Nonmulberry silk proteins: multipurpose ingredient in bio-functional assembly

Heterogeneous nucleation induced A. pernyi/B. mori silk fibroin coatings on AZ31 biometals with enhanced corrosion resistance, adhesion and biocompatibility

Silk fibroin coatings on biomedical magnesium alloys have garnered significant attention due to their enhanced corrosion resistance and biocompatibility. However, the utilization of wild A. pernyi silk fibroin, known for its RGD sequence that facilitates tissue regeneration, presents a challenge for corrosion-resistant coatings on magnesium alloys due to its weak adhesion and high dissolution rate. In this study, we employed hexafluoroisopropanol as a solvent to blend A. pernyi silk fibroin with B. mori silk fibroin. The resulting blended fibroin coating at a 3:7 mass ratio exhibited a heterogeneous nucleation effect, enhancing β-sheet content (32.3 %) and crystallinity (28.6 %). This improved β-sheet promoted the "labyrinth effect" with an Icorr of 2.15 × 10-6 A cm-2, resulting in significantly improved corrosion resistance, which is two orders of magnitude lower than that of pure magnesium alloy. Meanwhile, the increased content of exposed serine in zigzag β-sheet contributes to a higher adhesion strength. Cell cytotoxicity evaluation confirmed the enhanced cell adhesion and bioactivity. This work provides a facile approach for wild A. pernyi silk fibroin coatings on magnesium alloys with enhanced corrosion resistance, adhesion and biocompatibility.

Molecular and metabolic insights into purplish leaf coloration through the investigation of two mulberry (Morus alba) genotypes

BACKGROUND

Leaf coloration in plants, attributed to anthocyanin compounds, plays a crucial role in various physiological functions, and also for pharmaceutical and horticultural uses. However, the molecular mechanisms governing leaf coloration and the physiological significance of anthocyanins in leaves remain poorly understood.

RESULTS

In this study, we investigated leaf color variation in two closely related mulberry genotypes, one with purplish-red young leaves (EP) and another with normal leaf color (EW). We integrated transcriptomic and metabolomic approaches to gain insights into the metabolic and genetic basis of purplish-red leaf development in mulberry. Our results revealed that flavonoid biosynthesis, particularly the accumulation of delphinidin-3-O-glucoside, is a key determinant of leaf color. Additionally, the up-regulation of CHS genes and transcription factors, including MYB family members, likely contributes to the increased flavonoid content in purplish-red leaves.

CONCLUSION

These findings enhance our understanding of the molecular mechanisms responsible for the purplish coloration observed in mulberry leaves and also offer supporting evidence for the hypothesis that anthocyanins serve a protective function in plant tissues until the processes of light absorption and carbon fixation reach maturity, thereby ensuring a balanced equilibrium between energy capture and utilization.

Microfibre-Functionalised Silk Hydrogels

Silk hydrogels have shown potential for tissue engineering applications, but several gaps and challenges, such as a restricted ability to form hydrogels with tuned mechanics and structural features, still limit their utilisation. Here, Bombyx mori and Antheraea mylitta (Tasar) silk microfibres were embedded within self-assembling B. mori silk hydrogels to modify the bulk hydrogel mechanical properties. This approach is particularly attractive because it creates structured silk hydrogels. First, B. mori and Tasar microfibres were prepared with lengths between 250 and 500 μm. Secondary structure analyses showed high beta-sheet contents of 61% and 63% for B. mori and Tasar microfibres, respectively. Mixing either microfibre type, at either 2% or 10% (w/v) concentrations, into 3% (w/v) silk solutions during the solution-gel transition increased the initial stiffness of the resulting silk hydrogels, with the 10% (w/v) addition giving a greater increase. Microfibre addition also altered hydrogel stress relaxation, with the fastest stress relaxation observed with a rank order of 2% (w/v) > 10% (w/v) > unmodified hydrogels for either fibre type, although B. mori fibres showed a greater effect. The resulting data sets are interesting because they suggest that the presence of microfibres provided potential 'flow points' within these hydrogels. Assessment of the biological responses by monitoring cell attachment onto these two-dimensional hydrogel substrates revealed greater numbers of human induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) attached to the hydrogels containing 10% (w/v) B. mori microfibres as well as 2% (w/v) and 10% (w/v) Tasar microfibres at 24 h after seeding. Cytoskeleton staining revealed a more elongated and stretched morphology for the cells growing on hydrogels containing Tasar microfibres. Overall, these findings illustrate that hydrogel stiffness, stress relaxation and the iPSC-MSC responses towards silk hydrogels can be tuned using microfibres.

