Beyond the Vernacular: New Sources of Cells for Bone Tissue Engineering:

The effect of low-frequency electromagnetic field on human bone marrow stem/progenitor cell differentiation

Human bone marrow stromal cells (hBMSCs, also known as bone marrow-derived mesenchymal stem cells) are a population of progenitor cells that contain a subset of skeletal stem cells (hSSCs), able to recreate cartilage, bone, stroma that supports hematopoiesis and marrow adipocytes. As such, they have become an important resource in developing strategies for regenerative medicine and tissue engineering due to their self-renewal and differentiation capabilities. The differentiation of SSCs/BMSCs is dependent on exposure to biophysical and biochemical stimuli that favor early and rapid activation of the in vivo tissue repair process. Exposure to exogenous stimuli such as an electromagnetic field (EMF) can promote differentiation of SSCs/BMSCs via ion dynamics and small signaling molecules. The plasma membrane is often considered to be the main target for EMF signals and most results point to an effect on the rate of ion or ligand binding due to a receptor site acting as a modulator of signaling cascades. Ion fluxes are closely involved in differentiation control as stem cells move and grow in specific directions to form tissues and organs. EMF affects numerous biological functions such as gene expression, cell fate, and cell differentiation, but will only induce these effects within a certain range of low frequencies as well as low amplitudes. EMF has been reported to be effective in the enhancement of osteogenesis and chondrogenesis of hSSCs/BMSCs with no documented negative effects. Studies show specific EMF frequencies enhance hSSC/BMSC adherence, proliferation, differentiation, and viability, all of which play a key role in the use of hSSCs/BMSCs for tissue engineering. While many EMF studies report significant enhancement of the differentiation process, results differ depending on the experimental and environmental conditions. Here we review how specific EMF parameters (frequency, intensity, and time of exposure) significantly regulate hSSC/BMSC differentiation in vitro. We discuss optimal conditions and parameters for effective hSSC/BMSC differentiation using EMF treatment in an in vivo setting, and how these can be translated to clinical trials.

Ectopic osteogenesis of an injectable nHAC/CSH loaded with blood-acquired mesenchymal progenitor cells in a nude mice model

An injectable bone cement, nHAC/CSH, which consists of nano-hydroxyapatite/collagen (nHAC) and calcium sulphate hemihydrate (CaSO4.½H2O; CSH) was investigated as a tissue-engineered scaffold material with blood-acquired mesenchymal progenitor cells (BMPCs) as seeding cells. An in vitro study on the cytocompatability of nHAC/CSH and an in vivo study on the ectopic bone formation of nHAC/CSH loaded with dBMPCs were both conducted. The dBMPCs morphology, proliferation, differentiation and apoptosis assays were conducted using the direct contact and extract method. The cells tests exhibited normal growth and bioactive function in vitro. Studies in vivo showed that this injectable tissue engineered bone (ITB) formed bone structure in the heterotopic site of nude mice. These findings indicate that the ITB composed of nHAC/CSH and dBMPCs may represent a useful strategy for clinical reconstruction of irregular bone defects.

Effect of Recombinant Human Bone Morphogenetic Protein-2 and Adipose Tissue-Derived Stem Cell on New Bone Formation in High-Speed Distraction Osteogenesis

PURPOSE

The effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) and osteogenically differentiated adipose tissue-derived stem cells (ADSC) on new bone formation in high-speed distraction osteogenesis of adult rabbit cranium were investigated.

MATERIALS AND METHODS

A total of 41 adult rabbits were used in the study. Distraction began after a 5-day latency period at a rate of 1.5 mm twice a day until 10-mm length gain was obtained both in the control group, where a bone defect was induced, and in the experimental group, in which ADSC (group A), rhBMP-2 (group B), or both (group C) were injected in the distraction gap after distraction. At 4, 8, and 12 weeks after distraction, computed tomography analysis was done to determine the bone defect dimension and bone mineral density (BMD), while histologic examination was also done to calculate bone formation ratio.

RESULTS

Bone defect dimension significantly decreased in groups B and C, compared with the control group, at 4 and 12 weeks after distraction. BMD was significantly increased in groups B and C at 4 weeks. On histologic examination, bone formation ratio was significantly increased in group C only at 12 weeks.

CONCLUSION

This study suggests that the use of rhBMP-2 in combination with or without ADSC is helpful to promote bone regeneration in high-speed distraction osteogenesi s of adult rabbit cranium.

