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1.  Cell Adhesion on Polyelectrolyte Multilayer Coated Polydimethylsiloxane Surfaces with Varying Topographies 
Tissue engineering  2007;13(8):2105-2117.
This article demonstrates that the micro-topography of the surface with respect to the pattern size and pitch influences cell adhesion and proliferation. Extensive research has shown the dependence of cell proliferation on substrate chemistry, but the influence of substrate topography on cell attachment has only recently been appreciated. To evaluate the effect of substrate physical properties (i.e., periodic microstructures) on cell attachment and morphology, we compared the response of several cell types (fibroblasts, HeLa, and primary hepatocytes) cultured on various polydimethylsiloxane (PDMS) patterns. PDMS has been used as an artificial construct to mimic biological structures. Although PDMS is widely used in biomedical applications, membrane technology, and microlithography, it is difficult to maintain cells on PDMS for long periods, and the polymer has proved to be a relatively inefficient substrate for cell adhesion. To improve adhesion, we built polyelectrolyte multilayers (PEMs) on PDMS surfaces to increase surface wettability, thereby improving attachment and spreading of the cells. Micrographs demonstrate the cellular response to physical parameters, such as pattern size and pitch, and suggest that surface topography, in part, regulates cell adhesion and proliferation. Therefore, varying the surface topography may provide a method to influence cell attachment and proliferation for tissue-engineering applications.
PMCID: PMC4059019  PMID: 17518734
2.  Sustained Release of TGFβ3 from PLGA Microspheres and Its Effect on Early Osteogenic Differentiation of Human Mesenchymal Stem Cells 
Tissue engineering  2006;12(3):537-546.
Despite the widespread role of transforming growth factor-β3 (TGFβ3) in wound healing and tissue regeneration, its long-term controlled release has not been demonstrated. Here, we report microencapsulation of TGFβ3 in poly-d-l-lactic-co-glycolic acid (PLGA) microspheres and determine its bioactivity. The release profiles of PLGA-encapsulated TGFβ3 with 50:50 and 75:25 PLA:PGA ratios differed throughout the experimental period. To compare sterilization modalities of microspheres, bFGF was encapsulated in 50:50 PLGA microspheres and subjected to ethylene oxide (EO) gas, radiofrequency glow discharge (RFGD), or ultraviolet (UV) light. The release of bFGF was significantly attenuated by UV light, but not significantly altered by either EO or RFGD. To verify its bioactivity, TGFβ3 (1.35 ng/mL) was control-released to the culture of human mesenchymal stem cells (hMSC) under induced osteogenic differentiation. Alkaline phosphatase staining intensity was markedly reduced 1 week after exposing hMSC-derived osteogenic cells to TGFβ3. This was confirmed by lower alkaline phosphatase activity (2.25 ± 0.57 mU/mL/ng DNA) than controls (TGFβ3-free) at 5.8 ± 0.9 mU/mL/ng DNA (p < 0.05). Control-released TGFβ3 bioactivity was further confirmed by lack of significant differences in alkaline phosphatase upon direct addition of 1.35 ng/mL TGFβ3 to cell culture (p > 0.05). These findings provide baseline data for potential uses of microencapsulated TGFβ3 in wound healing and tissue-engineering applications.
PMCID: PMC4035024  PMID: 16579687
3.  Vascularized Adipose Tissue Grafts from Human Mesenchymal Stem Cells with Bioactive Cues and Microchannel Conduits 
Tissue engineering  2007;13(12):2881-2890.
Vascularization is critical to the survival of engineered tissues. This study combined biophysical and bioactive approaches to induce neovascularization in vivo. Further, we tested the effects of engineered vascularization on adipose tissue grafts. Hydrogel cylinders were fabricated from poly(ethylene glycol) diacrylate (PEG) in four configurations: PEG alone, PEG with basic fibroblast growth factor (bFGF), microchanneled PEG, or both bFGF-adsorbed and microchanneled PEG. In vivo implantation revealed no neovascularization in PEG, but substantial angiogenesis in bFGF-adsorbed and/or microchanneled PEG. The infiltrating host tissue consisted of erythrocyte-filled blood vessels lined by endothelial cells, and immunolocalized to vascular endothelial growth factor (VEGF). Human mesenchymal stem cells were differentiated into adipogenic cells, and encapsulated in PEG with both microchanneled and adsorbed bFGF. Upon in vivo implantation subcutaneously in immunodeficient mice, oil red O positive adipose tissue was present and interspersed with interstitial fibrous (IF) capsules. VEGF was immunolocalized in the IF capsules surrounding the engineered adipose tissue. These findings suggest that bioactive cues and/or microchannels promote the genesis of vascularized tissue phenotypes such as the tested adipose tissue grafts. Especially, engineered microchannels may provide a generic approach for modifying existing biomaterials by providing conduits for vascularization and/or diffusion.
