| Polymer microneedles are widely used in transdermal drug delivery systems due to their advantages of rapid separation,continuous drug delivery and selfadministration.Although many achievements have been made before regarding the functionality and pharmacology of polymer microneedles,the basic problem of how to fully penetrate the skin with less force and maintain structural integrity has not been fully resolved.Meanwhile,the current microneedle strength test or simulation only applies force to the microneedle tip,which cannot reflect the dynamic penetration process of the entire microneedle.In view of the above problems,this paper focuses on how to reduce the penetration force,improve the penetration efficiency and tip safety of polymer microneedles.By establishing the explicit dynamic model,the interaction between microneedles and skin is studied,aiming to explore the improvement strategies of microneedle structure,insertion conditions and material parameters.The main research content of this paper is as follows:(1)The finite element model of microneedle quasi-static penetration into the skin was established to explore the influence of geometric parameters on the maximum penetration force and penetration length of the microneedle,and to explain the skin deformation and destruction process when different microneedles penetrated.Then comprehensive comparations were made on the penetration performance of six microneedles with typical shapes.The results show that the slope microneedle is unsuitable for transdermal drug delivery;the penetration force of the conical microneedle and the pyramidal microneedle are small and the penetration performance is similar;the two-section microneedle possesses higher penetration efficiency.(2)A new three-section microneedle structure was designed.Its penetration performance and dosage were characterized by dynamic simulation results.Its strength was characterized by static and linear buckling analysis.The effects of tip height,base geometry and shaft width on the comprehensive drug delivery performance of three-section microneedles were explored,and the superiority of the three-section structure was expounded by comparing with conical microneedles and two-section microneedles.Compared with the standard conical microneedle,the optimized three-section microneedle with shaft width of 120 μm has a 30.5%-lower maximum penetration force,a higher effective penetration length of 81.6%,2.18 times the unit load dosage.(3)The finite element model of a single polymer microneedle penetrating the skin at high speed was established,and the displacement and stress/strain changes of the microneedle and skin were researched.The influence of different model parameters on microneedle penetration efficiency and tip strain was systematically explored.The results showed that tip safety needs to be considered while improving penetration efficiency by increasing microneedle height or insertion speed;the higher the stiffness of polymer material,the closer the penetration efficiency is to that of rigid microneedle;selecting the skin penetration area with low stiffness can reduce the tip plastic strain with little reduction in the penetration efficiency.And the polymer microneedle combined with three improved strategies showed more excellent penetration performance and tip safety.In order to improve the penetration performance of polymer microneedles while maintaining structural integrity,the finite element model of quasi-static and highspeed microneedle penetrating into the skin was constructed,and the effects of various microneedle geometries and insertion parameters on the transdermal drug delivery performance of polymer microneedles were systematically explored.The research results contribute to the optimization of polymer microneedle structure and penetration conditions. |
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