Cell Transplantation as Replacement Therapy for the Future

Bioreactors for Cardiac Tissue Engineering

The advances in biotechnology, biomechanics, and biomaterials can be used to develop organ models that aim to accurately emulate their natural counterparts. Heart disease, one of the leading causes of death in modern society, has attracted particular attention in the field of tissue engineering. To avoid incorrect prognosis of patients suffering from heart disease, or from adverse consequences of classical therapeutic approaches, as well as to address the shortage of heart donors, new solutions are urgently needed. Biotechnological advances in cardiac tissue engineering from a bioreactor perspective, in which recapitulation of functional, biochemical, and physiological characteristics of the cardiac tissue can be used to recreate its natural microenvironment, are reviewed. Detailed examples of functional and preclinical applications of engineered cardiac constructs and the state-of-the-art systems from a bioreactor perspective are provided. Finally, the current trends and future directions of the field for its translation to clinical settings are discussed.

Primary human hepatocytes on biodegradable poly(l-lactic acid) matrices: a promising model for improving transplantation efficiency with tissue engineering

Liver transplantation is an established treatment for acute and chronic liver disease. However, because of the shortage of donor organs, it does not fulfill the needs of all patients. Hepatocyte transplantation is promising as an alternative method for the treatment of end-stage liver disease and as bridging therapy until liver transplantation. Our group has been working on the optimization of matrix-based hepatocyte transplantation. In order to increase cell survival after transplantation, freshly isolated human hepatocytes were seeded onto biodegradable poly(l-lactic acid) (PLLA) polymer scaffolds and were cultured in a flow bioreactor. PLLA discs were seeded with human hepatocytes and exposed to a recirculated medium flow for 6 days. Human hepatocytes formed spheroidal aggregates with a liver-like morphology and active metabolic function. Phase contrast microscopy showed increasing numbers of spheroids of increasing diameter during the culture period. Hematoxylin and eosin histology showed viable and intact hepatocytes inside the spheroids. Immunohistochemistry confirmed sustained hepatocyte function and a preserved hepatocyte-specific cytoskeleton. Albumin, alpha-1-antitrypsin, and urea assays showed continued production during the culture period. Northern blot analysis demonstrated increasing albumin signals. Scanning electron micrographs showed hepatocyte spheroids with relatively smooth undulating surfaces and numerous microvilli. Transmission electron micrographs revealed intact hepatocytes and junctional complexes with coated pits and vesicles inside the spheroids. Therefore, we conclude that primary human hepatocytes, precultured in a flow bioreactor on a PLLA scaffold, reorganize to form morphologically intact liver neotissue, and this might offer an optimized method for hepatocyte transplantation because of the expected reduction of the initial cell loss, the high regenerative potential in vivo, and the preformed functional integrity.

Periodontal tissue engineering and regeneration: current approaches and expanding opportunities

The management of periodontal tissue defects that result from periodontitis represents a medical and socioeconomic challenge. Concerted efforts have been and still are being made to accelerate and augment periodontal tissue and bone regeneration, including a range of regenerative surgical procedures, the development of a variety of grafting materials, and the use of recombinant growth factors. More recently, tissue-engineering strategies, including new cell- and/or matrix-based dimensions, are also being developed, analyzed, and employed for periodontal regenerative therapies. Tissue engineering in periodontology applies the principles of engineering and life sciences toward the development of biological techniques that can restore lost alveolar bone, periodontal ligament, and root cementum. It is based on an understanding of the role of periodontal formation and aims to grow new functional tissues rather than to build new replacements of periodontium. Although tissue engineering has merged to create more opportunities for predictable and optimal periodontal tissue regeneration, the technique and design for preclinical and clinical studies remain in their early stages. To date, the reconstruction of small- to moderate-sized periodontal bone defects using engineered cell-scaffold constructs is technically feasible, and some of the currently developed concepts may represent alternatives for certain ideal clinical scenarios. However, the predictable reconstruction of the normal structure and functionality of a tooth-supporting apparatus remains challenging. This review summarizes current regenerative procedures for periodontal healing and regeneration and explores their progress and difficulties in clinical practice, with particular emphasis placed upon current challenges and future possibilities associated with tissue-engineering strategies in periodontal regenerative medicine.

Localization of chondrocyte precursors in periosteum

OBJECTIVE

Periosteal chondrogenesis is relevant to cartilage repair and fracture healing. Periosteum contains two distinct layers: a thick, outer fibrous layer and a thin, inner cambium layer which is adjacent to the bone. Specific chondrocyte precursors are known to exist in periosteum but have not yet been identified. In this study, the location of the chondrocyte precursors in periosteum was determined.

METHOD

One hundred and twenty periosteal explants from 30 2-month-old NZ rabbits were cultured for up to 42 days. Histomorphological changes and spatio-temporal localization of Col. II mRNA and protein were analysed.

