UV surface modification of a new nanocomposite polymer to improve cytocompatibility.

A novel modified nanocomposite was studied for the adhesion and proliferation of the human umbilical vein endothelial cell (HUVEC) line EA.hy926. The nanocomposite under investigation was poly(carbonate-urea)urethane with silsesquioxane nano-cages, here in the form of a mixture of two polyhedral oligomeric silsesquioxanes.

Silsesquioxane nanocomposites as tissue implants.

Background: Silicone implants are being used increasingly worldwide, especially in breast augmentation procedures. The most common morbidity observed is capsular contracture, which occurs in 15 percent of cases. To overcome this problem, the authors have developed a novel nanocomposite based on polyhedral oligomeric silsesquioxane-poly(carbonate-urea)urethane (POSS-PCU) for use as tissue implants.

Incorporation of a lauric acid-conjugated GRGDS peptide directly into the matrix of a poly(carbonate-urea)urethane polymer for use in cardiovascular bypass graft applications.

Gly-Arg-Gly-Asp-Ser (GRGDS) was modified by conjugation to lauric acid (LA) to facilitate incorporation into the matrix of a poly(carbonate-urea)urethane (PCU) used in vascular bypass grafts. GRGDS and LA-GRGDS were synthesized using solid phase Fmoc chemistry and characterized by high performance liquid chromatography and Fourier transform infrared spectroscopy. LA-GRGDS was passively coated and incorporated as nanoparticle dispersion on the PCU films.

The endothelialization of polyhedral oligomeric silsesquioxane nanocomposites: an in vitro study.

It has been recognized that seeding vascular bypass grafts with endothelial cells is the ideal method of improving their long-term patency rates. The aim of this study was to assess the in vitro cytocompatibility of a novel silica nanocomposite, polyhedral oligomeric silsesquioxane-poly(carbonate-urea)urethane (POSS-PCU) and hence elicit its feasibility at the vascular interface for potential use in cardiovascular devices such as vascular grafts. Using primary human umbilical vein endothelial cells (HUVEC), cell viability and adhesion were studied using AlamarBlue assays, whereas cell proliferation on the polymer was assessed using the PicoGreen dye assay.

Polyhedral oligomeric silsequioxane-polyurethane nanocomposite microvessels for an artificial capillary bed.

Fabricating artificial vascularised tissue would involve tissue-engineering techniques, but current technology limits this as cultured cells depend on growth media in vitro and on diffusion in vivo. Therefore, there is a need to construct a synthetic microvascular network, which would sustain these cultured cells in a similar manner to normal tissue. This is again hampered by the poor patency rates of current microvascular grafts.

Review paper: principles and applications of surface analytical techniques at the vascular interface.

Surface properties have been found to be one of the key parameters which cause degradation and of thrombogenicity in all polymers used in biomedical devices, thus signifying the importance and the necessity for quantitative and accurate characterization of the polymer surface itself as used in the construction of the device. The characterization techniques employed generally involve thermal and spectroscopic measurements, in which class the electrochemical investigations and scanning probe microscopies can also be included. Current hypotheses on the correlations that exist between surface parameters and hemocompatibility and degradation of polymers are examined herein, but concentrating on the field of clinically utilized polymeric materials as used within medical devices themselves.

The antithrombogenic potential of a polyhedral oligomeric silsesquioxane (POSS) nanocomposite.

We have developed a nanocomposite using a silica nanocomposite polyhedral oligomeric silsesquioxane (POSS) and poly(carbonate-urea)urethane (PCU) for potential use in cardiovascular bypass grafts and the microvascular component of artificial capillary beds. In this study, we sought to compare its antithrombogenicity to that of conventional polymers used in vascular bypass grafts so as to improve upon current patency rates, particularly in the microvascular setting. Using atomic force microscopy (AFM) and transmission electron microscopy (TEM), surface topography and composition were studied, respectively.

Cardiovascular tissue engineering: state of the art.

