Kelly M Schultz

University of Delaware | UDel UD

Rheological modifiers are used to tune rheology or induce phase transitions of products. Microfibrillated cellulose (MFC), a renewable material, has the potential to be used for rheological modification. However, the lack of studies on the evolution in rheological properties and structure during its phase transitions has prevented MFC from being ad...

Human mesenchymal stem cells (hMSCs) are instrumental in the wound healing process. They migrate to wounds from their native niche in response to chemical signals released during the inflammatory phase of healing. At the wound, hMSCs downregulate inflammation and regulate tissue regeneration. Delivering additional hMSCs to wounds using cell-laden i...

Rheological modifiers tune product rheology with a small amount of material. To effectively use rheological modifiers, characterizing the rheology of the system at different compositions is crucial. Two colloidal rod system, hydrogenated castor oil and polyamide, are characterized in a formulation that includes a surfactant (linear alkylbenzene sul...

Purpose Measurement of the viscosity of concentrated protein solutions is vital for the manufacture and delivery of protein therapeutics. Conventional methods for viscosity measurements require large solution volumes, creating a severe limitation during the early stage of protein development. The goal of this work is to develop a robust technique t...

Rheological modifiers are added to formulations to tune rheology, enable function and drive phase changes requiring an understanding of material structure and properties. We characterize two colloidal rod systems during phase transitions using multiple particle tracking microrheology, which measures the Brownian motion of probes embedded in a sampl...

During the wound healing process, human mesenchymal stem cells (hMSCs) are recruited to the injury where they regulate inflammation and initiate healing and tissue regeneration. To aid in healing, synthetic cell-laden hydrogel scaffolds are being designed to deliver additional hMSCs to wounds to enhance or restart the healing process. These scaffol...

Silver compounds have been used extensively for wound healing due to their antimicrobial properties, but high concentrations of silver are toxic to mammalian cells. We designed a peptide that binds silver and releases only small amounts of this ion over time, therefore overcoming a problem of silver toxicity. Silver binding was achieved through inc...

During wound healing, human mesenchymal stem cells (hMSCs) migrate to injuries to regulate inflammation and coordinate tissue regeneration. To enable migration, hMSCs re-engineer the extracellular matrix rheology. Our work determines the correlation between cell-engineered rheology and motility. We encapsulate hMSCs in a cell-degradable peptide-pol...

Cross-linked polymeric gels are an important class of materials with applications that broadly range from synthetic wound healing scaffolds to materials used in enhanced oil recovery. To effectively design these materials for each unique applications a deeper understanding of the structure and rheological properties as a function of polymeric inter...

Human mesenchymal stem cells (hMSCs) are motile cells that migrate from their native niche to wounded sites where they regulate inflammation during healing. New materials are being developed as hMSC delivery platforms to enhance wound healing. To act as an effective wound healing material, the hydrogel must degrade at the same rate as tissue regene...

Multiple particle tracking microrheology (MPT) is a powerful tool for quantitatively characterizing rheological properties of soft matter. Traditionally, MPT uses a single particle size to characterize rheological properties. But in complex systems, MPT measurements with a single size particle can characterize distinct properties that are linked to...

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement during previous phase changes and applied shear. To determine the extent of these changes, we have developed a microfluidic device that enables repeated phase transitions induced by exchange of the su...

Human mesenchymal stem cells (hMSCs) dynamically remodel their microenvironment during basic processes, such as migration and differentiation. Migration requires extracellular matrix invasion, necessitating dynamic cell-material interactions. Understanding these interactions is critical to advancing materials design that harness and manipulate thes...

Rheological modifiers are subject to processing steps, including mixing and dilution, that can have permanent structural effects. This work investigates rheological changes of a fibrous colloid, hydrogenated castor oil (HCO), when sheared during sample preparation. HCO is a polydisperse system that undergoes phase transitions in response to osmotic...

