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ABSTRACT: The field of tissue engineering and regenerative medicine will tremendously benefit from the development of three dimensional scaffolds with defined micro- and macro-architecture that replicate the geometry and chemical composition of native tissues. The current report describes a freeform fabrication technique that permits the development of nerve regeneration scaffolds with precisely engineered architecture that mimics that of native nerve, using the native extracellular matrix component hyaluronic acid (HA). To demonstrate the flexibility of the fabrication system, scaffolds exhibiting different geometries with varying pore shapes, sizes and controlled degradability were fabricated in a layer-by-layer fashion. To promote cell adhesion, scaffolds were covalently functionalized with laminin. This approach offers tremendous spatio-temporal flexibility to create architecturally complex structures such as scaffolds with branched tubes to mimic branched nerves at a plexus. We further demonstrate the ability to create bidirectional gradients within the microfabricated nerve conduits. We believe that combining the biological properties of HA with precise three dimensional micro-architecture could offer a useful platform for the development of a wide range of bioartificial organs.
Biomedical Microdevices 07/2011; 13(6):983-93. · 3.03 Impact Factor
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ABSTRACT: The development of biomedical scaffolds mimicking a heterogeneous cellular microenvironment for a specified regulation of cell-fates is very promising for tissue engineering. In this study, three-dimensional scaffolds with heterogeneous microstructure were developed using a DMD-PP apparatus. During the fabrication process, this apparatus can efficiently switch monomers to form microstructures with localized, different material properties; the resolution in the arrangement of material properties is comparable to the characteristic size of functional subunits in living organs, namely, a hundred microns. The effectiveness of this DMD-PP apparatus is demonstrated by a woodpile microstructure with heterogeneous fluorescence and also by a microporous cell-culturing scaffold with selected sites for protein adhesion. Cell-cultivation experiment was performed with the microporous scaffold, in which selective cell adhesion was observed.
Biomedical Microdevices 08/2010; 12(4):721-5. · 3.03 Impact Factor
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Biomaterials 02/2010; 31(6):1460. · 7.40 Impact Factor
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ABSTRACT: Various neural tissue engineering approaches that are under development for applications ranging from guidance conduits to cell-based therapies rely on the ability to encapsulate cells in three-dimensional (3D) scaffolds. Schwann cells play a key role in peripheral nerve regeneration by forming oriented paths for regrowing axons. We have engineered collagen and hyaluronic acid interpenetrating polymer network (IPN) hydrogels with and without laminin as a 3D culture system for Schwann cells in an attempt to devise novel neural regeneration therapies. Encapsulation of Schwann cells in 3D hydrogel constructs did not affect cell viability and cells were viable for 2 weeks in all hydrogel samples. Moreover, in hydrogels with high cell density, cells underwent spreading and proliferation, and the cell numbers increased by day 14 as assessed qualitatively using a Live/dead assay and scanning electron microscopy (SEM), and quantitatively using a CellTiter 96 AQueous non-radioactive cell proliferation assay. In some cases, the cells aligned parallel to each other and formed structures reminiscent of Bands of Büngner. Schwann cells in cell-hydrogel constructs with high cell density were not only viable but also actively secreting nerve growth factor and brain-derived neurotrophic factor. Of particular importance was the observation that addition of laminin in these hydrogels increased the overall production of nerve growth factor and brain-derived neurotrophic factor from the cells. Immunostaining revealed that S100 expression and cell spreading were differentially affected by cell density. Interestingly, in the co-culture of dissociated neurons with Schwann cells, neurons were able to extend neurites and some neurites were observed to follow Schwann cells. Therefore, we conclude that Schwann cells encapsulated in the 3D extracellular matrix-mimicking hydrogel may hold promise in nerve regeneration therapies and may form the basis for understanding the underlying mechanisms of Schwann cell interactions with neurons and various extracellular matrix components.
