Chemical modification and biosynthesis of silk-like polymers

Improving solubility of poorly water-soluble drugs by protein-based strategy: A review

Poorly water-soluble drugs are frequently encountered and present a most challengeable difficulty in pharmaceutical development. Poor solubility of drugs can lead to suboptimal bioavailability and therapeutic efficiency. Increasing efforts have been contributed to improve the solubility of poorly water-soluble drugs for better pharmacokinetics and pharmacodynamics. Among various solubility enhancement technologies, protein-based strategy to address poorly water-soluble drugs issues has special interests for natural advantages including versatile interactions between proteins and hydrophobic drugs, biocompatibility, biodegradation, and metabolization of proteins. The protein-drug formulations could be formed by covalent conjugations or noncovalent interactions to facilitate solubility of poorly water-soluble drugs. This review is to summarize the advances using proteins including plant proteins, mammalian proteins, and recombinant proteins, to enhance water solubility of poorly water-soluble drugs.

Development of New Bio-Composite of PEO/Silk Fibroin Blends Loaded with Piezoelectric Material

New bio-composite nanofibers composed of polyethylene oxide (PEO)/silk fibroin (SF)/barium titanate (BaTiO₃) are introduced in this study. The SF solution was added to the PEO solution to form a PEO/SF blend with different weight percentages (5, 10, 15, 20 wt.%). The PEO/15 wt.% SF blend was selected to continue the experimental plan based on the optimum nanofiber morphology. Different wt.% of BaTiO₃ particles (0.2, 0.4, 0.8, 1 wt.%) were added to the PEO/15 wt.% SF blend solution, and the suspensions obtained were introduced to an electrospinning device. The fabricated tissue was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The zeta potential of the solution and the piezoelectric performance of the fabricated tissue were characterized. A newly designed pizoTester was used to investigate piezoelectric properties. The results showed that a well-organized, smooth PEO/15 wt.% SF/0.2 wt.% BaTiO₃ nanofiber composite with low bead contents was obtained. Improved properties and electrical coupling were achieved in the newly introduced material. Electrospun PEO/15 wt.% SF/0.2 wt.% BaTiO₃ mats increased the output voltage (1150 mV) compared to pristine PEO and PEO/SF composite fibers (410 and 290 mV, respectively) upon applying 20 N force at 5 Hz frequency. The observed enhancement in piezoelectric properties suggests that the prepared composite could be a promising material in cardiac tissue engineering (CTE).

Strategies for the Biofunctionalization of Straining Flow Spinning Regenerated Bombyx mori Fibers

High-performance regenerated silkworm (Bombyx mori) silk fibers can be produced efficiently through the straining flow spinning (SFS) technique. In addition to an enhanced biocompatibility that results from the removal of contaminants during the processing of the material, regenerated silk fibers may be functionalized conveniently by using a range of different strategies. In this work, the possibility of implementing various functionalization techniques is explored, including the production of fluorescent fibers that may be tracked when implanted, the combination of the fibers with enzymes to yield fibers with catalytic properties, and the functionalization of the fibers with cell-adhesion motifs to modulate the adherence of different cell lineages to the material. When considered globally, all these techniques are a strong indication not only of the high versatility offered by the functionalization of regenerated fibers in terms of the different chemistries that can be employed, but also on the wide range of applications that can be covered with these functionalized fibers.

Chemical Modification of Silk Fibroin through Serine Amino Acid Residues

Silk fibroin (SF) is a natural protein polymer and promising biomaterial. Chemical modifications have attracted growing interest in expanding SF applications. However, the majority of amino acid residues in SF are non-reactive and most of the reactive ones are in the crystalline region. Herein, a modification was conducted to investigate the possibility of direct modification on the surface of natural SF by a reagent with a mild reactivity, the type and quantity of the residues involved in the reactions, and the structural changes upon modification. Infrared spectrum, ¹H NMR, titration and amino acid analyses, X-ray diffraction, and hemolysis test were used to analyze the materials. The results showed that sulfonic acid groups were grafted onto SF and the reaction occurred mainly at serine residues through hydroxyl groups. In total, 0.0958 mmol/g of residues participated in the modification with a modification efficiency of 7.6%. Moreover, the crystallinity and the content of β-sheet structure in SF increased upon modification. The modified material had good blood-compatibility. In conclusion, surface modification on native SF through serine residues was practicable and had the advantage of increased β-sheet structure. This will provide an alternative way for the modification of fibroin for the desired application in the biomedical field.

