Biofabrication and biomaterials for urinary tract reconstruction.

Reconstructive urologists are constantly facing diverse and complex pathologies that require structural and functional restoration of urinary organs. There is always a demand for a biocompatible material to repair or substitute the urinary tract instead of using patient's autologous tissues with its associated morbidity. Biomimetic approaches are tissue-engineering tactics aiming to tailor the material physical and biological properties to behave physiologically similar to the urinary system. This review highlights the different strategies to mimic urinary tissues including modifications in structure, surface chemistry, and cellular response of a range of biological and synthetic materials. The article also outlines the measures to minimize infectious complications, which might lead to graft failure. Relevant experimental and preclinical studies are discussed, as well as promising biomimetic approaches such as three-dimensional bioprinting.

A current affair: electrotherapy in wound healing.

New developments in accelerating wound healing can have immense beneficial socioeconomic impact. The wound healing process is a highly orchestrated series of mechanisms where a multitude of cells and biological cascades are involved. The skin battery and current of injury mechanisms have become topics of interest for their influence in chronic wounds. Electrostimulation therapy of wounds has shown to be a promising treatment option with no-device-related adverse effects. This review presents an overview of the understanding and use of applied electrical current in various aspects of wound healing. Rapid clinical translation of the evolving understanding of biomolecular mechanisms underlying the effects of electrical simulation on wound healing would positively impact upon enhancing patient's quality of life.

Dual-acting biofunctionalised scaffolds for applications in regenerative medicine.

Off the shelf scaffolds for replacing ultra-small diameter vascular grafts are valuable for reconstruction of diseased or damaged vessels. The limitations for such grafts include optimal handling with ready availability of varied lengths of grafts, graft patency with the ability to replace the function of active cellular mechanisms and adequate mechanical properties to maintain physicochemical function. We used a well-established, solvent casting method for potential tissue replacement scaffold fabrication with incorporated bioactive molecules, which we have previously explored to confer haemocompatibility. These grafts were tested in-vivo within the abdominal aorta of 10 Wistar rats and the patency was clinically and echographically evaluated. Haemocompatibility and endothelialisation were assessed on explants. Biofunctionalised scaffolds were also grafted subcutaneously and intraperitoneally to evaluate integration, inflammation and angiogenesis reactions. The potential wider applications of this dual acting scaffold were evaluated for its interactions with human dermal fibroblasts as well as bronchial epithelial cells. Physicochemical property evaluation of the functionalised grafts has clarified the mechanical strength and permeability. This study confirmed the microsurgical suturability of tubular grafts and graft patency of functionalized scaffolds. The study demonstrated the potential of a dual acting biofunctionalised scaffold's use for a wide range of tissue engineering applications where micro-porous, yet impermeable scaffolds are needed.

Biomimetic heterogenous elastic tissue development.

There is an unmet need for artificial tissue to address current limitations with donor organs and problems with donor site morbidity. Despite the success with sophisticated tissue engineering endeavours, which employ cells as building blocks, they are limited to dedicated labs suitable for cell culture, with associated high costs and long tissue maturation times before available for clinical use. Direct 3D printing presents rapid, bespoke, acellular solutions for skull and bone repair or replacement, and can potentially address the need for elastic tissue, which is a major constituent of smooth muscle, cartilage, ligaments and connective tissue that support organs. Thermoplastic polyurethanes are one of the most versatile elastomeric polymers. Their segmented block copolymeric nature, comprising of hard and soft segments allows for an almost limitless potential to control physical properties and mechanical behaviour. Here we show direct 3D printing of biocompatible thermoplastic polyurethanes with Fused Deposition Modelling, with a view to presenting cell independent in-situ tissue substitutes. This method can expeditiously and economically produce heterogenous, biomimetic elastic tissue substitutes with controlled porosity to potentially facilitate vascularisation. The flexibility of this application is shown here with tubular constructs as exemplars. We demonstrate how these 3D printed constructs can be post-processed to incorporate bioactive molecules. This efficacious strategy, when combined with the privileges of digital healthcare, can be used to produce bespoke elastic tissue substitutes in-situ, independent of extensive cell culture and may be developed as a point-of-care therapy approach.

A Material Conferring Hemocompatibility.

