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issn:1937-335
1.  Avidity-Controlled Delivery of Angiogenic Peptides from Injectable Molecular-Recognition Hydrogels 
Tissue Engineering. Part A  2014;20(15-16):2102-2114.
Peptide mimics of growth factors represent an emerging class of therapeutic drugs due to high biological specificity and relative ease of synthesis. However, maintaining efficacious therapeutic dosage at the therapy site has proven challenging owing to poor intestinal permeability and short circulating half-lives in the blood stream. In this work, we present the affinity immobilization and controlled release of QK, a vascular endothelial growth factor (VEGF) mimetic peptide, from an injectable mixing-induced two-component hydrogel (MITCH). The MITCH system is crosslinked by reversible interactions between WW domains and complementary proline-rich peptide modules. Fusion of the QK peptide to either one or two units of the proline-rich sequence creates bifunctional peptide conjugates capable of specific binding to MITCH while preserving their angiogenic bioactivity. Presenting two repeats of the proline-rich sequence increases the binding enthalpy 2.5 times due to avidity effects. Mixing of the drug conjugates with MITCH components results in drug encapsulation and extended release at rates consistent with the affinity immobilization strength. Human umbilical vein endothelial cells (HUVECs) treated with the soluble drug conjugates exhibit morphogenetic events of VEGF receptor 2 signal transduction followed by cell migration and organization into networks characteristic of early angiogenesis. In a three-dimensional model where HUVECs were cultured as spheroids in a matrix of collagen and fibronectin, injection of drug-releasing MITCH resulted in significantly more cell outgrowth than drugs injected in saline. This ability to sustain local drug availability is ideal for therapeutic angiogenesis applications, where spatiotemporal control over drug distribution is a key requirement for clinical success.
doi:10.1089/ten.tea.2013.0357
PMCID: PMC4137330  PMID: 24490588
2.  Sensory Neurons Accelerate Skin Reepithelialization via Substance P in an Innervated Tissue-Engineered Wound Healing Model 
Tissue Engineering. Part A  2014;20(15-16):2180-2188.
Keratinocytes are responsible for reepithelialization and restoration of the epidermal barrier during wound healing. The influence of sensory neurons on this mechanism is not fully understood. We tested whether sensory neurons influence wound closure via the secretion of the neuropeptide substance P (SP) with a new tissue-engineered wound healing model made of an upper-perforated epidermal compartment reconstructed with human keratinocytes expressing green fluorescent protein, stacked over a dermal compartment, innervated or not with sensory neurons. We showed that sensory neurons secreted SP in the construct and induced a two times faster wound closure in vitro. This effect was partially reproduced by addition of SP in the model without neurons, and completely blocked by a treatment with a specific antagonist of the SP receptor neurokinin-1 expressed by keratinocytes. However, this antagonist did not compromise wound closure compared with the control. Similar results were obtained when the model with or without neurons was transplanted on CD1 mice, while wound closure occurred faster. We conclude that sensory neurons play an important, but not essential, role in wound healing, even in absence of the immune system. This model is promising to study the influence of the nervous system on reepithelialization in normal and pathological conditions.
doi:10.1089/ten.tea.2013.0535
PMCID: PMC4137331  PMID: 24716723
3.  Serum- and Growth-Factor-Free Three-Dimensional Culture System Supports Cartilage Tissue Formation by Promoting Collagen Synthesis via Sox9–Col2a1 Interaction 
Tissue Engineering. Part A  2014;20(15-16):2224-2233.
Objective: One of the factors preventing clinical application of regenerative medicine to degenerative cartilage diseases is a suitable source of cells. Chondrocytes, the only cell type of cartilage, grown in vitro under culture conditions to expand cell numbers lose their phenotype along with the ability to generate hyaline cartilaginous tissue. In this study we determine that a serum- and growth-factor-free three-dimensional (3D) culture system restores the ability of the passaged chondrocytes to form cartilage tissue in vitro, a process that involves sox9.
Methods: Bovine articular chondrocytes were passaged twice to allow for cell number expansion (P2) and cultured at high density on 3D collagen-type-II-coated membranes in high glucose content media supplemented with insulin and dexamethasone (SF3D). The cells were characterized after monolayer expansion and following 3D culture by flow cytometry, gene expression, and histology. The early changes in signaling transduction pathways during redifferentiation were characterized.
Results: The P2 cells showed a progenitor-like antigen profile of 99% CD44+ and 40% CD105+ and a gene expression profile suggestive of interzone cells. P2 in SF3D expressed chondrogenic genes and accumulated extracellular matrix. Downregulating insulin receptor (IR) with HNMPA-(AM3) or the PI-3/AKT kinase pathway (activated by insulin treatment) with Wortmannin inhibited collagen synthesis. HNMPA-(AM3) reduced expression of Col2, Col11, and IR genes as well as Sox6 and -9. Co-immunoprecipitation and chromatin immunoprecipitation analyses of HNMPA-(AM3)-treated cells showed binding of the coactivators Sox6 and Med12 with Sox9 but reduced Sox9–Col2a1 binding.
Conclusions: We describe a novel culture method that allows for increase in the number of chondrocytes and promotes hyaline-like cartilage tissue formation in part by insulin-mediated Sox9–Col2a1 binding. The suitability of the tissue generated via this approach for use in joint repair needs to be examined in vivo.
doi:10.1089/ten.tea.2013.0559
PMCID: PMC4137332  PMID: 24606204
4.  Controlled Multiple Growth Factor Delivery from Bone Tissue Engineering Scaffolds via Designed Affinity 
Tissue Engineering. Part A  2013;20(15-16):2077-2087.
