Laura E. Dickinson

Dextran hydrogel scaffolds enhance angiogenic responses and promote complete skin regeneration during burn wound healing

Neovascularization is a critical determinant of wound-healing outcomes for deep burn injuries. We hypothesize that dextran-based hydrogels can serve as instructive scaffolds to promote neovascularization and skin regeneration in third-degree burn wounds. Dextran hydrogels are soft and pliable, offering opportunities to improve the management of burn wound treatment. We first developed a procedure to treat burn wounds on mice with dextran hydrogels. In this procedure, we followed clinical practice of wound excision to remove full-thickness burned skin, and then covered the wound with the dextran hydrogel and a dressing layer. Our procedure allows the hydrogel to remain intact and securely in place during the entire healing period, thus offering opportunities to simplify the management of burn wound treatment. A 3-week comparative study indicated that dextran hydrogel promoted dermal regeneration with complete skin appendages. The hydrogel scaffold facilitated early inflammatory cell infiltration that led to its rapid degradation, promoting the infiltration of angiogenic cells into the healing wounds. Endothelial cells homed into the hydrogel scaffolds to enable neovascularization by day 7, resulting in an increased blood flow significantly greater than treated and untreated controls. By day 21, burn wounds treated with hydrogel developed a mature epithelial structure with hair follicles and sebaceous glands. After 5 weeks of treatment, the hydrogel scaffolds promoted new hair growth and epidermal morphology and thickness similar to normal mouse skin. Collectively, our evidence shows that customized dextran-based hydrogel alone, with no additional growth factors, cytokines, or cells, promoted remarkable neovascularization and skin regeneration and may lead to novel treatments for dermal wounds.

Reconstructing the differentiation niche of embryonic stem cells using biomaterials.

The biochemical cues and topographical architecture of the extracellular environment extensively influence ES cell fate. The microenvironment surrounding the developing embryo presents these instructive cues in a complex and interactive manner in order to guide cell fate decisions. Current stem cell research aims to reconstruct this multifaceted embryonic niche to recapitulate development in vitro. This review focuses on 2D and 3D differentiation niches created from natural and synthetic biomaterials to guide the differentiation of ES cells toward specific lineages. Biomaterials engineered to present specific physical constraints are also reviewed for their role in differentiation.

Endothelial cell responses to micropillar substrates of varying dimensions and stiffness

In the vascular niche, the extracellular matrix (ECM) provides a structural scaffold with a rich ligand landscape of essential matrix proteins that supports the organization and stabilization of endothelial cells (ECs) into functional blood vessels. Many of the physical interactions between ECs and macromolecular components of the ECM occur at both the micron and submicron scale. In addition, the elasticity of the ECM has been shown to be a critical factor in the progress of the angiogenic cascade. Here, we sought to determine the effect of substrate topography and elasticity (stiffness) on EC behavior. Utilizing a unique SiO(2) substrate with an array of micropillars, we first demonstrate that micropillars with heights >3 μm significantly decrease EC adhesion and spreading. Fibronectin (Fn) patterning of 1 μm high micropillars enabled EC adhesion onto the micropillars and promoted alignment in a single-cell chain manner. We then developed a robust method to generate a soft micropillar substrate array made of polydimethylsiloxane (PDMS), similar to the SiO(2) substrate. Finally, we examined the kinetics of EC adhesion and spreading on the soft PDMS substrates compared to the stiff SiO(2) substrates. Culturing cells on the PDMS substrates demonstrated an enhanced EC elongation and alignment when compared to stiff SiO(2) with similar topographical features. We conclude that the elongation and alignment of ECs is coregulated by substrate topography and stiffness and can be harnessed to guide vascular organization.

Guiding endothelial progenitor cell tube formation using patterned fibronectin surfaces

Engineering vascular networks is a key initiative in regenerative medicine. Moreover, control over the formation of organized vascular networks in vitro may facilitate their rapid and functional integration with the host vasculature after implantation. The extracellular matrix provides a structural platform for endothelial progenitor cells (EPCs) to differentiate and assemble into a tubular structure. We demonstrate that optimized, patterned fibronectin surfaces guide the ordered adhesion of human EPCs, maintain EPC responsiveness to tumor necrosis factor-α, support their elongation along the culture period, and enhance von Willebrand factor expression. Using fibrin gel as the three-dimensional milieu allows the assembly of unidirectional chains and formation of tubular structures. High-resolution analysis shows a distinctive lumen, as well as numerous Weibel Palade bodies and caveolae, all indicating a typical progression in vascular morphogenesis and the angiogenic process. Altogether, this approach allows us to engineer the formation of well-organized vascular structures in vitro.

