Effects of Chemical and Radiation Sterilisation on the Biological and Biomechanical Properties of Decellularised Porcine Peripheral Nerves

There is a clinical need for novel graft materials for the repair of peripheral nerve defects. A decellularisation process has been developed for porcine peripheral nerves, yielding a material with potentially significant advantages over other devices currently being used clinically (such as autografts and nerve guidance conduits). Grafts derived from xenogeneic tissues should undergo sterilisation prior to clinical use. It has been reported that sterilisation methods may adversely affect the properties of decellularised tissues, and therefore potentially negatively impact on the ability to promote tissue regeneration. In this study, decellularised nerves were produced and sterilised by treatment with 0.1% (v/v) PAA, gamma radiation (25–28 kGy) or E Beam (33–37 kGy). The effect of sterilisation on the decellularised nerves was determined by cytotoxicity testing, histological staining, hydroxyproline assays, uniaxial tensile testing, antibody labelling for collagen type IV, laminin and fibronectin in the basal lamina, and differential scanning calorimetry. This study concluded that decellularised nerves retained biocompatibility following sterilisation. However, sterilisation affected the mechanical properties (PAA, gamma radiation), endoneurial structure and basement membrane composition (PAA) of decellularised nerves. No such alterations were observed following E Beam treatment, suggesting that this method may be preferable for the sterilisation of decellularised porcine peripheral nerves

Ex-vivo recellularisation and stem cell differentiation of a decellularised rat dental pulp matrix

Implementing the principles of tissue engineering within the clinical management of non-vital immature permanent teeth is of clinical interest. However, the ideal scaffold remains elusive. The aim of this work was to assess the feasibility of decellularising rat dental pulp tissue and evaluate the ability of such scaffold to support stem cell repopulation. Rat dental pulps were retrieved and divided into control and decellularised groups. The decellularisation protocol incorporated a low detergent concentration and hypotonic buffers. After decellularisation, the scaffolds were characterised histologically, immunohistochemistry and the residual DNA content quantified. Surface topography was also viewed under scanning electron microscopy. Biocompatibility was evaluated using cytotoxicity assays utilising L-929 cell line. Decellularised scaffolds were recellularised with human dental pulp stem cells up to 14 days in vitro. Cellular viability was assessed using LIVE/DEAD stain kit and the recellularised scaffolds were further assessed histologically and immunolabelled using makers for odontoblastic differentiation, cytoskeleton components and growth factors. Analysis of the decellularised scaffolds revealed an acellular matrix with histological preservation of structural components. Decellularised scaffolds were biocompatible and able to support stem cell survival following recellularisation. Immunolabelling of the recellularised scaffolds demonstrated positive cellular expression against the tested markers in culture. This study has demonstrated the feasibility of developing a biocompatible decellularised dental pulp scaffold, which is able to support dental pulp stem cell repopulation. Clinically, decellularised pulp tissue could possibly be a suitable scaffold for use within regenerative (reparative) endodontic techniques

Gamma-irradiated human amniotic membrane decellularised with sodium dodecyl sulfate is a more efficient substrate for the ex vivo expansion of limbal stem cells

yesThe gold standard substrate for the ex vivo expansion of human limbal stem cells (LSCs) remains the human amniotic membrane (HAM) but this is not a defined substrate and is subject to biological variabil-ity and the potential to transmit disease. To better define HAM and mitigate the risk of disease transmis-sion, we sought to determine if decellularisation and/or c-irradiation have an adverse effect on culture growth and LSC phenotype. Ex vivo limbal explant cultures were set up on fresh HAM, HAM decellularised with 0.5 M NaOH, and 0.5% (w/v) sodium dodecyl sulfate (SDS) with or without c-irradiation. Explant growth rate was measured and LSC phenotype was characterised by histology, immunostaining and qRT-PCR (ABCG2, DNp63, Ki67, CK12, and CK13). Ƴ-irradiation marginally stiffened HAM, as measured by Brillouin spectromicroscopy. HAM stiffness and c-irradiation did not significantly affect the LSC phe-notype, however LSCs expanded significantly faster on Ƴ-irradiated SDS decellularised HAM (p < 0.05) which was also corroborated by the highest expression of Ki67 and putative LSC marker, ABCG2. Colony forming efficiency assays showed a greater yield and proportion of holoclones in cells cultured on Ƴ-irradiated SDS decellularised HAM. Together our data indicate that SDS decellularised HAM may be a more efficacious substrate for the expansion of LSCs and the use of a c-irradiated HAM allows the user to start the manufacturing process with a sterile substrate, potentially making it safer

To what extent is behaviour a problem in English schools?:Exploring the scale and prevalence of deficits in classroom climate

The working atmosphere in the classroom is an important variable in the process of education in schools, with several studies suggesting that classroom climate is an important influence on pupil attainment. There are wide differences in the extent to which classroom climate is considered to be a problem in English schools. Some ‘official’ reports suggest that behaviour in schools is ‘satisfactory or better’ in the vast majority of schools; other sources have pointed to behaviour being a serious and widespread problem. The paper details four studies conducted over the past decade which aimed to explore these disparities. The aim of the research was to gain a more accurate insight into the extent to which deficits in classroom climate limit educational attainment and equality of educational opportunity in English schools. The findings question the suggestion that behaviour is satisfactory or better in 99.7% of English schools and the concluding section suggests ways in which deficits in classroom climate might be addressed. Although the study is limited to classrooms in England, OECD studies suggest that deficits in the working atmosphere in classrooms occur in many countries. The study therefore has potential relevance for education systems in other countries