Human mesenchymal stem cells (hMSCs) are encapsulated in synthetic matrix metalloproteinase (MMP) degradable poly(ethylene glycol)-peptide hydrogels to characterize cell-mediated degradation of the pericellular region using multiple particle tracking microrheology. The hydrogel scaffold is degraded by cell-secreted enzymes and cytoskeletal tension....

Cross-linked polymeric gels are widely used in applications ranging from biomaterial scaffolds to additives in enhanced oil recovery. Despite this, fundamental understanding of the effect of polymer concentration and reaction mechanism on the scaffold structure is lacking. We measure scaffold properties and structure during gelation using multiple...

Covalent adaptable hydrogels (CAHs) dynamically evolve when pushed out of equilibrium by force or change in environmental conditions. Adapting these materials for advanced biological applications, including 3D cell culture and drug delivery platforms, requires in-depth knowledge of the evolution of scaffold microstructure and rheological properties...

A microfluidic device is designed to measure repeated phase transitions, gelation and degradation, on a single sample by exchanging the surrounding fluid while minimizing shear stress. This device enables quantitative microrheological characterization of material properties over multiple phase transitions, determining whether the material returns t...

Rheological modifiers are essential ingredients in commercial materials that exploit facile and repeatable phase transitions. Although rheological modifiers are used to change flow behavior or quiescent stability, the complex properties of particulate gels during dilution is not well studied. We characterize a dynamically evolving colloidal gel, hy...

Significance Scaffolds that serve as synthetic mimics of the extracellular matrix have applications in wound healing, tissue engineering, and stem cell expansion. When cells are cultured in these tunable matrices, little is known about local microenvironmental changes during degradation and remodeling. Methods that provide quantitative and predicta...

The design of hydrogel matrices for cell encapsulation and tissue regeneration has become increasingly complex. Oftentimes, researchers seek to recapitulate specific biophysical and biochemical cues critical for the resident cell population and an in depth understanding of changes in the local microstructure and rheological properties of the synthe...

Many hydrogel materials of interest are homogeneous on the micrometer scale. Electrospinning, the formation of sub-micrometer to micrometer diameter fibers by a jet of fluid formed under an electric field, is one process being explored to create rich microstructures. However, electrospinning a hydrogel system as it reacts requires an understanding...

In light of the growing importance in understanding and controlling the physical cues presented to cells by artificial scaffolds, direct, temporally resolved measurements of the gel modulus are needed. We demonstrate that an interpolation of macro- and microrheology measurements provides a complete history of a hydrogel modulus during degradation t...

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 im...

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 t...

High-throughput rheological measurements in a microfluidic device are demonstrated. A series of microrheology samples are generated as droplets in an immiscible spacer fluid using a microfluidic T-junction. The compositions of the sample droplets are continuously varied over a wide range. Rheology measurements are made in each droplet using multipl...

High-throughput screening of material properties of therapeutic hydrogelators enables the engineering of these materials for applications such as wound healing and tissue regeneration. Designing material to mimic biologically relevant environments, such as the extracellular matrix, requires knowledge of both the hydrogelation reaction and the final...

We study PEG-heparin hydrogels to identify compositions that lead to gel formation and measure the corresponding gelation kinetics. The material consists of a maleimide-functionalized high molecular weight heparin (HMWH) backbone covalently cross-linked with bis-thiol poly(ethylene glycol) (PEG). Using multiple particle tracking microrheology, we i...

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,...

Multiple particle tracking microrheology is used to characterize the viscoelastic properties of biomaterial and synthetic polymer gels near the liquid-solid transition. Probe particles are dispersed in the gel precursors, and their dynamics are measured as a function of the extent of reaction during gel formation. We interpret the dynamics using th...

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 propertie...

The ability to controllably and continuously stretch large DNA molecules in a microfluidic format is important for gene mapping technologies such as Direct Linear Analysis (DLA). We have recently shown that electric field gradients can be readily generated in a microfluidic device and the resulting field is purely elongational. We present a single...