Tissue Engineering Part A 02/2010; 16(5):1703-16. · 4.64 Impact Factor
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ABSTRACT: Polymer-based, injectable systems that can simultaneously deliver multiple bioactive agents in a controlled manner could significantly enhance the efficacy of next generation therapeutics. For immunotherapies to be effective, both prophylactically or therapeutically, it is not only critical to drive the antigen (Ag)-specific immune response strongly towards either T helper type 1 (Th1) or Th2 phenotype, but also to promote recruitment of a high number of antigen-presenting cells (APCs) at the site of immunization. We have recently reported a microparticle-based system capable of simultaneously delivering siRNA and DNA to APCs. Here we present an in-situ crosslinkable, injectable formulation containing dendritic cell (DC)-chemo-attractants and dual-mode DNA-siRNA loaded microparticles to attract immature DCs and simultaneously deliver, to the migrated cells, immunomodulatory siRNA and plasmid DNA antigens. These low crosslink density hydrogels were designed to degrade within 2-7 days in vitro and released chemokines in a sustained manner. Chemokine carrying gels attracted 4-6 folds more DCs over a sustained period in vitro, compared to an equivalent bolus dose. Interestingly, migrated DCs were able to infiltrate the hydrogels and efficiently phagocytose the siRNA-DNA carrying microparticles. Hydrogel embedded microparticles co-delivering Interleukin-10 siRNA and plasmid DNA antigens exhibited efficient Interleukin-10 gene knockdown in migrated primary DCs in vitro.
Biomaterials 07/2009; 30(28):5187-200. · 7.40 Impact Factor
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ABSTRACT: Photofunctionalization has been utilized extensively for cell and tissue-engineering research, most commonly in the form of
photopolymerization and photografting. Photopolymerization can be performed in vivo, in a minimally invasive manner, and with
spatial and temporal control permitting the fabrication of complex scaffolds. A number of natural as well as synthetic polymers
have been photofunctionalized to engineer tissues such as bone, cartilage, and skin. In this chapter, we describe the basic
mechanism of photofunctionalization and different photoinitiators utilized in the biomedical field. The chapter also focuses
on the different photofunctionalization strategies including photopolymerization, photografting, and some advanced techniques,
and how these techniques have been explored to study cell, protein, and scaffold interactions. Some of the applications of
photofunctionalization in the field of neural, bone, and cartilage tissue engineering are also discussed.
01/1970: pages 297-318;
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ABSTRACT: To engineer complex tissues, it is necessary to create hybrid scaffolds with micropatterned structural and biomechanical properties, which can closely mimic the intricate body tissues. The current report describes the synthesis of a novel photocrosslinkable interpenetrating polymeric network (IPN) of collagen and hyaluronic acid (HA) with precisely controlled structural and biomechanical properties. Both collagen and HA are present in crosslinked form in IPNs, and the two networks are entangled with each other. IPNs were also compared with semi-IPNs (SIPN), in which only collagen was in network form and HA chains were entangled in the collagen network without being photocrosslinked. Scanning electron microscopy images revealed that IPNs are denser than SIPNs, which results in their molecular reinforcement. This was further confirmed by rheological experiments. Because of the presence of the HA crosslinked network, the storage modulus of IPNs was almost two orders of magnitude higher than SIPNs. The degradation of the collagen–HA IPNs was slower than the SIPNs because of the presence of the crosslinked HA network. Increasing concentration of HA further altered the properties among IPNs. Cytocompatibility of IPNs was confirmed by Schwann cell and dermal fibroblasts adhesion and proliferation studies. We also fabricated patterned scaffolds with regions of IPNs and SIPNs within a bulk hydrogel, resulting in zonal distribution of crosslinking densities, viscoelasticities, water content and pore sizes at the micro- and macro-scales. With the ability to fine-tune the scaffold properties by performing structural modifications and to create patterned scaffolds, these hydrogels can be employed as potential candidates for regenerative medicine applications.
Acta Biomaterialia.
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ABSTRACT: The purpose of a tissue engineered (TE) scaffold is to provide a support structure that can aid the regeneration of damaged tissue. Unlike native tissues, currently existing TE scaffolds are structurally simple, with homogeneous bulk properties that are unable to induce cells to regenerate architecturally complex healthy tissue. Thus, there is a need for methods that can create structural complexity within TE scaffolds to guide tissue regeneration. In this paper we have engineered novel dual-crosslinked hyaluronic acid hydrogel scaffolds with photopatterned anisotropic swelling. Anisotropic swelling can produce zonal distributions of crosslink density, water content and viscoelasticity on the macro- and micro-scales within the hydrogel scaffold. We have found that anisotropically swelling hydrogels can be obtained by a combination of chemical crosslinks and patterned photocrosslinks within a single dual-crosslinked hydrogel. According to our method an unswollen chemically crosslinked hydrogel substrate was spatially patterned with photocrosslinks that restricted swelling at selected sites. The resulting dual-crosslinked hydrogel swelled anisotropically because of differential crosslink densities between the photopatterned and non-photopatterned regions. Anisotropic swelling permitted the hydrogel to contort and evolve a shape different from that of the unswollen hydrogel. A biodegradable hydrogel with this unique swelling behavior yields a new, unexplored type of shape-changing TE scaffold.
Acta Biomaterialia.
