In Vitro Hydrodynamic Assessment of a New Transcatheter Heart Valve Concept (the TRISKELE).

This study presents the in vitro hydrodynamic assessment of the TRISKELE, a new system suitable for transcatheter aortic valve implantation (TAVI), aiming to mitigate the procedural challenges experienced with current technologies. The TRISKELE valve comprises three polymeric leaflet and an adaptive sealing cuff, supported by a novel fully retrievable self-expanding nitinol wire frame. Valve prototypes were manufactured in three sizes of 23, 26, and 29 mm by automated dip-coating of a biostable polymer, and tested in a hydrodynamic bench setup in mock aortic roots of 21, 23, 25, and 27 mm annulus, and compared to two reference valves suitable for equivalent implantation ranges: Edwards SAPIEN XT and Medtronic CoreValve. The TRISKELE valves demonstrated a global hydrodynamic performance comparable or superior to the controls with significant reduction in paravalvular leakage. The TRISKELE valve exhibits enhanced anchoring and improved sealing. The valve is currently under preclinical investigation.

Next generation covered stents made from nanocomposite materials: A complete assessment of uniformity, integrity and biomechanical properties.

Covered stents are stents wrapped with a thin polymeric membrane, and are typically used to treat vessel aneurysms and seal perforated arteries. Current covered stents suffer from restenosis due to limitations in material and fabrication methods which leaves metallic struts directly exposed to blood. We have developed a biocompatible and haemocompatible nanocomposite polymer, polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU). We devised a novel combination of ultrasonic spray atomisation system and dip-coating process to produce small calibre covered stents with metal struts fully embedded within the membrane, which also yields greater coating uniformity. Stent-polymer bonding was enhanced via silanisation and coating of reactive pre-polymer. Platelet studies supported the non-thrombogenicity of POSS-PCU. Biomechanical performances including diametrical compliance, bending strength, radial strength and recoil were evaluated and optimised. This proof-of-principle manufacturing technique could lead to the development of next-generation small calibre adult and paediatric covered stents. These stents are currently undergoing preclinical trial. From the Clinical Editor: The use of stents to treat vascular diseases is now the standard of care in the clinical setting. Nonetheless, a major problem of the current stents is the risk of restenosis and thrombosis. The authors developed a nanocomposite material using polyhedral oligomeric silsesquioxane and poly(carbonate-urea) urethane (POSS-PCU) and incorporated into metallic stents. Preliminary data have already shown promising results. It is envisaged that this would further lead to better stent technology in the future.

Development of a Cost-Effective and Simple Protocol for Decellularization and Preservation of Human Amniotic Membrane as a Soft Tissue Replacement and Delivery System for Bone Marrow Stromal Cells.

The aim of this study is to develop a simple and cost-effective method for decellularization and preservation of human amniotic membrane (HAM) as a soft tissue replacement and a delivery system for stem cells. The HAM is decellularized (D) using new chemical and mechanical techniques. The decellularization scaffold is evaluated histologically and fully characterized. The cell adhesion and proliferation on the scaffold are also investigated and the biocompatibility of D tissues is evaluated in vivo. The histological studies reveal that the cells are successfully removed from the D tissue. The DNA extraction shows more than 95% cell removal (p = 0.001). The in vitro results indicate that the decellularisation process does not deteriorate the mechanical properties of the tissue, whereas it increases the in vitro biodegradation value (p < 0.05). In the D samples, there is no significant cytotoxicity, and no changes are found in the rate of cell proliferation (p > 0.05). Immunohistochemistry staining indicates that all the tested components remain unchanged within the D tissues. The count of inflammatory cells show that the decellularization process slightly increases the biocompatibility of the tissue after 7 days post-surgery. The results indicate that scaffold proves to be reproducible, rapid, and cost-effective, with a potential role for clinical application.

Biomimetic modified clinical-grade POSS-PCU nanocomposite polymer for bypass graft applications: a preliminary assessment of endothelial cell adhesion and haemocompatibility.

