Ag+- and Zn2+-exchange kinetics and antimicrobial properties of 11 angstrom tobermorites

Ag+- and Zn2+-exchanged zeolites zeolites and clays have been used as coatings and in composites to confer broad-spectrum antimicrobial properties on a range of technical and biomedical materials. 11 angstrom tobermorite is a bioactive layer lattice ion exchanger whose potential as a carrier for Ag+ and Zn2+ ions in antimicrobial formulations has not yet been explored. In view of this, batch Ag+- and Zn2+-exchange kinetics of two structurally distinct synthetic 11 angstrom tobermorites and their subsequent bactericidal action against Staphylococcus aureus and Pseudomonas aeruginosa are reported. During the exchange reactions, Ag+ ions were found to replace labile interlayer cations; whereas, Zn2+ ions also displaced structural Ca2+ ions from the tobermorite lattice. In spite of these different mechanisms, a simple pseudo-second-order model provided a suitable description of both exchange processes (R-2 >= 0.996). The Ag+- and Zn2+-exchanged tobermorite phases exhibited marked bacteriostatic effects against both bacteria, and accordingly, their potential for use as antimicrobial materials for in situ bone tissue regeneration is discussed. (C) 2008 Elsevier Ltd. All rights reserved.

Accelerated degradation behaviour of poly(epsilon-caprolactone) via melt blending with poly(aspartic acid-co-lactide) (PAL)

Poly(epsilon-caprolactone) (PCL) has many favourable attributes for tissue engineering scaffold applications. A major drawback, however, is its slow degradation rate, typically greater than 3 years. In this study PCL was melt blended with a small percentage of poly(aspartic acid-co-lactide) (PAL) and the degradation behaviour was evaluated in phosphate buffer solution (PBS) at 37 degrees C. The addition of PAL was found to significantly enhance the degradation profile of PCL. Subsequent degradation behaviour was investigated in terms of the polymer's mechanical properties, Molecular weight (M-w), mass changes and thermal characteristics. The results indicate that the addition of PAL accelerates the degradation of PCL, with 20% mass loss recorded after just 7 months in vitro for samples containing 8 wt% PAL. The corresponding pure PCL samples exhibited no mass loss over the same time period. In vitro assessment of PCL and PCL/PAL composites in tissue Culture medium in the absence of cells revealed stable pH readings with time. SEM studies of cell/biomaterial interactions demonstrated biocompatibility of C3H10T1/2 cells with PCL and PCL/PAL composites at all concentrations of PAL additive. (C) 2008 Elsevier Ltd. All rights reserved.

Regenerative Medicine and New Labour Life Science Policy: Rhetorics of Success, Narratives of Sustainability and Survival

Advances in stem cell science and tissue engineering are being turned into applications and products through a novel medical paradigm known as regenerative medicine. This paper begins by examining the vulnerabilities and risks encountered by the regenerative medicine industry during a pivotal moment in its scientific infancy: the 2000s. Under the auspices of New Labour, British medical scientists and life science innovation firms associated with regenerative medicine, received demonstrative rhetorical pledges of support, aligned with the publication of a number of government initiated reports presaged by Bioscience 2015: Improving National Health, Increasing National Wealth. The Department of Health and the Department of Trade and Industry (and its successors) held industry consultations to determine the best means by which innovative bioscience cultures might be promoted and sustained in Britain. Bioscience 2015 encapsulates the first chapter of this sustainability narrative. By 2009, the tone of this storyline had changed to one of survivability. In the second part of the paper, we explore the ministerial interpretation of the ‘bioscience discussion cycle’ that embodies this narrative of expectation, using a computer-aided content analysis programme. Our analysis notes that the ministerial interpretation of these reports has continued to place key emphasis upon the distinctive and exceptional characteristics of the life science industries, such as their ability to perpetuate innovations in regenerative medicine and the optimism this portends – even though many of the economic expectations associated with this industry have remained unfulfilled.

The potential of electron beam radiation for simultaneous surface modification and bioresorption control of PLLA

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the fields of tissue engineering and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), Llactide/DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid (PLGA)). This work investigates the further potential of ebeam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. PLLA samples were subjected to e-beam treatments in air, with varying beam energies and doses. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy. Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA (as predicted). However, e-beam effects on surface properties were not shown to be dependent on beam energy or dose. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment.

