Bone marrow-derived mesenchymal stem cells become anti-angiogenic when chondrogenically or osteogenically differentiated:implications for bone and cartilage tissue engineering

Osteochondral tissue repair requires formation of vascularized bone and avascular cartilage. Mesenchymal stem cells stimulate angiogenesis both in vitro and in vivo but it is not known if these proangiogenic properties change as a result of chondrogenic or osteogenic differentiation. We investigated the angiogenic/antiangiogenic properties of equine bone marrow-derived mesenchymal stem cells (eBMSCs) before and after differentiation in vitro. Conditioned media from chondrogenic and osteogenic cell pellets and undifferentiated cells was applied to endothelial tube formation assays using Matrigel™. Additionally, the cell secretome was analysed using LC-MS/MS mass spectrometry and screened for angiogenesis and neurogenesis-related factors using protein arrays. Endothelial tube-like formation was supported by conditioned media from undifferentiated eBMSCs. Conversely, chondrogenic and osteogenic conditioned media was antiangiogenic as shown by significantly decreased length of endothelial tube-like structures and degree of branching compared to controls. Undifferentiated cells produced higher levels of angiogenesis-related proteins compared to chondrogenic and osteogenic pellets. In summary, eBMSCs produce an array of angiogenesis-related proteins and support angiogenesis in vitro via a paracrine mechanism. However, when these cells are differentiated chondrogenically or osteogenically, they produce a soluble factor(s) that inhibits angiogenesis. With respect to osteochondral tissue engineering, this may be beneficial for avascular articular cartilage formation but unfavourable for bone formation where a vascularized tissue is desired. © Copyright 2014, Mary Ann Liebert, Inc.

Measuring the dynamic mechanical response of hydrated mouse bone by nanoindentation

This study demonstrates a novel approach to characterizing hydrated bone's viscoelastic behavior at lamellar length scales using dynamic indentation techniques. We studied the submicron-level viscoelastic response of bone tissue from two different inbred mouse strains, A/J and B6, with known differences in whole bone and tissue-level mechanical properties. Our results show that bone having a higher collagen content or a lower mineral-to-matrix ratio demonstrates a trend towards a larger viscoelastic response. When normalized for anatomical location relative to biological growth patterns in the antero-medial (AM) cortex, bone tissue from B6 femora, known to have a lower mineral-to-matrix ratio, is shown to exhibit a significantly higher viscoelastic response compared to A/J tissue. Newer bone regions with a higher collagen content (closer to the endosteal edge of the AM cortex) showed a trend towards a larger viscoelastic response. Our study demonstrates the feasibility of this technique for analyzing local composition-property relationships in bone. Further, this technique of viscoelastic nanoindentation mapping of the bone surface at these submicron length scales is shown to be highly advantageous in studying subsurface features, such as porosity, of wet hydrated biological specimens, which are difficult to identify using other methods. © 2010 Elsevier Ltd.

Polycaprolactone fibres as a potential delivery system for collagen to support bone regeneration

Poly(e-caprolactone) (PCL) is biocompatible, non-immunogenic and non-toxic, and slowly degrades, allowing sufficient time for tissue regeneration. PCL has the potential for application in bone and cartilage repair as it may provide the essential structure required for bone regeneration, however, an ideal scaffold system is still undeveloped. PCL fibres were prepared using the gravity spinning technique, in which collagen was either incorporated into or coated onto the 'as-spun' fibres, in order to develop novel biodegradable polymer fibres which will effectively deliver collagen and support the attachment and proliferation of human osteoblast (HOB) cells for bone regeneration. The physical and mechanical characteristics and cell fibre interactions were analysed. The PCL fibres were found to be highly flexible and inclusion of collagen did not alter the mechanical properties of PCL fibres. Overall, HOB cells were shown to effectively adhere and proliferate on all fibre platforms tested, although proliferation rates were enhanced by surface coating PCL fibres with collagen compared to PCL fibres incorporating collagen and PCL-only fibres. These findings highlight the potential of using gravity spun PCL fibres as a delivery platform for extracellular matrix proteins, such as collagen, in order to enhance cell adherence and proliferation for tissue repair.