There is a need for biomimetic materials for use in blood-contacting devices. Blood contacting surfaces maintain their patency through physico-chemical properties of a functional endothelium. A poly(carbonate-urea) urethane (PCU) is used as a base material to examine the feasibility of L-Arginine methyl ester (L-AME) functionalized material for use in implants and coatings. The study hypothesizes that L-AME, incorporated into PCU, functions as a bioactive porogen, releasing upon contact with blood to interact with endothelial nitric oxide synthase (eNOS) present in blood. Endothelial progenitor cells (EPC) were successfully cultured on L-AME functionalized material, indicating that L-AME -increases cell viability. L-AME functionalized material potentially has broad applications in blood-contacting medical devices, as well as various other applications requiring endogenous up-regulation of nitric oxide, such as wound healing. This study presents an in-vitro investigation to demonstrate the novel anti-thrombogenic properties of L-AME, when in solution and when present within a polyurethane-based polymer.

Nitric oxide in paediatric respiratory disorders: novel interventions to address associated vascular phenomena?

Nitric oxide (NO) has a significant role in modulating the respiratory system and is being exploited therapeutically. Neonatal respiratory failure can affect around 2% of all live births and is responsible for over one third of all neonatal mortality. Current treatment method with inhaled NO (iNO) has demonstrated great benefits to patients with persistent pulmonary hypertension, bronchopulmonary dysplasia and neonatal respiratory distress syndrome. However, it is not without its drawbacks, which include the need for patients to be attached to mechanical ventilators. Notably, there is also a lack of identification of subgroups amongst abovementioned patients, and homogeneity in powered studies associated with iNO, which is one of the limitations. There are significant developments in drug delivery methods and there is a need to look at alternative or supplementary methods of NO delivery that could reduce current concerns. The addition of NO-independent activators and stimulators, or drugs such as prostaglandins to work in synergy with NO donors might be beneficial. It is of interest to consider such delivery methods within the respiratory system, where controlled release of NO can be introduced whilst minimizing the production of harmful byproducts. This article reviews current therapeutic application of iNO and the state-of-the-art technology methods for sustained delivery of NO that may be adapted and developed to address respiratory disorders. We envisage this perspective would prompt active investigation of such systems for their potential clinical benefit.

Is Nitric Oxide Assuming a Janus-Face in The Central Nervous System?

Nitric Oxide, synthesized from L-arginine by the nitric oxide synthases, has a complex role within the human body. It contributes to almost every physiological system and has been found to be both protective and toxic in disease states. An aging population faces an increasing incidence of neurodegenerative disease and the pathological action of nitric oxide in Alzheimer's and Parkinson's diseases may be important therapeutic targets for the future. Nitric oxide's protective effects are also important to consider, through inhibition of caspase-3, nitrosylation of NMDA and increased activation of protein kinase B and CREB transcription factor. Nitric oxide has been shown to play a part in long term potentiation, revealing its importance in synaptic plasticity. Due to nitric oxide's mixed effects it is an exciting and varied therapeutic target. Currently, the impact of these therapies has been explored and developed in animal studies, but is yet to be fully realized in human trials. This paper outlines both the pathological and protective roles of nitric oxide in the central nervous system and the potential pharmacological therapies and targets these indicate.

Tubular organ epithelialisation.

Hollow, tubular organs including oesophagus, trachea, stomach, intestine, bladder and urethra may require repair or replacement due to disease. Current treatment is considered an unmet clinical need, and tissue engineering strategies aim to overcome these by fabricating synthetic constructs as tissue replacements. Smart, functionalised synthetic materials can act as a scaffold base of an organ and multiple cell types, including stem cells can be used to repopulate these scaffolds to replace or repair the damaged or diseased organs. Epithelial cells have not yet completely shown to have efficacious cell-scaffold interactions or good functionality in artificial organs, thus limiting the success of tissue-engineered grafts. Epithelial cells play an essential part of respective organs to maintain their function. Without successful epithelialisation, hollow organs are liable to stenosis, collapse, extensive fibrosis and infection that limit patency. It is clear that the source of cells and physicochemical properties of scaffolds determine the successful epithelialisation. This article presents a review of tissue engineering studies on oesophagus, trachea, stomach, small intestine, bladder and urethral constructs conducted to actualise epithelialised grafts.

