Showing papers in "Tissue Engineering Part A in 2007"

Tissue Engineering by Self-Assembly of Cells Printed into Topologically Defined Structures

Abstract: Understanding the principles of biological self-assembly is indispensable for developing efficient strategies to build living tissues and organs. We exploit the self-organizing capacity of cells an...

Periodontal Tissue Regeneration with Adipose-Derived Stem Cells

Abstract: A number of surgical techniques have been developed to promote periodontal tissue regeneration. Bone marrow-derived stem cells have also been shown to promote periodontal tissue regeneration. In this study, we sought to determine whether adipose-derived stem cells (ASCs) can promote periodontal tissue regeneration as well. ASCs were isolated from a Wistar rat, passaged twice, mixed with platelet-rich plasma (PRP) obtained from inbred rats, and implanted into the periodontal tissue defect that had been generated in the test rats. Tissue specimens were harvested after 2, 4, and 8 weeks for histological analysis. Rats that received PRP only or were not implanted served as controls. A small amount of alveolar bone regeneration was observed 2 and 4 weeks after ASC/PRP implantation. Moreover, 8 weeks after implantation, a periodontal ligament-like structure was observed along with alveolar bone. These observations suggest that ASCs can promote periodontal tissue regeneration in vivo. Because large amounts of human lipoaspirates are readily available, and their procurement induces only low morbidity, ASCs may be useful in future clinical cell-based therapy for periodontal disease.

An islet-stabilizing implant constructed using a preformed vasculature.

Abstract: Islet transplantation for the purpose of treating insulin-sensitive diabetes is currently limited by several factors, including islet survival posttransplantation. In the current study, a tissue-engineered prevascularized pancreatic encapsulating device (PPED) was developed. Isolated islets were placed in collagen gels, and they exhibited fourfold more insulin release than islets not in collagen. The insulin released by β-cells in islets encapsulated in collagen exhibited unobstructed diffusion within the collagen gels. Subsequent studies evaluated the ability to create a sandwich comprised of two layers of prevascularized collagen gels around a central collagen gel containing islets. In vitro characterization of the islets showed that islets are functional and responded to glucose stimulation. The PPEDs were implanted subcutaneously into severe combined immunodeficient mice. Islet survival was assessed after 7, 14, and 28 days. Immunohistochemical analysis was performed on the implants to detect insulin ...

A biomaterial composed of collagen and solubilized elastin enhances angiogenesis and elastic fiber formation without calcification.

Abstract: Elastin is the prime protein in elastic tissues that contributes to elasticity of, for example, lung, aorta, and skin Upon injury, elastic fibers are not readily replaced, which hampers tissue regeneration Incorporation of solubilized elastin (hydrolyzed insoluble elastin fibers or elastin peptides) in biomaterials may improve regeneration, because solubilized elastin is able to promote proliferation as well as elastin synthesis Porous biomaterials composed of highly purified collagen without and without elastin fibers or solubilized elastin were prepared by freezing and lyophilization Solubilized elastin formed spherical structures that were incorporated in the collagenous part of the scaffolds and that persisted after chemical crosslinking of the scaffolds Crosslinked scaffolds were subcutaneously implanted in young Sprague Dawley rats Collagen-solubilized elastin and collagen scaffolds showed no calcification in this sensitive calcification model, in contrast to scaffolds containing elastin fibers Collagen-solubilized elastin scaffolds also induced angiogenesis, as revealed by type IV collagen staining, and promoted elastic fiber synthesis, as shown with antibodies against rat elastin and fibrillin-1 It is concluded that scaffolds produced from collagen and solubilized elastin present a non-calcifying biomaterial with a capacity for soft-tissue regeneration, especially in relation to elastic fiber synthesis

In vivo pulmonary tissue engineering: contribution of donor-derived endothelial cells to construct vascularization.

Abstract: Intrapulmonary engraftment of engineered lung tissues could provide a potential therapeutic approach for the treatment of pediatric and adult pulmonary diseases. In working toward this goal, we rep...

Isolation and Cultivation of Integrin α6β1–Expressing Salivary Gland Graft Cells: A Model for Use with an Artificial Salivary Gland

Abstract: Regeneration of the salivary glands' (SGs) normal function for patients with cancer of the head and neck treated with irradiation would be a major contribution to their quality of life. This could be accomplished by re-implantation of autologous SG cells into the residual irradiated tissue or by implantation of tissue-engineered artificial SGs. Both methods depend on the isolation of cells able to propagate and differentiate into SG epithelial cells. Recently, it has been shown that SG integrin alpha(6)beta(1)-expressing (SGIE) cells have stem cell capabilities, but these cells could be isolated only after duct ligation insult requiring surgical intervention. Because such an invasive procedure is not clinically acceptable for these patients, our aim in the present study was to explore the use of immuno-magnetic separation of untreated and short heat stress-conditioned rats as a less-insulting methodology for enhancement of these cells. Our results show that submandibular SGIE cells could be isolated and cultivated from untreated animals. However, short heat stress (HS) increased the number of isolated SGIE cells 4.7-fold and their proliferation and clonal capability 4.6-fold and 3 fold, respectively. We believe that SGIE graft cells may be suitable candidates for future tissue-engineered SGs that have been damaged by irradiation in patients with head and neck cancer.

Feasibility study of a novel urinary bladder bioreactor.