Evaluating transglutaminase crosslinked collagen gel systems for hard and soft tissue repair

Tissue Transglutaminase (TG2) and FXIIIa, members of the transglutaminase (TG) family, catalyses a transamidating reaction and form covalent bond between or within proteins. In bone development, both enzymes expressions correlate with the initial of the mineralisation process by osteoblasts and chondrocytes. Exogenous TG2 also promotes maturation of chondrocytes and mineralisation in pre-osteoblasts. To understand the role of endogenous TG2 in osteoblast mineralisation, the TG2 expression was examined during the human osteoblast (HOB) mineralisation. The expression of the endogenous TG2 increased during the mineralisation, yet, its expression was not essential for mineral deposition due to the compensation effect by other members in the TG family. The extracellular transamidating activity of HOBs was found increased during mineralisation and a shift from FXIIIa dominant- to TG2-dominant crosslinking activity was suggested after differentiation. However, the transamidating activity of both TG2 and FXIIIa were not critical for cell mineralisation. On the other hand, Exogenous TG2 was found to enhance wild type HOB and TG2 knockdown HOB mineral deposition. The transamidating activity of TG2 was not required but most likely a close conformation was essential for this enhancement. Results also demonstrated that exogenous TG2 may activate the ß-catenin pathway through LRP5 receptor thus contribute in cell mineralisation. This enhancement could be abolished by addition of ß-catenin inhibitors. Finally, using of TG2 crosslinked collagen gel for bone and cornea repair was evaluated. Crosslinked collagen gel showed promising results in improving HOB mineralisation, human corneal fibroblast (hCF) proliferation and migration. These effects might be resulted from the trapped TG2 within the collagen matrix and the alteration of matrix topography by TG2.

Investigating the role of capacitive coupling between the operating table and the return electrode of an electrosurgery unit in the modification of the current density distribution within the patients’ body

Background: Electrosurgery units are widely employed in modern surgery. Advances in technology have enhanced the safety of these devices, nevertheless, accidental burns are still regularly reported. This study focuses on possible causes of sacral burns as complication of the use of electrosurgery. Burns are caused by local densifications of the current, but the actual pathway of current within patient's body is unknown. Numerical electromagnetic analysis can help in understanding the issue. Methods: To this aim, an accurate heterogeneous model of human body (including seventy-seven different tissues), electrosurgery electrodes, operating table and mattress was build to resemble a typical surgery condition. The patient lays supine on the mattress with the active electrode placed onto the thorax and the return electrode on his back. Common operating frequencies of electrosurgery units were considered. Finite Difference Time Domain electromagnetic analysis was carried out to compute the spatial distribution of current density within the patient's body. A differential analysis by changing the electrical properties of the operating table from a conductor to an insulator was also performed. Results: Results revealed that distributed capacitive coupling between patient body and the conductive operating table offers an alternative path to the electrosurgery current. The patient's anatomy, the positioning and the different electromagnetic properties of tissues promote a densification of the current at the head and sacral region. In particular, high values of current density were located behind the sacral bone and beneath the skin. This did not occur in the case of non-conductive operating table. Conclusion: Results of the simulation highlight the role played from capacitive couplings between the return electrode and the conductive operating table. The concentration of current density may result in an undesired rise in temperature, originating burns in body region far from the electrodes. This outcome is concordant with the type of surgery-related sacral burns reported in literature. Such burns cannot be immediately detected after surgery, but appear later and can be confused with bedsores. In addition, the dosimetric analysis suggests that reducing the capacity coupling between the return electrode and the operating table can decrease or avoid this problem. © 2013 Bifulco et al.; licensee BioMed Central Ltd.