Evaluation of experimental methods for nitric oxide release from cardiovascular implants; bypass grafts as an exemplar.

BACKGROUND: There is a great potential for nitric oxide (NO) eluting biomaterials in biomedical applications. These include the development of cardiovascular implants, wound healing products, or applications in cancer and respiratory therapy. While the potential of these materials as a therapy is becoming clearer, the real-time monitoring of NO is not easy and the success in the development of such materials depends on the accurate quantification of NO release. METHOD: To emphasize on the importance of a measurement technique on the outcome of an experiment, we compared total NO released from S-nitroso-N-acetyl-d-penicillamine (SNAP) incorporated nanocomposite polymer in the form of bypass grafts under simulated physiological conditions using amperometric and chemiluminescence techniques. RESULTS: We found that the total amount of NO measured by the amperometric technique was 35.8% of the theoretical amount. Similarly, on measuring NO release from the bypass grafts, we demonstrated that the chemiluminesence technique detected NO at a relatively higher level. CONCLUSIONS: The results of this study clearly demonstrate the relative difference between analysis techniques for accurate NO detection that can be applied to distinct experimental models associated with NO-eluting cardiovascular implants.

A potential platform for developing 3D tubular scaffolds for paediatric organ development.

Children suffer from damaged or loss of hollow organs i.e. trachea, oesophagus or arteries from birth defects or diseases. Generally these organs possess an outer matrix consisting of collagen, elastin, and cells such as smooth muscle cells (SMC) and a luminal layer consisting of endothelial or epithelial cells, whilst presenting a barrier to luminal content. Tissue engineering research enables the construction of such organs and this study explores this possibility with a bioabsorbable nanocomposite biomaterial, polyhedral oligomeric silsesquioxane poly(ε-caprolactone) urea urethane (POSS-PCL).Our established methods of tubular graft extrusion were modified using a porogen-incorporated POSS-PCL and a new lamination method was explored. Porogen (40, 60 or 105 µm) were introduced to POSS-PCL, which were fabricated into a bilayered, dual topography matching the exterior and luminal interior of tubular organs. POSS-PCL with different amounts of porogen were tested for their suitability as a SMC layer by measuring optimal interactions with human adipose derived stem cells. Angiogenesis potential was tested with the chorioallantoic membrane assay. Tensile strength and burst pressures of bilayared tubular grafts were determined. Scaffolds made with 40 µm porogen demonstrated optimal adipose derived stem cell integration and the scaffolds were able to accommodate angiogenesis. Mechanical properties of the grafts confirmed their potential to match the relevant physiological and biophysical parameters. This study presents a platform for the development of hollow organs for transplantation based on POSS-PCL. These bilayered-tubular structures can be tailor-made for cellular integration and match physico-mechanical properties of physiological systems of interest. More specific luminal cell integration and sources of SMC for the external layer could be further explored.

The effect of TGF-ß1 and BMP-4 on bone marrow-derived stem cell morphology on a novel bioabsorbable nanocomposite material.

CONTEXT: Congenital heart disease is a leading cause of death in the first year, with an incidence of 1.5 million worldwide. It can be treated with bypass surgery, but due to the limited availability of autologous grafts, there has been research into developing a completely tissue-engineered vascular graft. Our group has developed a small diameter, biodegradable nanocomposite graft which is non-thrombogenic and biostable. OBJECTIVES: This study looks at the effects of the growth factors, TGF-ß1 and BMP-4 on bone marrow-derived stem cell (BMSC) morphology on a POSS PCL scaffold. MATERIALS AND METHODS: BMSCs were seeded onto a new nanocomposite of POSS (polyhedral oligomeric silsesquioxane) and PCL (poly[caprolactone-urea]urethane) and TGF-ß1 and BMP-4 were used to induce differentiation of the cells to smooth muscle cells. The distribution of the cells was examined using confocal and electron microscopies and the phenotype of the cells was assessed using immunohistochemistry. RESULTS: It was found that growth factor induction led to a decrease in cell growth on POSS PCL as compared to that of the control surface, and confocal microscopic analysis showed less cytoskeleton reorganization of these cells. After immunohistochemistry analysis, the BMSCs showed no differentiation to smooth muscle cells. DISCUSSION: Growth factor induction on the static scaffold discs led to a change in morphology, with less spreading of the cells, a lower proliferation rate and no differentiation into SMCs. These findings can be attributed to the POSS PCL being manufactured by a coagulation technique, resulting in a structure with low stiffness.