BACKGROUND: To date, there are no small internal diameter (<5mm) vascular grafts that are FDA approved for clinical use due to high failure rates from thrombosis and unwanted cell proliferation. The ideal conditions to enhance bioengineered grafts would be the blood contacting lumen of the bypass graft fully covered by endothelial cells (ECs). As a strategy towards this aim, we hypothesized that by immobilising biomolecules on the surface of the polyhedral oligomeric silsesquioxane-poly(carbonate-urea)urethane (POSS-PCU) nanocomposite polymers, which contain binding sites and ligands for cell surface receptors similar to extracellular matrix (ECM) will positively influence the attachment and proliferation of ECs. Since, the surface of POSS-PCU is inert and not directly suitable for immobilisation of biomolecules, plasma graft polymerisation is a suitable method to modify the surface properties ready for immobilisation and biofunctionalisation. METHODS: POSS-PCU was activated by plasma treatment in air/O2 to from hydroperoxides (-OH, -OOH), and then carboxylated via plasma polymerisation of a 30% acrylic acid solution (Poly-AA) using a two-step plasma treatment (TSPT) process. Collagen type I, a major component of ECM, was covalently immobilised to mimic the ECM structures to ECs (5mg/ml) using a two-step chemical reaction using EDC chemistry. Successful immobilisation of poly-AA and collagen on to the nanocomposites was confirmed using Toluidine Blue staining and the Bradford assay. Un-treated POSS-PCU served as a simple control. The impact of collagen grafting on the physical, mechanical and biological properties of POSS-PCU was evaluated via contact angle (θ) measurements, scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA), ECs adhesion and proliferation followed by platelet adhesion and haemolysis ratio (HR) tests. RESULTS: Poly-AA content on each of the plasma treated nanocomposite films increased on Low, Med and High samples due to more carboxylic acid (-COOH) groups at the surface forming amide (-NH2) bonds. The amount of -COOH groups on each of the Low, Med and High nanocomposites correlated with Poly-AA grafting density at 14.7±0.9, 18.9±0.9, and 34.2±2.4 µg/cm(2). Immobilisation of collagen type I on to nanocomposite surface was also found to increase significantly on the Low, Med and High samples from 22±4, 150±15, and 219±17 µg/cm(2), respectively. The level of ECs and their adhesion efficiency were improved with increasing amounts of grafted collagen I. The maximum adhesion of ECs was found on the highest collagen type I coated nanocomposites. Platelet adhesion and activation also increased with increasing collagen density. The obtained HR values for all of the treated samples were well within the acceptable standards for biomaterials (<5% HR). CONCLUSION: Poly-AA-g-POSS-PCU surfaces offer binding sites for the covalent bonding of collagen type I and other biomolecules such as fibronectin by exposure of RGD cell binding domains and growth factors using EDC cross-linking chemistry. Collagen type I modification can yield accelerated EC growth and enhance the endothelialisation of POSS-PCU nanocomposites, and the amount of immobilised collagen can control the level of platelet adhesion on functionalized POSS-PCU via TSPT and poly acrylic acid (poly-AA) treatment. Such surface modification procedures of polymeric surfaces can improve the patency rate of POSS-PCU nanocomposites as vascular bypass grafts in the preparation of a range of medical devices ready for pre-clinical and in vivo evaluation.

A polyhedral oligomeric silsesquioxane-based bilayered dermal scaffold seeded with adipose tissue-derived stem cells: in vitro assessment of biomechanical properties.

BACKGROUND: Although commercial skin substitutes are widely available, its use remains challenging at surgery and postoperatively. The high cost is also prohibitive. We designed and characterized a scaffold for dermal replacement, using advanced nanocomposite materials, which are known to have unique nanoscale features that enhance cellular behavior. METHODS: A bilayered scaffold was developed using the nanocomposite, polyhedral oligomeric silsesquioxane, incorporated into poly(caprolactone-urea)urethane, resulting in a mechanically robust bioabsorbable polymer; forming the inner layer, which was designed with a range of porosities. The removable outer layer contained nanosilver. Tensile testing, surface tension, permeability, and scanning electron microscopy were performed. Optimal pore morphology for cellular proliferation was elucidated through adipose tissue-derived stem cell culture and a cell viability assay. All tests were repeated on Integra Dermal Regeneration Template. RESULTS: The physical construct was easy to handle and clinically applicable. Macroporosity and permeability of scaffolds was demonstrated, confirmed by scanning electron microscopy. Both tensile strength and surface tension were comparable with skin; outer layer demonstrated hydrophobicity and inner layer showed hydrophilicity. Cell assay confirmed cellular proliferation onto the scaffold, comparable with Integra. CONCLUSIONS: We demonstrate that a porous bilayered dermal scaffold could form the basis of a new generation of skin substitute that is both mechanically robust and harbors the ability for enhancing cell regeneration.

An anti-CD34 antibody-functionalized clinical-grade POSS-PCU nanocomposite polymer for cardiovascular stent coating applications: a preliminary assessment of endothelial progenitor cell capture and hemocompatibility.