In patients requiring coronary or peripheral vascular bypass procedures, autogenous arterial or vein grafts remain as the conduit of choice even in the case of redo patients. It is in this class of redo patients that often natural tissue of suitable quality becomes unavailable; so that prosthetic material is then used. Prosthetic grafts are liable to fail due to graft occlusion caused by surface thrombogenicity and lack of elasticity.

Polyhedral oligomeric silsesquioxane nanocomposites: the next generation material for biomedical applications.

The unique properties of nanocomposites have seen them creating the next revolution in materials science. Their quantal properties as a result of their size have given them unique physical characteristics, previously not possible because of classical physical laws. There is now evidence that these may also extend into the world of biology and medicine.

The degradative resistance of polyhedral oligomeric silsesquioxane nanocore integrated polyurethanes: an in vitro study.

Polymer biostability is one of the critical parameters by which these materials are selected for use as biomedical devices. This is the major rationale for the use of polymers which are highly crystalline and stiff namely expanded polytetrafluoroethylene (ePTFE) and Dacron in particular, as arterial bypass grafts. While this is immaterial in high-flow states, it becomes critically important at lower flows with a greater need for more compliant vessels.

Single stage cell seeding of small diameter prosthetic cardiovascular grafts.

Small-diameter prosthetic cardiovascular bypass grafts have high occlusion rates. Thrombogenicity caused by the lack of endothelial cells (ECs) on the luminal surface of the grafts is one of the main reasons for its occlusion. One strategy to improve the clinical performance of cardiovascular prosthetic grafts has been to seed its luminal surface with a monolayer of the patient's own ECs.

Advancing cartilage tissue engineering: the application of stem cell technology.

The treatment of cartilage pathology and trauma face the challenges of poor regenerative potential and inferior repair. Nevertheless, recent advances in tissue engineering indicate that adult stem cells could provide a source of chondrocytes for tissue engineering that the isolation of mature chondrocytes has failed to achieve. Various adjuncts to their propagation and differentiation have been explored, such as biomaterials, bioreactors and growth hormones.

The contemporary role of antioxidant therapy in attenuating liver ischemia-reperfusion injury: a review.

Oxidative stress is an important factor in many pathological conditions such as inflammation, cancer, ageing and organ response to ischemia-reperfusion. Humans have developed a complex antioxidant system to eliminate or attenuate oxidative stress. Liver ischemia-reperfusion injury occurs in a number of clinical settings, including liver surgery, transplantation, and hemorrhagic shock with subsequent fluid resuscitation, leading to significant morbidity and mortality.

Advancing vascular tissue engineering: the role of stem cell technology.

Atherosclerosis and heart disease are still the leading causes of morbidity and mortality worldwide. The lack of suitable autologous grafts has produced a need for artificial grafts but the patency of such grafts is limited compared to natural materials. Tissue engineering, whereby living tissue replacements can be constructed, has emerged as a solution to some of these difficulties.

Interactions between endothelial cells and a poly(carbonate-silsesquioxane-bridge-urea)urethane.

We have recently developed a polymer which contains silsesquioxane in the form of nano-bridges poly(carbonate-silsesquioxane-bridge-urea)urethane (PCBSU) for cardiovascular device applications. The polymer has been characterised and the durability has been confirmed with long-term in vivo tests. The aim of this study was to test the cytocompatibility of the new polymer and to investigate any potential cytotoxic effects.

Artificial nerve conduits in peripheral-nerve repair.

Injuries to the nervous system are the result of mechanical, thermal, chemical or congenital pathologies and, if function is not restored, they lead to loss of muscle function, pain and impaired sensation. Current treatment modalities essentially coapt the two nerves ends together or place a nerve graft between the cut ends. However, clinical results have never been optimal, and therefore a quest for better options has taken place.

Current status of prosthetic bypass grafts: a review.

