Tissue engineering最新文献

Tissue engineering provides the revolutionary possibility for curing temporomandibular joint (TMJ) disorders. Although characterization of the mandibular condyle has been extensively studied, tissue engineering of the mandibular condyle is still in an inchoate stage. The purpose of this review is to provide a summary of advances relevant to tissue engineering of mandibular cartilage and bone, and to serve as a reference for future research in this field. A concise anatomical overview of the mandibular condyle is provided, and the structure and function of the mandibular condyle are reviewed, including the cell types, extracellular matrix (ECM) composition, and biomechanical properties. Collagens and proteoglycans are distributed heterogeneously (topographically and zonally). The complexity of collagen types (including types I, II, III, and X) and cell types (including fibroblast-like cells, mesenchymal cells, and differentiated chondrocytes) indicates that mandibular cartilage is an intermediate between fibrocartilage and hyaline cartilage. The fibrocartilaginous fibrous zone at the surface is separated from hyaline-like mature and hypertrophic zones below by a thin and highly cellular proliferative zone. Mechanically, the mandibular condylar cartilage is anisotropic under tension (stiffer anteroposteriorly) and heterogeneous under compression (anterior region stiffer than posterior). Tissue engineering of mandibular condylar cartilage and bone is reviewed, consisting of cell culture, growth factors, scaffolds, and bioreactors. Ideal engineered constructs for mandibular condyle regeneration must involve two distinct yet integrated stratified layers in a single osteochondral construct to meet the different demands for the regeneration of cartilage and bone tissues. We conclude this review with a brief discussion of tissue engineering strategies, along with future directions for tissue engineering the mandibular condyle.

The poorly vascularized fibrous capsule that develops around implantable biomedical devices (for drug delivery, biosensors, etc.) severely limits their applications. We tested the hypotheses that co-implantation of bone marrow-derived progenitor cells could stimulate the vascularization of implants. To assess the presence of functional peri-implant microvasculature, we developed a novel model of implanted device containing an oxygen (O(2))-sensing spin probe (detectable using electron paramagnetic resonance) placed inside a nanoporous filter-limited capsule. These devices were implanted subcutaneously in C57/Bl6 mice alone, with the addition of a Matrigel plug in front of the filter, or with the addition of Matrigel containing equal proportions of c-kit(+) and stem cell antigen-1(+) bone marrow-derived cells. Implants partial pressure of O(2) (pO(2)) were recorded non-invasively and periodically for up to 10 weeks. Tissue surrounding the implants was collected for immunohistochemistry. Initially, there were no differences in pO(2) between the experimental groups. After 3 weeks, the devices supplied with progenitor cells showed more than twice the O(2) concentrations as controls. This difference remained significant for 4 more weeks and then started to decrease slightly, still being 6 mmHg higher than in the controls at 10 weeks post-implantation. Collagen deposition was detected around the control implants, along with F4/80-positive macrophages and giant cells. In the plugs collected from the cell treatment group, we found an active process of adipogenesis, accompanied by neovascularization, and a highly vascularized adipose layer surrounding the implants. In conclusion, we successfully developed a cell therapy-type strategy to maintain vascularization around implanted devices using co-administration of bone marrow-derived progenitor cells, and we demonstrated a novel O(2)-sensing method to functionally monitor neovascularization in vivo.

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.

Synthesis of bone requires both essential progenitors to form the various structures and the correct microenvironment for their differentiation. To identify these factors, we have used a system that exploits bone morphogenetic protein's ability to induce endochondral bone formation rapidly. One of the earliest events observed was the influx and proliferation of fibroblastic cells that express both vascular smooth muscle cell markers, alpha smooth muscle actin (alpha SMA), smooth muscle myosin heavy chain, and the monocytic marker CD68. The expression of these factors was lost by days 4 to 5, coincident with the up-regulation of Sox9 and the appearance of chondrocytes. Studies with a cyclization recombination (Cre)/lox system, in which a myeloid-specific promoter driving Cre recombinase can irreversibly unblock expression of beta-galactosidase only in cells of myeloid origin, showed specific activity in the newly formed chondrocytes. These results suggest that early chondrocyte progenitors are of myeloid origin. Simultaneous with this recruitment, we determined that a numbers of these cells were in a hypoxic state, indicative of a low-oxygen environment. The cells in the hypoxic regions were undergoing chondrogenesis, whereas cells in adjacent normoxic regions appeared to be assembling into new vessels, suggesting that the oxygen microenvironment is critical for establishment of the cartilage.

