Chronic wounds represent a serious problem in daily medical routine requiring improved wound care. Silk of the domesticated silkworm (Bombyx mori) has been used to form a variety of biomaterials for medical applications. We genetically engineered B. mori to produce silk functionalized with growth factors to promote wound healing in vitro. In this study FGF-, EGF-, KGF-, PDGF- or VEGF-functionalized silk membranes were compared to native B. mori silk membranes without growth factors for their ability to support wound healing in vitro. All silk membranes were cytocompatible and supported macrophage secretion of neutrophil recruiting factor CXCL1 and monocyte chemoattractant protein 1 (MCP-1). VEGF-functionalized silk significantly outperformed other growth factor-functionalized silk membranes, but not native silk in angiogenesis assays. In addition, EGF- and VEGF-functionalized silk membranes slightly enhanced macrophage adhesion compared to silk without growth factors. In wound healing assays in vitro (reduction of wound lesion), dermal equivalents showed a higher wound healing capacity when covered with EGF-, FGF- or VEGF-functionalized silk membranes compared to native, KGF- or PDGF-functionalized silk membranes. Keratinocyte migration and growth is overstimulated by KGF- and VEGF-functionalized silk membranes. In conclusion, growth factor-functionalized silk membranes prepared from genetically engineered silk worm glands are promising wound dressings for future wound healing therapies.
Mesenchymal stem cells (MSC) are precursor cells of mesodermal tissue and, because of their trophic phenotype, they are known to play beneficial roles in wound healing. In addition, various tissue engineering strategies are based on MSC/biomaterial constructs. As the isolation and expansion of MSCs is a long-term process, a major goal is to develop an endogenous stem cell recruitment system that circumvents all ex vivo steps generally used for tissue engineering. Therefore collagen and silk fibroin were loaded with hepatocyte growth factor (HGF), a chemoattractant for MSCs. Collagen was mixed with HGF during polymerization, while silk fibroin and HGF were produced as fusion proteins by transgenic silkworms. To demonstrate release of active HGF, enzyme-linked immunosorbent assay, in vitro migration assays and animal studies were performed to demonstrate MSC migration in vivo, followed by detailed examinations of the immunological effects of the biomaterials. Hepatocyte growth factor was released burst-like, both from silk fibroin and collagen during the first 8 h and gradually for up to 168 h in vitro. Directed migration in vitro was demonstrated when MSCs were exposed to HGF. In vivo, HGF-loaded collagen and silk fibroin were tolerated as subcutaneous implants. In addition, it was proved that endogenous MSCs were recruited from the local environment. These results show for the first time recruitment of endogenous MSCs to HGF-loaded collagen (fast degradable) and silk fibroin scaffolds (long-term degradable) in vitro and in vivo. This knowledge could be applied to make off-the-shelf, readily available constructs for use in patients with chronic wound or burns. Copyright © 2016 John Wiley & Sons, Ltd.
The silkworm Bombyx mori represents an established in vivo system for the production of recombinant proteins. Baculoviruses have been extensively investigated and optimised for the expression of high protein levels inside the haemolymph of larvae and pupae of this lepidopteran insect. Current technology includes deletion of genes responsible for the activity of virus-borne proteases, which in wild-type viruses, cause liquefaction of the host insect and enhance horizontal transmission of newly synthesised virus particles. Besides the haemolymph, the silk gland of B. mori provides an additional expression system for recombinant proteins. In this paper, we investigated how silk gland can be efficiently infected by a Autographa californica multicapsid nuclear polyhedrosis virus (AcMNPV). We demonstrated that the viral chitinase and the cysteine protease cathepsin are necessary to permit viral entry into the silk gland cells of intrahaemocoelically infected B. mori larvae. Moreover, for the first time, we showed AcMNPV crossing the basal lamina of silk glands in B. mori larvae, and we assessed a new path of infection of silk gland cells that can be exploited for protein production.
Bone regeneration is a complex, well-organized physiological process of bone formation observed during normal fracture healing and involved in continuous remodeling throughout adult life. An ideal medical device for bone regeneration requires interconnected pores within the device to allow for penetration of blood vessels and cells, enabling material biodegradation and bone ingrowth. Additional mandatory characteristics include an excellent resorption rate, a 3D structure similar to natural bone, biocompatibility, and customizability to multiple patient-specific geometries combined with adequate mechanical strength. Therefore, endless silk fibers were spun from native silk solution isolated from silkworm larvae and functionalized with osteoconductive bioceramic materials. In addition, transgenic silkworms were generated to functionalize silk proteins with human platelet-derived growth factor (hPDGF). Both, PDGF-silk and bioceramic modified silk were then assembled into 3D textile implants using an additive manufacturing approach. Textile implants were characterized in terms of porosity, compressive strength, and cyclic load. In addition, osteogenic differentiation of mesenchymal stem cells was evaluated. Silk fiber-based 3D textile implants showed good cytocompatibility and stem cells cultured on bioceramic material functionalized silk implants were differentiating into bone cells. Thus, functionalized 3D interconnected porous textile scaffolds were shown to be promising biomaterials for bone regeneration.
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