Nitric oxide-eluting nanocomposite for cardiovascular implants.

Cardiovascular implants must resist thrombosis and intimal hyperplasia, but they are prone to such patency limiting conditions during graft implantation and prior to endothelialisation. Nitric oxide (NO) released from the endothelium has a complex protective role in the cardiovascular system, and this study has addressed: (1) in situ NO release profiles from S-nitrosothiols ((S-Nitroso-N-acetylpenicillamine (SNAP) and (S-Nitrosoglutathione (GSNO)) incorporated into polyhedral oligomeric silsesquioxanepoly(carbonate-urea)urethane (POSS-PCU) coronary artery bypass grafts (CABG) in a physiological pulsatile flow, and (2) the determination of their interaction with endothelial progenitor cells (EPCs), smooth muscle cells, platelets, whole blood kinetics. It was found that 1, 2, and 3 wt% SNAP/GSNO incorporated into POSS-PCU-CABG successfully eluted NO, but optimal elution was evident with 2 %-SNAP-POSS-PCU. NO release determined under static conditions using the Griess assay, and in situ measurements under pulsatile flow using amperometric probe was found to differ, thus confirming the significance of monitoring NO-elution under haemodynamic conditions. 2 %-SNAP-POSS-PCU demonstrated anti-thrombogenic kinetics through thromboelastography measurements, while metabolic activity using Alamar Blue™ assay and scanning electron microscopy demonstrated greater adhesion of EPCs and reduced adhesion of platelets.

Fumed silica nanoparticle mediated biomimicry for optimal cell-material interactions for artificial organ development.

Replacement of irreversibly damaged organs due to chronic disease, with suitable tissue engineered implants is now a familiar area of interest to clinicians and multidisciplinary scientists. Ideal tissue engineering approaches require scaffolds to be tailor made to mimic physiological environments of interest with specific surface topographical and biological properties for optimal cell-material interactions. This study demonstrates a single-step procedure for inducing biomimicry in a novel nanocomposite base material scaffold, to re-create the extracellular matrix, which is required for stem cell integration and differentiation to mature cells. Fumed silica nanoparticle mediated procedure of scaffold functionalization, can be potentially adapted with multiple bioactive molecules to induce cellular biomimicry, in the development human organs. The proposed nanocomposite materials already in patients for number of implants, including world first synthetic trachea, tear ducts and vascular bypass graft.

Arterial tissue regeneration for pediatric applications: inspiration from up-to-date tissue-engineered vascular bypass grafts.

The need for a valid replacement for autologous tissues in vascular surgery has led to the development of tissue-engineered vascular grafts (TEVGs). Currently, only three kinds of TEVG have been used in clinical trials: synthetic scaffold-based TEVGs, self-assembled grafts, and decellularized exogenous tissues. This review presents the current options in the construction of TEVG and the changes that have occurred in the design following the clinical experience while focusing on the potential for pediatric applications. The emerging trend in the field, which is also pertinent for pediatric applications, is a shift from the development of vascular analogues to implants composed of scaffolds with autologous cellular components. Designs of such implants are currently being fine-tuned so that a natural, functional tissue can gradually take over the role of scaffolds to stimulate the host's regenerative capacity and maintain the physiological homeostasis.

Inception to actualization: next generation coronary stent coatings incorporating nanotechnology.

Percutaneous coronary intervention (PCI) is used to treat blocked coronary arteries. Bare-metal stents (BMS) were first used in PCI but often necessitated repair procedures due to in-stent restenosis. Drug-eluting stents (DES) were developed to address this problem as the stent-incorporated anti-proliferative drugs prevented restenosis. However late-stent thrombosis arose with the use of DES due to polymer hypersensitivity and impaired re-endothelialization. Evidence suggests that using a combination of biofunctionalized polymers and antibody/peptide motifs can prevent thrombosis while ensuring in situ endothelialization. The advent of nanotechnology has engendered techniques like layer-by-layer self-assembly, and localized drug and gene delivery using nanoparticles. Therefore, this review seeks to explore the convergence of biotechnology and nanotechnology for the next generation coronary stent coatings, with an emphasis on its development from bench to beside.

