Stacy-Paul Wilshaw

Biocompatibility and Potential of Acellular Human Amniotic Membrane to Support the Attachment and Proliferation of Allogeneic Cells

The aim of this study was to determine the biocompatibility of an acellular human amniotic membrane biomaterial, which may have clinical utility for cell delivery. Human amniotic membrane was decellularized using 0.03% (w/v) sodium dodecyl sulfate (SDS), with hypotonic tris buffer and protease inhibitors and nuclease treatment. The membrane was terminally sterilized using an optimal concentration of peracetic acid. Residual SDS present within the acellular membrane was quantified using radio-labeled C14 SDS. In vivo biocompatibility was assessed by implantation of acellular human amniotic membrane subcutaneously into mice for 3 months and comparison with fresh and glutaraldehyde-fixed tissue. Cellular infiltrate into the explanted tissues was characterized using monoclonal antibodies against the following cell surface markers: CD3, CD4, CD34, and F4/80. Calcification was determined using the Von Kossas stain. The potential of acellular human amniotic membrane to support the attachment and proliferation, and maintain viability of primary human dermal fibroblasts and primary human dermal keratinocytes was assessed in vitro, using a static culture system. Peracetic acid at a concentration of 0.1% (v/v) was sufficient for the sterilization of acellular amniotic membrane. Levels of SDS present within the acellular tissue were 0.62 +/- 0.13 microg/mg. Analysis of explanted samples from the mice indicated that acellular amniotic membrane contained low numbers of T-cells and high numbers of fibroblastic cells, macrophages, and endothelial cells, indicative of a wound-healing response. There was no evidence of calcification present within explanted acellular amniotic membrane compared to explanted glutaraldehyde-fixed amniotic membrane. Acellular amniotic membrane was shown to be capable of supporting the attachment and proliferation of primary human fibroblasts and keratinocytes. The viability of the cells was maintained for up to 4 weeks. Cell-seeded acellular amniotic membrane has the potential for delivering autologous or allogeneic cells to treat a variety of conditions, including diabetic foot ulcers, corneal defects, and severe skin burns.

Cytocompatibility of poly(1,2 propandiol methacrylate) copolymer hydrogels and conetworks with or without alkyl amine functionality

The cytocompatibility and adhesion of cells to biomaterials are key to their success in the clinic. Here we report a study of the toxicity, cell-adhesive properties and biocompatibility of a range of alkyl-aminated hydrogels and amphiphilic conetworks comprising 1,2-propandiol-3-methacrylate (GMA) as the hydrophilic component. Previously we had shown that addition of amines containing alkyl spacers of at 3-6 carbons or addition of oligo(butyl methacrylate) sequences to crosslinked polyGMA hydrogels could be used to produce a step change in cell adhesion. In this work we produced two series of polymer networks, based on polyGMA, which contained both of these structural features and we examined the effects that these materials had on A549 epithelial cells and human dermal fibroblasts. No toxicity was observed from either direct contact or from supernatants extracted over 48h. Each of the alkyl-aminated materials provided a good substrate for adhesion of both cell types whereas the non-alkyl-aminated materials were essentially non-cell-adhesive. Peritoneal murine macrophages were present on all of the materials and the activation of these adhered macrophages was investigated by determining the production of the pro-inflammatory cytokines, TNF-alpha, IL1beta and IL-6. All of the materials behaved similarly to a clinically acceptable control, Permacol (a decellularized collagen-based porcine derived material), and each material was much less activating than when the macrophages were in contact with lipopolysaccharide endotoxin. There were no differences in the capacity of the materials to activate TNF-alpha production by macrophages however, there was a trend towards stimulation of lower levels of IL-6 and IL-1beta by the alkyl-aminated materials.

