Microneedle Arrays Allow Lower Microbial Penetration Than Hypodermic Needles In Vitro

Methods: In this study we determined, for the first time, the ability of microorganisms to traverse microneedle-induced holes using two different in vitro models.

Results: When employing Silescol® membranes, the numbers of Candida albicans, Pseudomonas aeruginosa and Staphylococcus epidermidis crossing the membranes were an order of magnitude lower when the membranes were punctured by microneedles rather than a 21G hypodermic needle. Apart from the movement of C. albicans across hypodermic needle-punctured membranes, where 40.2% of the microbial load on control membranes permeated the barrier over 24 h, the numbers of permeating microorganisms was less than 5% of the original microbial load on control membranes. Experiments employing excised porcine skin and radiolabelled microorganisms showed that the numbers of microorganisms penetrating skin beyond the stratum corneum were approximately an order of magnitude greater than the numbers crossing Silescol® membranes in the corresponding experiments. Approximately 103?cfu of each microorganism adhered to hypodermic needles during insertion. The numbers of microorganisms adhering to MN arrays were an order of magnitude higher in each case.

Conclusion: We have shown here that microneedle puncture resulted in significantly less microbial penetration than did hypodermic needle puncture and that no microorganisms crossed the viable epidermis in microneedle—punctured skin, in contrast to needle-punctured skin. Given the antimicrobial properties of skin, it is, therefore, likely that application of microneedle arrays to skin in an appropriate manner would not cause either local or systemic infection in normal circumstances in immune-competent patients. In supporting widespread clinical use of microneedle-based delivery systems, appropriate animal studies are now needed to conclusively demonstrate this in vivo. Safety in patients will be enhanced by aseptic or sterile manufacture and by fabricating microneedles from self-disabling materials (e.g. dissolving or biodegradable polymers) to prevent inappropriate or accidental reuse.

Re-organisation of the cytoskeleton during developmental programmed cell death in Picea abies embryos

Cell and tissue patterning in plant embryo development is well documented. Moreover, it has recently been shown that successful embryogenesis is reliant on programmed cell death (PCD). The cytoskeleton governs cell morphogenesis. However, surprisingly little is known about the role of the cytoskeleton in plant embryogenesis and associated PCD. We have used the gymnosperm, Picea abies , somatic embryogenesis model system to address this question. Formation of the apical-basal embryonic pattern in P. abies proceeds through the establishment of three major cell types: the meristematic cells of the embryonal mass on one pole and the terminally differentiated suspensor cells on the other, separated by the embryonal tube cells. The organisation of microtubules and F-actin changes successively from the embryonal mass towards the distal end of the embryo suspensor. The microtubule arrays appear normal in the embryonal mass cells, but the microtubule network is partially disorganised in the embryonal tube cells and the microtubules disrupted in the suspensor cells. In the same embryos, the microtubule-associated protein, MAP-65, is bound only to organised microtubules. In contrast, in a developmentally arrested cell line, which is incapable of normal embryonic pattern formation, MAP-65 does not bind the cortical microtubules and we suggest that this is a criterion for proembryogenic masses (PEMs) to passage into early embryogeny. In embryos, the organisation of F-actin gradually changes from a fine network in the embryonal mass cells to thick cables in the suspensor cells in which the microtubule network is completely degraded. F-actin de-polymerisation drugs abolish normal embryonic pattern formation and associated PCD in the suspensor, strongly suggesting that the actin network is vital in this PCD pathway.