It is known that angiogenesis plays an important role in bone regeneration and that release of angiogenic and osteogenic growth factors can enhance bone formation. Multiple growth factors play key roles in processes that lead to tissue formation/regeneration during natural tissue development and repair. Therefore, treatments aiming to mimic tissue regeneration can benefit from multiple growth factor release, and there remains a need for simple clinically relevant approaches for dual growth factor release. We hypothesized that mineral coatings could be used as a platform for controlled incorporation and release of multiple growth factors. Specifically, mineral-coated scaffolds were “dip coated” in multiple growth factor solutions, and growth factor binding and release were dictated by the growth factor-mineral binding affinity. Beta tricalcium phosphate (β-TCP) scaffolds were fabricated using indirect solid-free form fabrication techniques and coated with a thin conformal mineral layer. Mineral-coated β-TCP scaffolds were sequentially dipped in recombinant human vascular endothelial growth factor (rhVEGF) and a modular bone morphogenetic peptide, a mineral-binding version of bone morphogenetic protein 2 (BMP2), solutions to allow for the incorporation of each growth factor. The dual release profile showed sustained release of both growth factors for over more than 60 days. Scaffolds releasing either rhVEGF alone or the combination of growth factors showed an increase in blood vessel ingrowth in a dose-dependent manner in a sheep intramuscular implantation model. This approach demonstrates a “modular design” approach, in which a controllable biologics carrier is integrated into a structural scaffold as a thin surface coating.
doi:10.1089/ten.tea.2013.0358
PMCID: PMC4137333  PMID: 24350567
5.  Micropatterned Cell–Cell Interactions Enable Functional Encapsulation of Primary Hepatocytes in Hydrogel Microtissues 
Tissue Engineering. Part A  2014;20(15-16):2200-2212.
Drug-induced liver injury is a major cause of drug development failures and postmarket withdrawals. In vitro models that incorporate primary hepatocytes have been shown to be more predictive than model systems which rely on liver microsomes or hepatocellular carcinoma cell lines. Methods to phenotypically stabilize primary hepatocytes ex vivo often rely on mimicry of hepatic microenvironmental cues such as cell–cell interactions and cell–matrix interactions. In this work, we sought to incorporate phenotypically stable hepatocytes into three-dimensional (3D) microtissues, which, in turn, could be deployed in drug-screening platforms such as multiwell plates and diverse organ-on-a-chip devices. We first utilize micropatterning on collagen I to specify cell–cell interactions in two-dimensions, followed by collagenase digestion to produce well-controlled aggregates for 3D encapsulation in polyethylene glycol (PEG) diacrylate. Using this approach, we examined the influence of homotypic hepatocyte interactions and composition of the encapsulating hydrogel, and achieved the maintenance of liver-specific function for over 50 days. Optimally preaggregated structures were subsequently encapsulated using a microfluidic droplet-generator to produce 3D microtissues. Interactions of engineered hepatic microtissues with drugs was characterized by flow cytometry, and yielded both induction of P450 enzymes in response to prototypic small molecules and drug–drug interactions that give rise to hepatotoxicity. Collectively, this study establishes a pipeline for the manufacturing of 3D hepatic microtissues that exhibit stabilized liver-specific functions and can be incorporated into a wide array of emerging drug development platforms.
doi:10.1089/ten.tea.2013.0667
PMCID: PMC4137334  PMID: 24498910
6.  The Gene Expression of Human Endothelial Cells Is Modulated by Subendothelial Extracellular Matrix Proteins: Short-Term Response to Laminar Shear Stress 
Tissue Engineering. Part A  2014;20(15-16):2253-2264.
Vascular surgery for atherosclerosis is confronted by the lack of a suitable bypass material. Tissue engineering strives to produce bio-artificial conduits to provide resistance to thrombosis. The objectives of our study were to culture endothelial cells (EC) on composite assemblies of extracellular matrix proteins, and to evaluate the cellular phenotype under flow. Cell-adhesive assemblies were fabricated on glass slides as combinations of collagen (Co), laminin (LM), and fibronectin (FN), resulting in three samples: Co, Co/LM, and Co/FN. Surface topography, roughness, and wettability were determined. Human saphenous vein EC were harvested from cardiac patients, cultured on the assemblies and submitted to laminar shear stress (SS) of 12 dyn/cm2 for 40, 80, and 120 min. Cell retention was assessed and qRT-PCR of adhesion genes (VE-cadherin, vinculin, KDR, CD-31 or PECAM-1, β1-integrins) and metabolic genes (t-PA, NF-κB, eNOS and MMP-1) was performed. Quantitative immunofluorescence of VE cadherin, vinculin, KDR, and vonWillebrand factor was performed after 2 and 6 h of flow. Static samples were excluded from shearing. The cells reached confluence with similar growth curves. The cells on Co/LM and Co/FN were resistant to flow up to 120 min but minor desquamation occurred on Co corresponding with temporary downregulation of VE cadherin and vinculin-mRNA and decreased fluorescence of vinculin. The cells seeded on Co/LM initially more upregulated vinculin-mRNA and also the inflammatory factor NF-κB, and the cells plated on Co/FN changed the expression profile minimally in comparison with the static control. Fluorescence of VE cadherin and vonWillebrand factor was enhanced on Co/FN. The cells cultured on Co/LM and Co/FN increased the vinculin fluorescence and expressed more VE cadherin and KDR-mRNA than the cells on Co. The cells plated on Co/FN upregulated the mRNA of VE cadherin, CD-31, and MMP 1 to a greater extent than the cells on Co/LM and they enhanced the fluorescence of VE cadherin, KDR, and vonWillebrand factor. Some of these changes sustained up to 6 h of flow, as confirmed by immunofluorescence. Combined matrices Co/LM and Co/FN seem to be more suitable for EC seeding and retention under flow. Moreover, Co/FN matrix promoted slightly more favorable cellular phenotype than Co/LM under SS of 2–6 h.
doi:10.1089/ten.tea.2013.0153
PMCID: PMC4137337  PMID: 24606163
7.  Inhibition of TAK1 and/or JAK Can Rescue Impaired Chondrogenic Differentiation of Human Mesenchymal Stem Cells in Osteoarthritis-Like Conditions 
Tissue Engineering. Part A  2014;20(15-16):2243-2252.