Enhanced bone regeneration usingAntheraea mylittasilk fibroin and chitosan based scaffold:in-vivoandin-vitrostudy

In this study, highly interconnected porous scaffolds fromAntheraea mylittasilk fibroin (SF) and chitosan (CH) were fabricated using the freeze-drying method. The weight ratios of SF to CH were varied from 90:10 (SF90/CH10) to 50:50 (SF50/CH50) to prepare the scaffolds from the aqueous suspension of the protein-polysaccharide mix. From the initial optimization of scaffold composition with respect to their microstructure, porosity, and mechanical properties, the SF80/CH20scaffold exhibited the most suitable properties for bone tissue engineering application as compared to others compositions. Hencein-vitrohemocompatibility, protein adsorption, and MG-63 cell culture studies were carried out for SF80/CH20scaffold. The fabricated SF80/CH20scaffold showed a more controlled swelling percentage of 42.8%, with high BSA protein adsorption of 0.39 mg of BSA per gm of the scaffold at 24 h incubation period. Furthermore,in-vitroMG-63 cell culture study onto the fabricated SF80/CH20scaffold elicited excellent MG-63 cell attachment with better biocompatibility and cell viability with increased F-action production from day 3 to day 7 of the cell culture period.In vivobone defect healing in a rabbit tibia model revealed excellent bone healing capacity in SF80/CH20scaffold implanted specimens compared to control ones, as evident from histology and fluorochrome labeling analysis.

Relevant Properties and Potential Applications of Sericin in Bone Regeneration

The potential of sericin, a protein derived from silkworms, is explored in bone graft applications. Sericin's biocompatibility, hydrophilic nature, and cost-effectiveness make it a promising candidate for enhancing traditional graft materials. Its antioxidant, anti-inflammatory, and UV-resistant properties contribute to a healthier bone-healing environment, and its incorporation into 3D-printed grafts could lead to personalized medical solutions. However, despite these promising attributes, there are still gaps in our understanding. The precise mechanism through which sericin influences bone cell growth and healing is not fully understood, and more comprehensive clinical trials are needed to confirm its long-term biocompatibility in humans. Furthermore, the best methods for incorporating sericin into existing graft materials are still under investigation, and potential allergic reactions or immune responses to sericin need further study.

Development of bilayered porous silk scaffolds for thymus bioengineering

The thymus coordinates the development and selection of T cells. It is structured into two main compartments: the cortex and the medulla. The replication of such complex 3D environment has been challenged by bioengineering approaches. Nevertheless, the effect of the scaffold microstructure on thymic epithelial cell (TEC) cultures has not been deeply investigated. Here, we developed bilayered porous silk fibroin scaffolds and tested their effect on TEC co-cultures. The small and large pore scaffolds presented a mean pore size of 84.33 ± 21.51 μm and 194.90 ± 61.38 μm, respectively. The highly porous bilayered scaffolds presented a high water absorption and water content (> 94 %), together with mechanical properties in the range of the native tissue. TEC (i.e., medullary (mTEC) and cortical (cTEC) cell lines) proliferation is increased in scaffolds with larger pores. The co-culture of both TEC lines in the bilayered porous silk scaffolds presents enhanced cell proliferation and metabolic activity when compared with mTEC in single culture. Also, when the co-culture occurred with cTEC in the small pores layer and mTEC in the large pores layer, a 9.2- and 18.9-fold increase in Foxn1 and Icam1 gene expression in cTEC is evident. These results suggest that scaffold microstructure and the co-culture influence TEC's behaviour. Bilayered silk scaffolds with adjusted microstructure are a valid alternative for TEC culture, having possible applications in advanced thymus bioengineering strategies.

Delivering on the promise of recombinant silk-inspired proteins for drug delivery

Effective drug delivery is essential for the success of a medical treatment. Polymeric drug delivery systems (DDSs) are preferred over systemic administration of drugs due to their protection capacity, directed release, and reduced side effects. Among the numerous polymer sources, silks and recombinant silks have drawn significant attention over the past decade as DDSs. Native silk is produced from a variety of organisms, which are then used as sources or guides of genetic material for heterologous expression or engineered designs. Recombinant silks bear the outstanding properties of natural silk, such as processability in aqueous solution, self-assembly, drug loading capacity, drug stabilization/protection, and degradability, while incorporating specific properties beneficial for their success as DDS, such as monodispersity and tailored physicochemical properties. Moreover, the on-demand inclusion of sequences that customize the DDS for the specific application enhances efficiency. Often, inclusion of a drug into a DDS is achieved by simple mixing or diffusion and stabilized by non-specific molecular interactions; however, these interactions can be improved by the incorporation of drug-binding peptide sequences. In this review we provide an overview of native sources for silks and silk sequences, as well as the design and formulation of recombinant silk biomaterials as drug delivery systems in a variety of formats, such as films, hydrogels, porous sponges, or particles.

