Guiding Oligodendrocyte Progenitor Cell Maturation Using Electrospun Fiber Cues in a 3D Hyaluronic Acid Hydrogel Culture System.

The current lack of therapeutic approaches to demyelinating disorders and injuries stems from a lack of knowledge surrounding the underlying mechanisms of myelination. This knowledge gap motivates the development of effective models to study the role of environmental cues in oligodendrocyte progenitor cell (OPC) maturation. Such models should focus on determining, which factors influence OPCs to proliferate and differentiate into mature myelinating oligodendrocytes (OLs).

Effects of Cell-Adhesive Ligand Presentation on Pentapeptide Supramolecular Assembly and Gelation: Simulations and Experiments.

The extracellular matrix (ECM) is a complex, hierarchical material containing structural and bioactive components. This complexity makes decoupling the effects of biomechanical properties and cell-matrix interactions difficult, especially when studying cellular processes in a 3D environment. Matrix mechanics and cell adhesion are both known regulators of specific cellular processes such as stem cell proliferation and differentiation.

Peptide Stereocomplexation Orchestrates Supramolecular Assembly of Hydrogel Biomaterials.

Stereocomplexation, or specific interactions among complementary stereoregular macromolecules, is burgeoning as an increasingly impactful design tool, exerting exquisite control of material structure and properties. Since stereocomplexation of polymers produces remarkable transformations in mechanics, morphology, and degradation, we sought to leverage stereocomplexation to tune these properties in peptide-based biomaterials. We found that blending the pentapeptides l- and d-KYFIL triggers dual mechanical and morphological transformations from stiff fibrous hydrogels into less stiff networks of plates, starkly contrasting prior reports that blending l- and d-peptides produces stiffer fibrous hydrogels than the individual constituents.

Influence of Supraphysiologic Biomaterial Stiffness on Ventricular Mechanics and Myocardial Infarct Reinforcement.

Injectable intramyocardial biomaterials have promise to limit adverse ventricular remodeling through mechanical and biologic mechanisms. While some success has been observed by injecting materials to regenerate new tissue, optimal biomaterial stiffness to thicken and stiffen infarcted myocardium to limit adverse remodeling has not been determined. In this work, we present an in-vivo study of the impact of biomaterial stiffness over a wide range of stiffness moduli on ventricular mechanics.

Biomaterials via peptide assembly: Design, characterization, and application in tissue engineering.

A core challenge in biomaterials, with both fundamental significance and technological relevance, concerns the rational design of bioactive microenvironments. Designed properly, peptides can undergo supramolecular assembly into dynamic, physical hydrogels that mimic the mechanical, topological, and biochemical features of native tissue microenvironments. The relatively facile, inexpensive, and automatable preparation of peptides, coupled with low batch-to-batch variability, motivates the expanded use of assembling peptide hydrogels for biomedical applications.

3D Hyaluronic Acid Hydrogels for Modeling Oligodendrocyte Progenitor Cell Behavior as a Function of Matrix Stiffness.

The lack of regenerative solutions for demyelination within the central nervous system motivates the development of strategies to expand and drive the bioactivity of the cells, including oligodendrocyte progenitor cells (OPCs), that ultimately give rise to myelination. In this work, we introduce a 3D hyaluronic acid (HA) hydrogel system to study the effects of microenvironmental mechanical properties on the behavior of OPCs. We tuned the stiffness of the hydrogels to match the brain tissue (storage modulus 200-2000 Pa) and studied the effects of stiffness on metabolic activity, proliferation, and cell morphology of OPCs over a 7 day period.

Guiding Oligodendrocyte Precursor Cell Maturation With Urokinase Plasminogen Activator-Degradable Elastin-like Protein Hydrogels.

Demyelinating injuries and diseases, like multiple sclerosis, affect millions of people worldwide. Oligodendrocyte precursor cells (OPCs) have the potential to repair demyelinated tissues because they can both self-renew and differentiate into oligodendrocytes (OLs), the myelin producing cells of the central nervous system (CNS). Cell-matrix interactions impact OPC differentiation into OLs, but the process is not fully understood.

Engineering biomaterial microenvironments to promote myelination in the central nervous system.

Promoting remyelination and/or minimizing demyelination are key therapeutic strategies under investigation for diseases and injuries like multiple sclerosis (MS), spinal cord injury, stroke, and virus-induced encephalopathy. Myelination is essential for efficacious neuronal signaling. This myelination process is originated by oligodendrocyte progenitor cells (OPCs) in the central nervous system (CNS).

Rapidly Assembling Pentapeptides for Injectable Delivery (RAPID) Hydrogels as Cytoprotective Cell Carriers.