PMCID: PMC4035031  PMID: 17824832
4.  Treatment of Fulminant Hepatic Failure in Rats Using a Bioartificial Liver Device Containing Porcine Hepatocytes Producing Interleukin-1 Receptor Antagonist 
Tissue engineering  2006;12(5):1313-1323.
Fulminant hepatic failure (FHF) is a serious clinical condition that is associated with high mortality. There is evidence that FHF is an inflammatory disease, which is supported clinically by elevated serum levels of cytokines. In an effort to develop hepatocytes with additional functions for use in our bioartificial liver (BAL) device, we focused on interleukin-1 (IL-1) blockade as a therapeutic modality. Primary porcine hepatocytes were isolated from the livers of miniature swine and then transfected with an adenoviral vector encoding human interleukin-1 receptor antagonist (AdIL-1Ra). The transfected hepatocytes secreted human IL-1Ra. These transfected hepatocytes were incorporated into a flat-plate BAL device to evaluate their efficacy in treating D-galactosamine (GalN)-induced FHF in a rat model. After extracorporeal perfusion with the BAL device containing the transfected hepatocytes, there were significant reductions in the plasma levels of hepatic enzymes (aspartate aminotransferase and alanine aminotransferase) and cytokines (IL-1 and IL-6), indicating a beneficial effect. Animal survival was significantly improved in the treated group compared to the control group. These experiments demonstrate that combining inflammatory cytokine blockade with a functional BAL device may be an effective therapeutic option in the treatment of FHF.
PMCID: PMC3202215  PMID: 16771644
5.  Embryoid Body–Mediated Differentiation of Mouse Embryonic Stem Cells Along a Hepatocyte Lineage: Insights from Gene Expression Profiles 
Tissue engineering  2006;12(6):1515-1525.
Pluripotent embryonic stem (ES) cells represent a promising renewable cell source for the generation of functional differentiated cells. Previous studies incorporating embryoid body (EB)-mediated stem cell differentiation have, either spontaneously or after growth factor and extracellular matrix protein supplementation, yielded populations of hepatocyte lineage cells expressing mature hepatocyte markers such as albumin (ALB). In an effort to promote ES cell commitment to the hepatocyte lineage, we have evaluated the effects of four culture conditions on albumin and gene expression in differentiating ES cells. Quantitative in situ immunofluorescence and cDNA microarray analyses were used to describe not only lineage specificity but also to provide insights into the effects of disparate culture environments on the mechanisms of differentiation. The results of these studies suggest that spontaneous and collagen-mediated differentiation induce cells with the highest levels of ALB expression but mature liver specific genes were only expressed in the spontaneous condition. Further analysis of gene expression profiles indicated that two distinct mechanisms may govern spontaneous and collagen-mediated differentiation.
PMCID: PMC3199957  PMID: 16846348
6.  Mechanistic Exploration of Phthalimide Neovascular Factor 1 Using Network Analysis Tools 
Tissue engineering  2007;13(10):2561-2575.
Neovascularization is essential for the survival and successful integration of most engineering tissues after implantation in vivo. The objective of this study was to elucidate possible mechanisms of phthalimide neovascular factor 1 (PNF1), a new synthetic small molecule proposed for therapeutic induction of angiogenesis. Complementary deoxyribonucleic acid microarray analysis was used to identify 568 transcripts in human microvascular endothelial cells (HMVECs) that were significantly regulated after 24-h stimulation with 30 μM of PNF1, previously known as SC-3–149. Network analysis tools were used to identify genetic networks of the global biological processes involved in PNF1 stimulation and to describe known molecular and cellular functions that the drug regulated most highly. Examination of the most significantly perturbed networks identified gene products associated with transforming growth factor-beta (TGF-β), which has many known effects on angiogenesis, and related signal transduction pathways. These include molecules integral to the thrombospondin, plasminogen, fibroblast growth factor, epidermal growth factor, ephrin, Rho, and Ras signaling pathways that are essential to endothelial function. Moreover, real-time reverse-transcriptase polymerase chain reaction (RT-PCR) of select genes showed significant increases in TGF-β-associated receptors endoglin and beta glycan. These experiments provide important insight into the pro-angiogenic mechanism of PNF1, namely, TGF-β-associated signaling pathways, and may ultimately offer new molecular targets for directed drug discovery.
