• dermatoscopy
• moldless
• PDMS lenses
• skin cancer
• smartphone

According to the World Health Organization, skin cancer accounts for about 25% of all cancer cases and its incidence is constantly increasing [1],[2]. Since the early diagnosis of melanoma, the most aggressive among skin cancer, is a crucial factor in increasing patients' survival rate[3], it is essential to have screening tools accessible by all. Teledermatology, aiming to provide dermatological analysis through smartphones, could become a general purpose tool and represent a new triage system to enabling greater self-monitoring and early diagnosis, minimizing unnecessary biopsies and costs [4]. To date, the main obstacle to the large-scale use of mobile teledermatology is the need of expensive optical lens to transform the smartphone into a dermatoscope.
The purpose of this study is the characterization, optimization and low-cost production with different fabrication parameters of PDMS lenses for teledermoscopy. These lenses will be included in an ADD-ON to transform the smartphone in a low cost dermatoscope. Different lens parameters (i.e. diameter and volume) are tested to find the best trade-off solution and a A specific setup was created to have a controllable and repeatable manufacturing process. The confine sessile drop technique has been chosen for PDMS lens production among the state of the art techniques. PDMS lenses were characterized both geometrically ( i.e. real diameter, heigh, radius of curvature, focal length and volume) and optically (i.e. field of view, focus distance, image resolution, contrast and distortion). Lenses profiles were evaluated to determine lens variability within the batches.
Dermatoscopic images with a central region of 10mm x 10mm with a distortion rate< 10% and 22.7 µm average resolution are acquired with PDMS lens of 9mm diameter and volume of (41.69±4.21)µlt and (42.57±2.29)µlt, housed in the dedicated ADD-ON, mounted on an iPhone 11. Evaluation in the repeatability of the proposed fabrication procedure reported a 15% error rate, paving the way for future standardized mass production.