Fabrication of elastomeric silk fibers

Dynamics of nuclear matrix attachment regions during 5th instar posterior silk gland development in Bombyx mori

Background

Chromatin architecture is critical for gene expression during development. Matrix attachment regions (MARs) control and regulate chromatin dynamics. The position of MARs in the genome determines the expression of genes in the organism. In this study, we set out to elucidate how MARs temporally regulate the expression of the fibroin heavy chain (FIBH) gene during development. We addressed this by identifying MARs and studying their distribution and differentiation, in the posterior silk glands of Bombyx mori during 5th instar development.

Results

Of the MARs identified on three different days, 7.15% MARs were common to all 3 days, whereas, 1.41, 19.27 and 52.47% MARs were unique to day 1, day 5, and day 7, respectively highlighting the dynamic nature of the matrix associated DNA. The average chromatin loop length based on the chromosome wise distribution of MARs and the distances between these MAR regions decreased from day 1 (253.91 kb) to day 5 (73.54 kb) to day 7 (39.19 kb). Further significant changes in the MARs in the vicinity of the FIBH gene were found during different days of 5^th instar development which implied their role in the regulation and expression of the FIBH gene.

Conclusions

The presence of MARs in the flanking regions of genes found to exhibit differential expression during 5^th instar development indicates their possible role in the regulation of their expression. This reiterates the importance of MARs in the genomic functioning as regulators of the molecular mechanisms in the nucleus. This is the first study that takes into account the tissue specific genome-wide MAR association and the potential role of these MARs in developmentally regulated gene expression. The current study lays a foundation to understand the genome wide regulation of chromatin during development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08446-3.

Micropatterned Silk-Fibroin/Eumelanin Composite Films for Bioelectronic Applications

There has been growing interest in the use of natural bionanomaterials and nanostructured systems for diverse biomedical applications. Such materials can confer unique functional properties as well as address concerns pertaining to sustainability in production. In this work, we propose the biofabrication of micropatterned silk fibroin/eumelanin composite thin films to be used in electroactive and bioactive applications in bioelectronics and biomedical engineering. Eumelanin is the most common form of melanin, naturally derived from the ink of cuttlefish, having antioxidant and electroactive properties. Another natural biomaterial, the protein silk fibroin, is modified with photoreactive chemical groups, which allows the formation of electroactive eumelanin thin films with different microstructures. The silk fibroin/eumelanin composites are fabricated to obtain thin films as well as electroactive microstructures using UV curing. Here, we report for the first time the preparation, characterization, and physical, electrochemical, and biological properties of these natural silk fibroin/eumelanin composite films. Higher concentrations of eumelanin incorporated into the films exhibit a higher charge storage capacity and good electroactivity even after 100 redox cycles. In addition, the microscale structure and the cellular activity of the fibroin/eumelanin films are assessed for understanding of the biological properties of the composite. The developed micropatterned fibroin/eumelanin films can be applied as natural electroactive substrates for bioapplications (e.g., bioelectronics, sensing, and theranostics) because of their biocompatible properties.

Electrospun regenerated Antheraea pernyi silk fibroin scaffolds with improved pore size, mechanical properties and cytocompatibility using mesh collectors

Generally, electrospun silk fibroin scaffolds collected by traditional plates present limited pore size and mechanical properties, which may restrict their biomedical applications. Herein, regenerated Antheraea pernyi silk fibroin (RASF) with excellent inherent cell adhesion property was chosen as a raw material and the conductive metal meshes were used as collectors to prepare modified RASF scaffolds by electrospinning from its aqueous solution. A traditional intact plate was used as a control. The morphology and mechanical properties of the obtained scaffolds were investigated. Schwann cells were further used to assess the cytocompatibility and cell migration ability of the typical scaffolds. Interestingly, compared with the traditional intact plate, the mesh collector with an appropriate gap size (circa 7 mm) could significantly improve the pore size, porosity and mechanical properties of the RASF scaffolds simultaneously. In addition, the scaffold collected under this condition (RASF-7mmG) showed higher cell viability, deeper cell permeation and faster cell migration of Schwann cells. Combined with the excellent inherent properties of ASF and the obviously enhanced scaffold cytocompatibility and mechanical properties, the RASF-7mmG scaffold is expected to be a candidate with great potential for biomedical applications.

