Dialysis treatment, in vitro, and anticoagulation activity of polysulfone-polyacrylamide based-blend membranes: an experimental study

The majority of treatments are performed with polysulfone (PSf) membranes. The main issue of the PSf membrane is its lack of endothelial function, leading to various processes like platelet adhesion, protein adsorption, and thrombus formation when comes in contact with blood. The crucial aspect in the development of hemodialysis (HD) membrane materials is a biocompatibility factor. This study aims to improve the performance and biocompatibility of PSf membranes by utilizing polyethylene glycol (PEG) as a pore-forming agent and polyacrylamide (PAA) as a multifunctional modifying additive owing to its non-toxic, and biocompatible nature. The formulated HD membranes were characterized using Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), and Water Contact Angle (WCA) measurements. The biocompatibility results showed that PSf-PAA membranes reduced the adsorption of bovine serum albumin (BSA) protein, hemolysis process, thrombus formation, and platelets adhesion with improved in vitro cytotoxicity results as well as anticoagulation performance. The protein separation results showed that PSf-PAA membranes were able to reject 90.1% and 92.8% of BSA protein. The membranes also showed better uremic waste clearance for urea (76.56% and 78.24%) and creatinine (73.71% and 79.13%) solutes, respectively. It is conceivable that these modern-age membranes may surpass conventional HD membranes regarding both efficiency and effectiveness.

Challenges and Strategies for Endothelializing Decellularized Small-Diameter Tissue-Engineered Vessel Grafts

Vascular diseases are the leading cause of ischemic necrosis in tissues and organs, necessitating using vascular grafts to restore blood supply. Currently, small vessels for coronary artery bypass grafts are unavailable in clinical settings. Decellularized small-diameter tissue-engineered vessel grafts (SD-TEVGs) hold significant potential. However, they face challenges, as simple implantation of decellularized SD-TEVGs in animals leads to thrombosis and calcification due to incomplete endothelialization. Consequently, research and development focus has shifted toward enhancing the endothelialization process of decellularized SD-TEVGs. This paper reviews preclinical studies involving decellularized SD-TEVGs, highlighting different strategies and their advantages and disadvantages for achieving rapid endothelialization of these vascular grafts. Methods are analyzed to improve the process while addressing potential shortcomings. This paper aims to contribute to the future commercial viability of decellularized SD-TEVGs.

Zwitterionic polymers-armored amyloid-like protein surface combats thrombosis and biofouling

Proteins, cells and bacteria adhering to the surface of medical devices can lead to thrombosis and infection, resulting in significant clinical mortality. Here, we report a zwitterionic polymers-armored amyloid-like protein surface engineering strategy we called as "armored-tank" strategy for dual functionalization of medical devices. The "armored-tank" strategy is realized by decoration of partially conformational transformed LZM (PCTL) assembly through oxidant-mediated process, followed by armoring with super-hydrophilic poly-2-methacryloyloxyethyl phosphorylcholine (pMPC). The outer armor of the "armored-tank" shows potent and durable zone defense against fibrinogen, platelet and bacteria adhesion, leading to long-term antithrombogenic properties over 14 days in vivo without anticoagulation. Additionally, the "fired" PCTL from "armored-tank" actively and effectively kills both Gram-positive and Gram-negative bacterial over 30 days as a supplement to the lacking bactericidal functions of passive outer armor. Overall, this "armored-tank" surface engineering strategy serves as a promising solution for preventing biofouling and thrombotic occlusion of medical devices.

Functional regeneration at the blood-biomaterial interface

The use of cardiovascular implants is commonplace in clinical practice. However, reproducing the key bioactive and adaptive properties of native cardiovascular tissues with an artificial replacement is highly challenging. Exciting new treatment strategies are under development to regenerate (parts of) cardiovascular tissues directly in situ using immunomodulatory biomaterials. Direct exposure to the bloodstream and hemodynamic loads is a particular challenge, given the risk of thrombosis and adverse remodeling that it brings. However, the blood is also a source of (immune) cells and proteins that dominantly contribute to functional tissue regeneration. This review explores the potential of the blood as a source for the complete or partial in situ regeneration of cardiovascular tissues, with a particular focus on the endothelium, being the natural blood-tissue barrier. We pinpoint the current scientific challenges to enable rational engineering and testing of blood-contacting implants to leverage the regenerative potential of the blood.