Surface modification of a polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU) nanocomposite polymer as a stent coating for enhanced capture of endothelial progenitor cells.

An unmet need exists for the development of next-generation multifunctional nanocomposite materials for biomedical applications, particularly in the field of cardiovascular regenerative biology. Herein, we describe the preparation and characterization of a novel polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU) nanocomposite polymer with covalently attached anti-CD34 antibodies to enhance capture of circulating endothelial progenitor cells (EPC). This material may be used as a new coating for bare metal stents used after balloon angioplasty to improve re-endothelialization. Biophysical characterization techniques were used to assess POSS-PCU and its subsequent functionalization with anti-CD34 antibodies. Results indicated successful covalent attachment of anti-CD34 antibodies on the surface of POSS-PCU leading to an increased propensity for EPC capture, whilst maintaining in vitro biocompatibility and hemocompatibility. POSS-PCU has already been used in 3 first-in-man studies, as a bypass graft, lacrimal duct and a bioartificial trachea. We therefore postulate that its superior biocompatibility and unique biophysical properties would render it an ideal candidate for coating medical devices, with stents as a prime example. Taken together, anti-CD34 functionalized POSS-PCU could form the basis of a nano-inspired polymer platform for the next generation stent coatings.

Nitric oxide donors for cardiovascular implant applications.

In an era of increased cardiovascular disease burden in the ageing population, there is great demand for devices that come in to contact with the blood such as heart valves, stents, and bypass grafts that offer life saving treatments. Nitric oxide (NO) elution from healthy endothelial tissue that lines the vessels maintains haemostasis throughout the vasculature. Surgical devices that release NO are desirable treatment options and N-diazeniumdiolates and S-nitrosothiols are recognized as preferred donor molecules. There is a keen interest to investigate newer methods by which NO donors can be retained within biomaterials so that their release and kinetic profiles can be optimized. A range of polymeric scaffolds incorporating microparticles and nanomaterials are presenting solutions to current challenges, and have been investigated in a range of clinical applications. This review outlines the application of NO donors for cardiovascular therapy using biomaterials that release NO locally to prevent thrombosis and intimal hyperplasia (IH) and enhance endothelialization in the fabrication of next generation cardiovascular device technology.

Orchestrating cell/material interactions for tissue engineering of surgical implants.

Research groups are currently recognising a critical clinical need for innovative approaches to organ failure and agenesis. Allografting, autologous reconstruction and prosthetics are hampered with severe limitations. Pertinently, readily available 'laboratory-grown' organs and implants are becoming a reality. Tissue engineering constructs vary in their design complexity depending on the specific structural and functional demands. Expeditious methods on integrating autologous stem cells onto nanoarchitectured 3D nanocomposites, are being transferred from lab to patients with a number of successful first-in-man experiences. Despite the need for a complete understanding of cell/material interactions tissue engineering is offering a plethora of exciting possibilities in regenerative medicine.

Surface modification of biomaterials: a quest for blood compatibility.

Cardiovascular implants must resist thrombosis and intimal hyperplasia to maintain patency. These implants when in contact with blood face a challenge to oppose the natural coagulation process that becomes activated. Surface protein adsorption and their relevant 3D confirmation greatly determine the degree of blood compatibility. A great deal of research efforts are attributed towards realising such a surface, which comprise of a range of methods on surface modification. Surface modification methods can be broadly categorized as physicochemical modifications and biological modifications. These modifications aim to modulate platelet responses directly through modulation of thrombogenic proteins or by inducing antithrombogenic biomolecules that can be biofunctionalised onto surfaces or through inducing an active endothelium. Nanotechnology is recognising a great role in such surface modification of cardiovascular implants through biofunctionalisation of polymers and peptides in nanocomposites and through nanofabrication of polymers which will pave the way for finding a closer blood match through haemostasis when developing cardiovascular implants with a greater degree of patency.