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PubMed2003

Biodegradable synthetic polymers for tissue engineering.

This paper reviews biodegradable synthetic polymers focusing on their potential in tissue engineering applications. The major classes of polymers are briefly discussed with regard to synthesis, properties and biodegradability, and known degradation modes and products are indicated based on studies reported in the literature. A vast majority of biodegradable polymers studied belongs to the polyester family, which includes polyglycolides and polylactides. Some disadvantages of these polymers in tissue engineering applications are their poor biocompatibility, release of acidic degradation products, poor processability and loss of mechanical properties very early during degradation. Other degradable polymers such as polyorthoesters, polyanhydrides, polyphosphazenes, and polyurethanes are also discussed and their advantages and disadvantages summarised. With advancements in tissue engineering it has become necessary to develop polymers that meet more demanding requirements. Recent work has focused on developing injectable polymer compositions based on poly (propylene fumarate) and poly (anhydrides) to meet these requirements in orthopaedic tissue engineering. Polyurethanes have received recent attention for development of degradable polymers because of their great potential in tailoring polymer structure to achieve mechanical properties and biodegradability to suit a variety of applications.

Biocompatible Materials↗

PubMed2005

Midterm clinical result of tissue-engineered vascular autografts seeded with autologous bone marrow cells.

OBJECTIVE: Prosthetic and bioprosthetic materials currently in use lack growth potential and therefore must be repeatedly replaced in pediatric patients as they grow. Tissue engineering is a new discipline that offers the potential for creating replacement structures from autologous cells and biodegradable polymer scaffolds. In May 2000, we initiated clinical application of tissue-engineered vascular grafts seeded with cultured cells. However, cell culturing is time-consuming, and xenoserum must be used. To overcome these disadvantages, we began to use bone marrow cells, readily available on the day of surgery, as a cell source. The aim of the study was to assess the safety and feasibility of this technique for creating vascular tissue under low-pressure systems such as pulmonary artery or venous pressure. METHODS: Since September 2001, tissue-engineered grafts seeded with autologous bone marrow cells have been implanted in 42 patients. The patients or their parents were fully informed and had given consent to the procedure. A 5-mL/kg specimen of bone marrow was aspirated with the patient under general anesthesia before the skin incision. The polymer tube serving as a scaffold for the cells was composed of a copolymer of l -lactide and -caprolactone (50:50). This copolymer is degraded by hydrolysis. The matrix is more than 80% porous, and the diameter of each pore is 20 to 100 microm. Polyglycolic acid woven fabric with a thickness of 0.5 mm was used for reinforcement. Twenty-three tissue-engineered conduits (grafts for extracardiac total cavopulmonary connection) and 19 tissue-engineered patches were used for the repair of congenital heart defects. The patients' ages ranged from 1 to 24 years (median 5.5 years). All patients underwent a catheterization study, computed tomographic scan, or both, for evaluation after the operation. The patients received anticoagulation therapy for 3 to 6 months after surgery. RESULTS: Mean follow-up after surgery was 490 +/- 276 days (1.3-31.6 months, median 16.7 months). There were no complications such as thrombosis, stenosis, or obstruction of the tissue-engineered autografts. One late death at 3 months after total cavopulmonary connection was noted in patient with hypoplastic left heart syndrome; this was unrelated to the tissue-engineered graft function. There was no evidence of aneurysm formation or calcification on cineangiography or computed tomography. All tube grafts were patent, and the diameter of the tube graft increased with time (110% +/- 7 % of the implanted size). CONCLUSION: Biodegradable conduits or patches seeded with autologous bone marrow cells showed normal function (good patency to a maximum follow-up of 32 months). As living tissues, these vascular structures may have the potential for growth, repair, and remodeling. The tissue-engineering approach may provide an important alternative to the use of prosthetic materials in the field of pediatric cardiovascular surgery. Longer follow-up is necessary to confirm the durability of this approach.

Adolescent↗

PubMed2002

Recent development on computer aided tissue engineering--a review.