Regenerative medicine: implications for craniofacial surgery

Craniofacial reconstruction of cases with complex anatomy challenges surgeons. The recently emerging field of tissue engineering and regenerative medicine has resulted in a variety of novel therapeutic concepts particularly in the craniofacial area. However, researchers still face significant problems when translating scientific concepts from the bench to the bedside. Reconstruction procedures depend on sustainability, aesthetic outcome, and functionality. Tissue engineering approaches yield powerful tools for long-term satisfying results enabling customized reconstruction and supporting natural healing processes. In conclusion, further advances of tissue-engineered reconstruction need multidisciplinary research to create complex tissue structures and make satisfactory outcomes clinically achievable for most patients. This review highlights clinical advances in the field and gives an overview about current scientific concepts.

Stromal-cell-derived factor (SDF) 1-alpha in combination with BMP-2 and TGF-β1 induces site-directed cell homing and osteogenic and chondrogenic differentiation for tissue engineering without the requirement for cell seeding

The clinical translation of tissue engineering approaches is limited by the requirement of a cell source. Cell guidance is a new concept that provides an alternative approach, obviating a requirement for an external cell source. This relies on site-specific homing and differentiation of the patient's own cells to an implanted scaffold through controlled delivery of cytokines. In this study, we used stromal-cell-derived factor 1-alpha (SDF-1α) in combination with bone morphogenic protein (BMP)-2 or transforming growth factor (TGF)-β1 to induce cell migration and osteogenic or chondrogenic differentiation, respectively, in implanted scaffolds in a rat model. A customized cytokine microdelivery apparatus was used to ensure the constant rate and concentration of cytokine delivery around the scaffold. The formation of osteoid or early cartilage was observed after 4 weeks in specimens treated with SDF-1α and either BMP-2 or TGF-β1. The density of cellular infiltrate and formation of differentiated tissue were lower in scaffolds treated only with BMP-2 or TGF-β1. Thus, controlled SDF-1α delivery induces cell migration into scaffolds and can result in enhanced osteogenesis and chondrogenesis when used in combination with differentiation cytokines for purposes of tissue engineering.

Craniomaxillofacial reconstruction using allotransplantation and tissue engineering: challenges, opportunities, and potential synergy

The face is composed of an intricate underlying bony/cartilaginous framework that supports muscle, secretory organs, and sophisticated skin/subcutaneous structures. These components are attached through numerous ligaments and interact dynamically with a vast neurovascular network. The most sophisticated autologous reconstructive techniques, utilizing composite free-tissue flaps, are often inadequate to restore extensive maxillofacial defects. Massive craniomaxillofacial (CMF) defects resulting from trauma, oncologic resection, or congenital deformity present a unique challenge to reconstructive surgeons. Therefore, recent advances in craniofacial surgery and immunotherapy spurred the innovation of composite tissue allotransplantation (CTA), which permits reconstruction with tissue composed of all necessary components. However, CMF allotransplantation carries with it side effects of lifelong immunosuppression. Furthermore, the donor skeletal framework may not provide an ideal match, resulting in less than ideal occlusion and soft-tissue anthropometrics. An alternative to transplantation, tissue engineering, has provided hope for regenerating missing tissue and avoiding the need for immunosuppression. Many tissue subtypes, including bone and cartilage, have been successfully created, with sparse reports of clinical application. Tissue-engineered composite tissue required for complete CMF reconstruction continues to elude development, with vascular supply and tissue interactions posing the largest remaining obstacles. We report herein the current status and limitations of CTA and tissue engineering. Furthermore, we describe for the first time our vision of hybridization of CTA and engineering, utilizing the strengths of each strategy.

Effects of different media on proliferation and differentiation capacity of canine, equine and porcine adipose derived stem cells

Adult stem cells are of particular interest for therapeutic use in the field of regenerative medicine. Adipose-derived mesenchymal stem cells (ASCs) are an attractive stem cell source for all fields of regenerative medicine because adipose tissue - and therewith cells - can easily be harvested from each donor. However, common expansion using fetal bovine serum (FBS) can not be used for clinical applications as xenogenic proteins must be avoided. Adipose tissue from equine, canine and porcine donors was digested with collagenase to isolate ASCs. ASCs were either expanded in a cell culture medium supplemented with FBS or in a serum-free medium (UltraCulture; UC) supplemented with a serum substitute (UltroserG). From all three animal species, the adipogenic and osteogenic differentiation potential of ASCs cultured with different media was analyzed in vitro. Cell proliferation analysis showed a population doubling time of 48-68 h for canine cells, 54-65 h for porcine cells and 54-70 h for equine cells, expanded in different media. Except for porcine ASCs, cells cultured in media supplemented with FBS grew faster than cells expanded in UC medium with UltroserG. Yet, all cells maintained their potential to differentiate into adipocytes and osteoblasts. UltraCulture medium containing UltroserG can for all examined species be recommended if FBS needs to be avoided in the expansion of donor-derived (stem) cells.