PMCID: PMC3124853  PMID: 17723106
7.  Antibacterial Activity within Degradation Products of Biological Scaffolds Composed of Extracellular Matrix 
Tissue engineering  2006;12(10):2949-2955.
Biological scaffolds composed of extracellular matrix (ECM) have been shown to be resistant to deliberate bacterial contamination in preclinical in vivo studies. The present study evaluated the degradation products resulting from the acid digestion of ECM scaffolds for antibacterial effects against clinical strains of Staphylococcus aureus and Escherichia coli. The ECM scaffolds were derived from porcine urinary bladder (UBM-ECM) and liver (L-ECM). These biological scaffolds were digested with acid at high temperatures, fractionated using ammonium sulfate precipitation, and tested for antibacterial activity in a standardized in vitro assay. Degradation products from both UBM-ECM and L-ECM demonstrated antibacterial activity against both S. aureus and E. coli. Specific ammonium sulfate fractions that showed antimicrobial activity varied for the 2 different ECM scaffold types. The results of this study suggest that several different low-molecular-weight peptides with antibacterial activity exist within ECM and that these peptides may help explain the resistance to bacterial infection provided by such biological scaffolds.
PMCID: PMC3056877  PMID: 17518662
8.  Osterix Overexpression in Mesenchymal Stem cells Stimulates Healing of Critical-Sized Defects in Murine Calvarial Bone 
Tissue engineering  2007;13(10):2431-2440.
Osterix (Osx) is a zinc-finger-containing transcription factor that is expressed in osteoblasts of all endochondral and membranous bones. In Osx null mice, osteoblast differentiation is impaired, and bone formation is absent. We hypothesized that overexpression of Osx in bone marrow–derived mesenchymal stem cells (BMSCs) would enhance osteogenic differentiation during bone regeneration in vivo. Overexpression of Osx in mouse BMSCs was achieved using retroviral infection together with a green fluorescent protein (GFP) vector to monitor transduction efficiency and determine the source of regenerative cells in implantation studies. Bone regeneration in vivo was evaluated by implanting BMSCs overexpressing Osx into 4-mm calvarial bone defects in adult mice using type I collagen sponge as a carrier. New bone formation in the defects was quantified using radiological and histological procedures 5 weeks after implantation. The results showed that implantation of Osx-transduced BMSCs resulted in 85% healing of calvarial bone defects as detected using radiological analyses. Histological examination of the implants demonstrated that the Osx-transduced group exhibited amounts of newly formed bone that was five times as high as in a group transduced with the empty vector. Immunohistochemistry for GFP showed positive immunoreaction localized to areas of newly engineered bone in the Osx-transduced group. Immunohistochemistry with antibodies against the extracellular matrix protein bone sialoprotein resulted in strong staining in areas of new bone formation. In addition, the clonal BMSCs showed an osteogenic potential similar to that of primary cultures of BMSCs, suggesting the usefulness of this model in bone tissue engineering. These results indicate that ex vivo gene therapy of Osx is a useful therapeutic approach in regenerating adult bone tissue.
PMCID: PMC2835465  PMID: 17630878
9.  Engineering Complex Tissues 
Tissue engineering  2006;12(12):3307.
This article summarizes the views expressed at the third session of the workshop “Tissue Engineering—The Next Generation,” which was devoted to the engineering of complex tissue structures. Antonios Mikos described the engineering of complex oral and craniofacial tissues as a “guided interplay” between biomaterial scaffolds, growth factors, and local cell populations toward the restoration of the original architecture and function of complex tissues. Susan Herring, reviewing osteogenesis and vasculogenesis, explained that the vascular arrangement precedes and dictates the architecture of the new bone, and proposed that engineering of osseous tissues might benefit from preconstruction of an appropriate vasculature. Jennifer Elisseeff explored the formation of complex tissue structures based on the example of stratified cartilage engineered using stem cells and hydrogels. Helen Lu discussed engineering of tissue interfaces, a problem critical for biological fixation of tendons and ligaments, and the development of a new generation of fixation devices. Rita Kandel discussed the challenges related to the re-creation of the cartilage-bone interface, in the context of tissue engineered joint repair. Frederick Schoen emphasized, in the context of heart valve engineering, the need for including the requirements derived from “adult biology” of tissue remodeling and establishing reliable early predictors of success or failure of tissue engineered implants. Mehmet Toner presented a review of biopreservation techniques and stressed that a new breakthrough in this field may be necessary to meet all the needs of tissue engineering. David Mooney described systems providing temporal and spatial regulation of growth factor availability, which may find utility in virtually all tissue engineering and regeneration applications, including directed in vitro and in vivo vascularization of tissues. Anthony Atala offered a clinician’s perspective for functional tissue regeneration, and discussed new biomaterials that can be used to develop new regenerative technologies.
