NMR Analysis of the Fibronectin Cell-Adhesive Sequence, Arg-Gly-Asp, in a Recombinant Silk-Like Protein and a Model Peptide

Bombyx mori Silk Fibroin and Model Peptides Incorporating Arg-Gly-Asp Motifs and Their Application in Wound Dressings

Skin plays an important role in protecting the human body from the environment, dehydration, and infection. Burns, wounds, and disease cause the skin to lose its role, but tissue-engineered skin substitutes offer the opportunity to restore skin loss. Silk fibroin from Bombyx mori (SF) has proven to be an excellent wound dressing material. In this study, we aim to develop an excellent wound dressing material by introducing three-residue sequence Arg-Gly-Asp (RGD), which is the most well-known adhesion site of fibronectin, in the films of SF and the model peptide. Its usefulness as a wound dressing material was evaluated both in vitro and in vivo. First, we showed that the flexible structures of the RGD sequence are still maintained in SF with a rigid antiparallel β-sheet structure using NMR in association with excellent wound dressings of SF containing RGD. Then, in in vitro experiments, two types of normal cells derived from human skin, normal human neonatal epidermal keratinocytes and normal human neonatal dermal fibroblasts, were used to evaluate the cell adhesion. On the other hand, in in vivo experiments, the study was conducted using a rat model of a whole skin layer defect wound. The results showed that the high-functionalized SF developed here has the potential to play a significant role in the field of wound dressings.

An economical approach for peptide synthesis via regioselective C-N bond cleavage of lactams

An economical, solvent-free, and metal-free method for peptide synthesis via C-N bond cleavage using lactams has been developed. The method not only eliminates the need for condensation agents and their auxiliaries, which are essential for conventional peptide synthesis, but also exhibits high atom economy. The reaction is versatile because it can tolerate side chains bearing a range of functional groups, affording up to >99% yields of the corresponding peptides without racemisation or polymerisation. Moreover, the developed strategy enables peptide segment coupling, providing access to a hexapeptide that occurs as a repeat sequence in spider silk proteins.

Recent applications of QCM-D for the design, synthesis, and characterization of bioactive materials

The clinical translation of bioactive technologies is lacking compared to the number of novel technologies reported in the literature. This is in part due to the difficulties in characterizing bioactive materials to understand and predict their biological response. To progress the field and increase clinical success, more robust analytical techniques must be utilized when investigating novel bioactive materials. The quartz crystal microbalance with dissipation (QCM-D), a label-free sensing instrument based on an acoustic resonator, is used to quantify mass change and viscoelastic parameters from soft materials at the nanoscale, in situ, with precise temporal resolution and operation in both liquid and gaseous environments. The versatility of QCM-D has enhanced the characterization of bioactive polymers and sensing arrays for advanced applications of novel biotechnologies. In this review, we highlight exciting, recent applications of QCM-D for the investigation of bioactive materials. Attention is given to the dynamic mechanical properties of bioactive materials, discerning protein structure on surfaces, probing cell adhesion and cytoskeletal changes, and biosensing applications. We conclude that QCM-D has untapped utility in the pre-clinical investigation of bioactive materials and further utilization can improve the clinical success of novel technologies.

Biological effects different diameters of Tussah silk fibroin nanofibers on olfactory ensheathing cells

Transplantation of olfactory ensheathing cells (OECs) has potential for treating spinal cord and brain injury. However, they are void of an extracellular matrix to support cell growth and migration. Engineering of tissue to mimic the extracellular matrix is a potential solution for neural repair. Tussah silk fibroin (TSF) has good biocompatibility and an Arg-Gly-Asp tripeptide sequence. A small number of studies have assessed the effect of the diameter of TSF nanofibers on cell adhesion, growth and migration. In the present study, TSF nanofibers with a diameter of 400 and 1,200 nm were prepared using electrospinning technology; these were then used as scaffolds for OECs. The structure and morphology of the TSF nanofibers were characterized by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy. An inverted-phase contrast microscope and SEM were used to observe the morphology of OECs on the TSF nanofibers. The effect on the adhesion of the cells was observed following crystal violet staining. The phenotype of the cells and the maximum axon length on the scaffolds were evaluated by immunostaining for nerve growth factor receptor p75. Cell proliferation and viability were assessed by an MTT assay and a Live/Dead reagent kit. The migration efficiency of OECs was observed using live-cell microscopy. The results indicated that a 400-nm TSF fiber scaffold was more conducive to OEC adhesion, growth and migration compared with a 1,200-nm TSF scaffold. The phenotype of the OECs was normal, and no difference in OEC phenotype was observe when comparing those on TSF nanofibers to those on PLL. The present study may provide guidance regarding the preparation of tissue-engineered materials for neural repair.