Vascular guidance: microstructural scaffold patterning for inductive neovascularization

Current tissue engineering techniques are limited by inadequate vascularisation and perfusion of cell-scaffold constructs. Microstructural patterning through biomimetic vascular channels within a polymer scaffold might induce neovascularization, allowing fabrication of large engineered constructs. The network of vascular channels within a frontal-parietal defect in a patient, originating from the anterior branch of the middle meningeal artery, was modeled using computer-aided design (CAD) techniques and subsequently incorporated into polycaprolactone (PCL) scaffolds fabricated using fused deposition modeling (FDM). Bone marrow-derived mesenchymal stem cells (MSCs) were seeded onto the scaffolds and implanted into a rat model, with an arteriovenous bundle inserted at the proximal extent of the vascular network. After 3 weeks, scaffolds were elevated as a prefabricated composite tissue-polymer flap and transferred using microsurgical technique. Histological examination of explanted scaffolds revealed vascular ingrowth along patterned channels, with abundant capillary and connective tissue formation throughout experimental scaffolds, while control scaffolds showed only granulation tissue. All prefabricated constructs transferred as free flaps survived and were viable. We term this concept “vascular guidance,” whereby neovascularization is guided through customized channels in a scaffold. Our technique might potentially allow fabrication of much larger tissue-engineered constructs than current technologies allow, as well as allowing tailored construct fabrication with a patient-specific vessel network based on CT scan data and CAD technology.

Osteoblasts in bone tissue engineering

Osteoblasts are integral to the development, growth, function, repair and maintenance of bone. The osteoblast forms organic, non-mineralized bone matrix and is involved in complex interactions with a variety of factors, mediators and cell types. Degeneration, pathology, and trauma cause disruption and destruction of the normal skeletal environment and may lead to bone loss.

There is a rise in active populations involved in trauma, elderly patients with fragility fractures and an overall increase in primary, revision and reconstructive bone and joint surgery. Despite the rapid evolution of implant technologies and bone grafting techniques, there is still a great demand for novel bone replacement strategies.

Bone tissue engineering is the state of the art science with the potential to regenerate bone with natural form and function. This review presents the biology of osteoblasts and their current applications in bone tissue engineering biotechnologies and role in stem cell, bioactive factor, recombinant signalling molecule and gene therapy research.

Ectopic Bone Formation from Mandibular Osteoblasts Cultured in a Novel Human Serum-derived Albumin Scaffold

The aim of this study was to evaluate the ectopic bone formation using a novel serum-derived albumin scaffold and cultured human mandibular osteoblasts in nude mice. Osteoblasts were cultured with 10% human serum and plated in a novel spongy noncalcified protein scaffold prepared with plasmatic albumin crossed with a glutaraldehyde type agent. Hematoxylin-eosin staining revealed a bone-like extracellular matrix and in vitro mineralization was confirmed by von Kossa staining. Histological and immunohistochemical evaluation showed progression of mineralization in vivo. These results suggest the clinical feasibility of alveolar cells and albumin scaffold as a good alternative for bone regeneration.

Is tissue engineering a new paradigm in medicine? Consequences for the ethical evaluation of tissue engineering research

Ex-vivo tissue engineering is a quickly developing medical technology aiming to regenerate tissue through the introduction of an ex-vivo created tissue construct instead of restoring the damaged tissue to some level of functionality. Tissue engineering is considered by some as a new medical paradigm. We analyse this claim and identify tissue engineering's fundamental characteristics, focusing on the aim of the intervention and on the complexity and continuity of the process. We inquire how these features have an impact not only on the scientific research itself but also on the ethical evaluation of this research. We suggest that viewing tissue engineering as a new medical paradigm allows us to develop a wider perspective for successful investigation instead of focusing on isolated steps of the tissue engineering process in an anecdotal way, which may lead to an inadequate ethical evaluation. We argue that the concept of tissue engineering as a paradigm may benefit the way we address the ethical challenges presented by tissue engineering.