Study On Preparation And Application Of Conductive Hydrogel For Chronic Wound Repair

In recent years,due to the aging of the population and the increasing incidence of diabetes and obesity,chronic wounds have become a serious health problem worldwide.The current methods used in the clinical practice for treating chronic wounds are none-effeciency,high-cost and complicated to use.ES therapy is considered safe and easy to use,which is involved in numerous processes of wound healing and promotes the healing of chronic wounds.However,it still has the following disadvantages:1.Due to the large impedance of human skin,ES may require high voltage which could be harmful to the human body;2.The applied ES cannot cover the whole wound area,and the therapeutic outcome may be compromised;3.The electrode-based ES strategy may not be effective for large chronic wounds;4 It cannot provide a moist environment for wound healing.Wound healing requires the use of dressings.It has been reported that a moist environment with an occlusive dressing can significantly enhance the healing extent because the moist environment decreases the number of cells in the inflammatory phase and increases the number of cells in the proliferative phase.On the other hand,some cytokines such as fibroblast growth factor,vascular endothelial growth factor,and transforming growth factor-βare secreted from fibroblasts,lymphocytes,neutrophils,macrophages,and platelets.All these factors and cells can only effectively promote wound healing in a sufficiently humid environment.Therefore,the use of the hydrophilic wound dressing to maintain a moist environment of the wound can promote wound healing.Hydrogels are three-dimensional,hydrophilic,crosslinked networks that embed large amounts of water.Due to their high water content and polymeric network structure comparable to the native tissue matrix,hydrogels are widely used in tissue engineering applications.A biocompatible hydrogel can be used as a wound dressing.It has several advantages:1.It can remove excess exudate and toxin from the wound;2.It can be insulated at the wound and dressing interface;3.It allows gas exchange;4.It can prevent secondary infection;5.It is easy to remove from the wound without causing a second damage to the wound.Based on the above research background,we proposed a concept that the use of an ES therapy based on conductive hydrogels.A conductive hydrogel is a polymer composite composed of a network of highly aqueous polymers containing conductive components.Conductive hydrogels have similar flexibility,stretchability and high water content to soft tissues and are ideal materials for biomedical engineering.It not only has the advantages of ordinary hydrogels,but al so has the same electrical conductivity as human skin.We use conductive hydrogel as wound dressing to cover chronic wounds.The two ends of the hydrogel are loaded with current,and the external power source is used to simulate the endogenous electric fie ld,so as to stimulate the chronic wounds evenly.It has been carried out in a more in-depth,systematic study the synergistic effect of conductive hydrogel dressings and ES to promote chronic wound repair by the use of cell biology and other scientific me ans.The main research contents of this thesis include:Firstly,we explored the possibility of incorporating terbium ions(Tb³⁺)in a hydrogel to disrupt biofilms and treat infected chronic wounds.Sodium alginate（SA）and poly（vinyl alcohol）（PVA）were used as hydrogel matrices because of their excellent biocompatibility,water absorbing ability and resistance to protein absorption and bacterial adhesion.A strong hydrogen bond formed between PVA and SA would endow the hydrogel PVA-SA with good mechanical properties.We also found that compared with the PVA-SA hydrogel,the PVA-SA hydrogel containing Tb³⁺（PVA-SA-Tb）reduced the number of Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa in biofilms by 1.5 and 1 orders of magnitude,respectively.Further incorporation of r GO that did not exhibit antibacterial properties alone in the PVA-SA-Tb hydrogel（PVA-SA-Rgo-Tb）raised the killing efficacy of Staphylococcus aureus and Pseudomonas aeruginosa in biofilms by 1.5 and 2 orders of magnitude,respectively.Because the introduction of graphene sheets could enhance the antibacterial properties of the incorporated Tb³⁺ions because they could loosen the network of the hydrogel to promote Tb³⁺release.The introduction of graphene sheets could also enhance the electrical conductivity of the hydrogel dressing,which was conducive to maintaining the the endogenous electric field spontaneous formed at the wound.As a signal to induce wound healing,conductive hydrogel dressing was conducive to maintaining the wound current and accelerate wound healing.Finally,we also