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In order to increase the utilization rate of drug carried by microneedles and reduce waste, a two-step casting method was proposed to fabricate tip-loaded dissolving microneedles in this paper. The tip-loaded dissolving microneedles, also named layered microneedles, was consisted of two layers. The tip layer of the microneedles carried model drug, while the backing layer was fabricated with pure dissolving material. Polyvinyl alcohol, polyvinylpyrrolidone and hyaluronic acid were used as the base materials to fabricate the dissolving layers of the microneedle patches. Rhodamine B was chosen as the model drug to show the layered structure of tip-loaded microneedles. The material formulation and fabricating conditions of the tip-loaded dissolving microneedles and their transdermal insulin delivery efficiency were systematically studied. Nanoindentation testing showed that the tips of all three kinds of dissolving microneedles can bear the maximum loading of 50 mN with no damages, indicated sufficient mechanical strength for smooth skin puncturing as the minimum pressure required was 10 mN only. Moreover, our fabricated tip-loaded dissolving microneedles can greatly reduce the drug waste cause by unused backing layer in normal microneedles and realize a 30% enhancement of drug delivery efficiency after puncture treatment.

Polymeric microneedle is a highly effective, painless and safe method for transdermal drug delivery with broad market prospect and high application potential. In this paper, a novel method for the preparation of microneedle array with flexible substrate using the method of micro-injection compression molding was proposed. The influence of microneedle length on transdermal insulin delivery was investigated basing on the testing results of drug diffusion experiments. The results showed that the polymeric microneedles prepared by micro-injection compression molding had enough mechanical strength to pierce the skin without breaking. The correlations between dimensionless permeation amount of insulin and the ratio of surface area to microneedle length as well as the ratio of skin thickness to microneedle length were both obtained through optimal scaling analysis. The insulin penetration efficiency presented a 2.29 times improvement after treated with 337 μm microneedle compared with that of untreated skin. The modification of polymeric microneedles could enhance the transdermal penetration efficiency of insulin, and also provide technical basis for the study of transdermal penetration.