In Vitro Thrombogenicity Testing of Biomaterials in a Dynamic Flow Loop: Effects of Length and Quantity of Test Samples

The results of in vitro dynamic thrombogenicity testing of biomaterials and medical devices can be significantly impacted by test conditions. To develop and standardize a robust dynamic in vitro thrombogenicity tool, the key test parameters need to be appropriately evaluated and optimized. We used a flow loop test system previously developed in our laboratory to investigate the effects of sample length and the number of samples per test loop on the thrombogenicity results. Porcine blood heparinized to a donor-specific target concentration was recirculated at room temperature through polyvinyl chloride (PVC) tubing loops containing test materials for 1 h at 200 mL/min. Four test materials (polytetrafluoroethylene (PTFE), latex, PVC, and silicone) with various thrombotic potentials in two sample lengths (12 and 18 cm) were examined. For the 12-cm long materials, two different test configurations (one and two samples per loop) were compared. Thrombogenicity was assessed through percent thrombus surface coverage, thrombus weight, and platelet count reduction in the blood. The test system was able to effectively differentiate the thrombogenicity profile of the materials (latex > silicone > PVC ≥ PTFE) at all test configurations. Increasing test sample length by 50% did not significantly impact the test results as both 12 and 18 cm sample lengths were shown to equally differentiate thrombotic potentials between the materials. The addition of a second test sample to each loop did not increase the test sensitivity and may produce confounding results, and thus a single test sample per loop is recommended.

Preparation of Hyflon AD/Polypropylene Blend Membrane for Artificial Lung

A high-performance polypropylene hollow fiber membrane (PP-HFM) was prepared by using a binary environmentally friendly solvent of polypropylene as the raw material, adopting the thermally induced phase separation (TIPS) method, and adjusting the raw material ratio. The binary diluents were soybean oil (SO) and acetyl tributyl citrate (ATBC). The suitable SO/ATBC ratio of 7/3 was based on the size change of the L-L phase separation region in PP-SO/ATBC thermodynamic phase diagram. Through the characterization and comparison of the basic performance of PP-HFMs, it was found that with the increase of the diluent content in the raw materials, the micropores of outer surface of the PP-HFM became larger, and the cross section showed a sponge-like pore structure. The fluoropolymer, Hyflon ADx, was deposited on the outer surface of the hollow fiber membrane using a physical modification method of solution dipping. After modification, the surface pore size of the Hyflon AD40L modified membranes decreased; the contact angle increased to around 107°; the surface energy decreased to 17 mN·m^-1; and the surface roughness decreased to 17 nm. Hyflon AD40L/PP-HFMs also had more water resistance properties from the variation of wetting curve. For biocompatibility of the membrane, the adsorption capacity of the modified PP membrane for albumin decreased from approximately 1.2 mg·cm^-2 to 1.0 mg·cm^-2, and the adsorption of platelets decreased under fluorescence microscopy. The decrease in blood cells and protein adsorption in the blood prolonged the clotting time. In addition, the hemolysis rate of modified PP membrane was reduced to within the standard of 5%, and the cell survival rate of its precipitate was above 100%, which also indicated the excellent biocompatibility of fluoropolymer modified membrane. The improvement of hydrophobicity and blood compatibility makes Hyflon AD/PP-HFMs have the potential for application in membrane oxygenators.

Effect of Temperature on Thrombogenicity Testing of Biomaterials in an In Vitro Dynamic Flow Loop System

To develop and standardize a reliable in vitro dynamic thrombogenicity test protocol, the key test parameters that could impact thrombus formation need to be investigated and understood. In this study, we evaluated the effect of temperature on the thrombogenic responses (thrombus surface coverage, thrombus weight, and platelet count reduction) of various materials using an in vitro blood flow loop test system. Whole blood from live sheep and cow donors was used to assess four materials with varying thrombogenic potentials: negative-control polytetrafluoroethylene (PTFE), positive-control latex, silicone, and high-density polyethylene (HDPE). Blood, heparinized to a donor-specific concentration, was recirculated through a polyvinyl chloride tubing loop containing the test material at room temperature (22-24°C) for 1 hour, or at 37°C for 1 or 2 hours. The flow loop system could effectively differentiate a thrombogenic material (latex) from the other materials for both test temperatures and blood species ( p < 0.05). However, compared with 37°C, testing at room temperature appeared to have slightly better sensitivity in differentiating silicone (intermediate thrombogenic potential) from the relatively thromboresistant materials (PTFE and HDPE, p < 0.05). These data suggest that testing at room temperature may be a viable option for dynamic thrombogenicity assessment of biomaterials and medical devices.