Low cell survival after syringe injection hampers the success of preclinical and clinical cell transplantation trials. During syringe injection, cells experience mechanical forces that lead to cell-membrane disruption and decreased viability. To improve cell survival, we designed rapidly assembling pentapeptides for injectable delivery (RAPID) hydrogels that shear-thin, protect cells from extensional flow, form fibers, and provide mechanical properties similar to native tissue.

Impact of Elastin-like Protein Temperature Transition on PEG-ELP Hybrid Hydrogel Properties.

Biomaterial hydrogels are made by cross-linking either natural materials, which exhibit inherent bioactivity but suffer from batch-to-batch variations, or synthetic materials, which have a well-defined chemical structure but usually require chemical modification to exhibit bioactivity. Recombinant engineered proteins bridge the divide between natural and synthetic materials because proteins incorporate bioactive domains within the biopolymer backbone and have a well-defined amino acid structure and sequence. Recombinant engineered elastin-like proteins (ELPs) are modeled from the native tropoelastin sequence.

Stimuli-Responsive, Pentapeptide, Nanofiber Hydrogel for Tissue Engineering.

Short peptides are uniquely versatile building blocks for self-assembly. Supramolecular peptide assemblies can be used to construct functional hydrogel biomaterials-an attractive approach for neural tissue engineering. Here, we report a new class of short, five-residue peptides that form hydrogels with nanofiber structures.

Matrix Remodeling Enhances the Differentiation Capacity of Neural Progenitor Cells in 3D Hydrogels.

Neural progenitor cells (NPCs) are a promising cell source to repair damaged nervous tissue. However, expansion of therapeutically relevant numbers of NPCs and their efficient differentiation into desired mature cell types remains a challenge. Material-based strategies, including culture within 3D hydrogels, have the potential to overcome these current limitations.

Temperature-Dependent Complex Coacervation of Engineered Elastin-like Polypeptide and Hyaluronic Acid Polyelectrolytes.

Coacervates have enormous potential due to their diverse functional properties supporting a wide number of applications in personal care products, pharmaceuticals, and food processing. Normally, separation of coacervate phases is induced by changes in pH, ionic strength, and/or polyelectrolyte concentration. This study investigates the microphase separation and coacervate complex formation of two natural polyelectrolytes, elastin-like polypeptides (ELPs) and hyaluronic acid (HA), as simple models for biological coacervates.

Encapsulated oligodendrocyte precursor cell fate is dependent on PDGF-AA release kinetics in a 3D microparticle-hydrogel drug delivery system.

Biomaterial drug delivery systems (DDS) can be used to regulate growth factor release and combat the limited intrinsic regeneration capabilities of central nervous system (CNS) tissue following injury and disease. Of particular interest are systems that aid in oligodendrocyte regeneration, as oligodendrocytes generate myelin which surrounds neuronal axons and helps transmit signals throughout the CNS. Oligodendrocyte precursor cells (OPCs) are found in small numbers in the adult CNS, but are unable to effectively differentiate following CNS injury.

From de novo peptides to native proteins: advancements in biomaterial scaffolds for acute ischemic stroke repair.

An active area of research in the field of regenerative medicine involves the development of bioactive matrices that can promote cellular interactions and elicit desirable regenerative behavior in vivo. This is particularly important in the context of ischemic stroke where a focal lesion forms forestalling the regrowth of brain tissue. Protein-based molecules have been used as building blocks to create supramolecular structures that emulate the properties of the native healthy extracellular matrix (ECM) within the central nervous system (CNS).

Oligodendrocyte Precursor Cell Viability, Proliferation, and Morphology is Dependent on Mesh Size and Storage Modulus in 3D Poly(ethylene glycol)-Based Hydrogels.

Oligodendrocytes in the central nervous system (CNS) are responsible for generating myelin, an electrically insulating layer around neuronal axons. When myelin is damaged, neurons are incapable of sustaining normal communications, which can manifest in patients as pain and loss of mobility and vision. A plethora of research has used biomaterials to promote neuronal regeneration, but despite the wide implications of a disrupted myelin sheath, very little is known about how biomaterial environments impact proliferation of oligodendrocyte precursor cells (OPCs) or their differentiation into myelinating oligodendrocytes.

Maintenance of neural progenitor cell stemness in 3D hydrogels requires matrix remodelling.

Neural progenitor cell (NPC) culture within three-dimensional (3D) hydrogels is an attractive strategy for expanding a therapeutically relevant number of stem cells. However, relatively little is known about how 3D material properties such as stiffness and degradability affect the maintenance of NPC stemness in the absence of differentiation factors. Over a physiologically relevant range of stiffness from ∼0.

