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The need for hollow microneedle arrays is important for both drug delivery and wearable sensor applications; however, their fabrication poses many challenges. Hollow metal microneedle arrays residing on a flexible metal foil substrate were created by combining additive manufacturing, micromolding, and electroplating approaches in a process we refer to as electromolding. A solid microneedle with inward facing ledge was fabricated with a two photon polymerization (2PP) system utilizing laser direct write (LDW) and then molded with polydimethylsiloxane. These molds were then coated with a seed layer of Ti/Au and subsequently electroplated with pulsed deposition to create hollow microneedles. An inward facing ledge provided a physical blocking platform to restrict deposition of the metal seed layer for creation of the microneedle bore. Various ledge sizes were tested and showed that the resulting seed layer void could be controlled via the ledge length. Mechanical properties of the PDMS mold was adjusted via the precursor ratio to create a more ductile mold that eliminated tip damage to the microneedles upon removal from the molds. Master structures were capable of being molded numerous times and molds were able to be reused. SEM/EDX analysis showed that trace amounts of the PDMS mold were transferred to the metal microneedle upon removal. The microneedle substrate showed a degree of flexibility that withstood over 100 cycles of bending from side to side without damaging. Microneedles were tested for their fracture strength and were capable of puncturing porcine skin and injecting a dye.
Cover crops can offer erosion protection as well as soil and environmental quality benefits. Cereal rye (Secale cereale L.) is the most commonly used winter cover crop in corn–soybean rotations in the upper Midwest of the USA because of its superior winter hardiness and growth at cool temperatures. Cereal rye cover crops, however, can occasionally have negative impacts on the yield of a following corn crop, which discourages broader adoption and introduces substantial risk for corn farmers employing cover crops. We hypothesized that because cereal rye shares some pathogens with corn, it may be causing increased disease in corn seedlings planted soon after cereal rye termination. To test this, we performed a series of experiments in a controlled environment chamber to assess the response of corn seedlings with and without a commercial fungicide seed treatment to the presence of cereal rye or other species of cover crops that were terminated with herbicide prior to corn planting. Our results indicate that under cool and wet conditions, cereal rye reduces corn seedling growth performance and increases incidence of corn seedling root disease. Fungicide seed treatment had limited efficacy in preventing these effects, perhaps because environmental conditions were set to be very conducive for disease development. However, hairy vetch (Vicia villosa Roth) and winter canola (Brassica napus L.) cover crops had fewer negative impacts on corn seedlings compared with cereal rye. Thus, to expand the practice of cover cropping before corn, it should become a research priority to develop alternative management practices to reduce the risk of corn seedling root infection following cereal rye cover crops. Over the longer term, testing, selection and breeding efforts should identify potential cover crop species or genotypes that are able to match the winter hardiness, growth at cool temperatures and the conservation and environmental quality benefits of cereal rye, while avoiding the potential for negative impacts on corn seedlings when environmental conditions are suitable for disease development.
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