Objective: To rescue chondrogenic differentiation of human mesenchymal stem cells (hMSCs) in osteoarthritic conditions by inhibition of protein kinases.
Methods: hMSCs were cultured in pellets. During early chondrogenic differentiation, these were exposed to osteoarthritic synovium-conditioned medium (OAS-CM), combined with the Janus kinase (JAK)-inhibitor tofacitinib and/or the transforming growth factor β-activated kinase 1 (TAK1)-inhibitor oxozeaenol. To evaluate effects on chondrogenesis, the glycosaminoglycan (GAG) content of the pellets was measured at the time that chondrogenesis was manifest in control cultures. Moreover, mRNA levels of matrix molecules and enzymes were measured during this process, using real-time polymerase chain reaction (RT-PCR). Initial experiments were performed with hMSCs from a fetal donor, and results of these studies were confirmed with hMSCs from adult donors.
Results: Exposure to OAS-CM resulted in pellets with a much lower GAG content, reflecting inhibited chondrogenic differentiation. This was accompanied by decreased mRNA levels of aggrecan, type II collagen, and Sox9, and increased levels of matrix metalloproteinase (MMP)1, MMP3, MMP13, ADAMTS4, and ADAMTS5. Both tofacitinib (JAK-inhibitor) and oxozeaenol (TAK1 inhibitor) significantly increased the GAG content of the pellets in osteoarthritis (OA)-like conditions. The combination of both protein kinase inhibitors showed an additive effect on GAG content. In agreement with this, in the presence of OAS-CM, both tofacitinib and oxozeaenol increased mRNA expression of sox9. The expression of aggrecan and type II collagen was also up-regulated, but this only reached significance for aggrecan after TAK1 inhibition. Both inhibitors decreased the mRNA levels of MMP1, 3, and 13 in the presence of OAS-CM. Moreover, oxozeaenol also significantly down-regulated the mRNA levels of aggrecanases ADAMTS4 and ADAMTS5. When combined, the inhibitors caused additive reduction of OA-induced MMP1 mRNA expression. Counteraction of OAS-CM-induced inhibition of chondrogenesis by these protein kinase inhibitors was confirmed with hMSCs of two different adult donors. Both tofacitinib and oxozeaenol significantly improved GAG content in cell pellets from these adult donors.
Conclusions: Tofacitinib and oxozeaenol partially prevent the inhibition of chondrogenesis by factors secreted by OA synovium. Their effects are additive. This indicates that these protein kinase inhibitors can potentially be used to improve cartilage formation under the conditions occurring in osteoathritic, or otherwise inflamed, joints.
doi:10.1089/ten.tea.2013.0553
PMCID: PMC4137338  PMID: 24547725
8.  Bladder Acellular Matrix Conjugated with Basic Fibroblast Growth Factor for Bladder Regeneration 
Tissue Engineering. Part A  2014;20(15-16):2234-2242.
Basic fibroblast growth factor (bFGF) plays an important role in wound repair and tissue regeneration. Considerable research has been focused on the exploration of bFGF delivery systems for maintaining efficient local concentration at the injury sites. In this study, bFGF was chemically crosslinked to the bladder acellular matrix (BAM) to create specific binding between bFGF and BAM. The BAM scaffold conjugated with bFGF (CL-BAM/bFGF) could bind more bFGF and achieve controlled release of bFGF, which promoted human fibroblasts to proliferate in vitro and accelerated cellularization and vascularization after subcutaneous implantation. Using the rat bladder reconstruction model, the CL-BAM/bFGF group showed better tissue regeneration compared with the other groups. In summary, CL-BAM/bFGF could prevent the diffusion of bFGF from BAM and maintain its activity. Thus, the scaffold conjugated with growth factor systems could be an effective way for maintaining local therapy dosage at the target site in wound repair and tissue regeneration.
doi:10.1089/ten.tea.2013.0730
PMCID: PMC4137349  PMID: 24483233
9.  Adipose-Derived Stem Cells and BMP-2 Delivery in Chitosan-Based 3D Constructs to Enhance Bone Regeneration in a Rat Mandibular Defect Model 
Tissue Engineering. Part A  2014;20(15-16):2169-2179.
Reconstructing segmental mandiblular defects remains a challenge in the clinic. Tissue engineering strategies provide an alternative option to resolve this problem. The objective of the present study was to determine the effects of adipose-derived stem cells (ASCs) and bone morphogenetic proteins-2 (BMP-2) in three-dimensional (3D) scaffolds on mandibular repair in a small animal model. Noggin expression levels in ASCs were downregulated by a lentiviral short hairpin RNA strategy to enhance ASC osteogenesis (ASCsNog−). Chitosan (CH) and chondroitin sulfate (CS), natural polysaccharides, were fabricated into 3D porous scaffolds, which were further modified with apatite coatings for enhanced cellular responses and efficient delivery of BMP-2. The efficacy of 3D apatite-coated CH/CS scaffolds supplemented with ASCsNog− and BMP-2 were evaluated in a rat critical-sized mandibular defect model. After 8 weeks postimplantation, the scaffolds treated with ASCsNog− and BMP-2 significantly promoted rat mandibular regeneration as demonstrated by micro-computerized tomography, histology, and immunohistochemistry, compared with the groups treated with ASCsNog− or BMP-2 alone. These results suggest that our combinatorial strategy of ASCsNog−+BMP-2 in 3D apatite microenvironments can significantly promote mandibular regeneration, and these may provide a potential tissue engineering approach to repair large bony defects.
doi:10.1089/ten.tea.2013.0523
PMCID: PMC4137352  PMID: 24524819
10.  Nanoclay-Enriched Poly(ɛ-caprolactone) Electrospun Scaffolds for Osteogenic Differentiation of Human Mesenchymal Stem Cells 
Tissue Engineering. Part A  2014;20(15-16):2088-2101.