Enzyme-catalysed polymer cross-linking: Biocatalytic tools for chemical biology, materials science and beyond

Intermolecular cross-linking is one of the most important techniques that can be used to fundamentally alter the material properties of a polymer. The introduction of covalent bonds between individual polymer chains creates 3D macromolecular assemblies with enhanced mechanical properties and greater chemical or thermal tolerances. In contrast to many chemical cross-linking reactions, which are the basis of thermoset plastics, enzyme catalysed processes offer a complimentary paradigm for the assembly of cross-linked polymer networks through their predictability and high levels of control. Additionally, enzyme catalysed reactions offer an inherently 'greener' and more biocompatible approach to covalent bond formation, which could include the use of aqueous solvents, ambient temperatures, and heavy metal-free reagents. Here, we review recent progress in the development of biocatalytic methods for polymer cross-linking, with a specific focus on the most promising candidate enzyme classes and their underlying catalytic mechanisms. We also provide exemplars of the use of enzyme catalysed cross-linking reactions in industrially relevant applications, noting the limitations of these approaches and outlining strategies to mitigate reported deficiencies.

Characterization of silk-hyaluronic acid composite hydrogels towards vitreous humor substitutes

Multiple ophthalmic pathologies, such as retinal detachment and diabetic retinopathy, require the removal and replacement of the vitreous humor. Clinical tamponades such as silicone oil and fluorinated gases are utilized but limited due to complications and toxicity. Therefore, there is a need for biocompatible, stable, vitreous humor substitutes. In this study, enzymatically crosslinked silk-hyaluronic acid (HA) hydrogels formed using horseradish peroxidase and H2O2 were characterized for use as vitreous humor substitutes. The composite network structure was characterized with dynamic light scattering. In addition, the rheological, optical, and swelling properties of hydrogels with varying silk to HA ratios and crosslinking densities controlled via H2O2 were determined over time. Hydrogels had refractive indexes of 1.336 and were clear with 75-91% light transmission. Hydrogel shear storage modulus ranged between ~6 and 240 Pa where increased H2O2 increased the modulus. After 1 month of aging, there were no changes in modulus for hydrogels with lower silk ratios, while those with higher silk ratios exhibited a significant increase in modulus. Decreasing H2O2 concentration in the reactions led to increased hydrogel volume during swelling, with higher silk ratios returning to their original size after 15 days. Dynamic light scattering results show three diffusive modes, revealing the possible structures of the hydrogel composite and are consistent with the mechanical properties and swelling results. The normalized intraocular pressure of ex vivo porcine eyes after injecting hydrogels were comparable with those treated with silicone oil showing the potential clinical utility of the hydrogels as vitreous substitutes. The versatility of the silk-HA hydrogel system, the tunable swelling properties, and the stability of hydrogels with lower silk ratios show the benefit of utilizing silk-HA hydrogels as vitreous substitutes.

Enzymatically crosslinked silk and silk-gelatin hydrogels with tunable gelation kinetics, mechanical properties and bioactivity for cell culture and encapsulation

