3D fibrous structures as cardiovascular implants

Medical textiles are a highly specialised stream of technical textiles industry with a growing range of applications. A significant advancement has been achieved in surgical products or biomedical textiles (implantable/non-implantable) with the advent of 3D textile manufacturing techniques. Cardiovascular soft tissue implants (vascular grafts) have been a field of interest over decades for use of innovative 3D tubular structures in treatment of cardiovascular diseases. In the field of soft tissue implants, knitted and woven tubular structures are being used for large diameter blood vessel replacements. Advent of electrospinning and tissue engineering techniques has been able to provide promising answers to small diameter vascular grafts. The aim of this review is to outline the approaches in vascular graft development utilising different 3D tubular structure forming techniques. The emphasis is on vascular graft development techniques that can help improve treatment efficacy in future.

Amyloid formation results in recurrence of hyperglycaemia following transplantation of human IAPP transgenic mouse islets

Aims/hypothesis Islet transplantation is a potential cure for diabetes; however, rates of graft failure remain high. The aim of the present study was to determine whether amyloid deposition is associated with reduced beta cell volume in islet grafts and the recurrence of hyperglycaemia following islet transplantation.

Methods We transplanted a streptozotocin-induced mouse model of diabetes with 100 islets from human IAPP (which encodes islet amyloid polypeptide) transgenic mice that have the propensity to form islet amyloid (n = 8–12) or from non-transgenic mice that do not develop amyloid (n = 6–10) in sets of studies that lasted 1 or 6 weeks.

Results Plasma glucose levels before and for 1 week after transplantation were similar in mice that received transgenic or non-transgenic islets, and at that time amyloid was detected in all transgenic grafts and, as expected, in none of the non-transgenic grafts. However, over the 6 weeks following transplantation, plasma glucose levels increased in transgenic but remained stable in non-transgenic islet graft recipients (p < 0.05). At 6 weeks, amyloid was present in 92% of the transgenic grafts and in none of the non-transgenic grafts. Beta cell volume was reduced by 30% (p < 0.05), beta cell apoptosis was twofold higher (p < 0.05), and beta cell replication was reduced by 50% (p < 0.001) in transgenic vs non-transgenic grafts. In summary, amyloid deposition in islet grafts occurs prior to the recurrence of hyperglycaemia and its accumulation over time is associated with beta cell loss.

Conclusions/interpretation Islet amyloid formation may explain, in part, the non-immune loss of beta cells and recurrence of hyperglycaemia following clinical islet transplantation.

Optimization of bypass graft using FSI numerical method

It is well documented in literature that the coronary artery bypass graft is normally fail after a short period of time, due to the development of plaque known as intimal hyperplasia within the graft. Various in vivo and in vitro studies have linked the development of intimal hyperplasia to the abnormal hemodynamics and compliance mismatch. Therefore, it is essential to fully understand the relationship between the hemodynamics inside the coronary artery bypass and its mechanical and geometrical characteristics under the correct physiological conditions. In this work, hemodynamic of the bypass graft is studied numerically. The effect of the host and graft diameters ratio, the angle of anastomosis and the graft configuration on the local flow patterns and the distribution of wall shear stress are examined. The pulsatile waveforms boundary conditions are adopted from in vivo measurement data to study the hemodynamics of composite grafts namely Consequence and Y grafting in terms temporal and spatial distributions of the blood flows. Moreover, various non-Newtonian and Newtonian models of blood have been carried out to examine the numerical simulation of blood flow in stenosis artery. The results are presented and discussed for various operating conditions.

In vitro studying corrosion behaviour of biocorrodible Mg alloys

The idea of bioabsorbable/biocorrodible stents has gained increasing attention in the last decade. Permanent coronary stents, traditionally made from 316L grade stainless steel, are routinely used for the treatment of blocked arteries. However, these stents can cause complications such as restenosis, thrombosis and the need for the patient to undergo prolonged antiplatelet therapy. Biodegradable metal stents provide an opportunity for the stent to remain in place for a period to ensure restoration of function and then degrade through a carefully controlled bio-corrosion process. Among the number of potentially suitable materials, Magnesium alloys have shown great promise as a stent material due to their non-toxicity [1] and the corrosion rates attainable in biological environments. However, a carefully controlled corrosion process is essential in order to avoid hyper hydrogen generation and the fatal consequences that follow. In addition uniform corrosion is a basic requirement to maintain the mechanical integrity and load bearing characteristics. Work being undertaken in our laboratories focuses on controlling the corrosion behaviour of magnesium in a simulated biological environment in the presence of protein. In the investigation reported here the Mg alloy has been examined using Scanning Electrochemical Microscope (SECM) to visualize the corrosion process and identify the corrosion pattern. Complementary bulk electrochemical techniques (EIS and potentiodynamic polarization) have been used to acquire kinetic and mechanistic information. Early results obtained by SECM have revealed the tendency towards pitting corrosion in the early stages which subsequently develops in to filiform corrosion.

Elastin and collagen enhances electrospun aligned polyurethane as scaffolds for vascular graft

Mismatch in mechanical properties between synthetic vascular graft and arteries contribute to graft failure. The viscoelastic properties of arteries are conferred by elastin and collagen. In this study, the mechanical properties and cellular interactions of aligned nanofibrous polyurethane (PU) scaffolds blended with elastin, collagen or a mixture of both proteins were examined. Elastin softened PU to a peak stress and strain of 7.86 MPa and 112.28 % respectively, which are similar to those observed in blood vessels. Collagen-blended PU increased in peak stress to 28.14 MPa. The growth of smooth muscle cells (SMCs) on both collagen-blended and elastin/collagen-blended scaffold increased by 283 and 224 % respectively when compared to PU. Smooth muscle myosin staining indicated that the cells are contractile SMCs which are favored in vascular tissue engineering. Elastin and collagen are beneficial for creating compliant synthetic vascular grafts as elastin provided the necessary viscoelastic properties while collagen enhanced the cellular interactions.