Musculoskeletal tissue engineering aims at repairing and regenerating damaged tissues using biological tissue substitutes. One approach to achieve this aim is to develop osteoconductive scaffolds that facilitate the formation of functional bone tissue. We have fabricated nanoclay-enriched electrospun poly(ɛ-caprolactone) (PCL) scaffolds for osteogenic differentiation of human mesenchymal stem cells (hMSCs). A range of electrospun scaffolds is fabricated by varying the nanoclay concentrations within the PCL scaffolds. The addition of nanoclay decreases fiber diameter and increases surface roughness of electrospun fibers. The enrichment of PCL scaffold with nanoclay promotes in vitro biomineralization when subjected to simulated body fluid (SBF), indicating bioactive characteristics of the hybrid scaffolds. The degradation rate of PCL increases due to the addition of nanoclay. In addition, a significant increase in crystallization temperature of PCL is also observed due to enhanced surface interactions between PCL and nanoclay. The effect of nanoclay on the mechanical properties of electrospun fibers is also evaluated. The feasibility of using nanoclay-enriched PCL scaffolds for tissue engineering applications is investigated in vitro using hMSCs. The nanoclay-enriched electrospun PCL scaffolds support hMSCs adhesion and proliferation. The addition of nanoclay significantly enhances osteogenic differentiation of hMSCs on the electrospun scaffolds as evident by an increase in alkaline phosphates activity of hMSCs and higher deposition of mineralized extracellular matrix compared to PCL scaffolds. Given its unique bioactive characteristics, nanoclay-enriched PCL fibrous scaffold may be used for musculoskeletal tissue engineering.
doi:10.1089/ten.tea.2013.0281
PMCID: PMC4137355  PMID: 24842693
11.  Downregulation of Metabolic Activity Increases Cell Survival Under Hypoxic Conditions: Potential Applications for Tissue Engineering 
Tissue Engineering. Part A  2014;20(15-16):2265-2272.
A major challenge to the success of cell-based implants for tissue regeneration is an insufficient supply of oxygen before host vasculature is integrated into the implants, resulting in premature cell death and dysfunction. Whereas increasing oxygenation to the implants has been a major focus in the field, our strategy is aimed at lowering oxygen consumption by downregulating cellular metabolism of cell-based implants. Adenosine, which is a purine nucleoside that functions as an energy transferring molecule, has been reported to increase under hypoxia, resulting in reducing the adenosine triphosphate (ATP) demands of the Na+/K+ ATPase. In the present study, we investigated whether adenosine could be used to downregulate cellular metabolism to achieve prolonged survival under hypoxic conditions. Murine myoblasts (C2C12) lacking a self-survival mechanism were treated with adenosine under 0.1% hypoxic stress. The cells, cultured in the presence of 5 mM adenosine, maintained their viability under hypoxia, and regained their normal growth and function of forming myotubes when transferred to normoxic conditions at day 11 without further supply of adenosine, whereas nontreated cells failed to survive. An increase in adenosine concentrations shortened the onset of reproliferation after transfer to normoxic conditions. This increase correlated with an increase in metabolic downregulation during the early phase of hypoxia. A higher intracellular ATP level was observed in adenosine-treated cells throughout the duration of hypoxia. This strategy of increasing cell survival under hypoxic conditions through downregulating cellular metabolism may be utilized for cell-based tissue regeneration applications as well as protecting tissues against hypoxic injuries.
doi:10.1089/ten.tea.2013.0637
PMCID: PMC4137358  PMID: 24524875
12.  Synergistic Effects of Matrix Nanotopography and Stiffness on Vascular Smooth Muscle Cell Function 
Tissue Engineering. Part A  2014;20(15-16):2115-2126.
Vascular smooth muscle cells (vSMCs) retain the ability to undergo modulation in their phenotypic continuum, ranging from a mature contractile state to a proliferative, secretory state. vSMC differentiation is modulated by a complex array of microenvironmental cues, which include the biochemical milieu of the cells and the architecture and stiffness of the extracellular matrix. In this study, we demonstrate that by using UV-assisted capillary force lithography (CFL) to engineer a polyurethane substratum of defined nanotopography and stiffness, we can facilitate the differentiation of cultured vSMCs, reduce their inflammatory signature, and potentially promote the optimal functioning of the vSMC contractile and cytoskeletal machinery. Specifically, we found that the combination of medial tissue-like stiffness (11 MPa) and anisotropic nanotopography (ridge width_groove width_ridge height of 800_800_600 nm) resulted in significant upregulation of calponin, desmin, and smoothelin, in addition to the downregulation of intercellular adhesion molecule-1, tissue factor, interleukin-6, and monocyte chemoattractant protein-1. Further, our results allude to the mechanistic role of the RhoA/ROCK pathway and caveolin-1 in altered cellular mechanotransduction pathways via differential matrix nanotopography and stiffness. Notably, the nanopatterning of the stiffer substrata (1.1 GPa) resulted in the significant upregulation of RhoA, ROCK1, and ROCK2. This indicates that nanopatterning an 800_800_600 nm pattern on a stiff substratum may trigger the mechanical plasticity of vSMCs resulting in a hypercontractile vSMC phenotype, as observed in diabetes or hypertension. Given that matrix stiffness is an independent risk factor for cardiovascular disease and that CFL can create different matrix nanotopographic patterns with high pattern fidelity, we are poised to create a combinatorial library of arterial test beds, whether they are healthy, diseased, injured, or aged. Such high-throughput testing environments will pave the way for the evolution of the next generation of vascular scaffolds that can effectively crosstalk with the scaffold microenvironment and result in improved clinical outcomes.
