The Preparation Of Intelligent Response Drug Delivery Systems And Their Applications In Chronic Infected Wound Repairing

The complex microenvironment at wound sites and the multi-stage healing process of chronic wounds have brought major challenges to the development of wound repair treatment methods.At present,due to the rise of medical costs and the aging of the population,the chronic wound has imposed a heavy financial burden on human beings.The incidence rate is rising year by year,seriously threatening people’s lives and health.In the past decade,incorporating the unique advantages of nano-drug-loaded medicine into wound repair treatment methods has produced gratifying results.However,the current reported treatments cannot meet the drug demand in each wound healing stage due to their single-function nature as well as passive drug release property,which result in a slow healing rate of chronic wounds and high recurrence rate and consequently limited clinical applications.In recent years,smart responsive drug delivery systems have been widely used in the biomedical field.Compared with traditional drug delivery systems,they show great advantages in reducing the frequency of medication,prolonging the drug function time,improving treatment efficacy,reducing side effects,and especially in realizing precise and controllable drug release.With the introduction of the concept of precision medicine and drug delivery,it is more urgent for us to construct a smart responsive drug delivery system against the specific microenvironment of diseases to achieve its precise treatment.It is foreseeable that the maturity of precise medicine technology will significantly improve the diagnosis experience and treatment effect of patients,and will greatly promote the clinical transformation of smart responsive drug delivery systems.Based on the complexity and multi-stage characteristics of chronic wounds,herein we designed and constructed a series of smart responsive drug delivery systems for repairing chronic wounds with the use of chemical synthesis,materials characterization,cell biology,modern molecular biology,and other scientific methods.We also conducted in-depth and systematic research on their pro-healing mechanism.The main research contents are described as follows:First,we explored the possibility of multifunctional light-responsive nanoparticles for the treatment of chronic infected wounds.Through the formation of amide bonds between the carboxyl group of the photosensitizer Chlorin Ce6 and the amino group of the quaternary ammonium chitosan,quaternary ammonium chitosan（HTCC-Ce6）with a side-linked photosensitizer was prepared.Then,the phenolic hydroxyl group of EGCG was chelated with Mg²⁺,which can promote cell proliferation and migration,to form the Mg/EGCG complex Lastly,HTCC-Ce6,Mg/EGCG,and hyaluronic acid（HA）self-assemble to form nanoparticles through electrostatic interaction.On the one hand,when the formed nanoparticles are illuminated by a laser at wavelength 660 nm,besides the inherent chemical antibacterial ability of quaternary ammonium chitosan,the photosensitizer Ce6 can rapidly produce a large number of reactive oxygen species（ROS）,further killing the bacteria.On the other hand,high ROS and hyaluronidase at the wound site cause hyaluronic acid to degrade and oxidize EGCG into quinones,causing the decomposition of Mg/EGCG complex and the release of Mg²⁺,thus promote the proliferation and migration of endothelial cells and fibroblasts and accelerate wound healing.Besides,multifunctional nanoparticles show good blood compatibility and cytocompatibility.In conclusion,multifunctional responsive nanoparticles exhibit synergistic antibacterial ability through the photodynamic action of quaternary ammonium chitosan and Ce6,as well as the release of Mg²⁺in response to ROS to promote proliferation and migration of endothelial cells and fibroblasts at the wound site,and eventually accelerate the healing of chronic infected wounds.We hope that this new type of multifunctional nanoparticles can provide an effective treatment for bacterially infected chronic wounds or other chronic wounds.However,this study still has certain limitations,such as the inability to guarantee the long-term retention of responsive nanoparticles at the wound site.Second,to increase the retention time of the drugs at the wound site and prolong their function time,meanwhile achieving the on-demand responsive release of the drug at the chronic wound site,we designed a smart injectable hydrogel with an inflammation response.It has a variety of dynamic functions,such as self-healing,remodeling,and injectability.When the wounds are infected by bacteria,severe inflammation often occurs,resulting in an acidic environment and high levels of reactive oxygen at the wound site.Our design used an inflammation-responsive hydrogel as the carrier,antibiotics,and micelles encapsulating anti-inflammatory drugs are loaded into the hydrogel.The smart hydrogel is prepared with sodium alginate（ALG）and side-linked phenylboronic acid（BA）.As a dual-responsive hydrogel,it quickly disintegrates at the infected wound site,releasing the antibiotic amikacin to kill the bacteria.High levels of ROS and high expression of hyaluronidase at the wound site will also cause hyaluronic acid to degrade,leading to the breakdown of micelles and the release of the anti-inflammatory drug naproxen,which effectively inhibits the inflammation of the wound and realizes the rapid healing of chronic infected wounds.In general,this hydrogel formulation not only greatly extended the retention time and function time of the drug at the wound site,but also achieved a controlled