Supercritical carbon dioxide-decellularized arteries exhibit physiologic-like vessel regeneration following xenotransplantation in rats

Currently, many techniques are used for decellularization of grafts, including physical, enzymatic, and chemical treatments. Indeed, decellularized xenogenic grafts provide superior outcomes than alternative synthetic conduits. However, vascular grafts produced by these methods are not perfect; their defects include defective vessel wall structures, detergent residues, and the development of aneurysms after grafting. Therefore, it is essential to develop a more appropriate process to produce decellularized vascular grafts. Supercritical carbon dioxide (ScCO₂) has been used in decellularization technologies in recent years. It is beneficial for the long-term preservation of tissues and regeneration of new vessels. We have previously reported that ScCO₂-produced acellular porcine corneas show excellent biocompatibility following lamellar corneal transplantation in rabbits. In this study, we wanted to use this method to fabricate vascular grafts (ScCO₂-decellularized rabbit femoral artery (DFA)) and analyze their efficacy, parameters regarding rejection by the recipient's (ACI/NKyo rats) immune system and biocompatibility, structural regeneration, and functionality in vivo. The results indicated that the ScCO₂-DFA showed higher biocompatibility, enhanced chemotactic migration of endothelial progenitor cells, lower risk of vasculopathy, lower inflammatory and splenic immune responses, and better physiological-like tension responses after xenotransplantation (XTP) in ACI/NKyo rats compared with the results obtained after XTP using detergent decellularized vascular grafts (SDS-DFA). In conclusion, ScCO₂ is an excellent decellularization technique in the fabrication of biocompatible vascular grafts and has tremendous application in vascular regenerative medicine.

Comparison of Animal and Human Blood for In Vitro Dynamic Thrombogenicity Testing of Biomaterials

BACKGROUND

To determine suitable alternatives to human blood for in vitro dynamic thrombogenicity testing of biomaterials, four different animal blood sources (ovine, bovine, and porcine blood from live donors, and abattoir porcine blood) were compared to fresh human blood.

METHODS

To account for blood coagulability differences between individual donors and species, each blood pool was heparinized to a donor-specific concentration immediately before testing in a dynamic flow loop system. The target heparin level was established using a static thrombosis pre-test. For dynamic testing, whole blood was recirculated at room temperature for 1 hr at 200 mL/min through a flow loop containing a single test material. Four materials with varying thrombotic potentials were investigated: latex (positive control), polytetrafluoroethylene (PTFE) (negative control), silicone (intermediate thrombotic potential), and high-density polyethylene (HDPE) (historically thromboresistant). Thrombus weight and surface area coverage on the test materials were quantified, along with platelet count reduction in the blood.

RESULTS

While donor-specific heparin levels varied substantially from 0.6 U/ml to 7.0 U/mL among the different blood sources, each source was able to differentiate between the thrombogenic latex and the thromboresistant PTFE and HDPE materials (P< 0.05). However, only donor ovine and bovine blood were sensitive enough to differentiate an increased response for the intermediate thrombotic silicone material compared to PTFE and HDPE.

CONCLUSIONS

These results demonstrated that multiple animal blood sources (particularly donor ovine and bovine blood) may be suitable alternatives to fresh human blood for dynamic thrombogenicity testing when appropriate control materials and donor-specific anticoagulation levels are used.

Gelatin/sodium alginate hydrogel-coated decellularized porcine coronary artery to construct bilayer tissue engineered blood vessels

Cardiovascular diseases and vascular trauma can be commonly found in the population. Scholars worldwide hope to develop small-diameter vascular grafts that can replace autologous vessels for clinical use. Decellularized blood vessels can retain the original morphology, structure, and physical properties of blood vessels, which is conducive to cell growth, proliferation, and differentiation. In this study, porcine coronary arteries (PCAs) were decellularized to prepare decellularized porcine coronary artery (DPCA), and bilayer hybrid scaffolds were prepared by coating gelatin and sodium alginate mixed hydrogel of seven different proportions and combined with mouse fibroblasts (L929 cells) to study the construction of tissue engineering vessels in vitro. The obtained bilayer hybrid scaffolds were 3-7 cm in length, 5 mm in external diameter, and 1 mm in average wall thickness. All seven bilayer hybrid scaffolds showed good biocompatibility after cell inoculation. Compared with 2D culture, cells on 3D scaffolds grew relatively slowly in the first 4 days, and the number of cells proliferated rapidly at 7 days. In the same culture days, different concentrations of hydrogel also had an impact on cell proliferation. With the increase of hydrogel content, cells on the 3D scaffold formed cell colonies faster. The results showed that the scaffold had good biocompatibility and could meet the needs of artificial blood vessel construction.

End-Point Immobilization of Heparin on Electrospun Polycarbonate-Urethane Vascular Graft

There is a tremendous clinical need for synthetic vascular grafts either for bypass procedure or vascular access during hemodialysis. However, currently, there is no small-diameter vascular graft commercially available to meet long-term patency requirement due to frequent thrombus formation and intimal hyperplasia. This chapter describes the fabrication of electrospun small-diameter polycarbonate-urethane (PCU) vascular graft with a biomimetic fibrous structure. Additionally, the surface of the vascular graft is aminated via plasma treatment for the subsequently end-point heparin immobilization to enhance antithrombosis property.