doi:10.1089/ten.tea.2013.0455
PMCID: PMC4137359  PMID: 24694244
13.  Correction Re:Tissue Engineering, Part A, 2013;19(17–18):1931–1940 
Tissue Engineering. Part A  2014;20(13-14):2030.
doi:10.1089/ten.tea.2014.0226
PMCID: PMC4085817
14.  Perspectives on Tissue-Engineered Nerve Regeneration for the Treatment of Spinal Cord Injury 
Tissue Engineering. Part A  2014;20(13-14):1781-1783.
Over the past few decades, substantial progress has been made to safely improve nerve function in spinal cord injury (SCI) patients through the regeneration of injured nerve tissue. This perspective focuses on an extensive overview of SCI research as well as tissue-engineered nerve regeneration for the treatment of SCI.
doi:10.1089/ten.tea.2014.0094
PMCID: PMC4085818  PMID: 24568624
15.  Compliant 3D Microenvironment Improves β-Cell Cluster Insulin Expression Through Mechanosensing and β-Catenin Signaling 
Tissue Engineering. Part A  2014;20(13-14):1888-1895.
Type 1 diabetes is chronic disease with numerous complications and currently no cure. Tissue engineering strategies have shown promise in providing a therapeutic solution, but maintenance of islet function and survival within these therapies represents a formidable challenge. The islet microenvironment may hold the key for proper islet maintenance. To elucidate the microenvironmental conditions necessary for improved islet function and survival, three-dimensional (3D) polyacrylamide cell scaffolds were fabricated with stiffnesses of 0.1 and 10 kPa to regulate the spatial and mechanical control of biosignals. Specifically, we show a significant increase in insulin mRNA expression of 3D primary mouse islet-derived and Min6-derived β-cell clusters grown on compliant 0.1 kPa scaffolds. Moreover, these compliant 0.1 kPa scaffolds also increase glucose sensitivity in Min6-derived β-cell clusters as demonstrated by the increased glucose stimulation index. Our data suggest that stiffness-specific insulin processing is regulated through the myosin light chain kinase (MLCK) and Rho-associated protein kinase (ROCK) mechanosensing pathways. Additionally, β-catenin is required for regulation of stiffness-dependent insulin expression. Through activation or inhibition of β-catenin signaling, reversible control of insulin expression is achieved on the compliant 0.1 kPa and overly stiff 10 kPa substrates. Understanding the role of the microenvironment on islet function can enhance the therapeutic approaches necessary to treat diabetes for improving insulin sensitivity and response.
doi:10.1089/ten.tea.2013.0692
PMCID: PMC4085995  PMID: 24433489
16.  Dynamic Vibration Cooperates with Connective Tissue Growth Factor to Modulate Stem Cell Behaviors 
Tissue Engineering. Part A  2014;20(13-14):1922-1934.
Vocal fold disorders affect 3–9% of the U.S. population. Tissue engineering offers an alternative strategy for vocal fold repair. Successful engineering of vocal fold tissues requires a strategic combination of therapeutic cells, biomimetic scaffolds, and physiologically relevant mechanical and biochemical factors. Specifically, we aim to create a vocal fold-like microenvironment to coax stem cells to adopt the phenotype of vocal fold fibroblasts (VFFs). Herein, high frequency vibratory stimulations and soluble connective tissue growth factor (CTGF) were sequentially introduced to mesenchymal stem cells (MSCs) cultured on a poly(ɛ-caprolactone) (PCL)-derived microfibrous scaffold for a total of 6 days. The initial 3-day vibratory culture resulted in an increased production of hyaluronic acids (HA), tenascin-C (TNC), decorin (DCN), and matrix metalloproteinase-1 (MMP1). The subsequent 3-day CTGF treatment further enhanced the cellular production of TNC and DCN, whereas CTGF treatment alone without the vibratory preconditioning significantly promoted the synthesis of collagen I (Col 1) and sulfated glycosaminoglycans (sGAGs). The highest level of MMP1, TNC, Col III, and DCN production was found for cells being exposed to the combined vibration and CTGF treatment. Noteworthy, the vibration and CTGF elicited a differential stimulatory effect on elastin (ELN), HA synthase 1 (HAS1), and fibroblast-specific protein-1 (FSP-1). The mitogenic activity of CTGF was only elicited in naïve cells without the vibratory preconditioning. The combined treatment had profound, but opposite effects on mitogen-activated protein kinase (MAPK) pathways, Erk1/2 and p38, and the Erk1/2 pathway was critical for the observed mechano-biochemical responses. Collectively, vibratory stresses and CTGF signals cooperatively coaxed MSCs toward a VFF-like phenotype and accelerated the synthesis and remodeling of vocal fold matrices.
doi:10.1089/ten.tea.2013.0496
PMCID: PMC4086222  PMID: 24456068
17.  In Vitro Characterization of a Stem-Cell-Seeded Triple-Interpenetrating-Network Hydrogel for Functional Regeneration of the Nucleus Pulposus 
Tissue Engineering. Part A  2014;20(13-14):1841-1849.
