Enhanced Collagen-like Protein for Facile Biomaterial Fabrication

Thiolation-Based Protein-Protein Hydrogels for Improved Wound Healing

The limitations of protein-based hydrogels, including their insufficient mechanical properties and restricted biological functions, arise from the highly specific functions of proteins as natural building blocks. A potential solution to overcome these shortcomings is the development of protein-protein hydrogels, which integrate structural and functional proteins. In this study, a protein-protein hydrogel formed by crosslinking bovine serum albumin (BSA) and a genetically engineered intrinsically disordered collagen-like protein (CLP) through Ag─S bonding is introduced. The approach involves thiolating lysine residues of BSA and crosslinking CLP with Ag+ ions, utilizing thiolation of BSA and the free-cysteines of CLP. The resulting protein-protein hydrogels exhibit exceptional properties, including notable plasticity, inherent self-healing capabilities, and gel-sol transition in response to redox conditions. In comparison to standalone BSA hydrogels, these protein-protein hydrogels demonstrate enhanced cellular viability, and improved cellular migration. In vivo experiments provide conclusive evidence of accelerated wound healing, observed not only in murine models with streptozotocin (Step)-induced diabetes but also in zebrafish models subjected to UV-burn injuries. Detailed mechanistic insights, combined with assessments of proinflammatory cytokines and the expression of epidermal differentiation-related proteins, robustly validate the protein-protein hydrogel's effectiveness in promoting wound repair.

Biomimetic design of fibril-forming non-immunogenic collagen like proteins for tissue engineering

Collagen, a key component of extracellular matrix serves as a linchpin for maintaining structural integrity and functional resilience. Concerns over purity and immunogenicity of animal-derived collagens have spurred efforts to develop synthetic collagen-based biomaterials. Despite several collagen mimics, there remains limited exploration of non-immunogenic biomaterials with the capacity for effective self-assembly. To combat the lacuna, collagen like protein (CLP) variants were rationally designed and recombinantly expressed, incorporating human telopeptide sequences (CLP-N and CLP-NC) and bioactive binding sites (CLP-NB). Circular dichroism analyses of the variants confirmed the triple helical conformation, with variations in thermal stability and conformation attributed to the presence of telopeptides at one or both ends of CLP. The variants had propensity to form oligomers, setting the stage for fibrillogenesis. The CLP variants were biocompatible, hemocompatible and supported cell proliferation and migration, particularly CLP-NB with integrin-binding sites. Gene expression indicated a lack of significant upregulation of inflammatory markers, highlighting the non-immunogenic nature of these variants. Lyophilized CLP scaffolds maintained their triple-helical structure and offered favorable biomaterial characteristics. These results accentuate the potential of designed CLP variants in tissue engineering, regenerative medicine and industrial sectors, supporting the development of biocompatible scaffolds and implants for therapeutic and cosmetic purposes.

Genetically encoded zinc-binding collagen-like protein hybrid hydrogels for wound repair

Incorporating zinc oxide nanoparticles (ZnOnps) into collagen is a promising strategy for fabricating biomaterials with excellent antibacterial activity, but modifications are necessary due to the low zinc binding affinity of native collagen, which can cause disturbances to the functions of both ZnOnps and collagen and result in heterogeneous effects. To address this issue, we have developed a genetically encoded zinc-binding collagen-like protein, Zn-eCLP3, which was genetically modified by Scl2 collagen-like protein. Our study found that Zn-eCLP3 has a binding affinity for zinc that is 3-fold higher than that of commercialized type I collagen, as determined by isothermal titration calorimetry (ITC). Using ZnOnps-coordinated Zn-eCLP3 protein and xanthan gum, we prepared a hydrogel that showed significantly stronger antibacterial activity compared to a collagen hydrogel prepared in the same manner. In vitro cytocompatibility tests were conducted to assess the potential of the Zn-eCLP3 hydrogel for wound repair applications. In vivo experiments, which involved an S. aureus-infected mouse trauma model, showed that the application of the Zn-eCLP3 hydrogel resulted in rapid wound regeneration and increased expression of collagen-1α and cytokeratin-14. Our study highlights the potential of Zn-eCLP3 and the hybrid hydrogel for further studies and applications in wound repair.

