Fabrication and Characterization of Quad-Component Bioinspired Hydrogels to Model Elevated Fibrin Levels in Central Nervous Tissue Scaffolds.

Multicomponent interpenetrating polymer network (mIPN) hydrogels are promising tissue-engineering scaffolds that could closely resemble key characteristics of native tissues. The mechanical and biochemical properties of mIPNs can be finely controlled to mimic key features of target cellular microenvironments, regulating cell-matrix interactions. In this work, we fabricated hydrogels made of collagen type I (Col I), fibrin, hyaluronic acid (HA), and poly (ethylene glycol) diacrylate (PEGDA) using a network-by-network fabrication approach.

A Bioinspired Astrocyte-Derived Coating Promotes the In Vitro Proliferation of Human Neural Stem Cells While Maintaining Their Stemness.

The repair of neuronal tissue is a challenging process due to the limited proliferative capacity of neurons. Neural stem cells (NSCs) can aid in the regeneration process of neural tissue due to their high proliferation potential and capacity to differentiate into neurons. The therapeutic potential of these cells can only be achieved if sufficient cells are obtained without losing their differentiation potential.

Growth Factor Binding Peptides in Poly (Ethylene Glycol) Diacrylate (PEGDA)-Based Hydrogels for an Improved Healing Response of Human Dermal Fibroblasts.

Growth factors (GF) are critical cytokines in wound healing. However, the direct delivery of these biochemical cues into a wound site significantly increases the cost of wound dressings and can lead to a strong immunological response due to the introduction of a foreign source of GFs. To overcome this challenge, we designed a poly(ethylene glycol) diacrylate (PEGDA) hydrogel with the potential capacity to sequester autologous GFs directly from the wound site.

Modeling the effects of hyaluronic acid degradation on the regulation of human astrocyte phenotype using multicomponent interpenetrating polymer networks (mIPNs).

Hyaluronic acid (HA) is a highly abundant component in the extracellular matrix (ECM) and a fundamental element to the architecture and the physiology of the central nervous system (CNS). Often, HA degradation occurs when an overreactive inflammatory response, derived from tissue trauma or neurodegenerative diseases such as Alzheimer's, causes the ECM in the CNS to be remodeled. Herein, we studied the effects of HA content as a key regulator of human astrocyte (HAf) reactivity using multicomponent interpenetrating polymer networks (mIPNs) comprised of Collagen I, HA and poly(ethylene glycol) diacrylate.

Collagen Based Multicomponent Interpenetrating Networks as Promising Scaffolds for 3D Culture of Human Neural Stem Cells, Human Astrocytes, and Human Microglia.

This work describes for the first time the fabrication and characterization of multicomponent interpenetrating networks composed of collagen I, hyaluronic acid, and poly(ethylene glycol) diacrylate for the 3D culture of human neural stem cells, astrocytes, and microglia. The chemical composition of the scaffolds can be modulated while maintaining values of complex moduli within the range of the mechanical performance of brain tissue (∼6.9 kPa) and having cell viability exceeding 84%.

Refined assessment of the impact of cell shape on human mesenchymal stem cell differentiation in 3D contexts.

Numerous studies have demonstrated that the differentiation potential of human mesenchymal stem cells (hMSCs) can be modulated by chemical and physical cues. In 2D contexts, inducing different cell morphologies, by varying the shape, area and/or curvature of adhesive islands on patterned surfaces, has significant effects on hMSC multipotency and the onset of differentiation. In contrast, in vitro studies in 3D contexts have suggested that hMSC differentiation does not directly correlate with cell shape.

Toward zonally tailored scaffolds for osteochondral differentiation of synovial mesenchymal stem cells.

Synovium-derived mesenchymal stem cells (SMSCs) are an emerging cell source for regenerative medicine applications, including osteochondral defect (OCD) repair. However, in contrast to bone marrow MSCs, scaffold compositions which promote SMSC chondrogenesis/osteogenesis are still being identified. In the present manuscript, we examine poly(ethylene) glycol (PEG)-based scaffolds containing zonally-specific biochemical cues to guide SMSC osteochondral differentiation.

A canine in vitro model for evaluation of marrow-derived mesenchymal stromal cell-based bone scaffolds.

Tissue engineered bone grafts based on bone marrow mesenchymal stromal cells (MSCs) are being actively developed for craniomaxillofacial (CMF) applications. As for all tissue engineered implants, the bone-regenerating capacity of these MSC-based grafts must first be evaluated in animal models prior to human trials. Canine models have traditionally resulted in improved clinical translation of CMF grafts relative to other animal models.

An improved correlation to predict molecular weight between crosslinks based on equilibrium degree of swelling of hydrogel networks.

