Preparation Of Ultrasonic Responsive PLGA Microcapsules Loaded With Lidocaine And The Application Of Analgesic Therapy On Demand In CCI Model Rats

With the aggravation of the aging of the global population,the number of orthopedic operations continues to increase.The muscle and bone trauma caused by orthopedic operations usually causes strong postoperative pain and discomfort to patients.Therefore,orthopaedic pain management during perioperative period has become a global concern.Due to the complexity of postoperative pain and the limited clinical measures to deal with early postoperative acute pain,it mainly relies on the use of pain relief pump to inject analgesic drugs into the patient.While maintaining the basic pump amount,when the pain suddenly worsens,it can increase the instantaneous pump amount of analgesic drugs through the knob to quickly relieve the pain.To achieve the purpose of individualized treatment,however,in the process of clinical application,the defects of pain relief pump itself are increasingly obvious.Because pain relief pump pumps analgesics into veins and into systemic circulation through indwelling needles,patients often suffer serious side effects,such as:Nausea,vomiting,abdominal pain and other symptoms of gastrointestinal dysfunction,inhibition of cardiopulmonary function,paralysis of bladder nerve and inflammatory reactions such as redness and swelling around the indwelling needle.Therefore,there is an urgent need for a non-invasive drug delivery system with low toxicity and side effects,long effective analgesia time,and on-demand drug release analgesia.At present,the development of stimulation-responsive biointelligent sustained-release materials is expected to improve the shortage of biomedical materials.In addition to the function of long-term drug sustained-release,the biointelligent sustained-release materials have stimulation-responsive properties,among which the stimuli mainly include ultrasonic wave,infrared light,p H,temperature,magnetic field and different cellular and internal environments,and short-term controlled release of drugs can be achieved according to the stimuli.In contrast to other stimulus-responsive biointelligent slow-release materials（e.g.Compared with liposomes,chitosan,hydrogels,etc.）,Poly（lactic-co-glycolic）acid（PLGA）has become the most widely used biointelligent slow-release materials due to its sensitive stimulus response,good degradability,excellent biocompatibility and stability.Compared with other stimuli,ultrasonic and slow-release materials can form a good cavitation effect,so that the slow-release materials can better perceive ultrasonic,so that ultrasonic can be used as a good trigger factor of biological slow-release materials to regulate the release of encapsulated drugs,so as to achieve controlled release and on-demand release of drugs.Besides,considering the convenience and non-invasive use of ultrasonic,in this study,the advantage of on-demand analgesia was confirmed in a rat model of Chronic sciatic nerve injury（CCI）by pre-mixed membrane emulsion combined with PLGA supported lidocaine with ultrasound.In this study,PLGA microcapsules loaded with Lidocaine（Lidocaine@PLGA）were prepared successfully by premixed membrane emulsification method.Under Scanning Electron Microscope,Lidocaine@PLGA microcapsules were spherical,regular in shape,uniform in size and smooth in surface morphology.The particle size concentration of Lidocaine@PLGA microcapsules was further determined by Dynamic Light Scattering（DLS）,which was（3.11±0.37）μm.The maximum absorption peaks of PLGA,Lidocaine and Lidocaine@PLGA microcapsule components were determined by Fourier transform infrared spectroscopy,which revealed that PLGA and Lidocaine are not simply combined physically,but interact with each other through chemical bonds.The yield,drug loading and encapsulation rate of microcapsule were（49.33±3.40）%,（15.47±0.17）%and（15.26±0.92）%respectively by UV spectrophotometry.Cytotoxicity tests were conducted on microcapsules with different concentration gradients.The results showed that Lidocaine@PLGA microcapsules were incubated with L-929 cells for 24h at concentrations of 100,67,50μg·m L^-1,respectively.The cell survival rates were 81.8%,84.1%and 85.4%,respectively,indicating that the drug-carrying microcapsules had good biocompatibility.In vitro experiment,the relationship between cumulative drug release percentage changes of microcapsules under the influence of different ultrasonic instruments,different ultrasonic time and different ultrasonic media was compared.Finally,according to the above optimal conditions,the long-term drug release changes of microcapsules with or without ultrasonic intervention and microcapsules were studied.The toxicity of microcapsules to L929 cells was evaluated by CCK8 assay.Finally,based on the CCI model of SD rats,20 SD rats were randomly divided into blank group,saline group,lidocaine group and microcapsule group consisted of4 groups,5 in each group.The saline group,lidocaine group and microcapsule were injected with normal saline,lidocaine active agent and microcapsule around sciatic nerve ligation,respectively,and behavioral tests were conducted at designated points after injection.In the lidocaine group and Lidocaine@PLGA group,ultrasonic stimulation was performed on the injection site for 6 min before each test.The experimental results further demonstrated that the Lidocaine@PLGA could perform ultrasonic responsive release and achieve analgesic relief on demand.Luxol Fast Blue LFB（Luxol Fast Blue LFB）demyelination staining was performed on the rat sciatic nerve,which further confirmed the safety and reliability of Lidocaine@PLGA and handheld ultrasound instrument,and provided the research basis for further clinical transformation in the later stage.