studied the application of this conductive hydrogel wound dressing in the wound of a rat model of infectious diabetes.The in vivo assay using diabetic rats shows that the PVA-SA-r GO-Tb hydrogel was superior to the PVA-SA-r GO and PVA-SA-Tb hydrogels for treating infected chronic wounds.It was expected that the results might provide a new option for the development of novel dressings for infected chronic wounds.Then,we proposed a concept that the use of an electrically conductive hydrogel to cover the wound for ES could overcome the above-mentioned shortcomings of the electrode-based ES strategies.Since the flexible conductive hydrogel could fully cover the wound,application of ES through the hydrogel provided a feasibility to stimulate the whole wound area and significantly improved the therapeutic outcome.In this study,a conductive hydrogel based on polyhydroxyethyl methacrylate（poly HEMA）was designed,and polypyrrole that had good biocompatibility was chosen as the conductive component.To solve the problem that the conductivity of polypyrrole reduced in the weak alkaline physiological environment（p H=7.4）due to loss of the dopant,an anionic 3-sulfopropyl methacrylate（3SPMA）monomer was copolymerized in the hydrogel to in-situ dope the polypyrrole,and the covalent bonding between 3SPMA and the hydrogel could prevent its leaching.The results showed that the high conductivity was maintained in PBS for more than 7 days.Since the hydrophilic poly HEMA was a well-known antifouling material,it was used as the hydrogel matrix to improve the resistance to protein absorption and bacterial adhesion.The experimental results showed that,compared with the commercial Hydrosorb hydrogel,the amount of absorbed BSA protein of the HM hydrogel was more than 70%lower.The density of bacteria attached to the HM hydrogel was 93%lower than that on the commercial Hydrosorb hydrogel.We evaluated the chemical structure,mechanical properties,swelling ratio and water vapor transmission rate of hydrogels.We further found that ES through this conductive hydrogel promoted the migration of fibroblasts in vitro.Finally,we also studied the application of this ES through this conductive hydrogel in the wound of a rat model of infectious diabetes.The in vivo assay using diabetic rats shows that application of AC at 5 V and 40 Hz voltage through the conductive HM-PPY conductive hydrogel that covered the wound was superior to the ES through electrodes for promoting wound healing.Finally,N-glycinamide acrylamide（NAGA）and quaternized chitosan-g-polyaniline（QCSP）were used to prepare a conductive hydrogel with excellent mechanical properties and antibacterial anti-oxidant properties.We prepared the QCSP-g-PNAGA hydrogel by radical polymerization of NAGA monomer in the presence of QCSP,and the prepared QCSP-g-PNAGA-based supramolecular polymer hydrogels showed high stability and toughness because the dual amide motifs in the side chain of PNAGA could form multiple hydrogen bond interactions.The mechanical properties test results showed that the Young’s modulus of QCSP-G-PNAGA conductive hydrogel was about 0.3 MPa,and the elongation at break was more than 400%.QCSP improved the dispersibility of aniline oligomers in the hydrogels,enhanced the conductivity.The experimental results showed that the conductivity of QCSP-g-PNAGA hydrogel was about 2 m S/cm.The swelling ratio of QCSP-G-PNAGA hydrogel was 290%,and the water vapor transmittance was about 45 g/m²/h,which help absorb the exudate from the wound and maintain a moist environment at the wound area.We further evaluated the biocompatibility,antibacterial properties and free radical scavenging ability of the hydrogel.Cellular viability experiment showed that QCSP-G-PNAGA conducting hydrogel had good biocompatibility.The antibacterial experiments showed that the bactericidal ratios of the QCSP-g-PNAGA hydrogel were more than 80%against P.aeruginosa and S.aureus,showing a broad spectrum of antibacterial properties.This broad-spectrum antimicrobial activity was promising for the control of wound infection.Antioxidant efficiency experiment showed that the DPPH scavenging percentage of the QCSP-g-PNAGA hydrogel was 64%.We also studied the application of this ES through this conductive hydrogel in the wound in diabetic rats.The in vivo assay using diabetic rats shows that the conductive hydrogel-based ES strategy was better than the conventional electrode-based ES strategy in treating chronic wounds.In summary,this work is inspirated by the endogenous electric field at the wound that promotes wound healing.This work confirms that the ES therapy through conductive hydrogel healing overcomes the shortcomings of traditional electrical stimulation therapy,and also paves the way for a novel ES therapy to treat chronic wounds.