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PubMed2003

[Tissue engineering in urology. Basic principles and application].

Tissue engineering is a rather new field of science. Despite this fact, some experimental investigations have already been applied in clinical studies. Compared to other medical fields, tissue engineering in urology is well established. Tissue-engineered bulking agents and tissue-engineered bladder augments are being investigated in clinical trials. Even though the knowledge gained in recent years is promising, the results of cellular therapies need to be critically judged before being finally applied in patients. Genetic engineering and stem cell research (adult undifferentiated cells) have had major impact on the field of tissue engineering over the past 2 years. By using the technology of genetic engineering, biochemical and functional qualities of tissues may be modified. Adult stem cells may help to substitute lost tissue in an autologous fashion by isolating undifferentiated cells from the body and by differentiating them into a desired cell type. These cells may be used to form native functional tissue to replace a diseased organ or organ part.

Adult↗
PubMed2000

Sustained release of vascular endothelial growth factor from mineralized poly(lactide-co-glycolide) scaffolds for tissue engineering.

Strategies to engineer bone tissue have focused on either: (1) the use of scaffolds for osteogenic cell transplantation or as conductive substrates for guided bone regeneration; or (2) release of inductive bioactive factors from these scaffold materials. This study describes an approach to add an inductive component to an osteoconductive scaffold for bone tissue engineering. We report the release of bioactive vascular endothelial growth factor (VEGF) from a mineralized, porous, degradable polymer scaffold. Three dimensional, porous scaffolds of the copolymer 85 : 15 poly(lactide-co-glycolide) were fabricated by including the growth factor into a gas foaming/particulate leaching process. The scaffold was then mineralized via incubation in a simulated body fluid. Growth of a bone-like mineral film on the inner pore surfaces of the porous scaffold is confirmed by mass increase measurements and quantification of phosphate content within scaffolds. Release of 125I-labeled VEGF was tracked over a 15 day period to determine release kinetics from the mineralized scaffolds. Sustained release from the mineralized scaffolds was achieved, and growth of the mineral film had only a minor effect on the release kinetics from the scaffolds. The VEGF released from the mineralized and non-mineralized scaffolds was over 70% active for up to 12 days following mineralization treatment, and the growth of mineral had little effect on total scaffold porosity.

Biocompatible Materials↗
PubMed2000

[Tissue engineering: possibilities and perspectives].

Successful tissue engineering requires intensive co-oporation between clinicians, biologists (cell culture, gene therapy), chemical engineers (biomaterials) and industrial partners. In case of wound healing tissue engineered constructs have already been applied successfully in burns and chronic wounds. In order to improve carrier and matrix function biomaterials still have to be optimized. The potential of such constructs might even be enhanced by gene therapeutical methods. The complex mammalian organism has to be considered as the gold standard and the model for perfect tissue engineering. The problem of vascularization of complex organs yet has to be solved. In general it seems to be more promising to substitute deficient components in vivo and to rely on modulating influences within the host organism rather than to create complex organs ex vivo.

Animals↗
PubMed2000

Biomaterial developments for bone tissue engineering.

The development of bone tissue engineering is directly related to changes in materials technology. While the inclusion of materials requirements is standard in the design process of engineered bone substitutes, it is also critical to incorporate clinical requirements in order to engineer a clinically relevant device. This review presents the clinical need for bone tissue-engineered alternatives to the present materials used in bone grafting techniques, a status report on clinically available bone tissue-engineering devices, and recent advances in biomaterials research. The discussion of ongoing research includes the current state of osseoactive factors and the delivery of these factors using bioceramics and absorbable biopolymers. Suggestions are also presented as to the desirable design features that would make an engineered device clinically effective.

Biocompatible Materials↗
PubMed1998

Tissue engineering: generation of differentiated artificial tissues for biomedical applications.

A new field in biomedical science has been established. Cell biologists, engineers, and surgeons now work within a team. Artificial connective, epithelial, or neuronal tissues are being constructed using living cells and different kinds of biomaterials. Numerous companies and laboratories are presenting dynamic developments in this field. Prognoses predict that, at the beginning of the coming century, the industry of tissue engineering will reach the importance of the present genetic technology. An enormous demand for organ and tissue transplants motivates research activities and drives the acquisition of innovative techniques and creative solutions. At the front of this development is the creation of artificial skin for severely burned patients and the generation of artificial cartilage for implantation in articular joint diseases. Future challenges are the construction of liver organoids and the development of an artificial kidney on the basis of cultured cells. In this paper we show strategies, needs, tools, and equipment for tissue engineering. The presupposition for all projects is the induction, development, and maintenance of differentiation within the tissue under in vitro conditions. As experiments in conventional culture dishes continued to fail, new cell and tissue culture methods had to be developed. Tissues are cultured under conditions as close as possible to their natural environment. To optimize adherence or embedding, cells are grown on novel tissue carriers and on individually selected biomatrices or scaffolds. The tissues are subsequently transferred into different types of containers for permanent perfusion with fresh culture medium. This guarantees constant nutrition of the developing tissue and prevents the accumulation of harmful metabolites. An organo-typical environment for epithelial cells, for example, is obtained in gradient containers, which are permanently superfused at the apical and basal sides with different media. Long term experiments result in cultured tissues in a quality thus far unreached.

