Quantification of cell migration: metrics selection to model application.

Cell migration plays an essential role in physiological and pathological states, such as immune response, tissue generation and tumor development. This phenomenon can occur spontaneously or it can be triggered by an external stimuli, including biochemical, mechanical, or electrical cues that induce or direct cells to migrate. The migratory response to these cues is foundational to several fields including neuroscience, cancer and regenerative medicine.

Effect of Intraoperative Electrical Stimulation on Recovery after Rat Sciatic Nerve Isograft Repair.

Peripheral nerve injuries, associated with significant morbidity, can benefit from electrical stimulation (ES), as demonstrated in animal studies through improved axonal growth. This study combined the clinical gold standard of isograft repair in a rat model of sciatic nerve injury to evaluate the effects of intraoperative ES on functional tests and histology. Forty rats underwent a surgically induced gap injury to the right sciatic nerve and subsequent repair with an isograft.

RGD-Modified Nanofibers Enhance Outcomes in Rats after Sciatic Nerve Injury.

Nerve injuries requiring surgery are a significant problem without good clinical alternatives to the autograft. Tissue engineering strategies are critically needed to provide an alternative. In this study, we utilized aligned nanofibers that were click-modified with the bioactive peptide RGD for rat sciatic nerve repair.

Novel microgel-based scaffolds to study the effect of degradability on human dermal fibroblasts.

For improved cell integration, tissue engineering scaffolds must be designed to degrade over time. Typically, the chemistry of scaffolds is modified to alter the degradation profile by using different hydrolytic or enzymatic sites within a material. It is more challenging, however, to fabricate self-assembling, injectable scaffolds that provide tunable degradation.

The interplay of peptide affinity and scaffold stiffness on neuronal differentiation of neural stem cells.

Cells are sensitive to physical cues in their environment, such as the stiffness of the substrate, peptide density, and peptide affinity. Understanding how neural stem cells (NSCs) sense and respond to these matrix cues has the potential to improve disease outcome, particularly if a regenerative response can be exploited. While the material properties are known to influence other stem cells, little is known about how NSC differentiation is altered by this interplay of mechanical, or bulk properties, with peptide concentration and affinity, or microscale properties.

Electrical Stimulation Increases Random Migration of Human Dermal Fibroblasts.

Exogenous electrical stimulation (ES) has been investigated as a therapy for chronic wounds, as the skin produces currents and electrical fields (EFs) during wound healing. ES therapies operate by applying small EFs to the skin to mimic the transepithelial potentials that occur during the granulation phase of wound healing. Here, we investigated the effect of short duration (10 min) ES on the migration of HDFs using various magnitudes of physiologically relevant EFs.

Dorsal root ganglia neurite outgrowth measured as a function of changes in microelectrode array resistance.

Current research in prosthetic device design aims to mimic natural movements using a feedback system that connects to the patient's own nerves to control the device. The first step in using neurons to control motion is to make and maintain contact between neurons and the feedback sensors. Therefore, the goal of this project was to determine if changes in electrode resistance could be detected when a neuron extended a neurite to contact a sensor.

Tuning the Mechanical Properties of Poly(Ethylene Glycol) Microgel-Based Scaffolds to Increase 3D Schwann Cell Proliferation.

2D in vitro studies have demonstrated that Schwann cells prefer scaffolds with mechanical modulus approximately 10× higher than the modulus preferred by nerves, limiting the ability of many scaffolds to promote both neuron extension and Schwann cell proliferation. Therefore, the goals of this work are to develop and characterize microgel-based scaffolds that are tuned over the stiffness range relevant to neural tissue engineering and investigate Schwann cell morphology, viability, and proliferation within 3D scaffolds. Using thiol-ene reaction, microgels with surface thiols are produced and crosslinked into hydrogels using a multiarm vinylsulfone (VS).

Mechanotransduction of Neural Cells Through Cell-Substrate Interactions.

Neurons and neural stem cells are sensitive to their mechanical and topographical environment, and cell-substrate binding contributes to this sensitivity to activate signaling pathways for basic cell functions. Many transmembrane proteins transmit signals into and out of the cell, including integrins, growth factor receptors, G-protein-coupled receptors, cadherins, cell adhesion molecules, and ion channels. Specifically, integrins are one of the main transmembrane proteins that transmit force across the cell membrane between a cell and its extracellular matrix, making them critical in the study of cell-material interactions.

Development of a High-Throughput Ultrasound Technique for the Analysis of Tissue Engineering Constructs.

Development of hydrogel-based tissue engineering constructs is growing at a rapid rate, yet translation to patient use has been sluggish. Years of costly preclinical tests are required to predict clinical performance and safety of these devices. The tests are invasive, destructive to the samples and, in many cases, are not representative of the ultimate in vivo scenario.

Stimulation Frequency Alters the Dorsal Root Ganglion Neurite Growth and Directionality In Vitro.

Objective: To improve peripheral nerve repair, new techniques to increase the speed of regeneration are required. Studies have shown that the electrical stimulation can enhance nerve regeneration; however, stimulation parameters that regulate the growth increases are unknown. The objective of this study was to examine dorsal root ganglion (DRG) neurite extension, directionality, and density after using methods to specifically control ac electrical field intensity and frequency exposure.

Short-term electrical stimulation to promote nerve repair and functional recovery in a rat model.

Purpose: To evaluate the effect of duration of electrical stimulation on peripheral nerve regeneration and functional recovery. Based on previous work, we hypothesized that applying 10 minutes of electrical stimulation to a 10-mm rat sciatic nerve defect would significantly improve nerve regeneration and functional recovery compared with the non-electrical stimulation group.