Polymers such as Dacron and polytetrafluoroethylene (PTFE) have been used in high flow states with relative success but with limited application at lower flow states. Newer polymers with greater compliance, biomimicry, and ability to evolve into hybrid prostheses, suitable as smaller vessels, are now being introduced. In view of the advances in tissue engineering, this makes possible the creation of an ideal off-the-shelf bypass graft.

Development of an RNA isolation procedure for the characterisation of human endothelial cell interactions with polyurethane cardiovascular bypass grafts.

To date no reliable method has been developed for the isolation of RNA from cells seeded onto cylindrical vascular grafts. This study was performed in order to develop a reliable methodology for isolating RNA from cylindrical conduits made from poly(carbonate-urea)urethane (PU). Human umbilical vein EC were seeded onto PU vascular grafts and an Alamar blue assay performed to assess cell viability.

The roles of tissue engineering and vascularisation in the development of micro-vascular networks: a review.

The construction of tissue-engineered devices for medical applications is now possible in vitro using cell culture and bioreactors. Although methods of incorporating them back into the host are available, current constructs depend purely on diffusion which limits their potential. The absence of a vascular network capable of distributing oxygen and other nutrients within the tissue-engineered device is a major limiting factor in creating vascularised artificial tissues.

Shear-stress preconditioning and tissue-engineering-based paradigms for generating arterial substitutes.

In situ tissue engineering using shear-stress preconditioning and adhesive biomolecules is a new approach to autologous tissue engineering. In the present study, novel tissue-engineering grafts (TEGs) were preconditioned within an in vitro pulsatile flow circuit, with and without the addition of fibronectin (FN), to establish whether low-shear-stress conditions promoted endothelial cell (EC) retention and differentiation. TEGs ( n =24) were generated by the contraction and compaction of collagen(I) by porcine aortic smooth-muscle cells (SMCs) on to a compliant polyester graft scaffold.

The use of animal models in developing the discipline of cardiovascular tissue engineering: a review.

Cardiovascular disease remains one of the major causes of death and disability in the Western world. Tissue engineering offers the prospect of being able to meet the demand for replacement of heart valves, vessels for coronary and lower limb bypass surgery and the generation of cardiac tissue for addition to the diseased heart. In order to test prospective tissue-engineered devices, these constructs must first be proven in animal models before receiving CE marking or FDA approval for a clinical trial.

Surface functionalization and grafting of heparin and/or RGD by an aqueous-based process to a poly(carbonate-urea)urethane cardiovascular graft for cellular engineering applications.

An aqueous-based process is reported for surface functionalization and grafting of anticoagulant and cell attachment moieties, such as heparin and/or arginine-glycine- aspartate (RGD) onto the lumenal surface of a prefabricated cardiovascular graft (5 mm i.d.) made of poly(carbonate- urea)urethane (MyoLink).

In vivo biostability of a poly(carbonate-urea)urethane graft.

In peripheral and coronary bypass surgery, the patency of prosthetic grafts is inferior to autologous vein, mainly due to intimal hyperplasia caused in part by compliance mismatch between rigid graft and elastic host artery. We have developed a compliant poly(carbonate-urea)urethane vascular graft "MyoLink" which was biostable in vitro degradation studies. To further investigate the biostability of this material, we report a long-term in vivo study on 8 beagle dogs (15+/-3 kg) implanted with this graft (ID 5mm) in the aorta-iliac position; three grafts were harvested at 18 months to assess short-term biodegradation, with one animal having died from an unrelated infection.

An assessment of covalent grafting of RGD peptides to the surface of a compliant poly(carbonate-urea)urethane vascular conduit versus conventional biological coatings: its role in enhancing cellular retention.

The aim of sodding prosthetic grafts with endothelial cells (EC) is to establish a functioning antithrombogenic monolayer of EC. Application of basement membrane proteins improves EC adherence on ePTFE grafts. Their addition to a biodurable compliant poly(carbonate-urea)urethane graft (CPU) was studied with respect to EC adherence.