A novel 3D polymeric tool for accurate screening of the performance of immunodiagnostic polymeric microneedles

INTRODUCTION: Melanoma is the most lethal skin cancer, having a rapid increase of occurrenceover the past 30 years1. To date, the most effective treatment for melanoma is the early diagnosis, whichis followed by surgical resection. Therefore, in order to improve these disappointing statistical figures,it is essential to develop efficient diagnostic tools for rapid detection of the disease’s specific markers.Minimally invasive microneedles (MNs) are promising candidates, as they enable rapid and pain-freeprotein biomarker detection in situ. However, validating the developed microneedle (MN) systemsremains a bottleneck. To date, the most commonly used systems for in vitro microneedle validation areeither homogeneous solutions that contain the target antigen to be detected by the MNs or excisedanimal skin. Animal skin strikes many similarities with the human skin, however the animal skinproperties, such as stiffness, elasticity, porosity, which vary between different patients cannot be easilytuned/ tailored2. Furthermore, antigen solutions can be informative for a preliminary evaluation of theMN arrays, but they are not representative models of in vivo skin structure and biomarker concentration.Biomaterial based 3D structures can simulate important skin tissue features, such as stiffness, elasticity,porosity, structure, extracellular matrix presence that can vary between different patients, different skintypes and with ageing. Moreover, they can provide a realistic structural environment for the penetrationand action of MN. Therefore, these biomaterial based 3D structures have great potential as screeningtools for MN evaluation. The aim of this work was to validate the S100 expression, a marker that isupregulated in melanoma, on a microporous polymer based 3D melanoma model. S100 expression inthe model was confirmed using a novel immunodiagnostic microneedle device.METHODS: 3D polymer (PU) based microporous scaffolds (5x5x2.5mm3) were developed using theThermally Induced Phase Separation (TIPS) method, as described previously3. The porosity was 80%and the pore size 100-120 μm. Thereafter, the metastatic melanoma cell line A-375 was injected andcultured in those scaffolds for 5 weeks. Evaluation of cell distribution within the PU matrix wasconducted with Scanning Electron Microscopy (SEM). Viable (live) cells were visualised in situ withconfocal laser scanning microscopy (CLSM) of several sections of each scaffold. Furthermore, thedetection of the S100 marker was carried out with PLA microneedles both on the 3D scaffold and forthe cell culture supernatants. The PLA microneedle device was produced, surface modified and coatedwith the S100 antibody as previously described, followed by the detection of the antigen viaimmunoassay analysis on the microneedle surface4.RESULTS: The MN device was able to detect the S100 secretion from the melanoma cells in the scaffold after 35 days of a viable culture, producing a clear and visible detection signal similar to theone detected for the positive control samples. However, S100 gradients were not detected in the cellculture supernatants, suggesting that this versatile scaffolding tool can be an advantageous low costanimal free tool to be use as a surrogate for the in vitro evaluations of the MNs.REFERENCES: 1American Cancer Society, 2018. 2K. Moronkeji and R. Akhtar, in Mechanical Propertiesof Aging Soft Tissues, eds. B. Derby and R. Akhtar, Springer International Publishing, Cham, 2015, pp. 237-263. 3S. Totti, M. Allenby, S. B. d. Santos, A. Mantalaris and E. Velliou, RSC adv, 2018, 8, 20928-40 4 K. W. Ng, W. M. Lau and A. C. Williams, Drug Deliv Transl Res, 2015, 5, 387-396