Intervertebral disc degeneration is implicated as a major cause of low-back pain. There is a pressing need for new regenerative therapies for disc degeneration that restore native tissue structure and mechanical function. To that end we investigated the therapeutic potential of an injectable, triple-interpenetrating-network hydrogel comprised of dextran, chitosan, and teleostean, for functional regeneration of the nucleus pulposus (NP) of the intervertebral disc in a series of biomechanical, cytotoxicity, and tissue engineering studies. Biomechanical properties were evaluated as a function of gelation time, with the hydrogel reaching ∼90% of steady-state aggregate modulus within 10 h. Hydrogel mechanical properties evaluated in confined and unconfined compression were comparable to native human NP properties. To confirm containment within the disc under physiological loading, toluidine-blue-labeled hydrogel was injected into human cadaveric spine segments after creation of a nucleotomy defect, and the segments were subjected to 10,000 cycles of loading. Gross analysis demonstrated no implant extrusion, and further, that the hydrogel interdigitated well with native NP. Constructs were next surface-seeded with NP cells and cultured for 14 days, confirming lack of hydrogel cytotoxicity, with the hydrogel maintaining NP cell viability and promoting proliferation. Next, to evaluate the potential of the hydrogel to support cell-mediated matrix production, constructs were seeded with mesenchymal stem cells (MSCs) and cultured under prochondrogenic conditions for up to 42 days. Importantly, the hydrogel maintained MSC viability and promoted proliferation, as evidenced by increasing DNA content with culture duration. MSCs differentiated along a chondrogenic lineage, evidenced by upregulation of aggrecan and collagen II mRNA, and increased GAG and collagen content, and mechanical properties with increasing culture duration. Collectively, these results establish the therapeutic potential of this novel hydrogel for functional regeneration of the NP. Future work will confirm the ability of this hydrogel to normalize the mechanical stability of cadaveric human motion segments, and advance the material toward human translation using preclinical large-animal models.
doi:10.1089/ten.tea.2013.0516
PMCID: PMC4086360  PMID: 24410394
18.  Deformation Thresholds for Chondrocyte Death and the Protective Effect of the Pericellular Matrix 
Tissue Engineering. Part A  2014;20(13-14):1870-1876.
In cartilage tissue engineering studies, the stimulatory effect of mechanical perturbation declines after the first 2 weeks of culture. Similarly, it is known that chondrocyte–agarose constructs should not be loaded within the first days after seeding, to prevent considerable cell death, suggesting a mechanical threshold. This study aims to establish a relationship between chondrocyte deformation and death, and to evaluate the protective effect of the pericellular matrix (PCM) that is formed in 3D cultures. Chondrocyte viability was monitored every hour for 24 h after applying a strain range of 0% to 25% to agarose constructs containing chondrocytes, cultured for 1, 3, 5, 7, or 10 days. At these culture time points, the PCM thickness and chondrocyte deformation were assessed by means of histology and assayed for biochemical contents. Inverse finite element (FE) simulations were used to evaluate the change of mechanical properties of the chondrocyte and PCM over the 10-day culture duration. Chondrocyte death was demonstrated to be dependent on both the magnitude and duration of straining. The highest cell death was observed at day 1 (43%), reducing over culture duration (15% at day 3 and 2.5% at day 10). Cell deformation at 25% compression decreased significantly over culture duration (aspect ratio of 2.24±0.67 at day 1 and 1.45±0.24 at day 3) and with increased matrix production. Inverse FE simulations showed an increasing PCM Young's modulus of 45 kPa at day 3 to 162 kPa at day 10. The current results provide evidence for a mechanical threshold for chondrocyte death and for the protective effect of the PCM. As such, these insights may help in establishing mechanical loading protocols for cartilage tissue engineering studies.
doi:10.1089/ten.tea.2013.0436
PMCID: PMC4086379  PMID: 24438476
19.  Use of Myocardial Matrix in a Chitosan-Based Full-Thickness Heart Patch 
Tissue Engineering. Part A  2014;20(13-14):1877-1887.
A novel cardiac scaffold comprised of decellularized porcine heart matrix was investigated for use as a biodegradable patch with a potential for surgical reconstruction of the right ventricular outflow tract. Powdered heart matrix solution was blended with chitosan and lyophilized to form three-dimensional scaffolds. For this investigation, we examined the influence of different blending ratios of heart matrix to chitosan on porosity and mechanical properties, then gene expression and electrophysiological function of invading neonatal rat ventricular myocytes (NRVM) compared to type-A gelatin/chitosan composite scaffolds. Heart matrix/chitosan-blended hydrogels (1.6 mg/mL heart matrix) had similar porosity (109±34 μm), and elastic modulus (13.2±4.0 kPa) as previously published gelatin/chitosan scaffolds. Heart matrix/chitosan hydrogels maintained>80% viability and had higher NRVM retention (∼1000 cells/mm2) than gelatin/chitosan scaffolds. There was a significant increase in α-myosin heavy chain and connexin-43 expression in NRVM cultured on heart matrix/chitosan scaffolds after 14 days compared with gelatin/chitosan scaffolds. Further, heart matrix/chitosan scaffolds had significantly higher conduction velocity (12.6±4.9 cm/s) and contractile stress (0.79±0.13 mN/mm2) than gelatin/chitosan scaffolds. In summary, NRVM cultured on heart matrix scaffold showed improvements in contractile and electrophysiological function.
doi:10.1089/ten.tea.2013.0620
PMCID: PMC4086522  PMID: 24433519
20.  Three-Dimensional Printing of rhBMP-2-Loaded Scaffolds with Long-Term Delivery for Enhanced Bone Regeneration in a Rabbit Diaphyseal Defect 
Tissue Engineering. Part A  2014;20(13-14):1980-1992.