Endothelium-Mimicking Surface Combats Thrombosis and Biofouling via Synergistic Long- and Short-Distance Defense Strategy

Thrombosis and infections are the main causes of implant failures (e.g., extracorporeal circuits and indwelling medical devices), which induce significant morbidity and mortality. In this work, an endothelium-mimicking surface is engineered, which combines the nitric oxide (NO)-generating property and anti-fouling function of a healthy endothelium. The released gas signal molecules NO and the glycocalyx matrix macromolecules hyaluronic acid (HA) jointly combine long- and short-distance defense actions against thrombogenicity and biofouling. The biomimetic surface is efficiently fabricated by cografting a NO-generating species (i.e., Tri-tert-butyl 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetate-chelated Cu²⁺ , DTris@Cu) and the macromolecular HA on an aminated tube surface through one-pot amide condensation chemistry. The active attack (i.e., NO release) and zone defense (i.e., HA tethering) system endow the tubing surface with significant inhibition of platelets, fibrinogen, and bacteria adhesion, finally leading to long-term anti-thrombogenic and anti-fouling properties over 1 month. It is envisioned that this endothelium-mimicking surface engineering strategy will provide a promising solution to address the clinical issues of long-term blood-contacting devices associated with thrombosis and infection.

Preclinical Device Thrombogenicity Assessments: Key Messages From the 2018 FDA, Industry, and Academia Forum

Device-related thrombosis and thromboembolic complications remain a major clinical concern and often impact patient morbidity and mortality. Thus, improved preclinical thrombogenicity assessment methods that better predict clinical outcomes and enhance patient safety are needed. However, there are several challenges and limitations associated with developing and performing preclinical thrombogenicity assessments on the bench and in animals (e.g., the clinical relevance of most in vitro tests has not been established, animal studies may not accurately predict clinical thrombotic events). To facilitate a discussion on how to overcome some of these challenges and to promote collaboration between the Food and Drug Administration (FDA), industry, and academia for the development of more reliable test methods, a scientific forum was organized by FDA and held in Washington, DC, on June 15, 2018 at the ASAIO 64th Annual Conference. Three subject matter experts from the medical device industry and FDA presented their perspectives at this forum, and several audience experts provided input during the open dialogue session. This article summarizes the key messages from the forum regarding the current status and challenges of preclinical thrombogenicity testing, important areas of needed research, and mechanisms for working with FDA to further improve thrombogenicity evaluations of medical devices.

Rapid endothelialization of small diameter vascular grafts by a bioactive integrin-binding ligand specifically targeting endothelial progenitor cells and endothelial cells

Establishing and maintaining a healthy endothelium on vascular and intravascular devices is crucial for the prevention of thrombosis and stenosis. Generating a biofunctional surface on vascular devices to recruit endothelial progenitor cells (EPCs) and endothelial cells (ECs) has proven efficient in promoting in situ endothelialization. However, molecules conventionally used for EPC/EC capturing generally lack structural stability, capturing specificity, and biological functionalities, which have limited their applications. Discovery of effective, specific, and structurally stable EPC/EC capturing ligands is desperately needed. Using the high-throughput One-Bead One-Compound combinatorial library screening technology, we recently identified a disulfide cyclic octa-peptide LXW7 (cGRGDdvc), which possesses strong binding affinity and functionality to EPCs/ECs, weak binding to platelets, and no binding to inflammatory cells. Because LXW7 is cyclic and 4 out of the 8 amino acids are unnatural D-amino acids, LXW7 is highly proteolytically stable. In this study, we applied LXW7 to modify small diameter vascular grafts using a Click chemistry approach. In vitro studies demonstrated that LXW7-modified grafts significantly improved EPC attachment, proliferation and endothelial differentiation and suppressed platelet attachment. In a rat carotid artery bypass model, LXW7 modification of the small diameter vascular grafts significantly promoted EPC/EC recruitment and rapidly achieved endothelialization. At 6 weeks after implantation, LXW7-modified grafts retained a high patency of 83%, while the untreated grafts had a low patency of 17%. Our results demonstrate that LXW7 is a potent EPC/EC capturing and platelet suppressing ligand and LXW7-modified vascular grafts rapidly generate a healthy and stable endothelial interface between the graft surface and the circulation to reduce thrombosis and improve patency. STATEMENT OF SIGNIFICANCE: In this study, One-Bead One-Compound (OBOC) technology has been applied for the first time in discovering bioactive ligands for tissue regeneration applications. Current molecules used to modify artificial vascular grafts generally lack EPC/EC capturing specificity, biological functionalities and structural stability. Using OBOC technology, we identified LXW7, a constitutionally stable disulfide cyclic octa-peptide with strong binding affinity and biological functionality to EPCs/ECs, very weak binding to platelets and no binding to inflammatory cells. These characteristics are crucial for promoting rapid endothelialization to prevent thrombosis and improve patency of vascular grafts. LXW7 coating technology could be applied to a wide range of vascular and intravascular devices, including grafts, stents, cardiac valves, and catheters, where a "living" endothelium and healthy blood interface are needed.

