There is a wide gap between the number of patients requiring organ and tissue replacement and the organs available for transplantation. Regenerative Medicine holds the promise of narrowing this gap using cell therapy, bioengineering organs and harnessing the body’s ability to self-heal. This review describes progress made in the basic components of Regenerative Medicine (collecting and expanding cells, selecting appropriate biomaterials for their scaffolding, and employing bioactive molecules to aid in cell migration differentiation and growth) and identifies both gaps in knowledge and challenges in execution requiring further research.

Background: Several approaches for the development of tracheal substitutes for the treatment of extensive tissue defects have been explored over the years. However, a completely satisfactory approach has not been achieved. Previously, we described a composite tissue engineered trachea (TET) using chondrocytes seeded onto a polyglycolic acid (PGA) fiber-mesh. This study was considered to improve the design and functionality of the TET by using a porcine decellularized aorta as the scaffold.

Methods: Chondrocytes were harvested from sheep tracheal cartilage and were suspended in medium. The chondrocytes were then seeded onto PGA and incubated in vitro for 1week. A 3x4 cm piece was cut from a decellularized aorta and four 0.5x3 cm pieces were excised from one side in a comb like fashion. A silicon stent was inserted into this structure and the spaces were filled with chondrocyte seeded PGA. The three dimensional cell-polymer construct was then implanted into a subcutaneous pocket of a nude rat for 4 weeks. Both native and TET were analyzed for sulfated glycosaminoglycan (S-GAG) and hydroxyproline content, and stained for H&E, Safranin-O and Collagen Type- II antibody.

Results: The improved design of TET formed new cartilage rings in the structuralconfiguration of native trachea. Furthermore, the decellularized aorta connected well to the cartilage, which provided an excellent support to the rings, as well as good flexibility to the engineered trachea. Histological evaluation of TET showed the presence of mature cartilage. S-GAG and hydroxyproline content was similar to native cartilage levels.

Conclusion: This study demonstrates the feasibility of engineering a trachea with defined cartilage rings and similar flexibility to the native trachea.

Tissue engineering of human liver cells in a three dimensional cell culture system could improve pharmacological studies in terms of drug metabolism, drug toxicity or adverse drug effects by mimicking the in vivo situation. In this study, we produced 3D organotypic cultures of HepG2 cells using the hanging drop method. 250 – 8000 seeded cells formed organotypic cultures within 2–3 days which increased in size during the first week. Viability and metabolic parameters (glucose, lactate) were analyzed during almost three weeks of cultivation. Liver specific albumin production was higher in the organotypic cultures as compared to both monolayer and collagen-sandwich cultures. Amino acid quantification revealed high production of glutamate as well as uptake of glutamine, alanine and branched-chain amino acids. CYP1A induction capacity was significantly improved by organotypic cultivation. The acute toxicity (24 h) of tamoxifen, an anti-cancer drug, was lower in the 3D cultures as compared to monolayer and collagen-sandwich cultures. This could be explained by a higher drug efflux through membrane transporter (MRP-2). We conclude that the engineered HepG2 cultures could be used for the investigation of CYP450 induction, anti-cancer drug effects and for the study of chemotherapy resistance. Applied to other cell types such as the human primary cells these 3D organotypic cultures may have potential in long term toxicity screening of compounds.

Synthetic biology uses interchangeable and standardized “bio-parts” to construct complex genetic networks that include sensing, information processing and effector modules: these allow robust and tunable transgene expression in response to a change in signal input. The rise of this field has coincided closely with the emergence of regenerative medicine as a distinct discipline. Unlike synthetic biology, regenerative medicine uses the natural abilities of cells to make trophic factors and to produce new tissues as they would in normal development and tissue maintenance. In this article, we argue that bringing these young fields together, so that synthetic biology techniques are applied to the problem of regeneration, has the potential significantly to enhance our ability to help those in clinical need. We first review the synthetic tool kit available for engineered mammalian networks, then examine the main areas in which synthetic biology techniques might be applied to promote regeneration: (i) biosynthesis and controlled release of therapeutic molecules, (ii) synthesis of scaffold material, (iii) regulation of stem cells, and (iv) programming cells to organize themselves into novel tissues. We finally consider the long-term potential of synthetic biology for regenerative medicine, and the risks and challenges ahead.

Stem cells are undifferentiated cells that can renew themselves and generate specialized cell types with specific functions in the body. Patient- specific pluripotent stem cells might offer a limitless source for transplantable cells and tissues to treat sufferer without causing immune-rejection. Current reprogramming methods to generate pluripotent stem cells involve viral transduction or plasmid transfection that rely upon transient expression of the reprogramming factors without integration of ectopic DNA into the genome. However, the generation of stem cells with high efficiency and safety should be needed for the clinical use. We established human amnion-derived pluripotent cells (HAPCs) and HAPCs derived induced pluripotent stem cells. These cells expressed phenotypic marker characteristics of stem cells. Furthermore, HAPCs contributed to the formation of chimeric embryoid bodies and formed teratomas after injection to immno-deficient mice. We discuss here the possible application of human genetically unmodified pluripotent stem cells as well as induced pluripotent stem cells for regenerative medicine. Those stem cells that can be maintained by signaling through LIF/Stat3 may be required.

Stem cells are defined as cells that have the self-renew capacity and the ability to differentiate into one or more cell types. Recently, stem cell biology has become an interesting topic, especially because of the potential to use it in regenerative medicine. Several types of human stem cells have been isolated and identified in vivo and in vitro . This review highlights the characteristics and therapeutic potential of human dental progenitor/stem cells.

Background: Current treatment options for stable non-union fractures represent major clinical challenges, and are a major health issue. Fracture treatment can take many forms, usually requiring bone grafting and/or revisions of the fracture with open reduction and internal fixation (ORIF). Conservative care options such as bone morphogenic proteins and bone stimulators are also available. The purpose of this study was to determine if culture expanded, autologous MSC’s injected into non-union fractures under c-Arm fluoroscopy could represent an alternative treatment modality in recalcitrant fracture non-unions. This paper reports on the findings of 6 patients with fracture non-union treated with autologous MSC’s.

Patients and methods: We evaluated 6 consecutive patients with chronic fracture non-unions. Patients consisted of 4 women and 2 men with treatment intervention at an average of 8.75 months post-fracture (range 4- 18 months, one patient fracture not included in calculation was >100 mo.). All treated patients received autologous, culture expanded, mesenchymal stem cells injected percutaneously via fluoroscopic guidance into the site of the fracture non-union. Fracture union was evaluated with the use of follow up high-resolution x-ray and/or CT imaging. Phenotype of the culture-expanded MSCs was evaluated and quantified by flow cytometry of surface antigens.

Conclusion: The results of this study support the hypothesis that autologous MSC’s delivered via percutaneous re-implantation may be an alternative modality for the non-operative treatment of recalcitrant non-union fractures.