PMCID: PMC2821210  PMID: 17518671
10.  Structure and Functional Evaluation of Tendon–Skeletal Muscle Constructs Engineered in Vitro 
Tissue engineering  2006;12(11):3149-3158.
During muscle contraction, the integrity of the myotendinous junction (MTJ) is important for the transmission of force from muscle to tendon. We evaluated the contractile and structural characteristics of 3-dimensional (3-D) skeletal muscle constructs co-cultured with engineered self-organized tendon constructs (n = 4), or segments of adult (n = 4) or fetal (n = 5) rat-tail tendon. We hypothesized that the co-culture of tendon and muscle would produce constructs with viable muscle–tendon interfaces that remain intact during generation of force. Construct diameter (μm) and maximum isometric force (μN) were measured, and specific force (kPa) was determined. After measure of force, constructs were loaded at a constant strain rate until failure and surface strains were recorded optically across the tendon, the muscle and the interface and used to determine the tangent modulus (passive stiffness) of the construct. Frozen samples were used for Trichrome Masson staining and immunofluorescent analysis of the MTJ-specific protein paxillin. No differences were observed between the groups with respect to diameter, maximum force, or specific force. The MTJ was robust and withstood tensile loading beyond the physiological strain range. The majority of the constructs failed in the muscle region. At the MTJ, there is an increase in the expression and localization of paxillin. In conclusion, using 3 sources of tendon tissue, we successfully engineered 3-D muscle–tendon constructs with functionally viable MTJ, characterized by structural features and protein expression patterns resembling neonatal MTJs in vivo.
PMCID: PMC2798802  PMID: 17518629
11.  Effects of Auricular Chondrocyte Expansion on Neocartilage Formation in Photocrosslinked Hyaluronic Acid Networks 
Tissue engineering  2006;12(9):2665-2673.
The overall objective of this study was to examine the effects of in vitro expansion on neocartilage formation by auricular chondrocytes photoencapsulated in a hyaluronic acid (HA) hydrogel as a next step towards the clinical application of tissue engineering therapies for treatment of damaged cartilage. Swine auricular chondrocytes were encapsulated either directly after isolation (p = 0), or after further in vitro expansion (p = 1 and p = 2) in a 2 wt%, 50 kDa HA hydrogel and implanted subcutaneously in the dorsum of nude mice. After 12 weeks, constructs were explanted for mechanical testing and biochemical and immunohistochemical analysis and compared to controls of HA gels alone and native cartilage. The compressive equilibrium moduli of the p = 0 and p = 1 constructs (51.2 ± 8.0 and 72.5 ± 35.2 kPa, respectively) were greater than the p = 2 constructs (26.8 ± 14.9 kPa) and the control HA gel alone (12.3 ± 1.3 kPa) and comparable to auricular cartilage (35.1 ± 12.2 kPa). Biochemical analysis showed a general decrease in glycosaminoglycan (GAG), collagen, and elastin content with chondrocyte passage, though no significant differences were found between the p = 0 and p = 1 constructs for any of the analyses. Histological staining showed intense and uniform staining for aggrecan, as well as greater type II collagen versus type I collagen staining in all constructs. Overall, this study illustrates that constructs with the p = 0 and p = 1 auricular chondrocytes produced neocartilage tissue that resembled native auricular cartilage after 12 weeks in vivo. However, these results indicate that further expansion of the chondrocytes (p = 2) can lead to compromised tissue properties.
PMCID: PMC2678567  PMID: 16995800
cartilage; auricular chondrocyte; hyaluronic acid; hydrogel; passage number
12.  Tissue-Engineered Follicles Produce Live, Fertile Offspring 
Tissue engineering  2006;12(10):2739-2746.