RESULTS

On day 7, chondrocyte differentiation appeared in the most juxtaosseous region in the cambium layer. Col. II mRNA and protein were also evident in the same region. By day 14, chondrocyte differentiation progressed further into the juxtaosseous cambium layer, as did Col. II mRNA and protein. With growth of the neocartilage, the cambium layer gradually diminished to the extent that by 21-28 days it was no longer evident. Cartilage growth was significant and followed an appositional pattern, growing away from the fibrous layer. The fibrous layer remained essentially unchanged from 0-42 days, without evidence of hypertrophy or atrophy. Col. II mRNA expression was never seen in the fibrous layer.

CONCLUSION

From these data, three conclusions can be drawn concerning chondrogenesis from periosteum: (1) the chondrocyte precursors are located in the cambium layer of periosteum; (2) chondrogenesis commences in the juxtaosseous area in the cambium layer and progresses from the juxtaosseous region to the juxtafibrous region of the cambium layer; (3) neocartilage growth is appositional, which displaces the fibrous layer away from the cartilage already formed, as new cartilage is formed between these two layers. These findings suggest that the least differentiated (stem or reserve) cells are located in the cambium layer furthest from the bone.

CLINICAL RELEVANCE

These findings show that the chondrocyte precursors are located in the cambium layer of periosteum. Preservation of this layer is essential for chondrogenesis. As neocartilage growth is appositional, away from the fibrous layer, it can be expected that the new cartilage deposited in and adjacent to a periosteal graft would be expected to be located on the side of the cambium layer, rather than on the side of the fibrous layer of the graft.

Tissue engineering meniscus: cells and matrix

Tissue engineering, a relatively new field of research, was born as a result of a search for solutions to the limited alternatives currently used to replace structure and function lost because of failure or loss of tissues throughout the body. The field merges advances in cell biology, growth factor therapy, and material design. It encourages creation of tissue-engineered menisci for repair and replacement therapy and offers a means for developing a better understanding of meniscal cell and matrix biology.

Meniscal injury and repair: clinical status

Repair or resection of meniscal injuries is one of the most common operative procedures in orthopedics today. A variety of techniques for reconstruction have been attempted and experts are still unsure which treatment of meniscal lesions is best. This article reviews different techniques of meniscal repair and some novel approaches that may be used for treatment of meniscal lesions in the coming years.

Role of oxygen tension during cartilage formation by periosteum

Tissue engineering makes regeneration of cartilage possible but requires optimization of culture conditions. The effects of oxygen tension on cartilage metabolism are controversial in the literature, and we could find no information detailing the optimal oxygen concentration for growing new cartilage (neochondrogenesis). Periosteal cells and tissues can be used to grow cartilage in vivo and in vitro. In this study, using a standard periosteal organ culture model, we found that cartilage formation by periosteal explants is affected by the ambient oxygen concentrations. A total of 480 periosteal explants from 30 2-month-old New Zealand White rabbits were cultured in agarose suspension at different oxygen concentrations (1-90%) for 6 weeks. Chondrogenesis, which was analyzed by histomorphometry and quantitative collagen typing, was maximal at 12-15% oxygen. There were no significant differences in chondrogenesis in the range of 12-45%. There was inhibition of cartilage and type-II collagen formation at very high (90%) and very low (1-5%) oxygen concentrations. However, contrary to what some have thought, chondrogenesis is maximal under aerobic conditions. If this is true for systems other than periosteal implants, it would have important implications for growing cartilage in vitro.

The mesentery as a laminated vascular bed for hepatocyte transplantation

The small bowel mesentery provides a unique structure of a large vascularized surface area to support hepatocyte transplantation. Cell-seeded polymeric matrices can be juxtaposed in a relatively atraumatic manner between leaves of mesentery such that adequate exchange of nutrients and diffusion of gases can proceed in the interim while neovascularization occurs. Hepatocytes obtained from (RHA) Wistar rats by collagenase perfusion were seeded onto non-woven filamentous sheets of polyglycolic acid 1 x 3 cm in size and 2 mm thickness to a density of 500,000 cells/cm2. Twenty-six recipient Gunn rats (UDP-glucuronyl transferase deficient) underwent laparotomy. Hepatocyte-ladened polymer sheets were placed between leaves of mesentery. Eight sheets were placed per animal and the leaves were approximated, creating a functional implant 1 x 3 x 2 cm. Biopsies between 5-99 days after implantation revealed neovascularization, moderate inflammatory reaction and the presence of viable hepatocytes in 96% (25/26). Immunoperoxidase studies using anti-albumin antibody substantiated hepatocyte specific function in implants. HPLC profiles of bile from Gunn rats transplanted with hepatocytes from congeneic (RHA) rats demonstrated the presence of bilirubin conjugates. There were no conjugation fractions seen in control gunn rats without hepatocyte transplantation. Although total serum bilirubin did not significantly decrease, conjugated bilirubin was identified in 46% (12/26) animals after transplantation with congeneic hepatocytes. We conclude that the mesentery of the small bowel provides a large vascularized surface for cell transplantation. Large numbers of metabolically active hepatocytes can engraft, vascularize, and show function. The mesentery may be a potential bed for clinical hepatocyte transplantation.