Genetically encoded in situ gelation redox-responsive collagen-like protein hydrogel for accelerating diabetic wound healing

Genetically encoded collagen-like protein-based hydrogels have demonstrated remarkable efficacy in promoting the healing process in diabetic patients. However, the current methods for preparing these hydrogels pose significant challenges due to harsh reaction conditions and the reliance on chemical crosslinkers. In this study, we present a genetically encoded approach that allows for the creation of protein hydrogels without the need for chemical additives. Our design involves the genetic encoding of paired-cysteine residues at the C- and N-terminals of a meticulously engineered collagen-like recombination protein. The protein-based hydrogel undergoes a gel-sol transition in response to redox stimulation, achieving a gel-sol transition. We provide evidence that the co-incubation of the protein hydrogel with 3T3 cells not only enhances cell viability but also promotes cell migration. Moreover, the application of the protein hydrogel significantly accelerates the healing of diabetic wounds by upregulating the expression of collagen-1α (COL-1α) and Cytokeratin 14 (CK-14), while simultaneously reducing oxidant stress in the wound microenvironment. Our study highlights a straightforward strategy for the preparation of redox-responsive protein hydrogels, removing the need for additional chemical agents. Importantly, our findings underscore the potential of this hydrogel system for effectively treating diabetic wounds, offering a promising avenue for future therapeutic applications.

Properties of Dual-Crosslinked Collagen-Based Membranes as Corneal Repair Material

Corneal disease has become the second leading cause of blindness in the world. Corneal transplantation is currently considered to be one of the common treatments for vision loss. This paper presents a novel approach utilizing dual-crosslinked membranes composed of polyrotaxane multiple aldehydes (PRAs), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), and N-hydroxysuccinimide (NHS) in the development process. Collagen was crosslinked, respectively, by EDC/NHS and PRAs to form stable amide bonds and imine groups. Through the formation of a double interpenetrating network, dual-crosslinked (Col-EDC-PRA) membranes exhibited enhanced resistance to collagenase degradation and superior mechanical properties compared to membranes crosslinked with a single crosslinker. Furthermore, Col-EDC-PRA membranes display favorable light transmittance and water content characteristics. Cell experiments showed that Col-EDC-PRA membranes were noncytotoxic and were not significantly different from other membranes. In a rabbit keratoplasty model, corneal stromal repair occurred at 5 months, evidenced by the presence of stromal cells and neo-stroma, as depicted in hematoxylin-eosin-stained histologic sections and optical coherence tomography images of the anterior segment. Moreover, there was no inflammation and corneal neovascularization, as well as no corneal rejection reaction in the surgical area. Overall, the results demonstrated that the dual-crosslinked membranes served effectively for corneal tissue regeneration after corneal defect.

Polysaccharides and Structural Proteins as Components in Three-Dimensional Scaffolds for Breast Cancer Tissue Models: A Review

Breast cancer is the most common cancer among women, and even though treatments are available, efficiency varies with the patients. In vitro 2D models are commonly used to develop new treatments. However, 2D models overestimate drug efficiency, which increases the failure rate in later phase III clinical trials. New model systems that allow extensive and efficient drug screening are thus required. Three-dimensional printed hydrogels containing active components for cancer cell growth are interesting candidates for the preparation of next generation cancer cell models. Macromolecules, obtained from marine- and land-based resources, can form biopolymers (polysaccharides such as alginate, chitosan, hyaluronic acid, and cellulose) and bioactive components (structural proteins such as collagen, gelatin, and silk fibroin) in hydrogels with adequate physical properties in terms of porosity, rheology, and mechanical strength. Hence, in this study attention is given to biofabrication methods and to the modification with biological macromolecules to become bioactive and, thus, optimize 3D printed structures that better mimic the cancer cell microenvironment. Ink formulations combining polysaccharides for tuning the mechanical properties and bioactive polymers for controlling cell adhesion is key to optimizing the growth of the cancer cells.

