Kelly M. Schultz

Microrheology of biomaterial hydrogelators

Microrheology uses the motion of dispersed colloidal probe particles to measure the viscosity or viscoelastic moduli of soft materials. The distinct advantages of microrheology include small sample volume requirements, access to a large range of time scales for the dynamic response and short acquisition times. These advantages make microrheology important for studies of biomaterial hydrogelators. Recent advances have enabled the precise characterization of hydrogelator sol–gel transitions, measurements of rare and scarce materials and high-throughput screening of hydrogel rheology over a large composition space. In this review, we focus on multiple particle tracking microrheology, including the considerations that define its operating regimes and its recent applications. Those interested in biomaterial rheology will find these methods as accessible as bulk rheological measurements and straightforward to implement in their own work.

Rapid rheological screening to identify conditions of biomaterial hydrogelation.

Hydrogels engineered for biomedical applications consist of numerous components, each of which can affect the material assembly and final mechanical properties. We present methods that rapidly generate rheological libraries to identify regimes of hydrogel assembly in a large composition parameter space. This method conserves both material and time, and leads to critical insight into assembly mechanisms and mechanics, which can then be used for further materials development and optimization.

Rapid, high resolution screening of biomaterial hydrogelators by μ2rheology.

A combination of sample manipulation and rheological characterization at the microscale is used to identify the gelation of poly(ethylene glycol)-heparin hydrogels over a wide range of compositions. A microfluidic device produces 50-100 droplet samples, each with a different composition. Multiple particle tracking microrheology is used to measure the rheological state of each sample. This combination requires little material and enables efficient and rapid screening of gelation conditions. The high resolution data identifies the gelation reaction percolation boundaries and a lower limit of the total hydrogelator concentration for gelation to occur, which can be used for the subsequent engineering, testing, and processing of these materials.

Material Assembly and Gelation Kinetics of PEG‐Heparin Hydrogels using Multiple Particle Tracking Microrheology

Recently, heparin functionalized polymer scaffolds have been developed for tissue engineering applications. Such materials are designed to mimic the structural and mechanical properties of the extra‐cellular matrix, while providing controlled sequestration and release of soluble factors, such as growth factors. We investigate the material properties of these chemically crosslinked, synthetic hydrogel systems. The experimental system is composed of the crosslinker, linear dithiolated poly(ethylene glycol), and the network backbone, maleimide functionalized heparin. Multiple particle tracking is performed on material with 1 μm poly(styrene) probes embedded into it. Experiments capture the material response over short and long times. The short time data is taken to study the gelation kinetics of the material, while equilibrium measurements provide information about the final hydrogel properties. The hydrogel composition and the functionality of the heparin are systematically varied to establish regions of ge...