Biosafety chemistry and biosafety materials: a new perspective to solve biosafety problems

The Novel Coronavirus Disease (COVID-19) has rapidly swept around the globe since its first emergence near 2020. However, people have failed to fully understand its origin or mutation. Defined as an international biosafety incident, COVID-19 has again encouraged worldwide attention to reconsider the importance of biosafety due to the adverse impact on personal well-being and social stability. Most countries have already taken measures to advocate progress in biosafety-relevant research, aiming to prevent and solve biosafety problems with more advanced techniques and products. Herein, we propose a new concept of biosafety chemistry and reiterate the notion of biosafety materials, which refer to the interdisciplinary integration of biosafety and chemistry or materials. Here, we attempt to illustrate the exquisite association that chemistry and material science possess with biosafety fields and we hope to provide a pragmatic perspective on approaches to utilize the knowledge of these two subjects to handle specific biosafety issues such as detection and disinfection of pathogenic microorganisms, personal and collective protective equipment, vaccine adjuvants and specific drugs, preservation of biogenetic resources for human, animals, and plants. In addition, we hope to convey and promote the idea of multidisciplinary cooperation to strengthen biosafety research and development of relevant products for establishing possibly specific majors to defend national security in the future.

A review on advances in the applications of spider silk in biomedical issues

Spider silk, as one of the hardest natural and biocompatible substances with extraordinary strength and flexibility, have become an ideal option in various areas of science and have made their path onto the biomedical industry. Despite its growing popularity, the difficulties in the extraction of silks from spiders and farming them have made it unaffordable and almost impossible for industrial scale. Biotechnology helped production of spider silks recombinantly in different hosts and obtaining diverse morphologies out of them based on different processing and assembly procedures. Herein, the characteristics of these morphologies and their advantages and disadvantages are summarized. A detailed view about applications of recombinant silks in skin regeneration and cartilage, tendon, bone, teeth, cardiovascular, and neural tissues engineering are brought out, where there is a need for strong scaffolds to support cell growth. Likewise, spider silk proteins have applications as conduit constructs, medical sutures, and 3D printer bioinks. Other characteristics of spider silks, such as low immunogenicity, hydrophobicity, homogeneity, and adjustability, have attracted much attention in drug and gene delivery. Finally, the challenges and obstacles ahead for industrializing the production of spider silk proteins in sufficient quantities in biomedicine, along with solutions to overcome these barriers, are discussed.

Bioengineered elastin- and silk-biomaterials for drug and gene delivery

Advances in medical science have led to diverse new therapeutic modalities, as well as enhanced understanding of the progression of various disease states. These findings facilitate the design and development of more customized and exquisite drug delivery systems that aim to improve therapeutic indices of drugs to treat a variety of conditions. Synthetic polymer-based drug carriers have often been the focus of such research. However, these structures suffer from challenges with heterogeneity of the starting material, limited chemical features, complex functionalization methods, and in some cases a lack of biocompatibility. Consequently, protein-based polymers have garnered much attention in recent years due to their monodisperse features, ease of production and functionalization, and biocompatibility. Genetic engineering techniques enable the advancement of protein-based drug delivery systems with finely tuned physicochemical properties, and thus an expanded level of customization unavailable with synthetic polymers. Of these genetically engineered proteins, elastin-like proteins (ELP), silk-like proteins (SLP), and silk-elastin-like proteins (SELP) provide a unique set of alternatives for designing drug delivery systems due to their inherent chemical and physical properties and ease of engineering afforded by recombinant DNA technologies. In this review we examine the advantages of genetically engineered drug delivery systems with emphasis on ELP and SLP constructions. Methods for fabrication and relevant biomedical applications will also be discussed.

Evaluation of silk-based bioink during pre and post 3D bioprinting: A review

During past few decades, the demand for the replacement of damaged organs is increasing consistently. This is due to the advancement in tissue engineering, which opens the possibility of regeneration of damaged organs or tissues into functional parts with the help of 3D bioprinting. Bioprinting technology presents an excellent potential to develop complex structures with precise control over cell suspension and structure. A brief description of different types of 3D bioprinting techniques, including inkjet-based, laser-based, and extrusion-based bioprinting is presented here. Due to innate advantageous features like tunable biodegradability, biocompatibility, elasticity and mechanical robustness, silk has carved a niche in the realm of tissue engineering. In this review article, the focus is to highlight the possible approach of exploring silk as bioink for fabrication of bioprinted implants using 3D bioprinting. This review discusses different type of degumming, dissolution techniques for extraction of proteins from different sources of silk. Different recently reported 3D bioprinting techniques suitable for silk-based bioink are further elaborated. Postprinting characterization of resultant scaffolds are also describe here. However, there is an astounding progress in 3D bioprinting technology, still there is a need to develop further the current bioprinting technology to make it suitable for generation of heterogeneous tissue construct. The possibility of utilizing the adhesive property of sericin to consider it as bioink is elaborated.