Purification of recombinant bacterial collagens containing structural perturbations

Streptococcus pyogenes-derived recombinant bacterial collagen-like proteins (CLPs) are emerging as a potential biomaterial for biomedical research and applications. Bacterial CLPs form stable triple helices and lack specific interactions with human cell surface receptors, thus enabling the design of novel biomaterials with specific functional attributes. Bacterial collagens have been instrumental in understanding collagen structure and function in normal and pathological conditions. These proteins can be readily produced in E. coli, purified using affinity chromatography, and subsequently isolated after cleavage of the affinity tag. Trypsin is a widely used protease during this purification step since the triple helix structure is resistant to trypsin digestion. However, the introduction of Gly→X mutations or natural interruptions within CLPs can perturb the triple helix structure, making them susceptible to trypsin digestion. Consequently, removing the affinity tag and isolating collagen-like (CL) domains containing mutations is impossible without degradation of the product. We present an alternative method to isolate CL domains containing Gly→X mutations utilizing a TEV protease cleavage site. Protein expression and purification conditions were optimized for designed protein constructs to achieve high yield and purity. Enzymatic digestion assays demonstrated that CL domains from wild-type CLPs could be isolated by digestion with either trypsin or TEV protease. In contrast, CLPs containing Gly→Arg mutations are readily digested by trypsin while digestion with TEV protease cleaved the His6-tag, enabling the isolation of mutant CL domains. The developed method can be adapted to CLPs containing various new biological sequences to develop multifunctional biomaterials for tissue engineering applications.

Recombinant protein polymer-antibody conjugates for applications in nanotechnology and biomedicine

Currently, there are over 100 antibody-based therapeutics on the market for the treatment of various diseases. The increasing importance of antibody treatment is further highlighted by the recent FDA emergency use authorization of certain antibody therapies for COVID-19 treatment. Protein-based materials have gained momentum for antibody delivery due to their biocompatibility, tunable chemistry, monodispersity, and straightforward synthesis and purification. In this review, we discuss progress in engineering the molecular features of protein-based biomaterials, in particular recombinant protein polymers, for introducing novel functionalities and enhancing the delivery properties of antibodies and related binding protein domains.

Bacterial collagen-templated synthesis and assembly of inorganic particles

Collagen has been used as a common template for mineralization and assembly of inorganic particles, because of the special arrangement of its fibrils and the presence of charged residues. Streptococcal bacterial collagen, which is inherently secreted on the surface ofStreptococcus pyogenes, has been progressively used as an alternative for type I animal collagen. Bacterial collagen is rich in charged amino acids, which can act as a substrate for the nucleation and growth of inorganic particles. Here, we show that bacterial collagen can be used to nucleate three different inorganic materials: hydroxyapatite crystals, silver nanoparticles, and silica nanoparticles. Collagen/mineral composites show an even distribution of inorganic particles along the collagen fibers, and the particles have a more homogenous size compared with minerals that are formed in the absence of the collagen scaffold. Furthermore, the gelation of silica occurring during mineralization represents a means to produce processable self-standing collagen composites, which is challenging to achieve with bacterial collagen alone. Overall, we highlight the advantage of simply combining bacterial collagen with minerals to expand their applications in the fields of biomaterials and tissue engineering, especially for bone regenerative scaffolds.

Recombinant and genetic code expanded collagen-like protein as a tailorable biomaterial

Collagen occurs in nature with a dedicated triple helix structure and is the most preferred biomaterial in commercialized medical products. However, concerns on purity, disease transmission, and the reproducibility of animal derived collagen restrict its applications and warrants alternate recombinant sources. The expression of recombinant collagen in different prokaryotic and eukaryotic hosts has been reported with varying degrees of success, however, it is vital to elucidate the structural and biological characteristics of natural collagen. The recombinant production of biologically functional collagen is restricted by its high molecular weight and post-translational modification (PTM), especially the hydroxylation of proline to hydroxyproline. Hydroxyproline plays a key role in the structural stability and higher order self-assembly to form fibrillar matrices. Advancements in synthetic biology and recombinant technology are being explored for improving the yield and biomimicry of recombinant collagen. It emerges as reliable, sustainable source of collagen, promises tailorable properties and thereby custom-made protein biomaterials. Remarkably, the evolutionary existence of collagen-like proteins (CLPs) has been identified in single-cell organisms. Interestingly, CLPs exhibit remarkable ability to form stable triple helical structures similar to animal collagen and have gained increasing attention. Strategies to expand the genetic code of CLPs through the incorporation of unnatural amino acids promise the synthesis of highly tunable next-generation triple helical proteins required for the fabrication of smart biomaterials. The review outlines the importance of collagen, sources and diversification, and animal and recombinant collagen-based biomaterials and highlights the limitations of the existing collagen sources. The emphasis on genetic code expanded tailorable CLPs as the most sought alternate for the production of functional collagen and its advantages as translatable biomaterials has been highlighted.