Accurate characterization of hydrogel diffusional properties is of substantial importance for a range of biotechnological applications. The diffusional capacity of hydrogels has commonly been estimated using the average molecular weight between crosslinks (M ), which is calculated based on the equilibrium degree of swelling. However, the existing correlation linking M and equilibrium swelling fails to accurately reflect the diffusional properties of highly crosslinked hydrogel networks.

Evaluation of late outgrowth endothelial progenitor cell and umbilical vein endothelial cell responses to thromboresistant collagen-mimetic hydrogels.

Bioactive coatings which support the adhesion of late-outgrowth peripheral blood endothelial progenitor cells (EOCs) are actively being investigated as a means to promote rapid endothelialization of "off-the-shelf," small-caliber arterial graft prostheses following implantation. In the present work, we evaluated the behavior of EOCs on thromboresistant graft coatings based on the collagen-mimetic protein Scl2-2 and poly(ethylene glycol) (PEG) diacrylate. Specifically, the attachment, proliferation, migration, and phenotype of EOCs on PEG-Scl2-2 hydrogels were evaluated as a function of Scl2-2 concentration (4, 8, and 12 mg/mL) relative to human umbilical vein endothelial cells (HUVECs).

Mechanical Characterization of Hybrid Vesicles Based on Linear Poly(Dimethylsiloxane-b-Ethylene Oxide) and Poly(Butadiene-b-Ethylene Oxide) Block Copolymers.

Poly(dimethylsiloxane-ethylene oxide) (PDMS-PEO) and poly(butadiene-b-ethylene oxide) (PBd-PEO) are two block copolymers which separately form vesicles with disparate membrane permeabilities and fluidities. Thus, hybrid vesicles formed from both PDMS-PEO and PBd-PEO may ultimately allow for systematic, application-specific tuning of vesicle membrane fluidity and permeability. However, given the relatively low strength previously noted for comb-type PDMS-PEO vesicles, the mechanical robustness of the resulting hybrid vesicles must first be confirmed.

Osteoinductive PolyHIPE Foams as Injectable Bone Grafts.

We have recently fabricated biodegradable polyHIPEs as injectable bone grafts and characterized the mechanical properties, pore architecture, and cure rates. In this study, calcium phosphate nanoparticles and demineralized bone matrix (DBM) particles were incorporated into injectable polyHIPE foams to promote osteoblastic differentiation of mesenchymal stem cells (MSCs). Upon incorporation of each type of particle, stable monoliths were formed with compressive properties comparable to control polyHIPEs.

Evaluation of the Osteoinductive Capacity of Polydopamine-Coated Poly(-caprolactone) Diacrylate Shape Memory Foams.

Recently, a novel shape memory polymer foam based on the photopolymerization of poly(-caprolactone) diacrylate (PCLDA) has been developed. These PCLDA foams enter a temporary softened state when briefly treated with warm saline ( > of PCLDA), allowing them to conform to irregular bone defect "boundaries" prior to shape setting. When coated with a mechanically stable polydopamine (PD) layer, these PCLDA foams have previously been demonstrated to induce hydroxyapatite deposition.

Collagen-mimetic hydrogels promote human endothelial cell adhesion, migration and phenotypic maturation.

This work evaluates the response of human aortic endothelial cells (HAECs) to thromboresistant collagen-mimetic hydrogel coatings toward improving the biocompatibility of existing "off-the-shelf" small-caliber vascular grafts. Specifically, bioactive hydrogels - previously shown to support α/α integrin-mediated cell adhesion but to resist platelet activation - were fabricated by combining poly(ethylene glycol) (PEG) with a 120 kDa, triple-helical collagen-mimetic protein(Scl2-2) containing the GFPGER adhesion sequence. Analysis of HAECs seeded onto the resulting PEG-Scl2-2 hydrogels demonstrated that HAEC adhesion increased with increasing Scl2-2 concentration, while HAEC migration rate decreased over this same concentration range.

Characterization of sequential collagen-poly(ethylene glycol) diacrylate interpenetrating networks and initial assessment of their potential for vascular tissue engineering.

Collagen hydrogels have been widely investigated as scaffolds for vascular tissue engineering due in part to the capacity of collagen to promote robust cell adhesion and elongation. However, collagen hydrogels display relatively low stiffness and strength, are thrombogenic, and are highly susceptible to cell-mediated contraction. In the current work, we develop and characterize a sequentially-formed interpenetrating network (IPN) that retains the benefits of collagen, but which displays enhanced mechanical stiffness and strength, improved thromboresistance, high physical stability and resistance to contraction.

Poly(sophorolipid) structural variation: effects on biomaterial physical and biological properties.