The utilization of computer-aided technologies in tissue engineering has evolved in the development of a new field of computer-aided tissue engineering (CATE). This article reviews recent development and application of enabling computer technology, imaging technology, computer-aided design and computer-aided manufacturing (CAD and CAM), and rapid prototyping (RP) technology in tissue engineering, particularly, in computer-aided tissue anatomical modeling, three-dimensional (3-D) anatomy visualization and 3-D reconstruction, CAD-based anatomical modeling, computer-aided tissue classification, computer-aided tissue implantation and prototype modeling assisted surgical planning and reconstruction.

Animals↗

PubMed2000

[Tissue engineering with mesenchymal stem cells for cartilage and bone regeneration].

Tissue engineering offers the possibility to fabricate living substitutes for tissues and organs by combining histogenic cells and biocompatible carrier materials. Pluripotent mesenchymal stem cells are isolated and subcultured ex vivo and then their histogenic differentiation is induced by external factors. The fabrication of bone and cartilage constructs, their combinations and gene therapeutic approaches are demonstrated. Advantages and disadvantages of these methods are described by in vitro and in vitro testing. The proof of histotypical function after implantation in vivo is essential. The use of autologous cells and tissue engineering methods offers the possibility to overcome the disadvantages of classical tissue reconstruction--donor site morbidity of autologous grafts, immunogenicity of allogenic grafts and loosening of alloplastic implants. Furthermore, tissue engineering widens the spectrum of surgical indications in bone and cartilage reconstruction.

Bone Regeneration↗

PubMed2006

Tissue engineering of autologous human heart valves using cryopreserved vascular umbilical cord cells.

BACKGROUND: Tissue engineering of autologous heart valves with the potential to grow and to remodel represents a promising concept in pediatric cardiovascular surgery. Currently we are exploring the impact of cryopreserved human umbilical cord cells (CHUCCs) for the fabrication of tissue-engineered heart valves for patients diagnosed prenatally with congenital heart lesions, potentially enabling heart valve replacement in the early years of life. METHODS: Human umbilical cord cells were isolated from vascular segments of umbilical cords and cryopreserved in a cell bank. After 12 weeks the cryopreserved cells were again expanded in culture and characterized by histology, immunohistochemistry, and proliferation assays. Trileaflet heart valve scaffolds were fabricated from a porous polymer (P4HB, Tepha Inc, Cambridge, MA) and sequentially seeded with CHUCCs (n = 10). Five of the heart valve constructs were grown for 7 days in a pulse duplicator and, as a control, five constructs were grown under static cell culture conditions for 7 days. Analysis of all tissue-engineered heart valves included histology, immunohistochemistry, electron microscopy, functional analysis, and biomechanical and biochemical examination. RESULTS: We found that CHUCCs remained viable after 12 weeks of cryopreservation and showed a myofibroblast-like morphology that stained positive for alpha-actin and fibroblast specific marker. Histology of the tissue-engineered heart valves showed layered tissue formation, including connective tissue between the inside and the outside of the porous scaffold. Immunohistochemistry was positive for collagen (types I, III, and IV), desmin, laminin, and alpha-actin. Electron microscopy showed that the cells had grown into the pores and formed a confluent tissue layer during maturation in the pulsatile flow system. Biochemical examination showed an increase of extracellular matrix formation in constructs after pulsatile flow exposure compared with the static control group. Functional analysis demonstrated a physiological increase of the intracellular Ca2+ concentration of the recultivated cells and the conditioned constructs after stimulation with histamine. CONCLUSIONS: This study demonstrates in vitro generation of viable and functional human heart valves based on CHUCCs and biomimetic flow culture systems. The CHUCCs demonstrated excellent growth potential and abilities of in vitro tissue formation. These findings suggest the potential benefit of establishing autologous human cell banks for pediatric patients diagnosed intrauterinely with congenital defects that will potentially require heart valve replacement in the early years of life.

Actins↗

PubMed2003

Photocrosslinked hyaluronic acid hydrogels: natural, biodegradable tissue engineering scaffolds.