Engineering microbial systems for the production and functionalization of biomaterialsBiomaterials engineering with microorganisms

A new trend in biomaterials synthesis is harnessing the production of microorganisms, owing to the low cost and sustainability. Because microorganisms use DNA as a production code, it is possible for humans to reprogram these cells and thus build living factories for the production of biomaterials. Over the past decade, advances in genetic engineering have enabled the development of various intriguing biomaterials with useful properties, with commercially available biomaterials representing only a few of these. In this review, we discuss the common strategies for the production of bulk and commodity biogenic polymers, and highlight several notable approaches such as modular protein engineering and pathway optimization in achieving these goals. We finally investigate the available synthetic biology tools that allow engineering of living materials, and discuss how this emerging class of materials has expanded the application scope of biomaterials.

Extracellular Secretion and Simple Purification of Bacterial Collagen from Escherichia coli

Because of structural similarities with type-I animal collagen, recombinant bacterial collagen-like proteins have been progressively used as a source of collagen for biomaterial applications. However, the intracellular expression combined with current costly and time-consuming chromatography methods for purification makes the large-scale production of recombinant bacterial collagen challenging. Here, we report the use of an adapted secretion pathway, used natively byEscherichia colito secrete curli fibers, for extracellular secretion of the bacterial collagen. We confirmed that a considerable fraction of expressed collagen (∼70%) is being secreted freely into the extracellular medium, with an initial purity of ∼50% in the crude culture supernatant. To simplify the purification of extracellular collagen, we avoided cell lysis and used cross-flow filtration or acid precipitation to concentrate the voluminous supernatant and separate the collagen from impurities. We confirmed that the secreted collagen forms triple helical structures, using Sirius Red staining and circular dichroism. We also detected collagen biomarkers via Raman spectroscopy, further supporting that the recombinant collagen forms a stable triple helical conformation. We further studied the effect of the isolation methods on the morphology and secondary structure, concluding that the final collagen structure is process-dependent. Overall, we show that the curli secretion system can be adapted for extracellular secretion of the bacterial collagen, eliminating the need for cell lysis, which simplifies the collagen isolation process and enables a simple cost-effective method with potential for scale-up.

From the Matrix to the Nucleus and Back: Mechanobiology in the Light of Health, Pathologies, and Regeneration of Oral Periodontal Tissues

Among oral tissues, the periodontium is permanently subjected to mechanical forces resulting from chewing, mastication, or orthodontic appliances. Molecularly, these movements induce a series of subsequent signaling processes, which are embedded in the biological concept of cellular mechanotransduction (MT). Cell and tissue structures, ranging from the extracellular matrix (ECM) to the plasma membrane, the cytosol and the nucleus, are involved in MT. Dysregulation of the diverse, fine-tuned interaction of molecular players responsible for transmitting biophysical environmental information into the cell's inner milieu can lead to and promote serious diseases, such as periodontitis or oral squamous cell carcinoma (OSCC). Therefore, periodontal integrity and regeneration is highly dependent on the proper integration and regulation of mechanobiological signals in the context of cell behavior. Recent experimental findings have increased the understanding of classical cellular mechanosensing mechanisms by both integrating exogenic factors such as bacterial gingipain proteases and newly discovered cell-inherent functions of mechanoresponsive co-transcriptional regulators such as the Yes-associated protein 1 (YAP1) or the nuclear cytoskeleton. Regarding periodontal MT research, this review offers insights into the current trends and open aspects. Concerning oral regenerative medicine or weakening of periodontal tissue diseases, perspectives on future applications of mechanobiological principles are discussed.