In situ endothelialization of cardiovascular implants has emerged in recent years as an attractive means of targeting the persistent problems of thrombosis and intimal hyperplasia. This study aimed to investigate the efficacy of immobilizing anti-CD34 antibodies onto a POSS-PCU nanocomposite polymer surface to sequester endothelial progenitor cells (EPCs) from human blood, and to characterize the surface properties and hemocompatibility of this surface. Amine-functionalized fumed silica was used to covalently conjugate anti-CD34 to the polymer surface. Water contact angle, fluorescence microscopy, and scanning electron microscopy were used for surface characterization. Peripheral blood mononuclear cells (PBMCs) were seeded on modified and pristine POSS-PCU polymer films. After 7 days, adhered cells were immunostained for the expression of EPC and endothelial cell markers, and assessed for the formation of EPC colonies. Hemocompatibility was assessed by thromboelastography, and platelet activation and adhesion assays. The number of EPC colonies formed on anti-CD34-coated POSS-PCU surfaces was not significantly higher than that of POSS-PCU (5.0±1.0 vs. 1.7±0.6, p>0.05). However, antibody conjugation significantly improved hemocompatibility, as seen from the prolonged reaction and clotting times, decreased angle and maximum amplitude (p<0.05), as well as decreased platelet adhesion (76.8±7.8 vs. 8.4±0.7, p<0.05) and activation. Here, we demonstrate that POSS-PCU surface immobilized anti-CD34 antibodies selectively captured CD34+ cells from peripheral blood, although only a minority of these were EPCs. Nevertheless, antibody conjugation significantly improves the hemocompatibility of POSS-PCU, and should therefore continue to be explored in combination with other strategies to improve the specificity of EPC capture to promote in situ endothelialization.

Manufacturing and hydrodynamic assessment of a novel aortic valve made of a new nanocomposite polymer.

Synthetic leaflet heart valves have been widely studied as possible alternatives to the current mechanical and bioprosthetic valves. Assessing the in vitro hydrodynamic function of these prostheses is of great importance to predict their hemodynamic behaviour prior to implantation. This study introduces an innovative concept of a low-profile semi-stented surgical aortic valve (SSAV) made of a novel nanocomposite polyurethane with a polycarbonate soft segment (PCU) and polyhedral oligomeric silsesquioxane (POSS) nanoparticles covalently bonded as a pendant cage to the hard segment. The POSS-PCU is already used in surgical implants, including lacrimal duct, bypass graft, and recently, a tracheal replacement. Nine valves of three leaflet thicknesses (100, 150 and 200 µm) and 21 mm internal diameter were prepared using an automated dip-coating procedure, and assessed in vitro for their hydrodynamic performance on a pulse duplicator system. A commercially available porcine bioprosthetic valve (Epic™, St. Jude Medical) of equivalent size was selected as a control model. Compared to the bioprosthetic valve, the SSAVs showed a considerably lower transvalvular pressure drop and larger effective orifice area (EOA). They were also characterised by a lower systolic energy loss, especially at high cardiac outputs. The leaflet thickness was found to significantly affect the hydrodynamics of these valves (P<0.01). The SSAVs with 100 µm leaflets demonstrated improved flow characteristics compared to the bioprosthetic valve. The enhanced hydrodynamic function of the SSAV suggests that the proposed design together with the advanced POSS-PCU material can represent a significant step towards the introduction of polyurethane valves into the clinical application.

An aortic model for the physiological assessment of endovascular stent-grafts.

BACKGROUND: The aim of this study was to manufacture a new aortic model with physiological properties, which could be used for long-term durability testing of endovascular stent-grafts, as per the recommendations of the Food and Drug Administration. METHODS: Porcine abdominal aortas were acquired to establish values for compliance. The aortic model was manufactured using a nanocomposite polymer. Latex mock aorta was used for comparison. A pulsatile flow phantom perfused the aortas and synthetic tubes at physiological pulse pressure and flow. Diametrical compliance and stiffness index were calculated over mean pressures from 30 to 120 mm Hg. Data were analyzed using one-way analysis of variance and Bonferroni's test. RESULTS: Flow circuit hemodynamic values were similar for porcine aorta and synthetic tubes. Compliance of aorta ranged from 2.97 ± 0.72 (mean ± SD) to 1.42 ± 0.37%/mm Hg × 10⁻². The polymer model showed significantly better compliance (range, 3.66 ± 1.05-2.72 ± 0.28%/mm Hg × 10⁻²; p < 0.05), with no significant difference in elastic stiffness index (range, 101.6 ± 28.9-51.3 ± 10.7 for aorta and 39.8 ± 8.5-34.2 ± 3.8 for polymer model; p > 0.05). It also showed anisotropic behavior similar to the aorta. Latex tubes showed compliance that was lower than that in aorta (range, 0.87 ± 0.24-0.86 ± 0.2%/mm Hg × 10⁻²) and failed by a significant distension on increase in pressure from mean of 90 mm Hg. CONCLUSIONS: We have developed physiologically relevant aortic model showing compatible anatomy, compliance, and viscoelasticity, which could be used for long-term fatigue analysis of vascular stents and grafts. The latex mock aortas can fail at physiological pressures.