Ideally, rationally designed tissue engineering scaffolds promote natural wound healing and regeneration. Therefore, we sought to synthesize a biomimetic hydrogel specifically designed to promote tissue repair and chose hyaluronic acid (HA; also called hyaluronan) as our initial material. Hyaluronic acid is a naturally occurring polymer associated with various cellular processes involved in wound healing, such as angiogenesis. Hyaluronic acid also presents unique advantages: it is easy to produce and modify, hydrophilic and nonadhesive, and naturally biodegradable. We prepared a range of glycidyl methacrylate-HA (GMHA) conjugates, which were subsequently photopolymerized to form crosslinked GMHA hydrogels. A range of hydrogel degradation rates was achieved as well as a corresponding, modest range of material properties (e.g., swelling, mesh size). Increased amounts of conjugated methacrylate groups corresponded with increased crosslink densities and decreased degradation rates and yet had an insignificant effect on human aortic endothelial cell cytocompatibility and proliferation. Rat subcutaneous implants of the GMHA hydrogels showed good biocompatibility, little inflammatory response, and similar levels of vascularization at the implant edge compared with those of fibrin positive controls. Therefore, these novel GMHA hydrogels are suitable for modification with adhesive peptide sequences (e.g., RGD) and use in a variety of wound-healing applications.

Absorbable Implants↗

PubMed2000

Tissue engineering: challenges and opportunities.

This article reviews the key developments in the tissue engineering field over the past several years. The issues related to the development of the components of tissue-engineered products including cells, biomaterials, and biomolecules, and their integration into safe and effective products are presented. Moreover, the article outlines the challenges to the commercialization of tissue-engineered products, and highlights the ongoing efforts by the American Society for Testing and Materials (ASTM) in developing standards for tissue-engineered medical products. Furthermore, funding opportunities at the Advanced Technology Program at NIST are presented. Published 2000 John Wiley & Sons, Inc.

Animals↗

PubMed2006

Tissue engineering of tooth crown, root, and periodontium.

Tissue engineering of teeth requires the coordinated formation of correctly shaped crowns, roots, and periodontal ligament. Previous studies have shown that the dental mesenchyme controls crown morphogenesis and epithelial histogenesis during tooth development in vivo, but little is known about the inductive potential of dissociated mesenchymal cells used in ex vivo cultures. A 2-step method is described in which, by using different types of reassociations between epithelial and mesenchymal tissues and/or cells from mouse embryos, reassociations were cultured in vitro before in vivo implantation. In vitro, the reassociated tissues developed and resulted in tooth-like structures that exhibited normal epithelial histogenesis and allowed the functional differentiation of odontoblasts and ameloblasts. After implantation, the reassociations formed roots and periodontal ligament, the latter connected to developing bone. The shape of the crown, initially suspected to depend on the integrity of the mesenchyme, could be modulated by adjusting the number of dissociated mesenchymal cells reassociated with the epithelial compartment. Based on these results, we propose a refined strategy for tooth tissue engineering that may help to eventually generate morphologically defined teeth.

Animals↗

PubMed1999

Muscle tissue engineering.

Only recently have scientists come to appreciate that many tissues and cell populations that were formerly considered to be in a terminally differentiated state are capable of division and or dedifferentiation. It is the goal of the tissue engineer to understand and redirect this potential. Muscle tissue-engineering efforts will be directed toward building in vitro replacements for in vivo problems. Tissue-engineering advances will be interdependent with advances in gene therapy techniques to restore function at a cellular level.

Animals↗

PubMedDate not supplied

Fetal and adult liver stem cells for liver regeneration and tissue engineering.