Biomedical Engineering↗
PubMed2002

[Clinical application of tissue-engineered autologous oral mucosa transplants].

BACKGROUND: Tissue engineering of autogenous oral mucosa is a significant enrichment for various indications in oral and maxillofacial surgery. Besides preprosthetic surgery and prelamination of microvascular fasciocutaneous flaps, interdisciplinary work such as reconstruction procedures in cases of hypospadias and epispadias are the main indications for tissue-engineered oral mucosa. RESULTS: One main advantage of this technique is the reduction of second surgical procedures. The morbidity is decreased and the quality of life may be significantly increased. The manufacture of tissue-engineered autogenous oral mucosa up to 15 cm(2) requires a small biopsy of oral mucosa (4-8 mm(3)) and 40 ml of autogenous serum. DISCUSSION: The clinical and morphological long-term follow-up after different surgical procedures with tissue-engineered oral mucosa establishes this technique as an excellent additional tool in oral and maxillofacial surgery.

Female↗
PubMed2001

Construction and biological characterization of an HB-GAM/FGF-1 chimera for vascular tissue engineering.

OBJECTIVE: Cardiovascular tissue engineering approaches to vessel wall restoration have focused on the potent but relatively nonspecific and heparin-dependent mesenchymal cell mitogen fibroblast growth factor 1 (FGF-1). We hypothesized that linking FGF-1 to a sequence likely to bind to cell surface receptors relatively more abundant on endothelial cells (ECs) might induce a relative greater EC bioavailability of the FGF-1. We constructed a heparin-binding growth-associated molecule (HB-GAM)/FGF-1 chimera by linking full-length human HB-GAM to the amino-terminus of human FGF-1beta (21-154) and tested its activities on smooth muscle cells (SMCs) and ECs. METHODS: Primary canine carotid SMCs and jugular vein ECs were plated in 96-well plates in media containing 10% fetal bovine serum and grown to approximately 80% confluence. After being growth arrested in serum-free media for 24 hours, the cells were exposed to concentration ranges of cytokines and heparin, and proliferation was measured with tritiated-thymidine incorporation. Twenty percent fetal bovine serum was used as positive control, and phosphate-buffered saline was used as negative control. RESULTS: In the presence of heparin the HB-GAM/FGF-1 chimera stimulated less SMC proliferation than did the wild-type FGF-1 with a median effective dose of approximately 0.3 nmol versus approximately 0.1 nmol (P <.001). By contrast, the chimera retained full stimulating activity on EC proliferation with a median effective dose of 0.06 nmol for both cytokines. Unlike the wild-type protein, the chimera possessed heparin-independent activity. In the absence of heparin, the chimera induced dose-dependent EC and SMC proliferation at 0.06 nmol or more compared with the wild-type FGF-1, which stimulated minimal DNA synthesis at 6.0-nmol concentrations. CONCLUSIONS: The HB-GAM/FGF-1 chimera displays significantly greater and uniquely heparin-independent mitogenic activity for both cell types, and in the presence of heparin it displays a significantly greater EC specificity.

Animals↗
PubMed1996

Tissue engineering and autologous transplant formation: practical approaches with resorbable biomaterials and new cell culture techniques.

The engineering of living tissues in vivo requires new concepts in cell culture technology. In contrast to conventional cell cultures, the development of tissues depends on a three-dimensional arrangement of cells and the formation or synthesis of an appropriate extracellular matrix. Special emphasis is given to the major role of the extracellular matrix and cell differentiation in an artificial tissue. New technical approaches of in vitro tissue engineering are compared to the natural development of tissues in vivo. Current methods using resorbable biomaterials, tissue encapsulation and perfusion culture are discussed. Major consideration is given to scaffold structures of biomaterials that define a three-dimensional shape of a tissue or guide matrix formation. The different goals of tissue engineering such as in vitro models and transplant production are taken into account in the described techniques. Practical concepts comprising cell multiplication and differentiation in subsequent steps for future clinical applications are outlined.

Animals↗
PubMed1999

Bioreactor development for tissue-engineered cartilage.