Silk-fibronectin protein alloy fibres support cell adhesion and viability as a high strength, matrix fibre analogue

Silk is a natural polymer with broad utility in biomedical applications because it exhibits general biocompatibility and high tensile material properties. While mechanical integrity is important for most biomaterial applications, proper function and integration also requires biomaterial incorporation into complex surrounding tissues for many physiologically relevant processes such as wound healing. In this study, we spin silk fibroin into a protein alloy fibre with whole fibronectin using wet spinning approaches in order to synergize their respective strength and cell interaction capabilities. Results demonstrate that silk fibroin alone is a poor adhesive surface for fibroblasts, endothelial cells, and vascular smooth muscle cells in the absence of serum. However, significantly improved cell attachment is observed to silk-fibronectin alloy fibres without serum present while not compromising the fibres' mechanical integrity. Additionally, cell viability is improved up to six fold on alloy fibres when serum is present while migration and spreading generally increase as well. These findings demonstrate the utility of composite protein alloys as inexpensive and effective means to create durable, biologically active biomaterials.

A fibronectin mimetic motif improves integrin mediated cell biding to recombinant spider silk matrices

The cell binding motif RGD is the most widely used peptide to improve cell binding properties of various biomaterials, including recombinant spider silk. In this paper we use genetic engineering to further enhance the cell supportive capacity of spider silk by presenting the RGD motif as a turn loop, similar to the one found in fibronectin (FN), but in the silk stabilized by cysteines, and therefore denoted FNCC. Human primary cells cultured on FNCC-silk showed increased attachment, spreading, stress fiber formation and focal adhesions, not only compared to RGD-silk, but also to silk fused with linear controls of the RGD containing motif from fibronectin. Cell binding to FNCC-silk was shown to involve the α5β1 integrin, and to support proliferation and migration of keratinocytes. The FNCC-silk protein allowed efficient assembly, and could even be transformed into free standing films, on which keratinocytes could readily form a monolayer culture. The results hold promise for future applications within tissue engineering.

Bacterial cellulose and hyaluronic acid hybrid membranes: Production and characterization

In this study, the effect of the addition of hyaluronic acid (HA) on bacterial cellulose (BC) production, under static conditions was evaluated in terms of the properties of the resulting BC hybrid membranes. HA was added to the fermentation process in three distinct time points: first day (BC-T0), third day (BC-T3) and sixth day (BC-T6). Analyses of FT-IR and CP/MAS (13)C NMR confirmed the presence of HA in bacterial cellulose membranes. The crystal structure, crystallinity index (Ic) surface roughness, thermal stability and hybrophobic/hydrophilic character changed. Membranes with higher roughness were produced with HA added on the first and third day of fermentation process. The surface energy of BC/HA membranes was calculated and more hydrophilic membranes were produced by the addition of HA on the third and sixth day, also resulting in more thermally stable materials. The results demonstrate that bacterial cellulose/hyaluronic acid hybrid membranes can be produced in situ and suggest that HA interacts with the sub-elementary bacterial cellulose fibrils, changing the properties of the membranes. The study and understanding of the factors that affect those properties are of utmost importance for the safe and efficient use of BC as biomaterials in numerous applications, specifically in the biological field.

Photoresponsive retinal-modified silk-elastin copolymer

The chimeric proteins, silk-elastin-like protein polymers (SELPs), consist of repeating units of silk and elastin to retain the mechanical strength of silk, while incorporating the dynamic environmental sensitivity of elastin. A retinal-modified SELP was prepared, modified, and studied for photodynamic responses. The protein was designed, cloned, expressed, and purified with lysine present in the elastin repeats. The purified protein was then chemically modified with the biocompatible moiety retinal via the lysine side chains. Structural changes with the polymer were assessed before and after retinal modification using Fourier transform infrared spectroscopy and circular dichroism spectroscopy. Optical studies and spectral analysis were performed before and after retinal modification. The random-coil fraction of the protein increased after retinal modification while the β-sheet fraction significantly decreased. Birefringence of the modified protein was induced when irradiated with a linearly polarized 488 nm laser light. Retinal modification of this protein offers a useful strategy for potential use in biosensors, controlled drug delivery, and other areas of biomedical engineering.