Engineering a multimodal nerve conduit for repair of injured peripheral nerve

Injury to nerve tissue in the peripheral nervous system (PNS) results in long-term impairment of limb function, dysaesthesia and pain, often with associated psychological effects. Whilst minor injuries can be left to regenerate without intervention and short gaps up to 2 cm can be sutured, larger or more severe injuries commonly require autogenous nerve grafts harvested from elsewhere in the body (usually sensory nerves). Functional recovery is often suboptimal and associated with loss of sensation from the tissue innervated by the harvested nerve. The challenges that persist with nerve repair have resulted in development of nerve guides or conduits from non-neural biological tissues and various polymers to improve the prognosis for the repair of damaged nerves in the PNS. This study describes the design and fabrication of a multimodal controlled pore size nerve regeneration conduit using polylactic acid (PLA) and (PLA):poly(lactic-co-glycolic) acid (PLGA) fibers within a neurotrophin-enriched alginate hydrogel. The nerve repair conduit design consists of two types of PLGA fibers selected specifically for promotion of axonal outgrowth and Schwann cell growth (75:25 for axons; 85:15 for Schwann cells). These aligned fibers are contained within the lumen of a knitted PLA sheath coated with electrospun PLA nanofibers to control pore size. The PLGA guidance fibers within the nerve repair conduit lumen are supported within an alginate hydrogel impregnated with neurotrophic factors (NT-3 or BDNF with LIF, SMDF and MGF-1) to provide neuroprotection, stimulation of axonal growth and Schwann cell migration. The conduit was used to promote repair of transected sciatic nerve in rats over a period of 4 weeks. Over this period, it was observed that over-grooming and self-mutilation (autotomy) of the limb implanted with the conduit was significantly reduced in rats implanted with the full-configuration conduit compared to rats implanted with conduits containing only an alginate hydrogel. This indicates return of some feeling to the limb via the fully-configured conduit. Immunohistochemical analysis of the implanted conduits removed from the rats after the four-week implantation period confirmed the presence of myelinated axons within the conduit and distal to the site of implantation, further supporting that the conduit promoted nerve repair over this period of time. This study describes the design considerations and fabrication of a novel multicomponent, multimodal bio-engineered synthetic conduit for peripheral nerve repair.

Has carotid artery stenting found its place? A 10-year regional centre perspective

The post-Carotid Revascularization Endarterectomy versus Stenting Trial era has seen a dramatic decline in the practice of carotid artery stenting (CAS). A retrospective review of prospectively collected CAS outcomes over a 10-year period by a single operator was undertaken to determine if this change in practice is justified and to identify the place of carotid stenting in current practice.

Assessment of acute burn management in 32 low- and middle-income countries

BACKGROUND: The purpose of this study is to ascertain whether acute burn management (ABM) is available at health facilities in low- and middle-income countries (LMICs). METHOD: The study used the World Health Organization situational analysis tool (SAT) which is designed to assess emergency and essential surgical care and includes data points relevant to the acute management of burns. The SAT was available for 1413 health facilities in 59 countries. RESULTS: A majority (1036, 77.5 %) of the health facilities are able to perform ABM. The main reasons for the referral of ABM are lack of skills (53.4 %) and non-functioning equipment (52.2 %). Considering health centres and district/rural/community hospitals that referred due to lack of supplies/drugs and/or non-functioning equipment, almost half of the facilities were not able to provide continuous and consistent access to the equipment required either for resuscitation or to perform burn wound debridement. Out of the facilities that performed ABM, 379 (36.6 %) are capable of carrying out skin grafts and contracture release, which is indicative of their ability to manage full thickness burns. However the magnitude of full thickness burns managed was limited in half of these facilities, as they did not have access to a blood bank. CONCLUSION: The initial management of acute burns is generally available in LMICs, however it is constrained by the inability to perform resuscitation (19 %) and/or burn wound debridement (10 %). For more severe burns, an inability to perform skin grafting or contracture release limits definitive management of full thickness burns, whilst lack of availability to blood further compromises the treatment of major burns.

Medical textiles as vascular implants and their success to mimic natural arteries

Vascular implants belong to a specialised class of medical textiles. The basic purpose of a vascular implant (graft and stent) is to act as an artificial conduit or substitute for a diseased artery. However, the long-term healing function depends on its ability to mimic the mechanical and biological behaviour of the artery. This requires a thorough understanding of the structure and function of an artery, which can then be translated into a synthetic structure based on the capabilities of the manufacturing method utilised. Common textile manufacturing techniques, such as weaving, knitting, braiding, and electrospinning, are frequently used to design vascular implants for research and commercial purposes for the past decades. However, the ability to match attributes of a vascular substitute to those of a native artery still remains a challenge. The synthetic implants have been found to cause disturbance in biological, biomechanical, and hemodynamic parameters at the implant site, which has been widely attributed to their structural design. In this work, we reviewed the design aspect of textile vascular implants and compared them to the structure of a natural artery as a basis for assessing the level of success as an implant. The outcome of this work is expected to encourage future design strategies for developing improved long lasting vascular implants.