Protein-based And Rare-earth Regulated Biomedical Adhesives

Traditional adhesives such as cyanoacrylate and polyurethane are playing more and more important roles in industry and daily life.Nevertheless,these adhesives exist a number of drawbacks.The degradation process of them in natural environment are difficult and would appear toxic byproduct.Additionally,they also would induce inflammatory response around tissues and low biocompatibility when they were applied in human beings,and the binding progression of cyanoacrylate adhesive would release a lot of heat,eliciting cellular damage.All of these restrict their application value in biomedical field.Moreover,some marine creatures such as mussels and sandcastle worms have been given serious attention due to the outstanding wet adhesive property of the secreted proteins.But these biomimetic adhesive materials still exhibit lower bonding strength compared with traditional synthetic adhesives,which limit their further application in biomedicine and high technology fields.As a consequence,developing new types of biomedical adhesives with good biocompatibility and biodegradability,non-toxicity and strong adhesive strength holds special significance.In this dissertation,we constructed several non-chemical crosslinking elastin-like polypeptide-based adhesives with excellent bonding strength via genetic engineering technology.Furthermore,taking fish swim-bladder as raw material,we prepared a polysaccharide-protein complex biomedical adhesive.The major contents are demonstrated as follows:Firstly,on the basis of the amino acid sequence,(VPGXG)n,of elastin-like polypeptide,the fourth amino acid residue was replaced with lysine or glutamic acid residue to design the primary structure of target protein.The expression plasmid was constructed by genetic engineering technique and expressed in E.coli.The target proteins were prepared after a serious of purification procedures.The adhesion property and biocompatibility of protein-surfactant complex adhesives were explored.Results show that the lap shear strength is up to 10 Mpa,and these adhesives possess good biocompatibility and biodegradability.The effectiveness of wound healing enhancement of these adhesives was confirmed by rat models.To improve the adhesion strength further,rare earth Tb3+was introduced to the surfactants with catechol groups to form coordination crosslinking.The adhesion strength of Tb3+-doped adhesives has a significant improvement compared with original complex adhesives,which indicates the potential avenues of rare earth ions on the mechanical strength enhancement of biological adhesives.Secondly,a thermosensitive polypeptide fragment was genetically engineered to link with a lysine residue replaced elastin-like polypeptide.The fusion protein,V40K72,was expressed in E.coli and purified via thermal circulation.Next by electrostatically combining cationic V40K72 with the FDA-approved non-toxic surfactant of sodium dodecyl benzene sulfonate(SDBS),V40K72-SDBS formed an adhesive coacervate at room temperature.Mechanical performance of the bioglue system is actively tunable with thermal triggers.In cold condition,adhesion strength of the bioadhesive was only?50 kPa.By increasing temperature,the strength presented up to 600 kPa,which is remarkably stronger than other biological counterparts.This is probably due to the thermally triggered phase transition of the engineered protein and the formation of coacervate,thus leading to the enhanced wet adhesion bonding.And last,fish swim bladders were using as raw materials to prepare a bioadhesive with high adhesive strength.This bioadhesive,termed as fish swim-bladder glue(FSG),exhibits excellent adhesive characteristics on the rigid substrates including glass,mica and woods.It is worth noting that the highest shear strength is up to 18 MPa.The adhesion properties of FSG were performed ex vivo using porcine skin as substrates.As a result,the shear strength reaches a remarkable value of 150 kPa.Wound healing research on rats shows that FSG accelerates the healing process and reduce the inflammatory scar formation compared to commercial cyanoacrylate medical glue.Compared with other engineering protein adhesives,FSG is cheaper,and showed better adhesive performance in animal skin or rigid substrate.