) was dependent upon the number of hydroxyl groups on the various monosaccharide molecules [62].Osteoblasts-like cells that attached when cultured on 2% (w/v) silk fibroin hydrogels showed adherence and biocompatibility [13]. Addition of 30% glycerol to the hydrogel increased the proliferation of the cells [13]. Silk fibroin hydrogels injected in critical-sized femur defects in rabbits resulted in greater trabecular bone volume and thickness, significantly higher mineral and rate of bone formation when compared to poly(D,L lactide-glycolide) [63].Hydrogels combining the properties of silk and elastin were formed to generate biomaterials called silk-elastin-like protein polymers (SELPs). The water content in SELP hydrogels could be managed by time of gelation and concentration of polymer, while the properties were not affected by pH, ionic strength, or temperature [64, 65]. SELP hydrogels have been employed for the release of small molecules like theophylline, vitamin B12, and cytochrome c [65]. SELP hydrogels were also used for the controlled release of DNA. Size, conformation, and concentration of DNA determined release rates of DNA from SELP hydrogels. The transfection efficiency was 1–3 orders higher than DNA delivered without hydrogel [66].
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