Oocytes grown in vitro are of low quality and yield few live births, thus limiting the ability to store or bank the ova of women wishing to preserve their fertility. We applied tissue engineering principles to the culture of immature mouse follicles by designing an alginate hydrogel matrix to maintain the oocyte’s 3-dimensional (3D) architecture and cell-cell interactions in vitro. A 3D culture mimics the in vivo follicle environment, and hydrogel-encapsulated follicles develop mature oocytes within the capacity for fertilization similar to that of oocytes matured in vivo. Embryos derived from cultured oocytes fertilized in vitro and transferred to pseudopregnant female mice were viable, and both male and female offspring were fertile. Our results demonstrate that alginate hydrogel-based 3D in vitro culture of follicles permits normal growth and development of follicles and oocytes. This system creates new opportunities for discovery in follicle biology and establishes a core technology for human egg banks for preservation of fertility.
PMCID: PMC2648391  PMID: 17518643
13.  Effect of rhPDGF-BB Delivery on Mediators of Periodontal Wound Repair 
Tissue engineering  2006;12(6):1441-1450.
Growth factors such as platelet-derived growth factor (PDGF) exert potent effects on wound healing including the regeneration of tooth-supporting structures. This investigation examined the effect of the local delivery of PDGF-BB when combined with reconstructive periodontal surgery on local wound fluid (WF) levels of PDGF-AB, vascular endothelial growth factor (VEGF), and bone collagen telopeptide (ICTP) in humans with advanced periodontitis. Sixteen patients exhibiting localized periodontal osseous defects were randomized to one of three groups (β-TCP carrier alone, β-TCP + 0.3 mg/mL of recombinant human PDGF-BB [rhPDGF-BB], or β-TCP + 1.0 mg/mL of rhPDGF-BB) and monitored for 6 months. WF was harvested and analyzed for PDGF-AB, VEGF, and ICTP WF levels. Teeth contralateral to the target lesions served as controls. Increased levels of VEGF in the WF was observed for all surgical treatment groups with the 1.0 mg/mL rhPDGF-BB group showing the most pronounced difference at 3 weeks in the AUC analysis versus control (p < 0.0001). PDGF-AB WF levels were increased for the carrier alone group compared to both rhPDGF-BB groups. Low-dose rhPDGF-BB application elicited increases in ICTP at days 3–5 in the wound healing process, suggesting a promotion of bone turnover at early stages of the repair process (p < 0.02). These results demonstrate contrasting inducible expression patterns of PDGF-AB, VEGF, and ICTP during periodontal wound healing in humans.
PMCID: PMC2586965  PMID: 16846342
14.  Platelet-Derived Growth Factor Gene Delivery Stimulates ex Vivo Gingival Repair 
Tissue engineering  2003;9(4):745-756.
Destruction of tooth support due to the chronic inflammatory disease periodontitis is a major cause of tooth loss. There are limitations with available treatment options to tissue engineer soft tissue periodontal defects. The exogenous application of growth factors (GFs) such as platelet-derived growth factor (PDGF) has shown promise to enhance oral and periodontal tissue regeneration. However, the topical administration of GFs has not led to clinically significant improvements in tissue regeneration because of problems in maintaining therapeutic protein levels at the defect site. The utilization of PDGF gene transfer may circumvent many of the limitations with protein delivery to soft tissue wounds. The objective of this study was to test the effect of PDGF-A and PDGF-B gene transfer to human gingival fibroblasts (HGFs) on ex vivo repair in three-dimensional collagen lattices. HGFs were transduced with adenovirus encoding PDGF-A and PDGF-B genes. Defect fill of bilayer collagen gels was measured by image analysis of cell repopulation into the gingival defects. The modulation of gene expression at the defect site and periphery was measured by RT-PCR during a 10-day time course after gene delivery. The results demonstrated that PDGF-B gene transfer stimulated potent (>4-fold) increases in cell repopulation and defect fill above that of PDGF-A and corresponding controls. PDGF-A and PDGF-B gene expression was maintained for at least 10 days. PDGF gene transfer upregulated the expression of phosphatidylinosital 3-kinase and integrin α5 subunit at 5 days after adenovirus transduction. These results suggest that PDGF gene transfer has potential for periodontal soft tissue-engineering applications.
PMCID: PMC2586961  PMID: 13678451
15.  Review: Advances in Vascular Tissue Engineering Using Protein-Based Biomaterials 
Tissue engineering  2007;13(11):2601-2613.