Prospective assessment of lower-extremity peripheral arterial disease in diabetic patients using a novel automated optical device.

A new optical device based on the photoplethysmograph (PPG) method and an innovative algorithm for the assessment of lower-extremity peripheral arterial disease was investigated prospectively in patients with type II diabetes. This new functional PPG (fPPG) technique uses a cuffless functional test to assess diabetic peripheral arterial disease without operator dependency and the incompressible arteries, issues associated with ankle brachial pressure index (ABPI) measurement. Diabetic patients (n = 24; 47 legs; age, 70 +/- 3 years) were recruited from the vascular clinic, and controls (n = 15; 30 legs; age, 66 +/- 5 years) were recruited from the orthopedic outpatient clinic. All underwent resting ABPI, fPPG, and duplex angiography (DA) as "gold standard." fPPG requires the placement of an optical probe on the toe for acquisition of pulsatile arterial perfusion for a period of 30 seconds with the leg in supine and raised at 45 degrees positions. The data were analyzed, and indices were generated by an automated computer system. In those with diabetes, fPPG correlated significantly with DA (r = -.68, P < .01) and ABPI (r = -.65, P < .01). We also found a significant correlation between ABPI and DA (r = .81, P < .01). The analysis of the receiver operator curve showed that optimum sensitivity and specificity for ABPI and fPPG were 80% and 93% and 83% and 71%, respectively, against DA. This method uses changes in pulsatile arterial blood volume using a simple cuffless functional test. The fPPG investigation period was much shorter (5 minutes) with independence of operator skills, whereas ABPI took longer (10-15 minutes) and required operator experience. Although the fPPG results are promising, further improvement (eg, by incorporation of functional skin color and temperature changes) is required to improve the sensitivity and specificity of the system.

Optical techniques in the assessment of peripheral arterial disease.

A variety of optical techniques have been developed over the years for experimental use in vascular disease, mainly for the assessment of lower limb peripheral arterial disease (PAD). Optical techniques have several advantages over more traditional experimental approaches. Photoplethysmograph (PPG) was one of the earliest methods used for this purpose; PPG satisfies many of the conditions for a non-invasive technique to estimate skin blood flow using infrared light, not only for research but also in clinical practice. PPG is a promising, safe and easy-to-use tool for diagnosis and early screening of various atherosclerotic pathologies and could be useful for regular GP-assessment or even self-monitoring of PAD at home or during individual physical exercises. This review discusses the application of PPG in the assessment of PAD.

Assessment of lower extremity peripheral arterial disease using a novel automated optical device.

The resting ankle-brachial pressure index (rABPI) is used in the diagnosis of lower extremity peripheral arterial disease (PAD) in symptomatic and asymptomatic patients. This article compares the rABPI with a new optical device based on photoplethysmograph (PPG) technology with new algorithms for the assessment of PAD. Functional PPG (fPPG) is a promising noninvasive automated device using a novel cuffless functional test for assessing mild or significant PAD without the operator dependency issues associated with rABPI. This system utilizes both changes in pulsatile arterial blood volume and skin color redness in lower limbs. All subjects underwent rABPI, fPPG, and duplex angiography (DA). Significant correlation was found between fPPG and DA scores, rABPI and DA, and fPPG and rABPI. In the hands of operators with little experience, fPPG may prove to be superior to rABPI and may be useful as a simple screening tool for early detection of PAD in primary care.

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. Preclot, fibronectin, gelatin, and collagen were coated onto CPU. RGD peptide, heparin, and both RGD and heparin were chemically bonded to CPU. Human umbilical vein EC (HUVEC) labeled with 111-Indium oxine were sodded (1.8 x 10(6) EC/cm(2)) onto native and the modified CPU. The grafts were washed after 90 min and EC retention determined. The experiments were repeated six times. EC retention on native CPU was 1.0 +/- 0.2 x 10(5) EC/cm(2). The application of preclot, fibronectin, gelatin, and collagen did not improve EC retention, which was 0.8 +/- 0.1, 0.4 +/- 0.1, 0.3 +/- 0.08, and 0.5 +/- 0.2 x 10(5) EC/cm(2), respectively. Bonding RGD, heparin, and both RGD and heparin significantly improved EC retention to 1.9 +/- 0.6, 1.7 +/- 0.5, and 2.6 +/- 0.6 x 10(5) EC/cm(2), respectively (p < 0.01). Bonding of RGD, heparin, and both RGD and heparin accelerates and enhances EC retention onto CPU. Simple coating of basement membrane proteins confers no advantage over native CPU.