Proposed Implementation

Spider silk protein hydrogel bioink

Spider silk protein is well known for its good mechanical property and biocompatibility. As a high performance raw material, spider silk protein has an attractive application prospect in tissue engineering, such as artificial skin, tooth, tendon, ligament, and other tissue or organ parts. While, it is not practical to make use of natural spider silk due to the difficulty of breeding as spiders occupies a large area and kills each other. Furthermore, the spider silk production is quite small. In recent years, scientists from all over the world have made a series of studies on the chemical composition, structure and gene composition of spider silk proteins, and have developed synthetic spider silk using genetic technology. This provides us technical basis for working on this project.

With the development of 3D tissue engineering, the requirement of bioink with good adaptability and excellent biocompatibility for 3D printing is broadly increased. Considering recombinant spider silk protein has quite low immunogenicity and perfect biocompatibility and physical cross-linking ability, we set to explore and evaluate its potential as a novel bioink raw material for 3D printing. In our project, based on spider silk protein PySP1 (R in brief) produced by prokaryotic E.coli BL21 cells, we successfully built three systems: the R, R + GFP reporting system, and the mixed 3D printing bioink with R or GFP-R, which may further be applied to different scenario such as artificial skin, wound dressing or artificial tooth et.al.

What's more? Most recently, it has been reported that living cells can be loaded to the spider silk bioink and cell-loaded spider silk bioink can be distributed by robot for printing without the need for cross-linking additives or thickening agents for mechanical stabilization. In such spider silk scaffolds, cells were able to adhere and proliferate with good viability for at least a week. The introduction of cell-binding motifs into spider silk proteins further achieved fine regulatory control of cell-material interactions. Therefore, spider silk hydrogel bioink are a very potential and attractive novel raw biomaterials.

• Artificial skin and wound dressings

  As the largest tissue and organ of the human body, the skin is crucial in maintaining the stability of the internal environment and resisting external bacterial infections. According to statistics, tens of millions of patients worldwide need medical treatment every year due to burns, mechanical injuries or chronic skin ulcers, resulting in the annual cost of skin wound repairing is more than 1 trillion dollars. In some explosion accidents, most burn and scald patients need skin application during debridement. However, due to the lack of skin resources, nearly 100,000 patients with severe skin defects have died of timely and effective treatment exhaustion. Furthermore, in many cases, the amount of skin remain the limit to the needs of dressings and skin grafts. Thus, artificial skin or wound dressing has become an important resource for skin health care.

  • Wound dressing

    Burn wounds can be treated using spider silk bioink dressings or in combination with other medicinal materials. Spider silk protein not only show antimicrobial properties while supporting keratinocyte and fibroblast growth, but are also degradated within 8 weeks, thus eliminating the removal of the dressing from the process. A number of materials substantiate the use of RGD-labeled recombinant spider silk as wound dressings for second-degree burns in rats. These properties enable the prokaryotic expression of recombinant spider silk to induce the normal expression of basic fibroblast growth factor and the synthesis of hydroxyproline, the major amino acid in collagen fibers, indicating that the injured skin has a good regenerative capacity. Thus, our spider silk product may help patients induce certain skin layer growth or regenerate better restorative skin.

  • Artificial skin

    Although it is easy to formulate scaffolds with good mechanical properties, raw spider silk does not contain bioactive functions as natural skin. In future, we plan to combine spider silk bioink with bioactive factors like collagen and EGF et.al to make affordable functional tissue-engineered skins for skin transplantation. Nanofiber and microporous scaffolds made from spider silk filament have been reported for the overall intended function of improving cell adhesion, antimicrobial activity and growth factor cell-binding motifs, antimicrobial peptides, and growth factors. To this end, the spider silk filament properties were exploited to form an interaction among the spider silk filament, combined factors and the skin cells. This will give the artificial skin richer functions in the future.

• Artificial tooth and tendon

  • For patients with toothless jaws, tooth loss not only affects chewing and reduces quality of life, but also causes the maxillofacial area to collapse, making people look particularly old and affecting appearance. The global artificial teeth market is growing at a significant pace owing to increase in prevalence of oral diseases, rise in geriatric population, growth in the number of diabetic patients, and improvement in awareness about dental prosthetics among individuals. Some papers have reported that treated spider silk protein bars can be used to prepare tooth inlays.
  
  
  • Current surgical and therapeutic techniques require extended recovery time and the tendon is rarely returned to its original healthy state. Despite the high amount of sources for grafts to aid in surgical repair, all of the options have drawbacks such as availability, immune response, or poor mechanical properties. Spider silk bioink has the potential to enhance current tendon repair resulting in shorter patient recovery times and improved tendon strength and mobility after repair by allowing for early movement of the damaged tendon, which prevents scar formation and promotes growth.

• Other applications of Spider silk bioink

  • Applications in materials science: Spider silk protein bioink has certain application value.
  • Applications in preservation technology: Spider silk bioink can be designed to preserve food coatings.
  • Applications in the textile industry: Weaving spider silk protein bioink using existing technology.
  • Spider silk bioink has also been used for military purposes, for example, the ability of spider silk to consume foreign energy also makes it ideal for making body armor.

Safety considerations of recombinant spider silk hydrogel application

• In the process of preparing 3D printed hydrogels using recombinant spider silk proteins: the biocompatibility of the product should be tested, including whether there is cytotoxicity, carcinogenic and teratogenic risks.
• Pay attention to purification and removal of heat sources and allergens in the production of recombinant spider silk protein, meanwhile we should carefully assess the sensitization of recombinant spider silk protein.
• When it is applied to other medical-related uses, it is necessary to strictly comply with the relevant requirements and laws of local government.
• The application of recombinant spider silk proteins to animal experiments and other related research should also focus on bioethics and animal welfare issues.

Possible challenges and difficulties

• Spider silk protein can be produced by fusion with bioactive protein domains, but the recombination procedure is expensive and large-scale production is challenging.
• For biomedical applications such as cell scaffolds and therapeutic micro/nano robots, it is necessary to systematically evaluate the biocompatibility, physicochemical stability, and ease of functionalization of 3D fabricated structures.

Reference:

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