The development of tissue engineered cartilage is emerging as a potential treatment for the repair of cartilage defects. By seeding chondrocytes onto poly-glycolic acid (PGA) biodegradable scaffolds within a convective-flow bioreactor, the synthesis of tissue-engineered articular cartilage has been recently demonstrated. The ability to cultivate and manipulate this cell-polymer construct to possess specific dimensions, as well as biochemical and biomechanical properties is critical for potential application as an in vivo therapy of damaged articular surfaces. Bioreactor design requirements for stages from research to development to commercialization are discussed. Advantages and limitations to various bioreactor designs are critiqued. These studies illustrate the ability to synthesize tissue-engineered cartilage under convective-flow conditions for potential human tissue repair.

Bioreactors↗
PubMed1992

Tissue engineering in the USA.

Tissue engineering is the application of the principles and methods of engineering and the life sciences towards the development of biological substitutes to restore, maintain or improve functions. It is an area which is emerging in importance worldwide. In the USA it has been actively fostered by the National Science Foundation, both through research grants and the sponsorship of a series of workshops starting in 1988. This brief review of activities in the USA focuses on cell culture technology as a foundation for tissue engineering and then discusses examples of applications. These include artificial skin and the use of encapsulated cells in the development of bioartificial organs. Also discussed is the reconstitution of a blood vessel in culture, both for use in basic research and for implantation as an artificial blood vessel in bypass surgery. In conclusion, other potential applications are mentioned as well as generic areas of technology for future development.

Artificial Organs↗
PubMed2001

A tissue engineered cell-occlusive device for hard tissue regeneration--a preliminary report.

Tissue engineering is an emerging discipline that applies engineering principles to create devices for the study, restoration, modification, and assembly of functional tissues and organs from native or synthetic sources. In the field of guided bone regeneration (GBR), cellular matter engineering has been applied, more or less successfully, to the development of biodegradable and bioresorbable devices with chemical, physical, or mechanical properties, structure, or form that permit active tissue integration with desirable cell types and tissue components. The employment of synthetic and naturally occurring polymers as well as sophisticated manufacturing technologies allow the tissue engineering of matrix configurations so that the biophysical limitations of mass transfer can be satisfied. The configuration of such a hybrid matrix can also be manipulated to vary the surface area available for cell attachment, as well as to optimize the exposure of the attached cells to nutrients. A biodegradable and bioresorbable device made of synthetic and natural polymers was engineered specifically for GBR procedures. The degradation and resorption kinetics as well as the mechanical properties give the device the potential to function as a carrier for bone growth factors. This innovative device was applied as a GBR membrane in a clinical investigation in seven patients.

Absorbable Implants↗
PubMed2000

[Study of human tissue engineering cartilage].

OBJECTIVE: To investigate the technique of human tissue-engineered cartilage and to study the medical collagen membrane of guided tissue regeneration (GTR) as the carrier of in vitro chondrocytes culture. METHODS: Tissue engineering technique was used to make human Tissue-engineered cartilage, which was examined histologically and functionally. RESULTS: It was found that the chondrocytes seeded on the medical collagen membrane of GTR grew well. A layer of milk white and cartilage-like tissue grew on the surface of medical collagen membrane of GTR after 1 week. It was demonstrated that the cartilage-like tissue was strong enough to be transferred after being implanted for 8 weeks. The cartilage-like tissue was proved to be human tissue engineered cartilage by HE stain and Alcian blue-poncean S stain. The chondrocytes could secrete chondroitin sulfate as proved by Lev-Spicer stain. CONCLUSIONS: The medical collagen membrane of GTR has characteristics of three-dimensional structure and cell reticular function, and it has the possibility to be developed as a natural scaffold for tissue engineering. The results indicate that it is possible to make human tissue-engineered cartilage with tissue-engineering technique.

Animals↗
PubMed1999

Poly(alpha-hydroxyl acids)/hydroxyapatite porous composites for bone-tissue engineering. I. Preparation and morphology.

Tissue engineering has shown great promise for creating biological alternatives for implants. In this approach, scaffolding plays a pivotal role. Hydroxyapatite mimics the natural bone mineral and has shown good bone-bonding properties. This paper describes the preparation and morphologies of three-dimensional porous composites from poly(L-lactic acid) (PLLA) or poly(D,L-lactic acid-co-glycolic acid) (PLGA) solution and hydroxyapatite (HAP). A thermally induced phase separation technique was used to create the highly porous composite scaffolds for bone-tissue engineering. Freeze drying of the phase-separated polymer/HAP/solvent mixtures produced hard and tough foams with a co-continuous structure of interconnected pores and a polymer/HAP composite skeleton. The microstructure of the pores and the walls was controlled by varying the polymer concentration, HAP content, quenching temperature, polymer, and solvent utilized. The porosity increased with decreasing polymer concentration and HAP content. Foams with porosity as high as 95% were achieved. Pore sizes ranging from several microns to a few hundred microns were obtained. The composite foams showed a significant improvement in mechanical properties over pure polymer foams. They are promising scaffolds for bone-tissue engineering.

Adhesiveness↗
PubMed2000

Tissue engineering of vascular grafts.

