Silk Fibroin Microneedles For The Transdermal Delivery Of Colchince

Acute gouty arthritis（AGA）has a rapid onset and severe symptoms,which seriously affects the quality of people’s lives and urgently needs to be prevented and treated.Colchicine（COL）is a classic drug to prevent and treat AGA by oral administration.COL has a narrow therapeutic window and low oral bioavailability,excessive or long-term oral administration can cause gastrointestinal adverse reactions such as diarrhea and vomiting,which limits its clinical application.Therefore,in this study,a transdermal drug delivery system（TDDS）of COL was developed via microneedles technology,aiming to improve the transdermal absorption of COL and achieve the effect of preventing and treating AGA.In this study,biodegradable silk fibroin（SF）was used to prepare COL-loaded SF separable microneedles（SF-SMNs）and SF integrated microneedles（SF-IMNs）.The above microneedles were systematically investigated and compared.The main research contents and conclusions are shown as follows:（1）The determination method of COL content was established.The solubility and the oil-water partition coefficient of COL in different solvents were measured.Also,the preliminarily pharmacokinetic characteristics of COL aqueous solution after oral and transdermal administration in rats were investigated.The results showed that COL was soluble（>10 mg/m L）in aqueous solution and PBS（p H=7.4）,and the lg P values were about 1.Compared with oral administration,transdermal delivery of COL aqueous solution exhibited a certain sustained release effect,with a more stable plasma concentration and considerably longer peak and average residence times.However,the relative bioavailability of COL aqueous solution for transdermal administration was only（15.55±2.70）%.Therefore,it is of great significance to carry out TDDS research on COL microneedles.（2）SF-IMNs were prepared by a one-step method with SF solutions of various concentrations.The cocoon sericin was removed with alkaline hot water,and the degumming rate was（30.95±0.32）%.Lithium bromide method was used to dissolve degummed silk to obtain a clear and high-concentration SF solution.After dialysis and desalination,the SF solution was concentrated by polyethylene glycol-20000 reverse dialysis method,resulting in a concentration of SF of up to 26%.The 8%SF solution was selected as the optimal material for SF-IMNs preparation.The subsequent SF-IMNs had good flexibility,strong insertion ability,and the swelling rate in PBS（p H=7.4）could reach（197.91±11.71）%,while the dissolution rate was less than 10%.Furthermore,SF-SMNs were fabricated by a two-step method with PVP-K30 as the base and SF as the tips,and the formulation of SF-SMNs was optimized.The results showed that SF-SMNs prepared with 100μL of 40%PVP-K30 solution as the base and 8%SF solution as the tips had good insertion ability and insertion ability,with the drug utilization rate of the tips up to（82.15±1.12）%.（3）The properties of SF-IMNs and SF-SMNs were evaluated.The appearance and morphology observation showed that,the base of SF-SMNs was thick and flat,and the sodium fluorescein was concentrated in the tips of SF-SMNs,but evenly distributed in SF-IMNs.Infrared spectroscopy analysis showed that the characteristic peaks of the secondary structures of the tips of two SF microneedles were similar,both of which containedβ-sheet and random coil.After absorbing liquid,the tips of SF-IMNs swelled,whereas that of SF-SMNs separated from each other with the dissolution of the base.SF-SMNs had a breaking force of 4.05N/Needle and had higher mechanical strength,while SF-IMNs were softer without breaking force.Both SF microneedles could penetrate the skin stratum corneum barrier to the superficial dermis,but SF-SMNs exhibited a stronger penetrating power,and the tips of SF-SMNs could be successfully implanted into rat skin.The stability test showed that COL in the two SF microneedles would degrade under strong light,but could be stored stably for 60 d at 25°C and 4°C in the dark.The in vitro enzymatic degradation test showed that the majority of SF microneedles could be degraded by protease XIV,which preliminarily proved that they had certain biodegradability.The in vitro transdermal tests showed that SF microneedles could enhance the transdermal penetration of COL.In order to improve the patient’s compliance,the administration time of SF microneedles was shortened to 4 h,and the results showed that the drug penetration effect of SF-SMNs was better.Its drug release curve equation was Q=1.78t^0.62,r=0.9902,which was consistent with the Ritger-peppas model.The exponent value“0.62”in the equation indicated that the release behavior was a coupled result of COL diffusion and skeleton erosion of the tips.The skin irritation test showed that the skin irritation of SF-IMNs was significantly stronger and the duration was longer.（4）The effect of two kinds of COL-loaded SF microneedles（dosing every other day）on preventing and treating AGA were investigated with blank,model,and intragastric administration（daily dosing）as controls.The AGA model of mice was induced by sodium urate with injection into the ankle joint.Results showed that the foot swelling and pathological ankle alterations of mice in the SF-SMNs and intragastric administration groups were significantly reduced compared to the model control,while the SF-IMNs group had no significant effect.The results of TNF-αand IL-1βcontent in mouse serum showed that compared with COL intragastric and SF-IMNs administrations,SF-SMNs could maintain the above factors at relatively normal levels.These results showed that COL administered by SF-SMNs had better effect on the prevention and treatment of AGA in mice.In conclusion,this paper innovatively prepared COL-loaded SF-SMNs and SF-IMNs,and conducted a preliminary assessment of their prevention and treatment effects on AGA.Results revealed that SF-SMNs had the advantages of high mechanical strength,good insertion ability,less skin irritation,good biocompatibility,and sustained drug percutaneous penetration,etc.,which was more conducive to COL exerting its efficacy.The TDDS developed in this study has the potential to avoid the first-pass effect of COL,achieve the sustained release effect of COL transdermal administration,reduce the frequency of administrations,and is expected to reduce the side effects of COL,as well as expand the clinical application of COL and the research of microneedles.