Stretching-Induced Conformational Transition of [3-13C]Ser- and [3-13C]Tyr-Antheraea yamamai Silk Fibroin before Spinning Investigated with 13C Solid-State NMR Spectroscopy

The conformational transition of [3-¹³C]Ser- and [3-¹³C]Tyr-Antheraea yamamai silk fibroin before spinning induced by stretching was investigated with ¹³C CP/MAS NMR spectroscopy. The α-helix content of the silk fibroin before stretching was found to be 31.6% based on the Ala and Ser peaks. With increasing stretching ratio, the α-helix and the random coil Ala Cβ peaks decreased gradually, while the β-sheet peak was observed at a stretching ratio of ×5 and increased rapidly upon further stretching. For Ser residue, the α-helix peak decreased monotonically with increasing stretching ratio, but the random coil peak increased slightly till the stretching ratio of ×5 and then decreased. A small β-sheet peak was observed before stretching and then increased rapidly starting from the stretching ratio of ×7. In contrast, a gradual decrease of random coil peak and an increase of β-sheet peak were observed for the Tyr residue. The results of this investigation may be helpful for further studies of fiber formation mechanism in A. yamamai and in the future design of artificial silk materials.

Flat Silk Cocoon-Based Dressing: Daylight-Driven Rechargeable Antibacterial Membranes Accelerate Infected Wound Healing

One of the leading causes of death globally, especially in underdeveloped countries, is bacterial infection. Recently, the prevalence of infections from antibiotic-resistant bacteria has been increasing, which makes the need for innovative antibacterial wound dressings urgent. It is reported that g-C₃ N₄ -based flat silk cocoons (FSCs) with rechargeable antibacterial activity can efficiently generate reactive oxygen species (ROS) under daylight irradiation. The photoactive FSCs store the ROS and then release them in the dark. The engineered FSCs exhibit integrated properties of good biocompatibility, strong mechanical characteristics, robust photoactivity with photostorability, and excellent bactericidal efficiency (99.9% contact killing). In a rat model of infected wounds, the photoactive FSCs induce faster healing and reduce bacterial infections. The successful application of these FSC materials as wound dressings may provide a versatile platform for exploring the use of green photoactive antibacterial materials for accelerated wound healing and prevention of infections.

Nonmulberry silk fibroin-based biomaterials: Impact on cell behavior regulation and tissue regeneration

Silk fibroin (SF) is a promising biomaterial due to its good biocompatibility, easy availability, and high mechanical properties. Compared with mulberry silk fibroin (MSF), nonmulberry silk fibroin (NSF) isolated from typical nonmulberry silkworm silk exhibits unique arginine-glycine-aspartic acid (RGD) sequences with favorable cell adhesion enhancing effect. This inherent property probably makes the NSF more suitable for cell culture and tissue regeneration-related applications. Accordingly, various types of NSF-based biomaterials, such as particles, films, fiber mats, and 3D scaffolds, are constructed and their application potential in different biomedical fields is extensively investigated. Based on these promising NSF biomaterials, this review firstly makes a systematical comparison between the molecular structure and properties of MSF and typical NSF and highlights the unique properties of NSF. In addition, we summarize the effective fabrication strategies from degummed nonmulberry silk fibers to regenerated NSF-based biomaterials with controllable formats and their recent application progresses in cell behavior regulation and tissue regeneration. Finally, current challenges and future perspectives for the fabrication and application of NSF-based biomaterials are discussed. Related research and perspectives may provide valuable references for designing and modifying effective NSF-based and other natural biomaterials. STATEMENT OF SIGNIFICANCE: There exist many reviews about mulberry silk fibroin (MSF) biomaterials and their biomedical applications, while that about nonmulberry silk fibroin (NSF) biomaterials is scarce. Compared with MSF, NSF exhibits unique arginine-glycine-aspartic acid sequences with promising cell adhesion enhancing effect, which makes NSF more suitable for cell culture and tissue regeneration related applications. Focusing on these advanced NSF biomaterials, this review has systematically compared the structure and properties of MSF and NSF, and emphasized the unique properties of NSF. Following that, the effective construction strategies for NSF-based biomaterials are summarized, and their recent applications in cell behavior regulations and tissue regenerations are highlighted. Furthermore, current challenges and future perspectives for the fabrication and application of NSF-based biomaterials were discussed.