Fabricating PLGA microparticles with high loads of the small molecule antioxidant N-acetylcysteine that rescue oligodendrocyte progenitor cells from oxidative stress.

Reactive oxygen species (ROS), encompassing all oxygen radical or non-radical oxidizing agents, play key roles in disease progression. Controlled delivery of antioxidants is therapeutically relevant in such oxidant-stressed environments. Encapsulating small hydrophilic molecules into hydrophobic polymer microparticles via traditional emulsion methods has long been a challenge due to rapid mass transport of small molecules out of particle pores.

Engineering Biomaterials to Influence Oligodendroglial Growth, Maturation, and Myelin Production.

Millions of people suffer from damage or disease to the nervous system that results in a loss of myelin, such as through a spinal cord injury or multiple sclerosis. Diminished myelin levels lead to further cell death in which unmyelinated neurons die. In the central nervous system, a loss of myelin is especially detrimental because of its poor ability to regenerate.

Toward a Designable Extracellular Matrix: Molecular Dynamics Simulations of an Engineered Laminin-Mimetic, Elastin-Like Fusion Protein.

Native extracellular matrices (ECMs) exhibit networks of molecular interactions between specific matrix proteins and other tissue components. Guided by these naturally self-assembling supramolecular systems, we have designed a matrix-derived protein chimera that contains a laminin globular-like (LG) domain fused to an elastin-like polypeptide (ELP). This bipartite design offers a flexible protein engineering platform: (i) laminin is a key multifunctional component of the ECM in human brains and other neural tissues, making it an ideal bioactive component of our fusion, and (ii) ELPs, known to be well-tolerated in vivo, provide a self-assembly scaffold with tunable physicochemical (viscoelastic, thermoresponsive) properties.

Mimicking biological phenomena in hydrogel-based biomaterials to promote dynamic cellular responses.

Hydrogel-based biomaterials, often classified as synthetic or natural, have long been pursued for cell culture, tissue engineering, regenerative medicine, and drug delivery. This classification system is now being blurred as hybrid partially synthetic systems using elements of native and designer molecules gain traction. Partially synthetic polymer gels can offer protection of encapsulated cells or drugs and provide instructional biochemical and/or biophysical cues to cells.

Microfluidic gradients reveal enhanced neurite outgrowth but impaired guidance within 3D matrices with high integrin ligand densities.

The density of integrin-binding ligands in an extracellular matrix (ECM) is known to regulate cell migration speed by imposing a balance of traction forces between the leading and trailing edges of the cell, but the effect of cell-adhesive ligands on neurite chemoattraction is not well understood. A platform is presented here that combines gradient-generating microfluidic devices with 3D protein-engineered hydrogels to study the effect of RGD ligand density on neurite pathfinding from chick dorsal root ganglia-derived spheroids. Spheroids are encapsulated in elastin-like polypeptide (ELP) hydrogels presenting either 3.

Tetrakis(hydroxymethyl) phosphonium chloride as a covalent cross-linking agent for cell encapsulation within protein-based hydrogels.

Native tissues provide cells with complex, three-dimensional (3D) environments comprised of hydrated networks of extracellular matrix proteins and sugars. By mimicking the dimensionality of native tissue while deconstructing the effects of environmental parameters, protein-based hydrogels serve as attractive, in vitro platforms to investigate cell-matrix interactions. For cell encapsulation, the process of hydrogel formation through physical or covalent cross-linking must be mild and cell compatible.

Design of three-dimensional engineered protein hydrogels for tailored control of neurite growth.

The design of bioactive materials allows tailored studies probing cell-biomaterial interactions, however, relatively few studies have examined the effects of ligand density and material stiffness on neurite growth in three-dimensions. Elastin-like proteins (ELPs) have been designed with modular bioactive and structural regions to enable the systematic characterization of design parameters within three-dimensional (3-D) materials. To promote neurite out-growth and better understand the effects of common biomaterial design parameters on neuronal cultures we here focused on the cell-adhesive ligand density and hydrogel stiffness as design variables for ELP hydrogels.

Building stem cell niches from the molecule up through engineered peptide materials.

The native stem cell niche is a dynamic and complex microenvironment. Recapitulating this niche is a critical focus within the fields of stem cell biology, tissue engineering, and regenerative medicine and requires the development of well-defined, tunable materials. Recent biomaterial design strategies seek to create engineered matrices that interact with cells at the molecular scale and allow on-demand, cell-triggered matrix modifications.