drug release at the inflammation site.As far as we know,dual responsive smart hydrogel based on a single polymer,and the concept and design strategy for the multi-response and on-demand controlled release of different drugs in this smart hydrogel formulation have not been reported.We believe that this smart hydrogel formulation has high application potential in the topical treatment of various microbial infections.Third,we designed an inflammation-responsive hydrogel encapsulating dopamine silver nanoparticles and human-derived type III collagen to promote chronic infected diabetic wound healing,which reduces the possibility of antibiotics-led bacterial resistance.Polydopamine nanoparticles（PDA NPs）not only have good cytocompatibility and antioxidant properties but also perform good antibacterial effects.Besides,the aldehyde group in oxidized hyaluronic acid（HA）can not only graft triaminophenylboronic acid to the side chain and form the polymer HA-CHO-BA,but it can also graft recombinant human type III collagen（h Col III）onto HA-CHO-BA via Schiff base reaction.The hydrogel can be quickly prepared by mixing the polyvinyl alcohol（PVA）solution with the HA-CHO-BA solution.Lastly,to endow the hydrogel with antibacterial,cell proliferation,and angiogenesis functions,we added PDA@Ag and h Col III during the process of preparing the hydrogel.Differing from the physical encapsulation of PDA@Ag,here the Schiff base interaction between h Col III and HA-CHO-BA can achieve a slower release of h Col III than PDA@Ag,thus realizing sequential and controllable release of h Col III and PDA@Ag.To sum up,this designed hydrogel formulation can achieve a controlled and programmed responsive release of drugs in inflammatory wounds to match the different stages of wound healing.In the early stage of wound healing,the wound becomes severely inflammatory due to bacterial infection.The PDA@Ag are released first to quickly kill the bacteria and reduce inflammation.Then during the remodeling and re-epithelialization stage,the later released h Col III can promote cell proliferation,migration,and angiogenesis,and accelerate wound healing.In summary,we first proposed the concept and design strategy of the programmed,on-demand,and controlled drug release based on the inflammation-responsive hydrogel formulation of human-derived type III collagen.The designed smart hydrogel formulation not only has tremendous application potential in the treatment of chronic infected wounds,but it also broadens the biomedical applications of human-derived type III collagen.Finally,based on the above researches,we found that although hydrogels that are based on boronic ester bonds can prolong the retention time and function time of drugs at the wound site,compared with multifunctional nanoparticles,when such hydrogels are applied to chronic wounds,they’re easy to fall off from the wound,resulting in a limited function time of the drugs.In terms of this issue,we designed a mussel-inspired double-crosslinked smart responsive hydrogel.It has enhanced antibacterial and pro-angiogenesis properties and can release drugs locally in response to p H in the infected diabetic chronic wounds,thereby promoting wound healing.Dopamine（DA）is grafted to the side chain of oxidized dextran（OD-DA）via Schiff base reaction.Then,a mussel-inspired double-crosslinked smart hydrogel was prepared by mixing OD-DA and quaternary ammonium chitosan solution（HTCC）,with the existence of an appropriate amount of oxidant.The double cross-linking mechanism gives the hydrogel excellent mechanical properties,especially its adhesion.In this project,we selected a simple physical mixing method to load Ag NPs and deferoxamine methanesulfonate（DFO）,thus avoiding complex chemical cross-linking,and simplifying the preparation process and supervision during clinical transformation.By effectively encapsulating Ag NPs and the pro-angiogenic drug DFO,the hydrogel obtains antibacterial and pro-angiogenic properties.At the infected diabetic acidic wound site,the adhesion of the hydrogel enables the hydrogel to adhere tightly to the wound site at the start.Then,due to the breakdown of the double Schiff base mechanism,the hydrogel will disintegrate into solutions and achieve controlled release of Ag NPs and DFO on demand.Finally,the disintegrated hydrogel will naturally fall off from the wound without causing secondary damage.In general,the hydrogel designed in this project has strong adhesion to the wound skin,it can also kill bacteria,reduce inflammation and promote angiogenesis by the release of drugs.More importantly,the adhesive hydrogel will not cause secondary damage to the tissue after disintegration,but ultimately accelerate the repair of the chronic wound of infected diabetes.The above research work has gradually solved the problems during chronic wound treatment,such as short drug retention time,high bacterial resistance,and bad hydrogel-skin adhesion performance.The results of related experiments have also successfully confirmed the positive effects of smart response drug delivery systems on the treatment of infected chronic wounds.These smart response drug delivery systems can overcome the shortcoming of traditional administration systems,and more effectively solve the difficult problems in the clinical treatment of chronic wounds through two or more mechanisms that promote chronic wound repair.The research work herein broadens the road of a smart responsive drug delivery system for chronic wound repair.Besides,the smart responsive drug delivery systems herein have a simple preparation process,low costs,and good biocompatibility,and are highly potential in clinical application.