Thoracic aortic surgery: status and upcoming novelties

Several novel technological developments and surgical approaches have characterized the field of aortic surgery in the recent decade. The progressive introduction of endovascular procedures, minimally invasive surgical techniques and hybrid approaches have changed the practice in aortic surgery and generated new trends and questions. Also, the advancements in the manufacturing of tissue engineered vascular grafts as substitutes for aortic replacements are enlightening new avenues in the treatment of aortic disease. This review will provide an overview of the current novel perspectives, debates and trends in major thoracic aortic surgery.

New Approaches to Respiratory Assist: Bioengineering an Ambulatory, Miniaturized Bioartificial Lung

Although state-of-the-art treatments of respiratory failure clearly have made some progress in terms of survival in patients suffering from severe respiratory system disorders, such as acute respiratory distress syndrome (ARDS), they failed to significantly improve the quality of life in patients with acute or chronic lung failure, including severe acute exacerbations of chronic obstructive pulmonary disease or ARDS as well. Limitations of standard treatment modalities, which largely rely on conventional mechanical ventilation, emphasize the urgent, unmet clinical need for developing novel (bio)artificial respiratory assist devices that provide extracorporeal gas exchange with a focus on direct extracorporeal CO2 removal from the blood. In this review, we discuss some of the novel concepts and critical prerequisites for such respiratory lung assist devices that can be used with an adequate safety profile, in the intensive care setting, as well as for long-term domiciliary therapy in patients with chronic ventilatory failure. Specifically, we describe some of the pivotal steps, such as device miniaturization, passivation of the blood-contacting surfaces by chemical surface modifications, or endothelial cell seeding, all of which are required for converting current lung assist devices into ambulatory lung assist device for long-term use in critically ill patients. Finally, we also discuss some of the risks and challenges for the long-term use of ambulatory miniaturized bioartificial lungs.

Characterization of a heparinized decellularized scaffold and its effects on mechanical and structural properties

Decellularization is a promising approach in tissue engineering to generate small-diameter blood vessels. However, some challenges still exist. We performed two decellularization phases to develop an optimal decellularized scaffold and analyze the relationship between the extracellular matrix (ECM) composition and mechanical properties. In decellularization phase I, we tested sodium dodecylsulfate (SDS), Triton X-100 (TX100) and trypsin at different concentrations and exposure times. In decellularization phase II, we systematically compared five combined decellularization protocols based on the results of phase I to identify the optimal method. These protocols tested cell removal, ECM preservation, mechanical properties, and residual cytotoxicity. We further immobilized heparin to optimal decellularized scaffolds and determined its anticoagulant activity and mechanical properties. The combined decellularization protocol comprising treatment with 0.5% SDS followed by 1% TX100 could completely remove the cellular contents and preserve the mechanical properties and ECM architecture better. In addition, the heparinized decellularized scaffolds not only had sustained anticoagulant activity, but also similar mechanical properties to native vessels. In conclusion, heparinized decellularized scaffolds represent a promising direction for small-diameter vascular grafts, although further in vivo studies are needed.

An In Vitro Blood Flow Loop System for Evaluating the Thrombogenicity of Medical Devices and Biomaterials

A reliable in vitro dynamic test method to evaluate device thrombogenicity is very important for the improvement of the design and safety of blood-contacting medical devices, while reducing the use of animal studies. In this study, a recirculating flow loop system was developed for thrombogenicity testing, using donor sheep blood anticoagulated with Anticoagulant Citrate Dextrose Solution A (ACDA) and used within 24-36 hr postdraw. Immediately before testing, the blood was recalcified and heparinized to a donor-specific target concentration. The heparinization level was based on a static pretest, in which latex tubes were incubated at room temperature for 30 min in blood with a series of heparin concentrations and evaluated for thrombus deposition. For dynamic testing, blood was recirculated at room temperature through a polyvinyl chloride (PVC) tubing loop containing a test material for 1 hr at 200 ml/min using a roller pump. Nine materials were investigated: a negative control (polytetrafluoroethylene [PTFE]), a positive control (latex), and seven commonly used biomaterials including PVC, two silicones with different formulations (Q-Sil and V-Sil), nylon, polyurethane (PU), high-density polyethylene (HDPE), and polyether block amide (PEBAX). The results showed that latex was significantly more thrombogenic than all the other materials (p < 0.05), PVC and Q-Sil exhibited intermediate thrombogenicity with significantly more thrombus surface coverage and thrombus weight than PTFE (p < 0.05), whereas PTFE and the rest of the biomaterials had little to no thrombus deposition. In summary, the test loop system was able to effectively differentiate materials with different thrombogenic potentials.