The clinical need for improved blood vessel substitutes, especially in small-diameter applications, drives the field of vascular tissue engineering. The blood vessel has a well-characterized structure and function, but it is a complex tissue, and it has proven difficult to create engineered tissues that are suitable for widespread clinical use. This review is focused on approaches to vascular tissue engineering that use proteins as the primary matrix or “scaffold” material for creating fully biological blood vessel replacements. In particular, this review covers four main approaches to vascular tissue engineering: 1) cell-populated protein hydrogels, 2) cross-linked protein scaffolds, 3) decellularized native tissues, and 4) self-assembled scaffolds. Recent advances in each of these areas are discussed, along with advantages of and drawbacks to these approaches. The first fully biological engineered blood vessels have entered clinical trials, but important challenges remain before engineered vascular tissues will have a wide clinical effect. Cell sourcing and recapitulating the biological and mechanical function of the native blood vessel continue to be important outstanding hurdles. In addition, the path to commercialization for such tissues must be better defined. Continued progress in several complementary approaches to vascular tissue engineering is necessary before blood vessel substitutes can achieve their full potential in improving patient care.
PMCID: PMC2257983  PMID: 17961004
16.  Cartilage Tissue Engineering for Laryngotracheal Reconstruction: Comparison of Chondrocytes from Three Anatomic Locations in the Rabbit* 
Tissue engineering  2007;13(4):843-853.
Tissue engineering may provide a technique to generate cartilage grafts for laryngotracheal reconstruction in children. The present study used a rabbit model to characterize cartilage generated by a candidate tissue engineering approach to determine, under baseline conditions, which chondrocytes in the rabbit produce tissue-engineered cartilage suitable for in vivo testing in laryngotracheal reconstruction. We characterized tissue-engineered cartilage generated in perfused bioreactor chambers from three sources of rabbit chondrocytes: articular, auricular, and nasal cartilage. Biomechanical testing and histological, immunohistochemical, and biochemical assays were performed to determine equilibrium unconfined compression (Young's) modulus, and biochemical composition and structure. We found that cartilage samples generated from articular or nasal chondrocytes lacked the mechanical integrity and stiffness necessary for completion of the biomechanical testing, but five of six auricular samples completed the biomechanical testing (moduli of 210 ± 93 kPa in two samples at 3 weeks and 100 ± 65 kPa in three samples at 6 weeks). Auricular samples showed more consistent staining for proteoglycans and collagen II and had significantly higher glycosaminoglycan (GAG) content and concentration and higher collagen content than articular or nasal samples. In addition, the delayed gadolinium enhanced MRI of cartilage (dGEMRIC) method revealed variations in GAG spatial distribution in auricular samples that were not present in articular or nasal samples. The results indicate that, for the candidate tissue engineering approach under baseline conditions, only rabbit auricular chondrocytes produce tissue-engineered cartilage suitable for in vivotesting in laryngotracheal reconstruction. The results also suggest that this and similar tissue engineering approaches must be optimized for each potential source of chondrocytes.
PMCID: PMC2562571  PMID: 17394383
17.  Tissue Compatibility of Interfacial Polyelectrolyte Complexation Fibrous Scaffold: Evaluation of Blood Compatibility and Biocompatibility 
Tissue engineering  2007;13(2):423-433.
Interfacial polyelectrolyte complexation (PEC) fiber has been proposed as a biostructural unit and biological construct for tissue engineering applications, with its ability to incorporate proteins, drug molecules, DNA nanoparticles, and cells. In this study, we evaluated the biocompatibility and blood compatibility of PEC fiber in order to assess its potential for in vivo applications in tissue engineering. Although chitosan-alginate PEC fibrous scaffold was found to be thrombogenic, the blood compatibility of the scaffold could be significantly improved by incorporating a small amount of heparin in the polyelectrolyte solution during fiber formation. The platelet microparticle production and platelet adhesion on the chitosan-alginate-heparin fibrous scaffold were comparable to those on the resting control. In vitro cytotoxicity test showed that the scaffold was not toxic to human mesenchymal stem cells (hMSCs). In the in vivo biocompatibility test in rats, no acute inflammation was observed in the subcutaneously or intramuscularly implanted specimens. Good cell in-filtration and vascularization were observed after 2 months of implantations. Enhanced extracellular matrix (ECM) deposition was observed when hMSCs were cultured in the transforming growth factor-β3 (TGF-β3)-encapsulated PEC fibrous scaffold in vitro, or when the TGF-β3-encapsulated PEC was implanted intramuscularly in vivo. The results showed that this versatile PEC fibrous scaffold could be used in various tissue engineering applications for its good biocompatible and blood compatible properties.