The challenge of tissue engineering blood vessels with the mechanical properties of native vessels, and with the anti-thrombotic properties required is immense. Recent advances, however, indicate that the goal of providing a tissue-engineered vascular graft that will remain patent in vivo for substantial periods of time, is achievable. For instance, collagen gels have been used to fabricate a tissue in vitro that is representative of a native vessel: an acellular collagen tubular structure, when implanted as a vascular graft, was able to function, and to become populated with host cells. A completely cellular approach culturing cells into tissue sheets and wrapping these around a mandel was able to form a layered tubular structure with impressive strength. Culture of cells onto a biodegradable scaffold within a dynamic bioreactor, generated a tissue-engineered vascular graft with substantial stiffness and, when lined with endothelial cells, was able to remain patent for up to 4 weeks in vivo. In our experiments, use of a non-degradable polyurethane scaffold and culture with smooth muscle cells generated a construct with mechanical properties similar to native vessels. This composite tissue engineered vascular graft with an endothelial layer formed using fluid shear stress to align the endothelial cells, was able to remain patent with an neointima for up to 4 weeks. These results show that tissue engineering of vascular grafts has true potential for application in the clinical situation.

Biocompatible Materials↗
PubMed1999

Cardiac tissue engineering: cell seeding, cultivation parameters, and tissue construct characterization.

Cardiac tissue engineering has been motivated by the need to create functional tissue equivalents for scientific studies and cardiac tissue repair. We previously demonstrated that contractile cardiac cell-polymer constructs can be cultivated using isolated cells, 3-dimensional scaffolds, and bioreactors. In the present work, we examined the effects of (1) cell source (neonatal rat or embryonic chick), (2) initial cell seeding density, (3) cell seeding vessel, and (4) tissue culture vessel on the structure and composition of engineered cardiac muscle. Constructs seeded under well-mixed conditions with rat heart cells at a high initial density ((6-8) x 10(6) cells/polymer scaffold) maintained structural integrity and contained macroscopic contractile areas (approximately 20 mm(2)). Seeding in rotating vessels (laminar flow) rather than mixed flasks (turbulent flow) resulted in 23% higher seeding efficiency and 20% less cell damage as assessed by medium lactate dehydrogenase levels (p < 0.05). Advantages of culturing constructs under mixed rather than static conditions included the maintenance of metabolic parameters in physiological ranges, 2-4 times higher construct cellularity (p &le 0.0001), more aerobic cell metabolism, and a more physiological, elongated cell shape. Cultivations in rotating bioreactors, in which flow patterns are laminar and dynamic, yielded constructs with a more active, aerobic metabolism as compared to constructs cultured in mixed or static flasks. After 1-2 weeks of cultivation, tissue constructs expressed cardiac specific proteins and ultrastructural features and had approximately 2-6 times lower cellularity (p < 0.05) but similar metabolic activity per unit cell when compared to native cardiac tissue.

Animals↗
PubMed2001

Tissue-engineered heart valve leaflets: an animal study.

BACKGROUND: Tissue-engineered heart valve leaflets are a promising way to overcome the inherent limitations of current prosthetic valves. The aim of this study was to compare the biological responses of an autologous cell seeded scaffold and an acellular scaffold implanted in the pulmonary valve leaflet in the same animal. METHODS: Myofibroblasts and endothelial cells were isolated and cultured from an ovine artery. A synthetic biodegradable scaffold consisting of polyglycolic acid and polylactic acid was initially seeded with the myofibroblasts, then coated with endothelial cells. Cells were seeded using a medium containing collagen and cultured. A tissue-engineered construct and a plain scaffold were implanted as double pulmonary valve leaflet replacement in the same animal in an ovine model (n=3). Additionally, the tissue-engineered construct (n=2) and the plain scaffold (n=2) were implanted as single valve leaflet replacements for long-term analysis. After sacrifice, the implanted valve leaflet tissues were retrieved, analyzed visually and using light microscopy. RESULTS: Three animals that underwent replacement of two valve leaflets with a tissue-engineered construct and a plain scaffold, survived only a short-time (12, 24, 36 hours). The death was attributed to heart failure caused by severe pulmonary insufficiency. Animals that underwent single valve leaflet replacement survived longer and were electively sacrificed at 6 and 9 weeks after operation. The analysis of the leaflets from the short-term survivors showed that the tissue-engineered constructs contained less fibrins and protein exudates than the plain scaffold. In contrast, leaflets obtained from animals surviving 6 and 9 weeks showed similar well organized granulation tissues in the tissue-engineered constructs and the plain scaffolds. CONCLUSION: This animal experiment demonstrates that in the early phase of implantation, the tissue-engineered construct shows a better biological response in terms of antithrombogenicity than the plain scaffold, although both of them have similar results in the later reparative phase.

Animals↗