In this study, recombinant human bone morphogenetic protein-2 (rhBMP-2) delivery system with slow mode was successfully developed in three-dimensional (3D) printing-based polycaprolactone (PCL)/poly(lactic-co-glycolic acid) (PLGA) scaffolds for bone formation of critical-sized rabbit segmental diaphyseal defect. To control the delivery of the rhBMP-2, collagen (for long-term delivery up to 28 days) and gelatin (for shor-term delivery within a week) solutions encapsulating rhBMP-2 were dispensed into a hollow cylinderical type of PCL/PLGA scaffold. An effective dose of 5μg/mL was determined by measuring the alkaline phosphatase and osteocalcin gene expression levels of human nasal inferior turbinate-derived mesenchymal stromal cells (hTMSCs) seeded on the PCL/PLGA/collagen scaffold in vitro. However, it was found that a burst release of rhBMP-2 from the PCL/PLGA/gelatin scaffold did not induce the osteogenic differentiation of hTMSCs in vitro at an equivalent dose. In the in vivo animal experiements, microcomputed tomography and histological analyses confirmed that PCL/PLGA/collagen/rhBMP-2 scaffolds (long-term delivery mode) showed the best bone healing quality at both weeks 4 and 8 after implantation without inflammatory response. On the other hand, a large number of macrophages indicating severe inflammation provoked by burst release of rhBMP-2 were observed in the vicinity of PCL/PLGA/gelatin/rhBMP-2 (short-term delivery mode) at week 4.
doi:10.1089/ten.tea.2013.0513
PMCID: PMC4086523  PMID: 24517081
21.  Implantation of Autologous Adipose-Derived Cells Reconstructs Functional Urethral Sphincters in Rabbit Cryoinjured Urethra 
Tissue Engineering. Part A  2014;20(13-14):1971-1979.
We investigated the ability of autologous adipose-derived cells injected into cryoinjured rabbit urethras to improve urinary continence and explored the possible mechanisms by which it occurred. Adipose tissue was harvested from the perivesical region of nine 10-week-old female New Zealand White rabbits and cultured for 7 days. Immediately after harvesting the tissue, we injured the internal urethral orifice by spraying liquid nitrogen for 20 s. The cultured cells expressed the mesenchymal cell marker STRO1, but not muscle cell markers myoglobin or smooth muscle actin (SMA). Just before implantation, the adipose-derived cells were labeled with the PKH26 fluorescent cell linker. Autologous 2.0×106 adipose-derived cells (five rabbits) or a cell-free control solution (four rabbits) was injected around the cryoinjured urethras at 7 days after injury. Fourteen days later, the leak point pressure (LPP) was measured, and the urethras were harvested for immunohistochemical analyses. At 14 days after implantation, LPP of the cell-implanted group was significantly higher compared with the cell-free control group (p<0.05). In immunohistochemical examination, the reconstructed skeletal and smooth muscle areas in the cell-implanted regions were significantly more developed than those in controls (p<0.01). Implanted PKH26-labeled adipose-derived cells were immunohistochemically positive for myoglobin, SMA, and Pax7 antibodies, which are markers for skeletal muscles, smooth muscles, and myoblast progenitor cells, respectively. In addition, these implanted cells were positive for the nerve cell markers, tubulin β3, S100, and the vascular endothelial cell marker, von Willebrand factor. Furthermore, some of the implanted cells were positive for the transforming growth factor β1, nerve growth factor, and vascular endothelial growth factor. In conclusion, implantation of autologous adipose-derived cells into the cryoinjured rabbit urethras promoted the recovery of urethral function by myogenic differentiation, neuroregeneration, and neoangiogenesis of the implanted cells and/or the surrounding tissues as well as by bulking effects. Thus, treatment of human radical prostatectomy-related stress urinary incontinence by adipose-derived cell implantation could have significant therapeutic effects.
doi:10.1089/ten.tea.2013.0491
PMCID: PMC4086524  PMID: 24568564
22.  Different Forms of Tenascin-C with Tenascin-R Regulate Neural Differentiation in Bone Marrow-Derived Human Mesenchymal Stem Cells 
Tissue Engineering. Part A  2014;20(13-14):1908-1921.
Mesenchymal stem cells (MSCs) are currently thought to transdifferentiate into neural lineages under specific microenvironments. Studies have reported that the tenascin family members, tenascin-C (TnC) and tenascin-R (TnR), regulate differentiation and migration, in addition to neurite outgrowth and survival in numerous types of neurons and mesenchymal progenitor cells. However, the mechanisms by which TnC and TnR affect neuronal differentiation are not well understood. In this study, we hypothesized that different forms of tenascin might regulate the neural transdifferentiation of human bone marrow-derived mesenchymal stem cells. Human MSCs were cultured in media incorporated with soluble tenascins, or on precoated tenascins. In a qualitative polymerase chain reaction analysis, adding a soluble TnC and TnR mixture to the medium significantly enhanced the expression of neuronal and glial markers, whereas no synaptic markers were expressed. Conversely, in groups of cells treated with coated TnC, hMSCs showed neurite outgrowth and synaptic marker expression. After being treated with coated TnR, hMSCs exhibited neuronal differentiation; however, it inhibited neurite outgrowth and synaptic marker expression. A combination of TnC and TnR significantly promoted hMSC differentiation in neurons or oligodendrocytes, induced neurite formation, and inhibited differentiation into astrocytes. Furthermore, the effect of the tenascin mixture showed dose-dependent effects, and a mixture ratio of 1:1 to 1:2 (TnC:TnR) provided the most obvious differentiation of neurons and oligodendrocytes. In a functional blocking study, integrin α7 and α9β1-blocking antibodies inhibited, respectively, 80% and 20% of mRNA expression by hMSCs in the coated tenascin mixture. In summary, the coated combination of TnC and TnR appeared to regulate neural differentiation signaling through integrin α7 and α9β1 in bone marrow-derived hMSCs. Our findings demonstrate novel mechanisms by which tenascin regulates neural differentiation, and enable the use of cell therapy to treat neurodegenerative diseases.
doi:10.1089/ten.tea.2013.0188
PMCID: PMC4086655  PMID: 24829055
23.  Scaffold Architecture Controls Insulinoma Clustering, Viability, and Insulin Production 
Tissue Engineering. Part A  2014;20(13-14):1784-1793.