Diacetylated lactonic sophorolipids (polyLSL[6'Ac,6″Ac]), a biosurfactant, can be efficiently polymerized by ring-opening metathesis polymerization (ROMP). In this paper, enzyme-mediated chemical transformations are developed to regioselectively modify LSL[6'Ac,6″Ac] at sophorose primary hydroxyl positions (6' and 6″). The resulting modified LSLs were polymerized to expand polyLSL structural diversity, that is, polyLSL[6'OH,6″Ac], polyLSL[6'OH,6″OH], polyLSL[6'Bu,6″Ac], polyLSL[6'N3,6″Ac], and polyLSL[6'MA,6″Ac].

Influence of pressurized cyclic stretch and endothelial cell presence on multipotent stem cell osteogenic commitment.

Applied mechanical stretch and blood vessel invasion are key stimuli to which progenitor cells are exposed in post-natal endochondral bone formation. Understanding the combined effects of cyclic stretch and endothelial cell (EC) presence on multipotent stem cell (MSC) osteogenesis therefore has the potential to lead to improved MSC-based bone regeneration strategies. Toward this goal, 10T1/2 mouse MSCs were encapsulated in tubular poly(ethylene glycol) diacrylate [PEGDA] hydrogels with moduli within the "osteogenic" range in order to induce osteogenesis.

An approach for assessing hydrogel hydrophobicity.

Hydrogel hydrophobicity is an important modulator of mammalian cell behavior, drug payload release, and medical device fouling. Contact angle and protein adsorption measures are two common methods for evaluating hydrogel hydrophobicity. However, protein adsorption is a complex phenomenon which is challenging to interpret in terms of gel hydrophobicity alone.

Influence of select extracellular matrix proteins on mesenchymal stem cell osteogenic commitment in three-dimensional contexts.

Growth factors have been shown to be powerful mediators of mesenchymal stem cell (MSC) osteogenic differentiation. However, their use in tissue engineered scaffolds not only can be costly but also can induce undesired responses in surrounding tissues. Thus, the ability to specifically promote MSC osteogenic differentiation in the absence of exogenous growth factors via the manipulation of scaffold material properties would be beneficial.

Relative impact of form-induced stress vs. uniaxial alignment on multipotent stem cell myogenesis.

Tissue engineering strategies based on multipotent stem cells (MSCs) hold significant promise for the repair or replacement of damaged smooth muscle tissue. To design scaffolds which specifically induce MSC smooth muscle lineage progression requires a deeper understanding of the relative influence of various microenvironmental signals on myogenesis. For instance, MSC myogenic differentiation has been shown to be promoted by increases in active RhoA and FAK, both of which can be induced via increased cell-substrate stress.

Osteogenic potential of poly(ethylene glycol)-poly(dimethylsiloxane) hybrid hydrogels.

Growth factors have been shown to be potent mediators of osteogenesis. However, their use in tissue-engineered scaffolds not only can be costly but also can induce undesired responses in surrounding tissues. Thus, the ability to specifically induce osteogenic differentiation in the absence of exogenous growth factors through manipulation of scaffold material properties would be desirable for bone regeneration.

Influence of glycosaminoglycan identity on vocal fold fibroblast behavior.

Poly(ethylene glycol) (PEG) hydrogels have recently begun to be studied for the treatment of scarred vocal fold lamina propria due, in part, to their tunable mechanical properties, resistance to fibroblast-mediated contraction, and ability to be polymerized in situ. However, pure PEG gels lack intrinsic biochemical signals to guide cell behavior and generally fail to mimic the frequency-dependent viscoelastic response critical to normal superficial lamina propria function. Recent results suggest that incorporation of viscoelastic bioactive substances, such as glycosaminoglycans (GAGs), into PEG networks may allow these gels to more closely approach the mechanical responses of normal vocal fold lamina propria while also stimulating desired vocal fold fibroblast behaviors.

Regulation of smooth muscle cell phenotype by glycosaminoglycan identity.

The retention of lipoproteins in the arterial intima is an initial event in early atherosclerosis and occurs, in part, through interactions between negatively charged glycosaminoglycans (GAGs) and the positively charged residues of apolipoproteins. Smooth muscle cells (SMCs) which infiltrate into the lipoprotein-enriched intima have been observed to transform into lipid-laden foam cells. This phenotypic switch is associated with SMC acquisition of a macrophage-like capacity to phagocytose lipoproteins and/or of an adipocyte-like capacity to synthesize fatty acids de novo.

Approach for fabricating tissue engineered vascular grafts with stable endothelialization.

A major roadblock in the development of tissue engineered vascular grafts (TEVGs) is achieving construct endothelialization that is stable under physiological stresses. The aim of the current study was to validate an approach for generating a mechanically stable layer of endothelial cells (ECs) in the lumen of TEVGs. To accomplish this goal, a unique method was developed to fabricate a thin EC layer using poly(ethylene glycol) diacrylate (PEGDA) as an intercellular "cementing" agent.