Design And Evaluation Of Microneedles For Sustained Release Of Water-insoluble Drugs

Dissolvable microneedles(DMNs)are made of water-soluble polymers.They can penetrate the stratum corneum,which is barrier of skin permeation of drugs,and release the drug in skin by the dissolution of polymers.The incorporation of water insoluble drugs into DMNs can improve the bioavailability of the drugs during transdermal administration.However,it is difficult to achieve sustained release by DMNs alone because of the rapid dissolution of the DMNs after absorption of interstitial fluid from the skin,resulting in fast drug absorption and elimination.The aim of this study is to design DMNs that can prolong and control the release of insoluble drugs to reduce the frequency of administration and to improve patient compliance.In this study,indomethacin(IDM)was selected as a model drug.IDM loaded inclusion complex and mixed micelles were prepared to improve the water solubility of the drug.Further,the inclusion complex and mixed micelles were incorporated into DMNs respectively.And the properties such as appearance,morphology,mechanical strength and dissolution rate of the two kinds of microneedles were characterized.Then the ex vivo and in vivo release characteristics of the DMNs were investigated.The pharmacodynamic effects of IDM micelles loaded DMNs were evaluated via arthritis model in mice.The details of this study are as follows:Firstly,UV and HPLC analytical methods for the determination of IDM content were established.The maximum absorption wavelength of IDM was obtained by UV full wavelength scanning at 320 nm.And it was determined that the materials used for the preparation of inclusion complex,mixed micelles and microneedles did not interfere with the UV determination of IDM.Further,it was determined that the polymer materials and mouse skin extracted solution did not interfere with the HPLC determination of IDM.UV and HPLC methods with good linearity,high accuracy,precision and recovery were established.Based on the determination of the solubility of IDM in different medium,PBS(pH 7.4)was selected as the receiving medium for in vitro release studies,and 20%ethanol-PBS(pH 7.4)and 20% PEG400-PBS(pH 7.4)were selected as the receiving solution for transdermal experiments.IDM-HP-β-CD was prepared by solution stirring-freeze drying method.The stirring temperature,stirring time and stirring speed were selected as the main influencing factors,and the yield and encapsulation efficiency were selected as the evaluation indexes.The prescription of IDM-HP-β-CD was optimized by orthogonal test.The optimal prescription was obtained with stirring temperature of 60℃,stirring time of 5h and stirring speed of 1440 rpm.The yield of IDM-HP-β-CD obtained from this prescription was 87.28%,the encapsulation efficiency was 56.84% and the drug loading was 11.90%.The lyophilized powder was subjected to FT-IR and DSC to determine the structure of IDM-HP-β-CD and to verify the successful preparation of IDM-HP-β-CD.Further,a two-step method was used to combine IDM-HP-β-CD with DMNs to obtain a well-arranged microneedle array,in which the needle height was about 500 μm and the base width was about 250 μm.The penetration capability of IDM-HP-β-CD DMNs was investigated using Parafilm and rat skin.And the results showed that DMNs could successfully pierce the stratum corneum and enter the skin.Finally,the in vitro dissolution and transdermal penetration behaviors of IDM-HP-β-CD DMNs were evaluated using Parafilm and porcine skin to simulate human skin,respectively.The results showed that the in vitro release of IDM-HP-β-CD DMNs was slower compared to IDM DMNs.The needle tips were dissolved rapidly after entering into the skin and appeared a burst release,and then release the drug slowly at a steady rate.IDM-MMs were prepared by thin film hydration method using PF127 and Soluplus.The dosage,hydration time and volume of hydration medium were selected as the main influencing factors,and the encapsulation efficiency,particle size and PDI were selected as the evaluation indexes.The Box-Behnken response surface optimization method was used to optimize the prescription of IDM-MMs,and the optimal prescription was obtained as the dosage of 5 mg,hydration volume of 5 mL and hydration time of 1 h.The optimized IDM-MMs showed an encapsulation rate of 80.43%,drug loading of 5.04%,particle size of 58.7 nm,PDI of 0.113,and zeta potential of-8.72 mV.The morphology of IDM-MMs was characterized by TEM,which showed that IDM-MMs were distributed uniformly with solid spherical shape.The size under electron microscopy was consistent with the particle size results.The in vitro dissolution experiments indicated that the dissolution rate of IDM-MMs was slower than that of IDM suspension.And IDM-MMs could be stored for at least two months under different environment temperature.PVP/VA was finally selected as the material for the preparation of IDM-MMs DMNs by the results of compatibility and hygroscopicity experiments.The proportion of drug in the tip of DMNs was selected as the evaluation index.The prescription of IDM-MMs DMNs was optimized to be with 7.5% PVP/VA in tip solution,45 μL of tip solution,50% PVP/VA in base solution and 150 μL of base solution.The needle portion of DMNs could be completely dissolved in the skin within 10 min.The results of in vitro release and transdermal permeation experiments showed that IDM-MMs DMNs were released more slowly than IDM DMNs.The pharmacokinetics of IDM-HP-β-CD DMNs and IDM-MMs DMNs were further compared.The HPLC method for the determination of IDM content in rat plasma was established to exclude the interference of plasma endogenous substances.A standard curve with good linearity was obtained.Then the rats were grouped,administered and blood collected.The results showed that IDM-MMs DMNs reached their peak concentration faster and were longer-acting than commercially available patches.Compared with IDM-HP-β-CD DMNs,which can only maintain a lower concentration for 24 h after reaching to the peak concentration quickly at 0.5h,the extended-release effect of IDM-MMs DMNs is more prominent.Finally,IDM-MMs DMNs with better extended-release property were selected for pharmacodynamic experiments.The AIA model was established by injecting CFA into the plantar of mice,and then the stability of the model and the efficiency of IDM-MMs DMNs were evaluated in five aspects: swelling ratio,arthritis index,spleen index,histopathology,and inflammatory factors,respectively.The results showed that all the above indexes were significantly improved after the administration of IDM-MMs DMNs(p<0.01).Further,the therapeutic effect of IDM-MMs DMNs administered twice a day was consistent with that of commercially available patches administered daily,which preliminarily proved the long-acting effect of IDM-MMs DMNs.In conclusion,the IDM-MMs significantly improve the water solubility and bioavailability of IDM.The novel IDM-MMs loaded DMNs are simple to prepare,and easy to use.More importantly,sustained release of IDM was obtained which may reduce the time interval of administration,and greatly improve patient compliance.These results suggest that the MMs loaded DMNs can be a useful method for an enhanced and sustained skin permeation of water insoluble drugs.