Recently, in vitro diagnostic tools have shifted focus toward personalized medicine by incorporating patient cells into traditional test beds. These cell-based platforms commonly utilize two-dimensional substrates that lack the ability to support three-dimensional cell structures seen in vivo. As monolayer cell cultures have previously been shown to function differently than cells in vivo, the results of such in vitro tests may not accurately reflect cell response in vivo. It is therefore of interest to determine the relationships between substrate architecture, cell structure, and cell function in 3D cell-based platforms. To investigate the effect of substrate architecture on insulinoma organization and function, insulinomas were seeded onto 2D gelatin substrates and 3D fibrous gelatin scaffolds with three distinct fiber diameters and fiber densities. Cell viability and clustering was assessed at culture days 3, 5, and 7 with baseline insulin secretion and glucose-stimulated insulin production measured at day 7. Small, closely spaced gelatin fibers promoted the formation of large, rounded insulinoma clusters, whereas monolayer organization and large fibers prevented cell clustering and reduced glucose-stimulated insulin production. Taken together, these data show that scaffold properties can be used to control the organization and function of insulin-producing cells and may be useful as a 3D test bed for diabetes drug development.
doi:10.1089/ten.tea.2013.0107
PMCID: PMC4086656  PMID: 24410263
24.  Electrospun PLGA Fibers Incorporated with Functionalized Biomolecules for Cardiac Tissue Engineering 
Tissue Engineering. Part A  2014;20(13-14):1896-1907.
Structural similarity of electrospun fibers (ESFs) to the native extracellular matrix provides great potential for the application of biofunctional ESFs in tissue engineering. This study aimed to synthesize biofunctionalized poly (L-lactide-co-glycolide) (PLGA) ESFs for investigating the potential for cardiac tissue engineering application. We developed a simple but novel strategy to incorporate adhesive peptides in PLGA ESFs. Two adhesive peptides derived from laminin, YIGSR, and RGD, were covalently conjugated to poly-L-lysine, and then mingled with PLGA solution for electrospinning. Peptides were uniformly distributed on the surface and in the interior of ESFs. PLGA ESFs incorporated with YIGSR or RGD or adsorbed with laminin significantly enhanced the adhesion of cardiomyocytes isolated from neonatal rats. Furthermore, the cells were found to adhere better on ESFs compared with flat substrates after 7 days of culture. Immunofluorescent staining of F-actin, vinculin, a-actinin, and N-cadherin indicated that cardiomyocytes adhered and formed striated α-actinin better on the laminin-coated ESFs and the YIGSR-incorporated ESFs compared with the RGD-incorporated ESFs. The expression of α-myosin heavy chain and β-tubulin on the YIGSR-incorporated ESFs was significantly higher compared with the expression level on PLGA and RGD-incorporated samples. Furthermore, the contraction of cardiomyocytes was faster and lasted longer on the laminin-coated ESFs and YIGSR-incorporated ESFs. The results suggest that aligned YIGSR-incorporated PLGA ESFs is a better candidate for the formation of cardiac patches. This study demonstrated the potential of using peptide-incorporated ESFs as designable-scaffold platform for tissue engineering.
doi:10.1089/ten.tea.2013.0008
PMCID: PMC4086675  PMID: 24471778
25.  Nonwoven-Based Gelatin/Polycaprolactone Membrane Proves Suitability in a Preclinical Assessment for Treatment of Soft Tissue Defects 
Tissue Engineering. Part A  2014;20(13-14):1935-1947.
Standard preclinical assessments in vitro often have limitations regarding their transferability to human beings, mainly evoked by their nonhuman and tissue-different/nontissue-specific source. Here, we aimed at employing tissue-authentic simple and complex interactive fibroblast-epithelial cell systems and their in vivo-relevant biomarkers for preclinical in vitro assessment of nonwoven-based gelatin/polycaprolactone membranes (NBMs) for treatment of soft tissue defects. NBMs were composed of electrospun gelatin and polycaprolactone nanofiber nonwovens. Scanning electron microscopy in conjunction with actin/focal contact integrin fluorescence revealed successful adhesion and proper morphogenesis of keratinocytes and fibroblasts, along with cells' derived extracellular matrix deposits. The “feel-good factor” of cells under study on the NBM was substantiated by forming a confluent connective tissue entity, which was concomitant with a stratified epithelial equivalent. Immunohistochemistry proved tissue authenticity over time by abundance of the biomarker vimentin in the connective tissue entity, and chronological increase of keratins KRT1/10 and involucrin expression in epithelial equivalents. Suitability of the novel NBM as wound dressing was evidenced by an almost completion of epithelial wound closure in a pilot mini-pig study, after a surgical intervention-caused gingival dehiscence. In summary, preclinical assessment by tissue-authentic cell systems and the animal pilot study revealed the NBM as an encouraging therapeutic medical device for prospective clinical applications.
doi:10.1089/ten.tea.2013.0594
PMCID: PMC4086676  PMID: 24494668

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