Surface-Modifying Polymers for Blood-Contacting Polymeric Biomaterials

Bulk blending is considered as one of the most effective and straightforward ways to improve the hemo-compatibility of blood-contacting polymeric biomaterials among many surface modification methods. Zwitterionic structure-, glycocalyx-like structure-, and heparin-like structure-based oligomers have been synthesized as additives and blended with base polymers to improve the blood compatibility of base polymers. Fluorinated end- and side-functionalized oligomers could promote the migration of functionalized groups to the surface of biomedical polymers without changing their bulk properties, and it highly depends on the number and concentration of functional groups. Moreover, oligomers having both zwitterion and fluorine are receiving considerable attention due to their desirable phase separation, which can avoid undesired protein adsorption and platelet adhesion. The surface analysis of the surface-modified materials is usually investigated by analytical tools such as contact angle measurement, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Blood compatibility is mainly evaluated via platelet adhesion and protein adsorption test, and the result showed a significant decrease in the amount of undesirable adsorption. These analyses indicated that surface modification using bulk blending technique effectively improves blood compatibility of polymeric biomaterials.

General Study and Gene Expression Profiling of Endotheliocytes Cultivated on Electrospun Materials

Endothelization of the luminal surface of vascular grafts is required for their long-term functioning. Here, we have cultivated human endothelial cells (HUVEC) on different 3D matrices to assess cell proliferation, gene expression and select the best substrate for endothelization. 3D matrices were produced by electrospinning from solutions of poly(D,L-lactide-co-glycolide) (PLGA), polycaprolactone (PCL), and blends of PCL with gelatin (Gl) in hexafluoroisopropanol. Structure and surface properties of 3D matrices were characterized by SEM, AFM, and sessile drop analysis. Cell adhesion, viability, and proliferation were studied by SEM, Alamar Blue staining, and 5-ethynyl-2’-deoxyuridine (EdU) assay. Gene expression profiling was done on an Illumina HiSeq 2500 platform. Obtained data indicated that 3D matrices produced from PCL with Gl and treated with glutaraldehyde provide the most suitable support for HUVEC adhesion and proliferation. Transcriptome sequencing has demonstrated a minimal difference of gene expression profile in HUVEC cultivated on the surface of these matrices as compared to tissue culture plastic, thus confirming these matrices as the best support for endothelization.

Hemodialysis performance and anticoagulant activities of PVP-k25 and carboxylic-multiwall nanotube composite blended Polyethersulfone membrane

Non-covalent electrostatic interaction between amide nitrogen and carbonyl carbon of shorter chain length of polyvinylpyrrolidone (PVP-k25) was developed with in-house carboxylic oxidized multiwall carbon nanotubes (O-MWCNT) and then blended with Polyethersulfone (PES) polymer. FTIR analysis was utilized to confirm bonding nature of nano-composites (NCs) of O-MWCNT/PVP-k25 and casting membranes. Non-solvent induces phase separation process developed regular finger-like channels in composite membranes whereas pristine PES exhibited spongy entities as studied by cross sectional analysis report of FESEM. Further, FESEM instrument was also utilized to observe the dispersion of O-MWCNT/PVP based nanocomposite (NCs) with PES and membranes leaching phenomena analysis. Contact angle experiments described 24% improvement of hydrophilic behaviour, leaching ratio of additives was reduced to 1.89%, whereas water flux enhanced up to 6 times. Bovine serum albumin (BSA) and lysozyme based antifouling analysis shown up to 25% improvement, whereas 84% of water flux was regained after protein fouling than pristine PES. Anticoagulant activity was reported by estimating prothrombin, thrombin, plasma re-calcification times and production of fibrinogen cluster with platelets-adhesions photographs and hemolysis experiments. Composite membranes exhibited 3.4 and 3 times better dialysis clearance ratios of urea and creatinine solutes as compared to the raw PES membrane.

Clopidogrel eluting electrospun polyurethane/polyethylene glycol thromboresistant, hemocompatible nanofibrous scaffolds

