Preparation And Properties Of Gelatin-Based Functional Bioadhesives

With the introduction of the national strategy of "Healthy China",the medical biomaterials,which are good for people’s life and health,have ushered in unprecedented opportunities and challenges as the key material basis for realizing this strategy.Animal skin is an important renewable biomass resource in nature,and there is great significance of its high-value resource transformation and utilization.As a degradation product of animal skin,gelatin has unique biomimetic properties and biological activity due to its natural spatial conformation and chemical composition,so it has been widely used as the biomedical materials.In view of the many shortcomings of traditional tissue adhesion methods,such as high difficulty in operation,time-consuming,strong pain,great harm,inconvenience,susceptibility to infection,and difficulty in recovery.And the performance defects of the current gelatin-based bioadhesion,for examples,poor underwater adhesion,single function,and poor thermal stability.In this research,the gelatin extracted from the raw hide scraps without chemical cross-linking treatment in the leather manufacturing process by the self-designed hierarchical degradable method is used as the raw material.After the chemical modification is employed to improve the viscosity of gelatin and endow it with lots of functions,the gelatin is further applied to preparing a multifunctional gelatin-based bioadhesive with high adhesive strength.The prepared multifunctional adhesive not only has excellent biocoMPatibility,good adhesion and can be used to promote wound healing,but also has other clinically practical functions:(1)Temperature sensitivity:this property enables the adhesive and wound shape to match better and achieves the injectability of the adhesive.(2)Underwater adhesion:based on the advantages of dynamic covalent bonds and hydrophilic polymer backbone,this property makes the adhesive can be coMPatible with wet surfaces and better adapt to the dynamic motion of the tissue,which increases the practical clinical applicability of this material.(3)Intelligence:By quickly responding to the stimuli of light and thermal,this property makes the adhesive can reversibly adhere to the target substrate and separate on demand.This research provides the new ideas for the controllable preparation of high-performance gelatin and the fabrication of functional gelatin-based bioadhesives.The prepared bioadhesive has the potential to become a new generation of functional gelatin-based absorbable medical adhesives.The specific research contents and results are as follows:(1)The raw hide scraps without chemically cross-linking in the leather manufacturing process were used as the raw material for gelatin extraction,and gelatin was extracted from biomimetic high-level collagen aggregates(CA)through a self-designed hierarchical controllable degradation method.The collagen aggregates were prepared by an In Situ Gradient Acid method,and gelatin(G-CA)was obtained by a traditional hydrothermal method using CA as a substrate.The extraction rate of collagen aggregates was used as the investigation index,the effects of extraction medium,acid concentration,solid-liquid ratio,extraction temperature,and extraction time on the extraction of collagen aggregates were studied.Under the optimal conditions,the extraction rate of CA was 66.30%,and the original aggregated structure of natural collagen(typical Dperiod striated structure)was completely preserved,and the stripe spacing was about 61.35 nm.The CA was further stirred at 80℃ for 8 h,and G-CA was obtained after fractional extraction,filtration and gel purification.CoMPared with conventional alkaline-extracted gelatin(G-Al)and commercial gelatin(CG),GCA extracted from CA had a wide molecular mass distribution range(124～236 kDa),high transparency,high viscosity,and high gel strength(～268 Bloom g),indicating the hierarchically controlled degradation method based on biomimetic CA extracted gelatin could become a new general extraction method for highperformance gelatin.(2)Using G-CA as raw material and the complex chemical cross-linking strategy of catechol-Fe3+ and NIPAAm-methacryloyl group,a double-injection method with high clinical practicability was used to prepare a biomimetic multifunctional mussel injectable dual network gelatin hydrogel adhesive(DNGel).The optimal preparation conditions of the composite gel were determined by investigating the effects of dopamine addition amounts,Fe3+concentrations,and the addition ratio of GMD to NIPAAm on the properties of the adhesive,such as temperature sensitivity,mechanical strength,adhesive strength,swelling,and degradation.Under the optimal conditions,the adhesive strength of DNGel was 3.6 MPa,and the DNGel could good temperature sensitivity and had a high equilibrium swelling rate and good biodegradability.The chemical structure analysis confirmed that methacrylic anhydride and dopamine were successfully introduced into DNGel,and Dopa and NIPAAm were uniformly dispersed in DNGel,which ensured the stability of the material’s structure and properties.The test tube inversion method showed that the gelation time of DNGel was 8 min,which could cause spontaneous blood coagulation when applied to the wound,and the strong adhesive strength could effectively avoid the secondary bleeding of the wound.Meanwhile,DNGel had good self-healing properties,which could prolong the used time and enhance biosafety when used for wound closure.In addition,the adhesive strength of DNGel to biological tissues was 3.6 MPa,which was much greater than that of commercial fibrin glue(0.65 MPa).Meanwhile,DNGel could be disassembled on demand through acetic acid solution,and its LCST was close to the physiological temperature of the human body,which can quickly respond to external stimuli and is conducive to in-situ polymerization to form injectable hydrogels to adapt to different sizes and shapes of wounds.Therefore,the obtainedDNGel had a wide range of applicability.Animal in vivo and in vitro experiments showed that DNGel had good biocoMPatibility,antibacterial,and hemostatic properties,and also could promote vascular remodeling and accelerate wound healing.(3)In order to further solve the problems of poor underwater adhesion of bioadhesives and insufficient bioactivity of gelatin due to the preparation and degradation process.In this research,chitosan and anthraaldehydepolyethyleneimine(9-anth-PEI)were introduced into gelatin as adhesive layer,and acidified multi-walled carbon nanotubes(H-MWNTs)were used as the conductive unit and introduced into the dissipative matrix layer.and a skin biomimetic gelatin-based composite thermosensitive reversible underwater conductive double-layer adhesive(DLGel)was prepared through physical and chemical modification and structural model design.Meanwhile,the wound healing effect of the material was improved by promoting tissue healing via electrical stimulation.The effects of chitosan molecular weights,concentrations and bridging polymer compositions on the adhesive properties of the final composite adhesive were explored.Under the optimal conditions,the underwater adhesive strength of DLGel on pigskin was 1.28 MPa,and DLGel also had remarkable adhesion to various substrates,such as silicone rubber,glass,and iron.The chemical structure analysis showed that 9-anth-PEI was successfully synthesized,and H-MWNTs,gelatin,chitosan,and 9-anth-PEI were uniformly dispersed in DLGel,ensuring the DLGel has stable conductivity and adhesion.Meanwhile,the adhesive strength of DLGel can reach a maximum value of 1.28 MPa after 3 min irradiation of blue light,and the effective adhesive transition can be maintained for at least 3 cycles by switching the physical stimuli of radiation and heating,achieving an efficient and reversible underwater adhesion.More importantly,the combination of DLGel and electrical stimulation can significantly promote the in vitro proliferative activity of hamster lung epithelial cells,and exhibit a superior inductive repair effect in a rat full-thickness skin defect model.Meanwhile,the wound recovery in vivo was actively accelerated through wound area reduction,granulation tissue formation,enhanced collagen deposition,vascularization,and re-epithelialization.Futhermore,the electrochemical performance test showed that DLGel had high sensitivity and motion monitoring ability,which confirmed that DLGel could not only be used as a smart sensor for monitoring human motion,but also as medical adhesive for wound healing,realizing the integration of "real-time monitoring of human health-induction of repair and regeneration".