Development of holographic optical elements for use in wound monitoring

Wounds that fail to heal impact the quality of life of 2.5 % of the total population. The costs of chronic wound care will reach $15–22 billion by 2024. These alarming statistics reveal the financial strain for both the medical industry and society. A solution can be found in compact and accessible sensors that offer real-time analysis of the wound site, facilitating continuous monitoring and immediate treatment, if required. Benefits of these sensors include reduction of cost and can extend the reach of healthcare to remote areas. The progression of a wound site can be closely monitored with holographic optical elements (HOEs) by real-time quantification of wound healing biomarkers, such as oxygen, temperature, pH and lactate. Fabrication of such wound monitoring sensors requires biocompatible, water-resistant photosensitive materials suitable for specific functionalisation with respect to wound analytes. Here, the design and fabrication of a HOE for delivering an excitation light beam to the sample chamber of a photoluminescence-based wound monitoring system is reported. We present a photopolymerisable hybrid sol gel (PHSG) material, capable of recording a 60 % diffraction efficiency holographic waveguide. A 1692 ± 5 lines/mm slanted transmission HOE has been theoretically designed and fabricated in PHSG films to in-couple a 633 nm beam into the oxygen sensing site. An identical grating has been used to out-couple the 633 nm beam out of the system. Stability of the PHSG grating post 476.5 nm recording was achieved by two techniques, 532 nm uniform illumination and UV-curing. The unform exposure to laser light was proved to be the more successful method since UV exposure was demonstrated to result in layer damage due to accumulated stress. The potential of waveguides as light filtering optical elements is also explored.