Recombinant Spidroins as the Basis for New Materials

Spider web proteins are unique materials created by nature that, considering the combination of their properties, do not have analogues among natural or human-created materials. Obtaining significant amounts of these proteins from natural sources is not feasible. Biotechnological manufacturing in heterological systems is complicated by the very high molecular weight of spidroins and their specific amino acid composition. Obtaining recombinant analogues of spidroins in heterological systems, mainly in bacteria and yeast, has become a compromise solution. Because they can self-assemble, these proteins can form various materials, such as fibers, films, 3D-foams, hydrogels, tubes, and microcapsules. The effectiveness of spidroin hydrogels in deep wound healing, as 3D scaffolds for bone tissue regeneration and as oriented fibers for axon growth and nerve tissue regeneration, was demonstrated in animal models. The possibility to use spidroin micro- and nanoparticles for drug delivery was demonstrated, including the use of modified spidroins for virus-free DNA delivery into animal cell nuclei. In the past few years, significant interest has arisen concerning the use of these materials as biocompatible and biodegradable soft optics to construct photonic crystal super lenses and fiber optics and as soft electronics to use in triboelectric nanogenerators. This review summarizes the latest achievements in the field of spidroin production, the creation of materials based on them, the study of these materials as a scaffold for the growth, proliferation, and differentiation of various types of cells, and the prospects for using these materials for medical applications (e.g., tissue engineering, drug delivery, coating medical devices), soft optics, and electronics. Accumulated data suggest the use of recombinant spidroins in medical practice in the near future.

Transgenic and Diet-Enhanced Silk Production for Reinforced Biomaterials: A Metamaterial Perspective

Silk fibers, which are protein-based biopolymers produced by spiders and silkworms, are fascinating biomaterials that have been extensively studied for numerous biomedical applications. Silk fibers often have remarkable physical and biological properties that typical synthetic materials do not exhibit. These attributes have prompted a wide variety of silk research, including genetic engineering, biotechnological synthesis, and bioinspired fiber spinning, to produce silk proteins on a large scale and to further enhance their properties. In this review, we describe the basic properties of spider silk and silkworm silk and the important production methods for silk proteins. We discuss recent advances in reinforced silk using silkworm transgenesis and functional additive diets with a focus on biomedical applications. We also explain that reinforced silk has an analogy with metamaterials such that user-designed atypical responses can be engineered beyond what naturally occurring materials offer. These insights into reinforced silk can guide better engineering of superior synthetic biomaterials and lead to discoveries of unexplored biological and medical applications of silk.

How to define and study structural proteins as biopolymer materials

Structural proteins, including silk fibroins, play an important role in shaping the skeletons and structures of cells, tissues, and organisms. The amino acid sequences of structural proteins often show characteristic features, such as a repeating tandem motif, that are notably different from those of functional proteins such as enzymes and antibodies. In recent years, materials composed of or containing structural proteins have been studied and developed as biomedical, apparel, and structural materials. This review outlines the definition of structural proteins, methods for characterizing structural proteins as polymeric materials, and potential applications.

Biofunctionalization of Natural Fiber-Reinforced Biocomposites for Biomedical Applications

In the last ten years, environmental consciousness has increased worldwide, leading to the development of eco-friendly materials to replace synthetic ones. Natural fibers are extracted from renewable resources at low cost. Their combination with synthetic polymers as reinforcement materials has been an important step forward in that direction. The sustainability and excellent physical and biological (e.g., biocompatibility, antimicrobial activity) properties of these biocomposites have extended their application to the biomedical field. This paper offers a detailed overview of the extraction and separation processes applied to natural fibers and their posterior chemical and physical modifications for biocomposite fabrication. Because of the requirements for biomedical device production, specialized biomolecules are currently being incorporated onto these biocomposites. From antibiotics to peptides and plant extracts, to name a few, this review explores their impact on the final biocomposite product, in light of their individual or combined effect, and analyzes the most recurrent strategies for biomolecule immobilization.

A covalently crosslinked silk fibroin hydrogel using enzymatic oxidation and chemoenzymatically synthesized copolypeptide crosslinkers consisting of a GPG tripeptide motif and tyrosine: control of gelation and resilience

A covalently crosslinked silk fibroin hydrogel was successfully formedviaan enzymatic crosslinking reaction using copolypeptides, which consist of a glycine–proline–glycine tripeptide motif and tyrosine, as linker molecules.