Abstract: We have devised a bioreactor to simulate normal urinary bladder dynamics. The design permits a cell-seeded scaffold made from a modified porcine acellular matrix to be placed between 2 closed chambers filled with culture medium and be mechanically stimulated in a physiologically relevant manner. Specifically designed software increased hydrostatic pressure from 0 to 10 cm of water in a linear fashion in 1 chamber, resulting in mechanical stretch and strain on the scaffold. Pressure was increased over 55 min (filling) and then decreased to 0 over 10 s (voiding). Commercially available small intestinal submucosa scaffolds were used to test the mechanical capabilities of the bioreactor, and pressure waveforms were generated for up to 18 h. Scaffolds were seeded with bladder smooth muscle or urothelial cells and incubated in the bioreactor, which generated pressure waveforms for 6 h. Scaffold integrity was preserved as seen through Masson's trichrome staining. No obvious contamination of the system was noted. Hematoxylin and eosin staining showed presence of cells after incubation in the bioreactor, and immunohistochemistry and real-time reverse transcriptase polymerase chain reaction suggested continued cellular activity. Cellular orientation tended to be perpendicular to the applied pressure. Preliminary results suggest that our bioreactor is a suitable model for simulating normal physiological conditions of bladder cycling in an ex vivo system.

Microstructures in 3D biological gels affect cell proliferation.

Abstract: Controlling the microscale environment in three-dimensional (3D) matrices for tissue engineering applications is a challenging but necessary goal. In this work, the effect of discrete microscale structures (microrods) on cell proliferation was assessed in 3D gels. Microrods were fabricated out of SU-8 with dimensions of 100 x 15 x 15 microm (L x H x W) and incorporated into Matrigel seeded with fibroblasts. The 3D microrod-Matrigel composite system inhibited proliferation of both primary and cell-line fibroblasts compared to cells seeded in Matrigel alone. To rule out bulk mechanical effects, the bulk shear modulus (G') and loss modulus (G") were assessed between 0.1 and 5 Hz for both Matrigel and microrod-Matrigel composites. The incorporation of microrods did not change the bulk stiffness of the gel. Moreover, it was determined that the chemistry of the microrod material itself did not inhibit cell proliferation. Therefore, results indicate that the presence of suspended microscale structures in three dimensions can regulate cell proliferation in a dose-dependent manner. This system provides a biocompatible, long-term way to modulate cell growth in 3D cultures and is amenable to in vivo applications.

Differential effects of natriuretic peptide stimulation on tissue-engineered cartilage.

Abstract: Tissue engineering is a promising approach for articular cartilage repair; however, it still has proven a challenge to produce substantial quantities of tissue from the limited number of cells that can be extracted from a single individual. Although several approaches have been investigated to enhance the production of cartilaginous tissue in vitro, relatively few techniques exist to reliably increase the population of cells needed for this approach. Alternatively, a single modulator of chondrocyte function, such as the C-type natriuretic peptide (CNP), may serve to address both of these issues. CNP is expressed in the growth plate and regulates cartilage growth through chondrocyte proliferation and differentiation. Thus, the purpose of this study was to determine the effects of CNP stimulation on tissue-engineered cartilage. Isolated bovine articular chondrocytes were seeded on Millicell filters and cultured in the presence of CNP (10 pM to 10 nM) for 4 weeks. Stimulation with CNP resulted in differential effects depending on the dose of the peptide. Low doses of CNP (10 to 100 pM) elicited chondrocyte proliferation with a maximal response observed at 100 pM (43% increase in cellularity). However, high doses of CNP (10 nM) stimulated matrix deposition (36% and 137% increase in proteoglycans and collagen) without an associated change in tissue cellularity. CNP stimulation also downregulated the expression of type X collagen, an early hypertrophic marker associated with endochondral ossification. Thus, by regulating the dose of CNP, it may be possible to produce engineered tissue from the limited number of cells that can be reasonably extracted from a single individual for therapeutic purposes.

Heparanase enhances early hepatocyte inclusion in the recipient liver after transplantation in partially hepatectomized rats.

Abstract: Hepatocyte transplantation is an emerging approach for the treatment of liver diseases. However, broad clinical application of this method has been limited by restricted source of cells and low efficiency of cell integration within the recipient liver. Heparanase cleaves heparan sulfate proteoglycans in the extracellular matrix and basement membrane, activity that affects cellular invasion associated with cancer metastasis and inflammation. This activity has a multifunctional effect on cell-cell interaction, cell adhesion, and angiogenesis. All these factors are important for successful integration of transplanted hepatocytes. Male donor hepatocytes pretreated with heparanase or untreated were transplanted into recipient female rat spleen following partial hepatectomy. Engraftment efficacy was evaluated by PCR for Y chromosome, histology and PCNA, and heparanase immunohistochemistry. In addition, proliferative activity of hepatocytes in vitro was determined by bromodeoxyuridine immunostaining. The number of heparanase-treated cells detected in the recipient liver was significantly increased three- to fivefold within 24-48 h posttransplantation and twofold at 14 days compared with untreated cells. The transplanted hepatocytes treated with heparanase were clearly seen inside portal vein radicles as cell aggregates up to 72 h posttransplantation. The number of portal radicles filled with heparanase-treated hepatocytes was increased compared to control early after transplantation. Heparanase treatment enhanced hepatocyte and sinusoidal endothelial cell proliferation in the liver, and hepatocyte proliferation within the spleen tissue. Preliminary in vitro studies with isolated hepatocytes treated with heparanase showed increased proliferative activity within 24-48 h of cell culture. These results suggest that preincubation of hepatocytes with heparanase increases the presence of hepatocytes within the recipient liver early following cell transplantation and stimulates both hepatocyte and sinusoidal endothelial cell proliferation.