The Use of Antithrombotic Therapies in Reducing Synthetic Small-Diameter Vascular Graft Thrombosis:

Background. Thrombosis of synthetic small-diameter bypass grafts remains a major problem. The aim of this article is to review the antithrombotic strategies that have been used in an attempt to reduce graft thrombogenicity. Methods. A PubMed/MEDLINE search was performed using the search terms “vascular graft thrombosis,” “small-diameter graft thrombosis,” “synthetic graft thrombosis” combined with “antithrombotic,” “antiplatelet,” “anticoagulant,” “Dacron,” “PTFE,” and “polyurethane.” Results. The majority of studies on antithrombotic therapies have used either in vitro models or in vivo animal experiments. Many of the therapies used in these settings do show antithrombotic efficacy against synthetic graft materials. There is however, a distinct lack of human in vivo studies to further delineate the performance and limitations of therapies displaying good antithrombotic characteristics. Conclusion. Very few antithrombotic therapies have translated into clinical use. More human in vivo studies are required to assess the efficacy and safety of such therapies.

Decellularisation and histological characterisation of porcine peripheral nerves

Peripheral nerve injuries affect a large proportion of the global population, often causing significant morbidity and loss of function. Current treatment strategies include the use of implantable nerve guide conduits (NGCs) to direct regenerating axons between the proximal and distal ends of the nerve gap. However, NGCs are limited in their effectiveness at promoting regeneration Current NGCs are not suitable as substrates for supporting either neuronal or Schwann cell growth, as they lack an architecture similar to that of the native extracellular matrix (ECM) of the nerve. The aim of this study was to create an acellular porcine peripheral nerve using a novel decellularisation protocol, in order to eliminate the immunogenic cellular components of the tissue, while preserving the three‐dimensional histoarchitecture and ECM components. Porcine peripheral nerve (sciatic branches were decellularised using a low concentration (0.1%; w/v) sodium dodecyl sulphate in conjunction with hypotonic buffers and protease inhibitors, and then sterilised using 0.1% (v/v) peracetic acid. Quantitative and qualitative analysis revealed a ≥95% (w/w) reduction in DNA content as well as preservation of the nerve fascicles and connective tissue. Acellular nerves were shown to have retained key ECM components such as collagen, laminin and fibronectin. Slow strain rate to failure testing demonstrated the biomechanical properties of acellular nerves to be comparable to fresh controls. In conclusion, we report the production of a biocompatible, biomechanically functional acellular scaffold, which may have use in peripheral nerve repair. Biotechnol. Bioeng. 2016;113: 2041–2053.

Investigation of the Antiadhesive Properties of Human Mesothelial Cells Cultured In Vitro on Implantable Surgical Materials

The aim of the study was to evaluate the interactions of Permacol, Prolene mesh, Surgisis Gold, and Alloderm with human mesothelial cells in vitro. The capacity of primary human mesothelial cells to adhere to the surface of Alloderm, Surgisis Gold, Prolene mesh, and Permacol as well as support the proliferation and viability of the seeded cells was determined. Production of antifibrinolytic, fibrinolytic, and inflammatory mediators (IL-8, TPA, MMP-1, PAI-1, and TGF-beta) was assessed over an 8-day period. The adhesive nature of the implantable materials was determined by assessment of the strength of any fibrin clots formed between two surfaces of each implant material. Surgisis Gold and Permacol were capable of supporting the attachment and proliferation of primary human mesothelial cells and maintaining viability over an 8-day culture period. Mesothelial cells were shown to have covered the surface of Permacol and Surgisis Gold in a monolayer. The viability of cells cultured on Permacol was significantly greater than the other implant materials tested. Mesothelial cells cultured on Permacol or Surgisis were shown to be producing high levels of fibrinolytic compounds and low levels of antifibrinolytic and inflammatory mediators. Alloderm was shown to produce high levels of IL-8 and antifibrinolytic mediators when compared with the other implantable materials. Permacol was shown to be an unreliable surface for clot formation in vitro and any clots formed were shown to be significantly weaker than the clots produced between two surfaces of tissue culture plastic, Prolene mesh, Alloderm, and Surgisis Gold. This in vitro study indicated that Permacol and Surgisis Gold supported the growth and fibrinolytic activity of human mesothelial cells; however, Permacol was shown to be superior in this respect.

