In the first 16 months, we successfully transitioned the intelligent Surface Thermal (iST) microfilm concept from theoretical simulation to functional microchip samples :
WP1: Development of iST Microfilms (Led by NTUA, FHG)
A transient 2D finite element model was used to optimise the SU8/metal/glass microheater, evaluating 800 design scenarios and selecting six near-optimal options. The best design achieved 11.89 J/cm² energy density, a 297 ms rise time, and only a 2 K temperature variation at 473 K, confirming sub-second activation and high temperature uniformity. A full cleanroom fabrication process was established for flexible iST chips, including metallization, photolithography, etching, and SU-8 structuring, alongside chemical strengthening of 100 µm glass enabling bending to a 20 mm diameter and successful assembly of first wire-bonded chips on PCB carriers. Thermo-electrical characterisation defined the microheater TCR and supported development of a portable closed-loop activation unit with precise temperature control and non-contact finger detection. The chip exceeded 150°C within 100 ms, meeting requirements for the door-handle proof-of-concept, and demonstrated stability over more than 8,000 thermal cycles. A multilayer thermal model further assessed burn risk, defining safe operating windows and showing that, under accidental contact conditions, residual heat transfer remains confined to the epidermis.
WP2 : Methodology Optimisation for Antimicrobial Testing:
- Systematically evaluated the originally planned touch-transfer and modified ISO 22196 methods, and identified that the iST microfilm’s hydrophobic SU8 surface and low bacterial adhesion required a revised approach.
- Compared swab-based, drop-based, and loop-assisted inoculation methods, and found that contact plate transfer is the most reliable recovery method, while liquid recovery showed higher variability. This established a reproducible baseline protocol for future efficacy testing.
- Successfully completed cytocompatibility assessment according to ISO 10993-5 using L929 fibroblast cells exposed to iST microfilm extracts prepared per ISO 10993-12, providing the first validated in vitro evidence of biocompatibility under the tested conditions and establishing a safety baseline for the final device formulation.
WP3: Proof-of-Concept Development
- Finalised a functional CAD design for a retrofittable smart door handle proof-of-concept, integrating the iST microfilm directly into the hand-contact zone.
- Developed a split-electronics architecture, positioning batteries and the Wi‑Fi controller in the rosette (wall plate) and the power amplifier in the handle to minimise cabling across the mechanical pivot.
- Implemented a modular electronic control system comprising a power management subsystem, a power delivery stage with FET driver and back-EMF protection, and a precision measurement subsystem with a 16-bit ADC, 1 mA constant current source, and 0.1°C measurement precision.
- Designed a complete ESP32-S3 firmware framework enabling fixed-duration and temperature-targeted pulse modes, cooldown protection logic, and onboard CSV data logging.
- Delivered a full API infrastructure, including a Postman collection and endpoints for device status, scheduling, & firmware updates, alongside a cross-platform web application for remote device management, real-time monitoring, & schedule programming.
WP4: Safe & Sustainable by Design, SSbD Step 1 & 2 Implementation:
- Completed Step 1 of the EC’s SSbD framework, identifying and categorising 30 chemicals used in the iST manufacturing process according to hazard profiles.
- Critical Safety Outcome: Two substances (2-methoxypropyl acetate and tetramethylammonium hydroxide) were classified as Level 0 (requires immediate substitution). Seven substances as Level 1, fifteen as Level 2, and six as Level 3. FHG was notified and has already initiated substitution plans, aligning with the project’s safe-by-design principles. Life Cycle Assessment (LCA) Baseline:
- Defined the functional unit for LCA as: “Disinfection of one door handle with measured effectiveness,” comparing iST technology against a baseline of chemical disinfection in a hospital setting (San Sebastian Hospital).
- Developed a methodological framework to calculate a break-even point, determining the disinfection efficiency threshold at which the iST technology becomes environmentally preferable to chemical methods.