Methods: A silicone tube filled with a collagen gel was used to bridge a 10-mm nerve defect in rats, and either 10 minutes or 60 minutes of electrical stimulation was applied to the nerve during surgery.

Short duration electrical stimulation to enhance neurite outgrowth and maturation of adult neural stem progenitor cells.

New therapies are desperately needed for human central nervous system (CNS) regeneration to circumvent the lack of innate regenerative ability following traumatic injuries. Previously attempted therapies have been stymied by barriers to CNS regeneration largely because of protective mechanisms such as the blood brain barrier, inhibitory molecules, and glial scar formation. The application of electric stimulation (ES) has shown promise for enhancing peripheral nervous system regeneration, but is in its infancy in CNS regeneration.

The dynamics of shrinking and expanding drug-loaded microspheres: A semi-empirical approach.

The dynamics of shrinking and expanding drug-loaded microspheres were studied using a diffusion equation in spherical coordinates. A movable boundary condition was incorporated as a convection term in the original model. The resulting convective-diffusive problem was solved using Laplace transform techniques with the Bromwich integral and the residue theorem.

Characteristics of precipitation-formed polyethylene glycol microgels are controlled by molecular weight of reactants.

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Precipitation reactions offer several advantages over traditional microsphere fabrication techniques. Contrary to emulsion, suspension, and dispersion techniques, microgels formed by precipitation are of uniform shape and size, i.

Comparison of neurite growth in three dimensional natural and synthetic hydrogels.

Extracellular matrix incorporated within a scaffold plays an important role in assisting cell behavior in neural tissue engineering. In this study, we investigated how the concentration of fibronectin (FN) affected neurite growth when incorporated within a synthetic polymer gel made of poly(ethylene glycol) (PEG) or a natural polymer gel of collagen I. Mechanical and chemical properties of the scaffold were varied by using a range of concentrations of gels and FN.

The impact of laminin on 3D neurite extension in collagen gels.

The primary goal of this research was to characterize the effect of laminin on three-dimensional (3D) neurite growth. Gels were formed using type I collagen at concentrations of 0.4-2.

Modular poly(ethylene glycol) scaffolds provide the ability to decouple the effects of stiffness and protein concentration on PC12 cells.

This research focused on developing a modular poly(ethylene glycol) (PEG) scaffold, assembled from PEG microgels and collagen I, to provide an environment to decouple the chemical and mechanical cues within a three-dimensional scaffold. We first characterized the microgel fabrication process, examining the size, polydispersity, swelling ratio, mesh size and storage modulus of the polymer particles. The resulting microgels had a low polydispersity index, PDI=1.

Student award winner in the undergraduate's degree category for the Society for Biomaterials 35th Annual Meeting, Orlando, Florida, April 13-16, 2011. Neurite growth in PEG gels: effect of mechanical stiffness and laminin concentration.

Within a 3D environment, the chemical and mechanical properties of a scaffold can significantly influence nerve behavior. How these properties influence with nerve cells is important for optimizing neurite extension within a scaffold. The purpose of this study was to investigate the effect of low concentration poly(ethylene glycol) (PEG) with added laminin on 3D growth of dissociated dorsal root ganglia.

Poly(ethylene glycol) microparticles produced by precipitation polymerization in aqueous solution.

Methods were developed to perform precipitation photopolymerization of PEG-diacrylate. Previously, comonomers have been added to PEG when precipitation polymerization was desired. In the present method, the LCST of the PEG itself was lowered by the addition of the kosmotropic salt sodium sulfate to an aqueous solution.

Characterization of poly(ethylene glycol) gels with added collagen for neural tissue engineering.

Over the past decade, it has been increasingly recognized that both chemical and mechanical properties of scaffolds influence neural cell behavior, ranging from growth to differentiation to migration. However, mechanical properties are difficult to control for in the design of scaffolds for nerve regeneration, as properties change over time for most biologically derived scaffolds. The focus of this project was to examine how the mechanical properties of a nondegradable scaffold, poly(ethylene glycol) (PEG) gels, influenced nerve cell behavior.

Modular scaffolds assembled around living cells using poly(ethylene glycol) microspheres with macroporation via a non-cytotoxic porogen.

Modular, bioactive, macroporous scaffolds were formed by crosslinking poly(ethylene glycol) (PEG) microspheres around living cells. Hydrogel microspheres were produced from reactive PEG derivatives in aqueous sodium sulfate solutions without the use of surfactants or copolymers. Microspheres were formed following thermally induced phase separation if the gel point was reached prior to extensive coarsening of the PEG-rich domains.

Applied electric field enhances DRG neurite growth: influence of stimulation media, surface coating and growth supplements.

Electrical therapies have been found to aid repair of nerve injuries and have been shown to increase and direct neurite outgrowth during stimulation. This enhanced neural growth existed even after the electric field (EF) or stimulation was removed, but the factors that may influence the enhanced growth, such as stimulation media or surface coating, have not been fully investigated. This study characterized neurite outgrowth and branching under various conditions: EF magnitude and application time, ECM surface coating, medium during EF application and growth supplements.

Maintaining bioactivity of NGF for controlled release from PLGA using PEG.

The goal of this work was to investigate methods to retain bioactivity of nerve growth factor (NGF) after encapsulation in poly(lactic-co-glycolic acid) (PLGA) discs for controlled release. Poly(ethylene glycol) (PEG) was chosen as a porogen not only to control the release rate of NGF but also because it has been used to help maintain bioactivity of molecules in organic solvents. NGF and PEG were encapsulated in PLGA via standard dissolution-evaporation techniques with methylene chloride as the solvent.