An anatomical study of porcine peripheral nerve and its potential use in nerve tissue engineering

Current nerve tissue engineering applications are adopting xenogeneic nerve tissue as potential nerve grafts to help aid nerve regeneration. However, there is little literature that describes the exact location, anatomy and physiology of these nerves to highlight their potential as a donor graft. The aim of this study was to identify and characterise the structural and extracellular matrix (ECM) components of porcine peripheral nerves in the hind leg. Methods included the dissection of porcine nerves, localisation, characterisation and quantification of the ECM components and identification of nerve cells. Results showed a noticeable variance between porcine and rat nerve (a commonly studied species) in terms of fascicle number. The study also revealed that when porcine peripheral nerves branch, a decrease in fascicle number and size was evident. Porcine ECM and nerve fascicles were found to be predominately comprised of collagen together with glycosaminoglycans, laminin and fibronectin. Immunolabelling for nerve growth factor receptor p75 also revealed the localisation of Schwann cells around and inside the fascicles. In conclusion, it is shown that porcine peripheral nerves possess a microstructure similar to that found in rat, and is not dissimilar to human. This finding could extend to the suggestion that due to the similarities in anatomy to human nerve, porcine nerves may have utility as a nerve graft providing guidance and support to regenerating axons.

Recovery of low volumes of wear debris from rat stifle joint tissues using a novel particle isolation method

Less than optimal particle isolation techniques have impeded analysis of orthopaedic wear debris in vivo. The purpose of this research was to develop and test an improved method for particle isolation from tissue. A volume of 0.018 mm3 of clinically relevant CoCrMo, Ti-6Al-4V or Si3N4 particles was injected into rat stifle joints for seven days of in vivo exposure. Following sacrifice, particles were located within tissues using histology. The particles were recovered by enzymatic digestion of periarticular tissue with papain and proteinase K, followed by ultracentrifugation using a sodium polytungstate density gradient. Particles were recovered from all samples, observed using SEM and the particle composition was verified using EDX, which demonstrated that all isolated particles were free from contamination. Particle size, aspect ratio and circularity were measured using image analysis software. There were no significant changes to the measured parameters of CoCrMo or Si3N4 particles before and after the recovery process (KS tests, p > 0.05). Titanium particles were too few before and after isolation to analyse statistically, though size and morphologies were similar. Overall the method demonstrated a significant improvement to current particle isolation methods from tissue in terms of sensitivity and efficacy at removal of protein, and has the potential to be used for the isolation of ultra-low wearing total joint replacement materials from periprosthetic tissues. STATEMENT OF SIGNIFICANCE This research presents a novel method for the isolation of wear particles from tissue. Methodology outlined in this work would be a valuable resource for future researchers wishing to isolate particles from tissues, either as part of preclinical testing, or from explants from patients for diagnostic purposes. It is increasingly recognised that analysis of wear particles is critical to evaluating the safety of an orthopaedic device.

Development and optimisation data of a tissue digestion method for the isolation of orthopaedic wear particles

The data contained within this article relate to several enzymatic tissue digestion experiments which were performed to produce an optimised protocol for the digestion of tissue samples. The digestion experiments involved a total of four different digestion protocols. The first protocol involved digestion with proteinase K, without the use of glycine. The second protocol involved digestion with proteinase K in the presence of glycine. The third protocol consisted of proteinase K digestion in the presence of glycine, with more frequent enzyme replenishment. The final protocol was similar to the third protocol but included a papain digestion stage prior to digestion with proteinase K. The data contained within this article are photographs of tissue samples which were captured at key stages of the four protocols and written descriptions based on visual observation of the tissue samples, which document the appearance of the tissue digests.

Recovery rate data for silicon nitride nanoparticle isolation using sodium polytungstate density gradients

The average recovery rate of silicon nitride nanoparticles isolated from serum using the method detailed in previous article “A novel method for isolation and recovery of ceramic nanoparticles and metal wear debris from serum lubricants at ultra-low wear rate” (Lal et al., 2016) [1] was tested gravimetrically by weighing particles doped into serum before and after the isolation process. An average recovery rate of approximately 89.6% (± 7.1 SD) was achieved.

Validation of a novel particle isolation procedure using particle doped tissue samples

A novel particle isolation method for tissue samples was developed and tested using particle-doped peri-articular tissues from ovine cadavers. This enabled sensitivity of the isolation technique to be established by doping tissue samples of 0.25 g with very low particle volumes of 2.5 µm3 per sample. Image analysis was used to verify that the method caused no changes to particle size or morphologies.