Silk fibroin (SF) was enzymatically crosslinked with tyramine-substituted silk fibroin (SF-TA) or gelatin (G-TA) to fabricate hybrid hydrogels with tunable gelation kinetics, mechanical properties and bioactivity. Horseradish peroxidase (HRP)/hydrogen peroxide (H2O2) mediated crosslinking of SF in physiological buffers results in slow gelation and limited mechanical properties. Moreover, SF lacks cell attachment sequences, leading to poor cell-material interactions. These shortcomings can limit the uses of enzymatically crosslinked silk hydrogels in injectable tissue fillings, 3D bioprinting or cell microencapsulation, where rapid gelation and high bioactivity are desired. Here SF/SF-TA and SF/G-TA composite hydrogels were characterized for hydrogel properties and the influence of conjugated cyclic arginine-glycine-aspartic acid (RGD) peptide or G-TA content on bioactivity was explored. Both SF-TA and G-TA significantly increased gelation kinetics, improved mechanical properties and delayed enzymatic degradation in a concentration-dependent manner. β-Sheet formation and hydrogel stiffening were accelerated by SF-TA content but delayed by G-TA. Both cyclic RGD and G-TA significantly improved morphology and metabolic activity of human mesenchymal stem cells (hMSCs) cultured on or encapsulated in composite hydrogels. The hydrogel formulations introduced in this study provide improved control of gel formation and properties, along with biocompatible systems that can be utilized in tissue engineering and cell delivery applications.

Osteogenesis enhancement of silk fibroin/ α-TCP cement by N-acetyl cysteine through Wnt/β-catenin signaling pathway in vivo and vitro

High brittleness and lack osteogenesis are two major limitations of calcium phosphate cement (CPC) in application in bone defect reconstruction. Here we prepared a composite calcium phosphate cement by mixing N-acetyl cysteine loaded silk fibroin solution with α-tricalcium phosphate. In vitro cytology experiment revealed that SF-NAC/α-TCP could significantly increase the activity of exocrine ALP and up-regulated expression of bone-related genes. However, NAC up-regulated gene expression could be significantly suppressed by DKK1. We propose that NAC functioning as osteogenic factor by activating the Wnt/β-catenin signaling pathway may be the possible mechanism of up-regulation of osteogenic genes. Bone regeneration in vivo shown in a rat femur defect was enhanced by the addition of NAC in SF/α-TCP. In addition, the combination intensity of cement-bone interface was improved. The combination SF-NAC/α-TCP might be developed into a promising tool for bone tissue repair in the clinic.

Hydrophobic Antifouling Electrospun Mats from Zwitterionic Amphiphilic Copolymers

A porous material that is both hydrophobic and fouling-resistant is needed in many applications, such as water purification by membrane distillation. In this work, we take a novel approach to fabricating such membranes. Using the zwitterionic amphiphilic copolymer poly(trifluoroethyl methacrylate- random-sulfobetaine methacrylate), we electrospin nonwoven, porous membranes that combine high hydrophobicity with resistance to protein adsorption. By changing the electrospinning parameters and the solution composition, membranes can be prepared with a wide range of fiber morphologies including beaded, bead-free, wrinkly, and ribbonlike fibers, with diameters ranging between ∼150 nm and 1.5 μm. The addition of LiCl to the spinning solution not only helps control the fiber morphology but also increases the segregation of zwitterionic groups on the membrane surface. The resultant electrospun membranes are highly porous and very hydrophobic, yet resist the adsorption of proteins and retain a high contact angle (∼140°) even after exposure to a protein solution. This makes these materials promising candidates for the membrane distillation of contaminated wastewater streams and as self-cleaning materials.

Bioactive Silk Hydrogels with Tunable Mechanical Properties

Developing bioactive hydrogels with potential to guide the differentiation behavior of stem cells has become increasingly important in the biomaterials field. Here, silk hydrogels with tunable mechanical properties were developed by introducing inert silk fibroin nanofibers (SNF) within an enzyme crosslinked system of regenerated silk fibroin (RSF). After the crosslinking reaction of RSF, the inert SNF was embedded into the RSF hydrogel matrix, resulting in improved mechanical properties. Tunable stiffness in the range of 9-60 KPa was achieved by adjusting the amount of the added NSF, significantly higher than SNF-free hydrogels formed under same conditions (about 1 KPa). In addition, the proliferation of rat bone marrow derived mesenchymal stem cells cultured on the composite hydrogels and differentiated into endothelial cells, myoblast and osteoblast cells was improved, putatively due to the control of stiffness of the hydrogels. Bioactive and tunable silk-based hydrogels were prepared via a composite SNF and crosslinked RSF system, providing a new strategy to design silk biomaterials with tunable mechanical and biological performance.