For the development of innovative cell-based liver directed therapies, e.g. liver tissue engineering, the use of stem cells might be very attractive to overcome the limitation of donor liver tissue. Liver specific differentiation of embryonic, fetal or adult stem cells is currently under investigation. Different types of fetal liver (stem) cells during development were identified, and their advantageous growth potential and bipotential differentiation capacity were shown. However, ethical and legal issues have to be addressed before using fetal cells. Use of adult stem cells is clinically established, e.g. transplantation of hematopoietic stem cells. Other bone marrow derived liver stem cells might be mesenchymal stem cells (MSC). However, the transdifferentiation potential is still in question due to the observation of cellular fusion in several in vivo experiments. In vitro experiments revealed a crucial role of the environment (e.g. growth factors and extracellular matrix) for specific differentiation of stem cells. Co-cultured liver cells also seemed to be important for hepatic gene expression of MSC. For successful liver cell transplantation, a novel approach of tissue engineering by orthotopic transplantation of gel-immobilized cells could be promising, providing optimal environment for the injected cells. Moreover, an orthotopic tissue engineering approach using bipotential stem cells could lead to a repopulation of the recipients liver with healthy liver and biliary cells, thus providing both hepatic functions and biliary excretion. Future studies have to investigate, which stem cell and environmental conditions would be most suitable for the use of stem cells for liver regeneration or tissue engineering approaches.

Animals↗

PubMed2003

Preadipocyte-loaded collagen scaffolds with enlarged pore size for improved soft tissue engineering.

Extended soft tissue defects after extensive deep burns or tumor resections are still an unresolved problem in plastic and reconstructive surgery. There is a clinical need for an adequate solution to this problem but currently, no adequate implant material is available for the correction of these defects. Since the autologous transplantation of mature adipose tissue gives poor results, this study explores the advantages of using human preadipocytes in collagen sponges for tissue reconstruction purposes. Human preadipocytes of young adults were isolated, cultured, seeded onto collagen sponges with uniform pore size, and implanted into immunodeficient mice. After 24 hours of incubation in vitro and after explantation at 3, 8, and 12 weeks, sponges were examined for macroscopic appearance, weight, thickness, histology, immuno-histochemistry, and ultrastructure. We find good penetration of cells into the scaffold, layers of adipose tissue, and new vessels on all grafts while controls appear unchanged. These results are promising for improving the reconstruction of soft tissue defects.

Adipocytes↗

PubMed2006

Technology Insight: adult stem cells in cartilage regeneration and tissue engineering.

Articular cartilage, the load-bearing tissue of the joint, has limited repair and regeneration potential. The scarcity of treatment modalities for large chondral defects has motivated attempts to engineer cartilage tissue constructs that can meet the functional demands of this tissue in vivo. Cartilage tissue engineering requires three components: cells, scaffold, and environment. Adult stem cells, specifically multipotent mesenchymal stem cells, are considered the cell type of choice for tissue engineering, because of the ease with which they can be isolated and expanded and their multilineage differentiation capabilities. Successful outcome of cell-based cartilage tissue engineering ultimately depends on the proper differentiation of stem cells into chondrocytes and the assembly of the appropriate cartilaginous matrix to achieve the load-bearing capabilities of the natural articular cartilage. Multiple requirements, including growth factors, signaling molecules, and physical influences, need to be met. Adult mesenchymal stem-cell-based tissue engineering is a promising technology for the development of a transplantable cartilage replacement to improve joint function.

Cartilage, Articular↗

PubMedDate not supplied

Modulation of in vitro angiogenesis in a three-dimensional spheroidal coculture model for bone tissue engineering.

One of the major challenges in tissue engineering of bone substitutes remains vascularization of the transplant. We have developed a three-dimensional collagen-based coculture system to assess interactions between human endothelial cells (hECs) and human osteoblasts (hOBs) in vitro. Human umbilical vein endothelial cells (HUVECs) were grown as three-dimensional multicellular spheroids and seeded in a collagen matrix to assess sprouting of the spheroids, that is, formation of tubelike structures resembling early capillaries. Direct cell contact between hOBs and HUVECs was established by incorporating hOBs into the EC spheroids, thus forming heterogeneous cospheroids. Spatial organization of cospheroids and sprout configuration were assessed by immunohistochemical wholemount staining techniques and confocal laser microscopy. Cumulative sprout length of spheroids was quantitatively analyzed by digital imaging planimetry. In this model HUVECs and hOBs formed heterogeneous cospheroids with distinct spatial organization. The ability of HUVEC spheroids to form tubelike structures on angiogenic stimulation with vascular endothelial growth factor and basic fibroblast growth factor was suppressed in heterogeneous HUVEC/hOB cospheroids. The model system introduced in this study may be useful to assess the mechanisms involved in regulating angiogenesis during bone formation and to further investigate the mechanisms by which heterotypic cell-cell interactions inhibit endothelial tube formation for applications in bone tissue engineering.