Functional surfaces for high-resolution analysis of cancer cell interactions on exogenous hyaluronic acid

Hyaluronic acid, a nonsulfated, linear glycosaminoglycan, is ubiquitously distributed in the extracellular matrix and is known to facilitate tumor progression by enhancing invasion, growth, and angiogenesis. Native HA has been attached to substrates to create patterned surfaces resistant to cell adhesion, and has been utilized in a variety of cell adhesion studies using either non covalently bound layers patterned by soft lithography or related methods. We use a new approach to study cell interactions with HA-presenting regions, by covalently linking HA adjacent to PEG-ylated regions, which resist cell adhesion. Colon and breast cancer cells seeded on the patterned HA surfaces adhere preferentially on HA-presenting regions and proliferate there. Furthermore, we demonstrate that cell adhesion is inhibited with the blocking of HA receptor, CD44, and that cellular adhesive processes, through protrusions spreading onto the HA surface, enhance spreading and movement outside the HA-presenting regions. Overall, this approach allows high-resolution analysis of cancer cell attachment, growth, and migration on exogenous native HA.

Engineered Biopolymeric Scaffolds for Chronic Wound Healing

Skin regeneration requires the coordinated integration of concomitant biological and molecular events in the extracellular wound environment during overlapping phases of inflammation, proliferation, and matrix remodeling. This process is highly efficient during normal wound healing. However, chronic wounds fail to progress through the ordered and reparative wound healing process and are unable to heal, requiring long-term treatment at high costs. There are many advanced skin substitutes, which mostly comprise bioactive dressings containing mammalian derived matrix components, and/or human cells, in clinical use. However, it is presently hypothesized that no treatment significantly outperforms the others. To address this unmet challenge, recent research has focused on developing innovative acellular biopolymeric scaffolds as more efficacious wound healing therapies. These biomaterial-based skin substitutes are precisely engineered and fine-tuned to recapitulate aspects of the wound healing milieu and target specific events in the wound healing cascade to facilitate complete skin repair with restored function and tissue integrity. This mini-review will provide a brief overview of chronic wound healing and current skin substitute treatment strategies while focusing on recent engineering approaches that regenerate skin using synthetic, biopolymeric scaffolds. We discuss key polymeric scaffold design criteria, including degradation, biocompatibility, and microstructure, and how they translate to inductive microenvironments that stimulate cell infiltration and vascularization to enhance chronic wound healing. As healthcare moves toward precision medicine-based strategies, the potential and therapeutic implications of synthetic, biopolymeric scaffolds as tunable treatment modalities for chronic wounds will be considered.

Applying torque to the Escherichia coli flagellar motor using magnetic tweezers

The bacterial flagellar motor of Escherichia coli is a nanoscale rotary engine essential for bacterial propulsion. Studies on the power output of single motors rely on the measurement of motor torque and rotation under external load. Here, we investigate the use of magnetic tweezers, which in principle allow the application and active control of a calibrated load torque, to study single flagellar motors in Escherichia coli. We manipulate the external load on the motor by adjusting the magnetic field experienced by a magnetic bead linked to the motor, and we probe the motor’s response. A simple model describes the average motor speed over the entire range of applied fields. We extract the motor torque at stall and find it to be similar to the motor torque at drag-limited speed. In addition, use of the magnetic tweezers allows us to force motor rotation in both forward and backward directions. We monitor the motor’s performance before and after periods of forced rotation and observe no destructive effects on the motor. Our experiments show how magnetic tweezers can provide active and fast control of the external load while also exposing remaining challenges in calibration. Through their non-invasive character and straightforward parallelization, magnetic tweezers provide an attractive platform to study nanoscale rotary motors at the single-motor level.

Cell–biomaterial interactions for blood vessel formation

Abstract: Our knowledge of human vascular development and growth has been considerably augmented by biomaterial-based approaches. This chapter first discusses the architecture of the vasculature, from its cellular to extracellular matrix components. In the following sections, engineering of biomaterials to study the mechanisms of vascular morphogenesis and angiogenesis, including cancer-associated angiogenesis, are explored. The final section focuses on materials designed with defined spatial arrangements of molecules or complex topographical features to recapitulate aspects within the native vascular microenvironment.