Scanning Laser Cavitation Rheology for mesoscopic mapping of shear moduli of soft materials at high strain rates

Mechanical characterization of soft biomaterials is essential for understanding biological function, injury response, and the design of engineered tissues. Conventional techniques such as parallel-plate rheometry are restricted to bulk measurements at low to moderate mechanical strain rates (< 10² s^-1) and have limited relevance for the examination of high strain rate processes. We introduce scanning Laser Cavitation Rheology (sLCR) as a non-contact technique that utilizes single laser-generated microcavitation bubbles (μCBs) to map local shear modulus in soft hydrogels at strain rates exceeding 10⁴ s^-1. Through a combination of probe beam measurement and single-frame shadowgraphy, we use a single pulsed laser exposure to measure the dynamics of μCB expansion and collapse to fit for shear modulus without high-speed videography, exogenous particles or repeated loading. We apply sLCR to type-I collagen (T1C) hydrogels and measure concentration-dependent shear moduli, establish relationships between local shear modulus and fiber architecture, and provide a practical framework for sLCR usage by defining sensitivity and spatial resolution limits. These results establish sLCR as a platform to provide localized, high strain rate measurements in biologically relevant 3D matrices, offering broad utility for mechanobiology, injury modeling, and mechanical characterization of complex soft biomaterials. STATEMENT OF SIGNIFICANCE: Mechanical characterization tools typically resolve microscale properties at low strain rates or report bulk properties without spatial information. Scanning Laser Cavitation Rheology (sLCR) complements these methods by using single laser-generated microcavitation bubbles to measure mesoscale mechanical properties of soft biomaterials at high strain rates. We demonstrate the use of sLCR to measure concentration-dependent stiffening of type-I collagen, relate local elastic modulus to fiber architecture, and provide sensitivity and resolution limits. This method is compatible with commercial microscopy platforms, making it suitable for broad adoption. By enabling high strain rate, spatially resolved characterization of soft biomaterials, sLCR equips researchers to interrogate rapid loading events (e.g. blast injury, laser surgery) and chronic tissue remodeling (e.g. cancer, fibrosis).