Holographic Photopolymer Gratings: A Step toward Wound Temperature Sensing

This study presents the development and optimization of acrylamide-based photopolymer volume transmission gratings for wound temperature monitoring, addressing the need for accessible, user-friendly real-time biomedical sensors. Temperature variations in the narrow range of 33-37 °C are clinically significant for wound healing, offering insights into inflammation and infection prior to visual indications. Leveraging the inherent sensitivity of grating diffraction efficiency to Bragg angle detuning, 15° slanted gratings were recorded with an initial diffraction efficiency of 50%. These gratings are designed to provide a selective and reversible response to temperature fluctuations, ensuring compatibility with wound care applications. The photopolymer composition was systematically tailored by varying the ratios of acrylamide (AA) and diacetone acrylamide (DA) monomers, as well as the concentration of the cross-linker, N,N′-methylenebis(acrylamide) (BA). Laminated samples were tested across multiple temperature cycles, demonstrating consistent and repeatable changes in normalized diffracted beam intensity of 72 ± 5% across 10 cycles, revealing a sensitivity of 18%/°C. For the optimized composition, an improved thermal sensitivity, stability, and repeatability, maintaining performance after 20 days of aging was demonstrated. The findings highlight the influence of monomer ratios and cross-linker concentration on thermal responsiveness and material durability. This work underscores the potential of photopolymer gratings as cost-effective, robust, and scalable solutions for wound temperature monitoring, particularly in resource-limited environments. Future studies will focus on integrating these gratings into a flexible wound patch framework for practical clinical applications, further investigating their utility in improving wound care management.