Poly(vinyl chloride-co-vinyl acetate-co-maleic acid) (vinyl chloride 83%, vinyl acetate 13%, carboxylated 1%) was found to be a substrate favoring the deposition of vaterite crystals from stable supersaturated solutions at pH 8.50 and 25 °C. Induction times preceding calcium carbonate precipitation were inversely proportional to the solution supersaturation, and a surface energy of 23 mJm-2 was calculated according to classical nucleation theory. The relatively low value may be attributed to the heterogeneous character of vaterite nucleation. The linear dependence of the rates of vaterite formation on the solution supersaturation, in which the crystallization took place, in combination with the independence of the measured rates on the fluid dynamics, suggested that vaterite overgrowth was controlled by surface diffusion. This finding was in agreement with the results obtained for the crystallization of vaterite on cholesterol. Our results suggest that the kinetics of overgrowth may be very important for the stabilization of transient mineral phases. The structure of the polymeric substrates also plays a role, mainly through the development of active growth sites, which should show chemical and structural affinity to the mineral phase.

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A novel inkjet printing technology is introduced as a process to coat metal microneedle arrays with three anticancer agents 5-fluororacil, curcumin and cisplatin for transdermal delivery. The hydrophilic graft copolymer Soluplus® was used as a drug carrier and the coating formulations consisted of drug -polymer solutions at various ratios. A piezoelectric dispenser jetted microdroplets on the microneedle surface to develop uniform, accurate and reproducible coating layers without any material losses. Inkjet printing was found to depend on the nozzle size, the applied voltage (mV) and the duration of the pulse (s). The drug release rates were determined in vitro using Franz type diffusion cells with dermatomed porcine skin. The drug release rates depended on the drug-polymer ratio, the drug lipophilicity and the skin thickness. All drugs presented increased release profiles (750 m skin thickness), which were retarded for 900 m skin thickness. Soluplus assisted the drug release especially for the water insoluble curcumin and cisplatin due to its solubilizing capacity. Inkjet printing was proved an effective technology for coating of metal microneedles which can then be used for further transdermal drug delivery applications.

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