Bone Substitutes↗

PubMed2006

A new biodegradable polyester elastomer for cartilage tissue engineering.

The objective of this study is to assess whether a new biodegradable elastomer, poly(1,8-octanediol citrate) (POC), would be a suitable material to engineer elastomeric scaffolds for cartilage tissue engineering. Porous POC scaffolds were prepared via the salt-leaching method and initially assessed for their ability to rapidly recover from compressive deformation (% recovery ratio). Controls consisted of scaffolds made from other materials commonly used in cartilage tissue engineering, including 2% agarose, 4% alginate, non woven poly(glycolic acid) (PGA) meshes, and non woven poly(L-lactide-co-glycolide) (PLGA) meshes. Articular chondrocytes from bovine knee were isolated and seeded onto porous disk-shaped POC scaffolds, which were subsequently cultured in vitro for up to 28 days. POC scaffolds completely recover from compressive deformation, and the stress-strain curve is typical of an elastomer (recovery ratio>98%). Agarose gel (2%) scaffolds broke during the compression test. The recovery ratio of 4% alginate gel scaffolds, PLLA, and PGA were 72, 85, and 88%, respectively. The Young's modulus of POC-chondrocyte constructs and cell-free POC scaffolds cultured for 28 days were 12.02+/-2.26 kPa and 3.27+/-0.72 kPa, respectively. After 28 days of culture, the recovery ratio of POC-chondrocyte constructs and cell-free POC scaffolds were 93% and 99%, respectively. The glycosaminoglycan (GAG) and collagen content at day 28 was 36% and 26% of that found in bovine knee cartilage explants. Histology/immunohistochemistry evaluations confirm that chondrocytes were able to attach to the pore walls within the scaffold, maintain cell phenotype, and form a cartilaginous tissue during the 28 days of culture.

Absorbable Implants↗

PubMedDate not supplied

Application of stereolithography for scaffold fabrication for tissue engineered heart valves.

A crucial factor in tissue engineering of heart valves is the functional and physiologic scaffold design. In our current experiment, we describe a new fabrication technique for heart valve scaffolds, derived from x-ray computed tomography data linked to the rapid prototyping technique of stereolithography. To recreate the complex anatomic structure of a human pulmonary and aortic homograft, we have used stereolithographic models derived from x-ray computed tomography and specific software (CP, Aachen, Germany). These stereolithographic models were used to generate biocompatible and biodegradable heart valve scaffolds by a thermal processing technique. The scaffold forming polymer was a thermoplastic elastomer, a poly-4-hydroxybutyrate (P4HB) and a polyhydroxyoctanoate (PHOH) (Tepha, Inc., Cambridge, MA). We fabricated one human aortic root scaffold and one pulmonary heart valve scaffold. Analysis of the heart valve included functional testing in a pulsatile bioreactor under subphysiological and supraphysiological flow and pressure conditions. Using stereolithography, we were able to fabricate plastic models with accurate anatomy of a human valvular homograft. Moreover, we fabricated heart valve scaffolds with a physiologic valve design, which included the sinus of Valsalva, and that resembled our reconstructed aortic root and pulmonary valve. One advantage of P4HB and PHOH was the ability to mold a complete trileaflet heart valve scaffold from a stereolithographic model without the need for suturing. The heart valves were tested in a pulsatile bioreactor, and it was noted that the leaflets opened and closed synchronously under subphysiological and supraphysiological flow conditions. Our preliminary results suggest that the reproduction of complex anatomic structures by rapid prototyping techniques may be useful to fabricate custom made polymeric scaffolds for the tissue engineering of heart valves.