Towards high efficiency inversion layer cells based on ion-charged dielectrics

This work investigates the production and performance of p-type Inversion Layer (IL) Si solar cells, manufactured with an ion-injection technique that produces a highly charged dielectric nanolayer. Ions are applied to the front dielectric layer and then driven towards the c-Si/SiO2 interface by an electric field before stabilisation with an anneal. As this process can be performed in minutes at temperatures below 500 °C, it potentially provides a fast, yet controllable way for IL cell manufacturing. We demonstrate by simulations using Sentaurus TCAD that for the 1 ·cm p-type Si/thermal oxide model defined in this work, the sheet resistance of the field-induced electron layer can reach 1.1 k/sq in the dark by reducing band-tail interface state density to below 1014 eV-1cm-2 and increasing the dielectric charge density to above 2 × 1013 cm-2. Additionally, we present a proof-of-concept p-type IL cell on a non-gettered, non-hydrogenated substrate with an efficiency of 10.8%, and an open-circuit voltage (VOC) equivalent to that in a cell with a diffused phosphorous emitter. Lastly, we perform Sentaurus TCAD simulations to assess the efficiency potential of such IL cells. By incorporating optimal passivation, gettering, hydrogenation and metallisation, IL cells are predicted to reach an efficiency of 24.5% on 5 ·cm, and beyond 24.8% on 10 ·cm p-type substrates, provided the dielectric charge density reaches 2 × 1013 cm-2, which has been experimentally demonstrated to be possible. IL cells are therefore, in principle, a potential competitive candidate in the photovoltaic industry

Development and characterisation of a large diameter decellularised vascular allograft

The aims of this study were to develop a biological large diameter vascular graft by decellularisation of native human aorta to remove the immunogenic cells whilst retaining the essential biomechanical, and biochemical properties for the ultimate benefit of patients with infected synthetic grafts. Donor aortas (n = 6) were subjected to an adaptation of a propriety decellularisation process to remove the cells and acellularity assessed by histological analysis and extraction and quantification of total DNA. The biocompatibility of the acellular aortas was determined using standard contact cytotoxicity tests. Collagen and denatured collagen content of aortas was determined and immunohistochemistry was used to determine the presence of specific extracellular matrix proteins. Donor aortas (n = 6) were divided into two, with one half subject to decellularisation and the other half retained as native tissue. The native and decellularised aorta sections were then subject to uniaxial tensile testing to failure [axial and circumferential directions] and suture retention testing. The data was compared using a paired t-test. Histological evaluation showed an absence of cells in the treated aortas and retention of histoarchitecture including elastin content. The decellularised aortas had less than 15 ng mg¯¹ total DNA per dry weight (mean 94% reduction) and were biocompatible as determined by in vitro contact cytotoxicity tests. There were no gross changes in the histoarchitecture [elastin and collagen matrix] of the acellular aortas compared to native controls. The decellularisation process also reduced calcium deposits within the tissue. The uniaxial tensile and suture retention testing revealed no significant differences in the material properties (p > 0.05) of decellularised aorta. The decellularisation procedure resulted in minimal changes to the biological and biomechanical properties of the donor aortas. Acellular donor aorta has excellent potential for use as a large diameter vascular graft

A Criterion for Brittle Failure of Rocks Using the Theory of Critical Distances

This paper presents a new analytical criterion for brittle failure of rocks and heavily overconsolidated soils. Griffith’s model of a randomly oriented defect under a biaxial stress state is used to keep the criterion simple. The Griffith’s criterion is improved because the maximum tensile strength is not evaluated at the boundary of the defect but at a certain distance from the boundary, known as the critical distance. This fracture criterion is known as the Point Method, and is part of the Theory of Critical Distances, which is utilized in fracture mechanics. The proposed failure criterion has two parameters: the inherent tensile strength, ó0, and the ratio of the half-length of the initial crack/flaw to the critical distance, a/L. These parameters are difficult to measure but they may be correlated with the uniaxial compressive and tensile strengths, óc and ót. The proposed criterion is able to reproduce the common range of strength ratios for rocks and heavily overconsolidated soils (óc/ót=3-50) and the influence of several microstructural rock properties, such as texture and porosity. Good agreement with laboratory tests reported in the literature is found for tensile and low confining stresses.The work presented was initiated during a research project on “Structural integrity assessments of notch-type defects", for the Spanish Ministry of Science and Innovation (Ref.: MAT2010-15721)

AN ELECTRON-BEAM-INDUCED CURRENT STUDY OF DISLOCATIONS IN GAAS

Well-characterized α, β and screw dislocations have been created in GaAs specimens. dislocation segments which thread the semiconductor surface at a known angle have been studied in terms of their behavior as recombination centres and an analysis of the minority carrier diffusion length LD, has been performed. In liquid-encapsulated Czochralski (LEC) and liquid-phase epitaxy (LPE) material LD is small (less than 1.6 μm) and varies strongly with temperatures and incident beam current. A simulation using numerical integration and a realistic Monte Carlo generation function has been developed which allows the electron-beam-induced current (EBIC) contrast of dislocations of any geometry to be modelled