Embryonic stem cell differentiation into smooth muscle cells is mediated by Nox4-produced H2O2

NADPH oxidase (Nox4) produces reactive oxygen species (ROS) that are important for vascular smooth muscle cell (SMC) behavior, but the potential impact of Nox4 in stem cell differentiation is unknown. When mouse embryonic stem (ES) cells were plated on collagen IV-coated dishes/flasks, a panel of SMC-specific genes was significantly and consistently upregulated. Nox4 expression was markedly correlated with such a gene induction as confirmed by real-time PCR, immunofluorescence, and Western blot analysis. Overexpression of Nox4 specifically resulted in increased SMC marker production, whereas knockdown of Nox4 induced a decrease. Furthermore, SMC-specific transcription factors, including serum response factor (SRF) and myocardin were activated by Nox4 gene expression. Moreover, Nox4 was demonstrated to drive SMC differentiation through generation of H(2)O(2). Confocal microscopy analysis indicates that SRF was translocated into the nucleus during SMC differentiation in which SRF was phosphorylated. Additionally, autosecreted transforming growth factor (TGF)-beta(1) activated Nox4 and promoted SMC differentiation. Interestingly, cell lines generated from stem cells by Nox4 transfection and G418 selection displayed a characteristic of mature SMCs, including expression of SMC markers and cells with contractile function. Thus we demonstrate for the first time that Nox4 is crucial for SMC differentiation from ES cells, and enforced Nox4 expression can maintain differentiation status and functional features of stem cell-derived SMCs, highlighting its impact on vessel formation in vivo and vascular tissue engineering in the future.

Ex Vivo Expansion of Human Outgrowth Endothelial Cells Leads to IL-8-Mediated Replicative Senescence and Impaired Vasoreparative Function

Harnessing outgrowth endothelial cells (OECs) for vasoreparative therapy and tissue-engineering requires efficient ex-vivo expansion. How such expansion impacts on OEC function is largely unknown. In this study, we show that OECs become permanently cell-cycle arrested after ex-vivo expansion, which is associated with enlarged cell size, ß-galactosidase activity, DNA damage, tumour suppressor pathway activation and significant transcriptome changes. These senescence hallmarks were coupled with low telomerase activity and telomere shortening, indicating replicative senescence. OEC senescence limited their regenerative potential by impairing vasoreparative properties in-vitro and in-vivo. Integrated transcriptome-proteome analysis identified inflammatory signalling pathways as major mechanistic components of the OEC senescence programme. In particular, IL8 was an important facilitator of this senescence; depletion of IL8 in OECs significantly extended ex-vivo lifespan, delayed replicative senescence and enhanced function. While the ability to expand OEC numbers prior to autologous or allogeneic therapy remains a useful property, their replicative senescence and associated impairment of vasorepair needs to be considered. The current study also suggests that modulation of the senescence-associated secretory phenotype (SASP) could be used to optimise OEC therapy.

A novel three-dimensional culture system for isolation and clonal propagation of neural stem cells using a thermo-reversible gelation polymer

In the present study, we examined the possible utility of a three-dimensional culture system using a thermo-reversible gelation polymer to isolate and expand neural stem cells (NSCs). The polymer is a synthetic biologically inert polymer and gelates at temperatures higher than the gel-sol transition point ( approximately 20 degrees C). When fetal mouse brain cells were inoculated into the gel, spherical colonies were formed ( approximately 1% in primary culture and approximately 9% in passage cultures). The spheroid-forming cells were positive for expression of the NSC markers nestin and Musashi. Under conditions facilitating spontaneous neural differentiation, the spheroid-forming cells expressed genes characteristic to astrocytes, oligodendrocytes, and neurons. The cells could be successively propagated at least to 80 poly-D-lysines over a period of 20 weeks in the gel culture with a growth rate higher than that observed in suspension culture. The spheroids formed by fetal mouse brain cells in the gel were shown to be of clonal origin. These results indicate that the spheroid culture system is a convenient and powerful tool for isolation and clonal expansion of NSCs in vitro.