Bioprosthesis↗

PubMed2005

Selection of cell source for ligament tissue engineering.

Use of appropriate types of cells could potentially improve the functionality and structure of tissue engineered constructs, but little is known about the optimal cell source for ligament tissue engineering. The object of this study was to determine the optimal cell source for anterior cruciate ligament (ACL) tissue engineering. Fibroblasts isolated from anterior cruciate ligament, medial collateral ligament (MCL), as well as bone marrow mesenchymal stem cells (MSC) were compared using the following parameters: proliferation rate, collagen excretion, expression of collagen type I, II, and III, as well as alpha-smooth muscle actin. Green fluorescent protein (GFP) transfected MSCs were used to trace their fate in the knee joints. MSC, ACL, and MCL fibroblasts were all highly stained with antibodies for collagen types I and III and alpha-smooth muscle actin while negatively stained with collagen type II. Proliferation rate and collagen excretion of MSCs were higher than ACL and MCL fibroblasts (p < 0.05), and MSCs could survive for at least 6 weeks in knee joints. In summary, MSC is potentially a better cell source than ACL and MCL fibroblasts for anterior cruciate ligament tissue engineering.

Animals↗

PubMedDate not supplied

Maturation and integration of tissue-engineered cartilages within an in vitro defect repair model.

This study compared the behavior of four different engineered cartilages in a hybrid culture system. First, the growth and maturation of tissue-engineered cartilages in isolation were compared to those grown in an in vitro articular cartilage defect repair model. Tissue-engineered cartilages using fibrin, agarose, or poly(glycolic acid) scaffolds were implanted into annular explants of articular cartilage and cultured for 20 or 40 days. Native tissue had a substantial influence on the DNA, sulfated glycosaminoglycan, and hydroxyproline content of the engineered tissues, suggesting that the presence of living tissue in the culture significantly altered cell proliferation and matrix accumulation. Second, the adhesion strength of various engineered cartilages to native tissue was measured and compared with the biochemical content of the engineered tissues. All scaffold treatments adhered to the native cartilage, but there were statistically significant differences in adhesive strength between the different scaffolds. The adhesive strength of all engineered scaffolds was significantly lower than that of native tissue to itself. In the engineered tissues, neither failure stress nor energy to failure correlated with gross biochemical content, suggesting that adhesion between native and engineered tissues is not purely a function of gross matrix synthesis.

Animals↗

PubMed2006

[Effects of impaction on tissue engineered bone modified by BMP-2 gene].

OBJECTIVE: To observe effects of the direct impaction on the cell survival and the bone formation of the tissue engineered bone modified by the adenovirus mediated human bone morphogenetic protein 2 (Adv-hBMP2) gene and to verify the feasibility of the impacted grafting with it. METHODS: The marrow stromal cells (MSCs) were separated from the canine bone marrow and were cultured. MSCs were transfected with the Adv-hBMP2 gene and combined with the freeze-dried cancellous bone (FDB) to form the tissue engineered bone. Four days after the combination, the tissue engineered bone was impacted in a simulated impactor in vitro and implanted in the mouse. The cell survivals were evaluated with SEM 1 and 4 days after the combination, immediately after the impaction, and 1 and 4 days after the impaction, respectively. The bone formation and the allograft absorption were histologically evaluated respectively. RESULTS: There were multiple layers of the cells and much collagen on FDB before the impaction. Immediately after the impaction, most of the cells on the direct contact area disappeared and there was much debris on the section. Some of the cells died and separated from the surface of FDB at 1 day, the number of the cells decreased but the collagen increased on the surface at 4 days. Histologically, only the fibrous tissue was found in FDB without the cells, the bone formation on FDB was even in distribution and mass in appearance before the impaction, but declined and was mainly on the periphery after the impaction in the Adv-hBMP-2 modified tissue-engineered bone. CONCLUSION: The simulated impaction can decrease the cells survival and the bone formation of the Adv-hBMP-2 modified tissue-engineered bone. The survival cells still function well. It is feasible to use the tissue engineered bone in the impaction graft.

Adenoviridae↗