Formylation of Recombinant Spider Silk in Formic Acid and Wet Spinning Studied Using Nuclear Magnetic Resonance and Infrared Spectroscopies

We reported wet spinning of recombinant spider silk protein (RSSP) and formylation of RSSP in formic acid (FA). First, FA was selected as the spinning solvent and the detailed spinning condition was determined. Next, the mechanical property was compared between the RSSP fiber spun after allowing the spinning solution dissolved in FA to stand for 2 days and the fiber spun immediately after being dissolved in FA for 4 h. The tensile strength of the former fiber was lower than the strength of the latter fiber. This difference can be explained by the difference in the degree of formylation as follows. FA is a known formylating agent, although most researchers who prepared silk fiber by wet spinning with FA have not pointed out about formylation. The formylation of the Ser OH group was confirmed by ¹³C solution nuclear magnetic resonance (NMR), and the time course of formylation of the RSSP film prepared from the FA solution was tracked by Fourier transform infrared spectroscopy. The ¹³C solid-state NMR spectra were also compared between two kinds of the formylated RSSP fibers and indicated that the packing state was tighter for the latter fiber than the former one, which could explain higher tensile strength of the latter fiber in the dry state. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis indicated that the RSSP sample decomposed gradually with storage time in FA and the decomposition has begun partly even at 2 h after dissolution in FA. The decomposition by formylation seems to have no significant effect on the backbone structure of the RSSP fiber, although the packing of the fiber becomes loose as a whole. Finally, preliminary trial of deformylation of the formylated RSSP fiber was performed.

3D Printing for Bone-Cartilage Interface Regeneration

Due to the vasculature defects and/or the avascular nature of cartilage, as well as the complex gradients for bone-cartilage interface regeneration and the layered zonal architecture, self-repair of cartilage and subchondral bone is challenging. Currently, the primary osteochondral defect treatment strategies, including artificial joint replacement and autologous and allogeneic bone graft, are limited by their ability to simply repair, rather than induce regeneration of tissues. Meanwhile, over the past two decades, three-dimension (3D) printing technology has achieved admirable advancements in bone and cartilage reconstruction, providing a new strategy for restoring joint function. The advantages of 3D printing hybrid materials include rapid and accurate molding, as well as personalized therapy. However, certain challenges also exist. For instance, 3D printing technology for osteochondral reconstruction must simulate the histological structure of cartilage and subchondral bone, thus, it is necessary to determine the optimal bioink concentrations to maintain mechanical strength and cell viability, while also identifying biomaterials with dual bioactivities capable of simultaneously regenerating cartilage. The study showed that the regeneration of bone-cartilage interface is crucial for the repair of osteochondral defect. In this review, we focus on the significant progress and application of 3D printing technology for bone-cartilage interface regeneration, while also expounding the potential prospects for 3D printing technology and highlighting some of the most significant challenges currently facing this field.

Fabrication of flexible conductive silk fibroin/polythiophene membrane and its properties

Silk fibroin (SF) film is an insulating material, which can be combined with polythiophene derivatives with electrical conductivity to obtain a flexible conductive material. In this work, poly(3,4-ethylenedioxythiophene) (PEDOT) was used to graft a silk protein film. The hydroxyl radical is formed by activation and oxidation of the silk protein film polymerized with the PEDOT radical formed by oxidation of 3,4-ethylenedioxythiophene to obtain a conductive silk film. The SF/PEDOT film, when tested, showed excellent electrical conductivity with resistance up to 63 Ω·cm−2, good flexibility, mechanical properties, fastness, and biocompatibility.

Precision biomaterials in cancer theranostics and modelling

Despite significant achievements in the understanding and treatment of cancer, it remains a major burden. Traditional therapeutic approaches based on the 'one-size-fits-all' paradigm are becoming obsolete, as demonstrated by the increasing number of patients failing to respond to treatments. In contrast, more precise approaches based on individualized genetic profiling of tumors have already demonstrated their potential. However, even more personalized treatments display shortcomings mainly associated with systemic delivery, such as low local drug efficacy or specificity. A large amount of effort is currently being invested in developing precision medicine-based strategies for improving the efficiency of cancer theranostics and modelling, which are envisioned to be more accurate, standardized, localized, and less expensive. To this end, interdisciplinary research fields, such as biomedicine, material sciences, pharmacology, chemistry, tissue engineering, and nanotechnology, must converge for boosting the precision cancer ecosystem. In this regard, precision biomaterials have emerged as a promising strategy to detect, model, and treat cancer more efficiently. These are defined as those biomaterials precisely engineered with specific theranostic functions and bioactive components, with the possibility to be tailored to the cancer patient needs, thus having a vast potential in the increasing demand for more efficient treatments. In this review, we discuss the latest advances in the field of precision biomaterials in cancer research, which are expected to revolutionize disease management, focusing on their uses for cancer modelling, detection, and therapeutic applications. We finally comment on the needed requirements to accelerate their application in the clinic to improve cancer patient prognosis.