Biomaterials used as blood-contacting material must be hemocompatible and exhibit lower thrombotic potential while maintaining hemostasis and angiogenesis. With the aim of developing thromboresistant, hemocompatible nanofibrous scaffolds, polyurethane/polyethylene glycol scaffolds incorporated with 1, 5, and 10 wt% Clopidogrel were fabricated and evaluated for their physiochemical properties, biocompatibility, hemocompatibility, and antithrombotic potential. The results of physicochemical characterization revealed the fabrication of nanometer-sized scaffolds with smooth surfaces. The incorporation of both polyethylene glycol and Clopidogrel to polyurethane enhanced the hydrophilicity and water uptake potential of polyurethane/polyethylene glycol/Clopidogrel scaffolds. The dynamic mechanical analysis revealed the enhancement in mechanical strength of the polyurethane/polyethylene glycol scaffolds on incorporation of Clopidogrel. The polyurethane/polyethylene glycol/Clopidogrel scaffolds showed a tri-phasic drug release pattern. The results of hemocompatibility assessment demonstrated the excellent blood compatibility of the polyurethane/polyethylene glycol/Clopidogrel scaffolds, with the developed scaffolds exhibiting lower hemolysis, increased albumin and plasma protein adsorption while reduction in fibrinogen adsorption. Further, the platelet adhesion was highly suppressed and significant increase in coagulation period was observed for Clopidogrel incorporated scaffolds. The results of cell adhesion and cell viability substantiate the biocompatibility of the developed nanofibrous scaffolds with the HUVEC cell viability on polyurethane/polyethylene glycol, polyurethane/polyethylene glycol/Clopidogrel-1, 5, and 10% at day 7 found to be 12.35, 13.36, 14.85, and 4.18% higher as compared to polyurethane scaffolds, and the NIH/3T3 cell viability found to be 35.27, 70.82, 36.60, and 7.95% higher as compared to polyurethane scaffolds, respectively. Altogether the results of the study advocate the incorporation of Clopidogrel to the polyurethane/polyethylene glycol blend in order to fabricate scaffolds with appropriate antithrombotic property, hemocompatibility, and cell proliferation capacity and thus, might be successfully used as antithrombotic material for biomedical application.

End Point Versus Backbone Specificity Governs Characteristics of Antibody Binding to Poly(ethylene glycol) Brushes

End-grafted poly(ethylene glycol) (PEG) brushes are widely used in order to suppress undesired protein adsorption to surfaces exposed to blood or other biological fluids. The specific adsorption of antibodies (Abs) to PEG brushes associated with PEG's antigenicity is drawing increasing attention because it can affect clinical applications. Here, the adsorption to PEG brushes of two Ab types, specifically binding the polymer backbone and the polymer endpoints, is structurally characterized by neutron reflectometry. The measurements yield volume fraction profiles of PEG and of the adsorbed Abs with sub-nanometer resolution perpendicular to the surface. For all brush parameters in terms of grafting density and polymerization degree, the Ab profiles clearly differ between backbone binders and endpoint binders. The adsorbed Ab amount per unit area is substantial for both Ab types and for all brush parameters investigated, even for dense brushes, which impose a considerable osmotic barrier to Ab insertion. The results therefore indicate that variation of brush parameters alone is insufficient to prevent undesired Ab adsorption. Instead, our work motivates further efforts in the search for nonantigenic brush chemistry.

Generating vascular conduits: from tissue engineering to three-dimensional bioprinting

Vascular disease - including coronary artery disease, carotid artery disease, and peripheral vascular disease - is a leading cause of morbidity and mortality worldwide. The standard of care for restoring patency or bypassing occluded vessels involves using autologous grafts, typically the saphenous veins or internal mammary arteries. Yet, many patients who need life- or limb-saving procedures have poor outcomes, and a third of patients who need vascular intervention have multivessel disease and therefore lack appropriate vasculature to harvest autologous grafts from. Given the steady increase in the prevalence of vascular disease, there is great need for grafts with the biological and mechanical properties of native vessels that can be used as vascular conduits. In this review, we present an overview of methods that have been employed to generate suitable vascular conduits, focusing on the advances in tissue engineering methods and current three-dimensional (3D) bioprinting methods. Tissue-engineered vascular grafts have been fabricated using a variety of approaches such as using preexisting scaffolds and acellular organic compounds. We also give an extensive overview of the novel use of 3D bioprinting as means of generating new vascular conduits. Different strategies have been employed in bioprinting, and the use of cell-based inks to create de novo structures offers a promising solution to bridge the gap of paucity of optimal donor grafts. Lastly, we provide a glimpse of our work to create scaffold-free, bioreactor-free, 3D bioprinted vessels from a combination of rat vascular smooth muscle cells and fibroblasts that remain patent and retain the tensile and mechanical strength of native vessels.

The Heart and Great Vessels

Cardiovascular disease is the leading cause of mortality worldwide. We have made large strides over the past few decades in management, but definitive therapeutic options to address this health-care burden are still limited. Given the ever-increasing need, much effort has been spent creating engineered tissue to replaced diseased tissue. This article gives a general overview of this work as it pertains to the development of great vessels, myocardium, and heart valves. In each area, we focus on currently studied methods, limitations, and areas for future study.