Collagen gels have many favorable attributes for tissue engineering, but the gels undergo dramatic contraction when cells are added because of the weak noncovalent bonds that form during spontaneous gelation. We hypothesized that photochemically cross-linking collagen gels would make suitable scaffolds for tissue engineering with favorable cell viability and minimal gel contraction. Rose Bengal and riboflavin were chosen as candidate photo-initiators for gel cross-linking using 532- and 458-nm-light wavelengths, respectively. Chondrocyte viability was measured after initial gelation for several concentrations of initiators. Cell viability and gel contraction were then measured using chondrocytes and fibroblasts over 7 days of culture. Rose Bengal used at concentrations necessary for gelation resulted in little or no cell viability. Short-term viability results showed that 0.25- or 0.5-mM concentrations of riboflavin, and 40 s of illumination permitted more than 90% cell viability. Using riboflavin concentrations of 0.25 or 0.5 mM, long-term chondrocyte viability was 113.1 +/- 11.6% and 25.4 +/- 2.7%, respectively, at day 7. Although non-cross-linked chondrocyte constructs contracted to 59.9 +/- 11.8% of their original diameter and fibroblasts contracted to 24.9 +/- 5.0% of their original diameter by day 7, the cross-linked constructs retained 88.8 +/- 7.4% and 85.5 +/- 5.0% of the original diameter, respectively. In conclusion, by photochemically cross-linking collagen gels using riboflavin and visible light, stable gel scaffolds with favorable cell survival can be produced.

Organ printing, a novel approach in tissue engineering, applies layered computer-driven deposition of cells and gels to create complex 3-dimensional cell-laden structures. It shows great promise in regenerative medicine, because it may help to solve the problem of limited donor grafts for tissue and organ repair. The technique enables anatomical cell arrangement using incorporation of cells and growth factors at predefined locations in the printed hydrogel scaffolds. This way, 3-dimensional biological structures, such as blood vessels, are already constructed. Organ printing is developing fast, and there are exciting new possibilities in this area. Hydrogels are highly hydrated polymer networks used as scaffolding materials in organ printing. These hydrogel matrices are natural or synthetic polymers that provide a supportive environment for cells to attach to and proliferate and differentiate in. Successful cell embedding requires hydrogels that are complemented with biomimetic and extracellular matrix components, to provide biological cues to elicit specific cellular responses and direct new tissue formation. This review surveys the use of hydrogels in organ printing and provides an evaluation of the recent advances in the development of hydrogels that are promising for use in skeletal regenerative medicine. Special emphasis is put on survival, proliferation and differentiation of skeletal connective tissue cells inside various hydrogel matrices.

Myocardial tissue engineering aims to repair, replace, and regenerate damaged cardiac tissue using tissue constructs created ex vivo. This approach may one day provide a full treatment for several cardiac disorders, including congenital diseases or ventricular dysfunction after myocardial infarction. Although the ex vivo construction of a myocardium-like tissue is faced with many challenges, it is nevertheless a pressing objective for cardiac reparative medicine. Multidisciplinary efforts have already led to the development of promising viable muscle constructs. In this article, we review the various concepts of cardiac tissue engineering and their specific challenges. We also review the different types of existing biografts and their physiological relevance. Although many investigators have favored cardiomyocytes, we discuss the potential of other clinically relevant cells, as well as the various hypotheses proposed to explain the functional benefit of cell transplantation.

Facilitated endogenous repair is a novel approach to tissue engineering that avoids the ex vivo culture of autologous cells and the need for manufactured scaffolds, while minimizing the number and invasiveness of associated clinical procedures. The strategy relies on harnessing the intrinsic regenerative potential of endogenous tissues using molecular stimuli, such as gene transfer, to initiate reparative processes in situ. In the simplest example, direct percutaneous injection of an osteogenic vector is used to stimulate bone healing. If necessary, additional progenitor cells and space-filling scaffolds can be provided by autologous bone marrow, muscle, fat, and perhaps other tissues. These can be harvested, processed, and reimplanted by simple, expedited, intraoperative procedures. Examples of repair of experimental osseous and osteochondral lesions in laboratory animals are described. If successful, these strategies will provide methods for tissue regeneration that are not only effective but also inexpensive, safe, and clinically expeditious. Although orthopaedic examples are given here, the technology should be more generally applicable.

Despite many years of research, daily insulin injections remain the gold standard for diabetes treatment. Gene therapy may provide an alternative strategy by imparting the ability to secrete insulin from an ectopic site. The epidermis is a self-renewing tissue that is easily accessible and can provide large numbers of autologous cells to generate insulin-secreting skin substitutes. Here we used a recombinant retrovirus to modify human epidermal keratinocytes with a gene encoding for human proinsulin containing the furin recognition sequences at the A-C and B-C junctions. Keratinocytes were able to process proinsulin and secrete active insulin that promoted glucose uptake. Primary epidermal cells produced higher amounts of insulin than cell lines, suggesting that insulin secretion may depend on the physiological state of the producer cells. Modified cells maintained the ability to stratify into 3-dimensional skin equivalents that expressed insulin at the basal and suprabasal layers. Modifications at the furin recognition sites did not improve proinsulin processing, but a single amino acid substitution in the proinsulin B chain enhanced C-peptide secretion from cultured cells and bioengineered skin substitutes 10- and 28-fold, respectively. These results suggest that gene-modified bioengineered skin may provide an alternative means of insulin delivery for treatment of diabetes.

Evidence is provided pointing out certain basic similarities, though not an identity, between the mechanisms of early fetal regeneration and induced organ regeneration in adults. These similarities favor a model of induced organ regeneration in which biologically active scaffolds block wound contraction and scar formation.