Hierarchical materials based on polydimethylsiloxane as tissue-like phantoms for photoacoustic imaging and diffusive optics

The rise of multimodal imaging and treatments, particularly with optical tools, promises to make a disruptive impact on clinical problems such as cancer and infectious conditions, especially in critical sites like the lungs. However, ethical concerns and the high costs of using lab animals represent significant barriers in the early stages of development. In this context, significantly enhancing the relevance of multimodal phantoms for unbiased technical specification validation within a controlled lab setting may constitute a major advancement. Here, we propose a concept of hierarchical manufacturing as an approach to encode multiple mechanisms of physical contrast based on water-in-elastomer micro-emulsions made of a continuous phase of hydrophobic polydimethylsiloxane and micro-droplets of hydrophilic solutions. Specifically, we investigate the potential to engineer the overall morphology of the ensemble to mimic the intricate anatomical structure of complex organs, such as the unique porosity of lung tissue. Concurrently, we aim to precisely control the optical properties of the system in critical scenarios, such as enabling the recreation of diverse skin tones and varying levels of vascularization in relevant applications. We believe that a hierarchical approach to fabricating anatomical phantoms represents a robust and adaptable alternative to animal models in the early stages of translational research involving hybrid or multimodal imaging techniques. This approach will prove particularly valuable in developing artificial intelligence solutions for emerging modalities like photoacoustic imaging, which face fundamental challenges due to the limited availability of accurate ground truth data from animal studies.