PMCID: PMC2440513  PMID: 17518574
18.  A Rapid Seeding Technique for the Assembly of Large Cell/Scaffold Composite Constructs* 
Tissue engineering  2006;12(7):1851-1863.
These studies address critical technical issues involved in creating human mesenchymal stem cell (hMSC)/scaffold implants for cartilage repair. These issues include obtaining a high cell density and uniform spatial cell distribution within the scaffold, factors that are critical in the initiation and homogeneity of chondrogenic differentiation. For any given scaffold, the initial seeding influences cell density, retention, and spatial distribution within the scaffold, which eventually will affect the function of the construct. Here, we discuss the development of a vacuum-aided seeding technique for HYAFF®-11 sponges which we compared to passive infiltration. Our results show that, under the conditions tested, hMSCs were quantitatively and homogeneously loaded into the scaffolds with 90+% retention rates after 24 h in perfusion culture with no negative effect on cell viability or chondrogenic potential. The retention rates of the vacuum-seeded constructs were at least 2 times greater than those of passively seeded constructs at 72 h. Histomorphometric analysis revealed that the core of the vacuum-seeded constructs contained 240% more cells than the core of passively infiltrated scaffolds. The vacuum seeding technique is safe, rapid, reproducible, and results in controlled quantitative cell loading, high retention, and uniform distribution.
PMCID: PMC1858629  PMID: 16889515
19.  Chondrogenic Differentiation on Perlecan Domain I, Collagen II and Bone Morphogenetic Protein 2-Based Matrices 
Tissue engineering  2006;12(7):2009-2024.
Extracellular matrix (ECM) molecules in cartilage, cooperate with growth factors to regulate chondrogenic differentiation and cartilage development. Domain I of perlecan (Pln) bears heparan sulfate chains that bind and release heparin binding growth factors (HBGFs). Our hypothesis was that Pln domain I (PlnDI) might be complexed with collagen II (P-C) fibrils to improve binding of bone morphogenetic protein-2 (BMP-2) and better support chondrogenesis and cartilage-like tissue formation in vitro. Our results showed that P-C fibrils bound more BMP-2 than collagen II fibrils alone, and better sustained BMP-2 release. Polylactic acid (PLA)-based scaffolds coated with P-C fibrils immobilized more BMP-2 than either PLA scaffolds or PLA scaffolds coated with collagen II fibrils alone. Multipotential mouse embryonic mesenchymal cells, C3H10T1/2, were cultured on two-dimensional P-C fibrils or three dimensional P-C/BMP-2-coasted (P-C-B) PLA scaffolds. Chondrogenic differentiation was indexed by glycosaminoglycan (GAG) production, and expression of the pro-chondrogenic transcription factor, Sox9, as well as cartilaginous ECM proteins, collagen II and aggrecan. Immunostaining for aggrecan, perlecan, tenascin and collagen X revealed that both C3H10T1/2 cells and primary mouse embryonic fibroblasts cultured on P-C-B fibrils showed the highest expression of chondrogenic markers among all treatment groups. Safranin O-Fast Green staining indicated that cartilage-like tissue was formed in the P-C-B scaffolds, while no obvious cartilage-like tissue formed in other scaffolds. We have concluded that P-C fibrils provide an improved biomimetic material for the binding and retention of BMP-2 and support chondrogenenic differentiation.
PMCID: PMC1774589  PMID: 16889529
Chondrogenesis; Perlecan; Bone Morphogenetic Protein-2 (BMP-2); Collagen II; Mesenchymal Cells; Tissue Engineering
20.  Perlecan Domain I Promotes Fibroblast Growth Factor 2 Delivery in Collagen I Fibril Scaffolds 
Tissue engineering  2005;11(1-2):76-89.
Perlecan, a heparan sulfate proteoglycan, is widely distributed in developing and adult tissues and plays multiple, important physiological roles. Studies with knockout mouse models indicate that expression of perlecan and heparan sulfate is critical for proper skeletal morphogenesis. Heparan sulfate chains bind and potentiate the activities of various growth factors such as fibroblast growth factor 2 (FGF-2). Previous studies indicate that important biological activities are associated with the heparan sulfate-bearing domain I of perlecan (PlnDI; French et al. J. Bone Miner. Res. 17, 48, 2002). In the present study, we have used recombinant, glycosaminoglycan-bearing PlnDI to reconstitute three-dimensional scaffolds of collagen I. Collagen I fibrils bound PlnDI much better than native collagen I monomers or heat-denatured collagen I preparations. Heparitinase digestion demonstrated that recombinant PlnDI was substituted with heparan sulfate and that these heparan sulfate chains were critically important not only for efficient integration of PlnDI into scaffolds, but also for FGF-2 binding and retention. PlnDI-containing collagen I scaffolds to which FGF-2 was bound sustained growth of both MG63, an osteoblastic cell line, and human bone marrow stromal cells (hBMSCs) significantly better than scaffolds lacking either PlnDI or FGF-2. Collectively, these studies demonstrate the utility of PlnDI in creating scaffolds that better mimic natural extracellular matrices and better support key biological activities.
PMCID: PMC1635240  PMID: 15738663
21.  Polyglycolic acid induced inflammation 
Tissue engineering  2006;12(2):301-308.
Tissue and organ replacement have quickly outpaced available supply. Tissue bioengineering holds the promise for additional tissue availability. Various scaffolds are currently used, whereas polyglycolic acid (PGA), which is currently used in absorbable sutures and orthopedic pins, provides an excellent support for tissue development. Unfortunately, PGA can induce a local inflammatory response following implantation, so we investigated the molecular mechanism of inflammation in vitro and in vivo. Degraded PGA induced an acute peritonitis, characterized by neutrophil (PMN) infiltration following intraperitoneal injection in mice. Similar observations were observed using the metabolite of PGA, glycolide. Dissolved PGA or glycolide, but not native PGA, activated the classical complement pathway in human sera, as determined by classical complement pathway hemolytic assays, C3a and C5a production, C3 and immunoglobulin deposition. To investigate whether these in vitro observations translated to in vivo findings, we used genetically engineered mice. Intraperitoneal administration of glycolide or dissolved PGA in mice deficient in C1q, factor D, C1q and factor D or C2 and factor B demonstrated significantly reduced PMN infiltration compared to congenic controls (WT). Mice deficient in C6 also demonstrated acute peritonitis. However, treatment of WT or C6 deficient mice with a monoclonal antibody against C5 prevented the inflammatory response. These data suggest that the hydrolysis of PGA to glycolide activates the classical complement pathway. Further, complement is amplified via the alternative pathway and inflammation is induced by C5a generation. Inhibition of C5a may provide a potential therapeutic approach to limit the inflammation associated with PGA derived materials following implantation.
PMCID: PMC1769522  PMID: 16548688
tissue bioengineering; C5a; peritonitis; neutrophils
22.  Human Endothelial Cell Interaction with Biomimetic Surfactant Polymers Containing Peptide Ligands from the Heparin Binding Domain of Fibronectin 
Tissue engineering  2005;11(1-2):226-236.
Biomimetic materials that mimic the extracellular matrix (ECM) provide a means to control cellular functions such as adhesion and growth, which are vital to successful engineering of tissue-incorporated biomaterials. Novel “ECM-like” biomimetic surfactant polymers consisting of a poly(vinyl amine) backbone with pendant cell-adhesive peptides derived from one of the heparin-binding domains of fibronectin were developed to improve endothelial cell adhesion and growth on vascular biomaterials. Heparin-binding peptide (HBP) sequences, alone and in combination with RGD peptides, were examined for their ability to promote human pulmonary artery endothelial cell (HPAEC) adhesion and growth (HBP1, WQPPRARI; HBP2, SPPRRARVT; HBP1:RGD; and HBP2:RGD) and compared with cell adhesion and growth on fibronectin and on negative control polymer surfaces in which alanines were substituted for the positively charged arginine residues in the two peptides. The results showed that HPAECs adhered and spread equally well on all HBP-containing polymers and the positive fibronectin control, showing similar stress fiber and focal adhesion formation. However, the HBP alone was unable to support long-term HPAEC growth and survival, showing a loss of focal adhesions and cytoskeletal disorganization by 24 h after seeding. With the addition of RGD, the surfaces behaved similarly or better than fibronectin. The negative control polymers showed little to no initial cell attachment, and the addition of soluble heparin to the medium reduced initial cell adhesion on both the HBP2 and HBP2:RGD surfaces. These results indicate that the HBP surfaces promote initial HPAEC adhesion and spreading, but not long-term survival.
PMCID: PMC1236992  PMID: 15738677

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