A new textured polyphosphazene biomaterial with improved blood coagulation and microbial infection responses

A new poly[bis(octafluoropentoxy) phosphazene] (OFP) was synthesized for the purpose of blood contacting medical devices. OFP was further either developed into crosslinkable polyphosphazene (X-OFP) or blended with polyurethane (PU) as the mixture (OFP/PU) for improvement of mechanical property of polyphosphazene polymers. All the materials were fabricated as smooth films or further textured with submicron pillars for the assay of antimicrobial and antithrombotic properties. Results showed that crosslinkable OFP (X-OFP) and blends of OFP/PU successfully improved the mechanical strength of OFP and fewer defects of pillars were found on the textured polyphosphazene surfaces. The antithrombotic experiments showed that polyphosphazene OFP materials reduced human Factor XII activation and platelet adhesion, thereby being resistant to plasma coagulation and thrombosis. The bacterial adhesion and biofilm experiments demonstrated that OFP materials inhibited staphylococcal bacterial adhesion and biofilm formation. The surface texturing further reduced the platelet adhesion and bacterial adhesion, and inhibited biofilm formation up to 23 days. The data suggested that textured OFP materials may provide a practical approach to improve the biocompatibility of current biomaterials in the application of blood contacting medical devices with significant reduction in risk of pathogenic infection and thrombosis.

STATEMENT OF SIGNIFICANCE

The thromboembolic events and microbial infection have been the significant barriers for the long term use of biomaterials in blood-contacting medical devices. The development of new materials with multiple functions including anti-thrombosis and antibacterial surfaces is a high research priority. This study synthesized new biostable and biocompatible polyphosphazene polymers, poly[bis(octafluoropentoxy)phosphazene] (OFP) and crosslinkable OFP, and successfully improved the mechanical strength of polyphosphazenes. Polymers were fabricated into textured films with submicron pillars on the surfaces. The antimicrobial and antithrombotic assays demonstrated that new materials combined with surface physical modification have significant reduction in risk of pathogenic infection and thrombosis, and improve the biocompatibility of current biomaterials in the application of blood-contacting medical devices. It would be interest to biomaterials and bioengineering related communities.

A human pericardium biopolymeric scaffold for autologous heart valve tissue engineering: cellular and extracellular matrix structure and biomechanical properties in comparison with a normal aortic heart valve

The objective of our study was to compare the cellular and extracellular matrix (ECM) structure and the biomechanical properties of human pericardium (HP) with the normal human aortic heart valve (NAV). HP tissues (from 12 patients) and NAV samples (from 5 patients) were harvested during heart surgery. The main cells in HP were pericardial interstitial cells, which are fibroblast-like cells of mesenchymal origin similar to the valvular interstitial cells in NAV tissue. The ECM of HP had a statistically significantly (p < 0.001) higher collagen I content, a lower collagen III and elastin content, and a similar glycosaminoglycans (GAGs) content, in comparison with the NAV, as measured by ECM integrated density. However, the relative thickness of the main load-bearing structures of the two tissues, the dense part of fibrous HP (49 ± 2%) and the lamina fibrosa of NAV (47 ± 4%), was similar. In both tissues, the secant elastic modulus (Es) was significantly lower in the transversal direction (p < 0.05) than in the longitudinal direction. This proved that both tissues were anisotropic. No statistically significant differences in UTS (ultimate tensile strength) values and in calculated bending stiffness values in the longitudinal or transversal direction were found between HP and NAV. Our study confirms that HP has an advantageous ECM biopolymeric structure and has the biomechanical properties required for a tissue from which an autologous heart valve replacement may be constructed.

Honeycomb-structured metasurfaces for the adaptive nesting of endothelial cells under hemodynamic loads

The thrombogenicity of artificial materials comprising ventricular assist devices (VADs) limits their long-term integration in the human body.

Neutron Reflectometry Elucidates Protein Adsorption from Human Blood Serum onto PEG Brushes

Poly(ethylene glycol) (PEG) brushes are reputed for their ability to prevent undesired protein adsorption to material surfaces exposed to biological fluids. Here, protein adsorption out of human blood serum onto PEG brushes anchored to solid-supported lipid monolayers was characterized by neutron reflectometry, yielding volume fraction profiles of lipid headgroups, PEG, and adsorbed proteins at subnanometer resolution. For both PEGylated and non-PEGylated lipid surfaces, serum proteins adsorb as a thin layer of approximately 10 Å, overlapping with the headgroup region. This layer corresponds to primary adsorption at the grafting surface and resists rinsing. A second diffuse protein layer overlaps with the periphery of the PEG brush and is attributed to ternary adsorption due to protein-PEG attraction. This second layer disappears upon rinsing, thus providing a first observation of the structural effect of rinsing on protein adsorption to PEG brushes.

Engineering the mechanical and biological properties of nanofibrous vascular grafts for in situ vascular tissue engineering

Synthetic small diameter vascular grafts have a high failure rate, and endothelialization is critical for preventing thrombosis and graft occlusion. A promising approach is in situ tissue engineering, whereby an acellular scaffold is implanted and provides stimulatory cues to guide the in situ remodeling into a functional blood vessel. An ideal scaffold should have sufficient binding sites for biomolecule immobilization and a mechanical property similar to native tissue. Here we developed a novel method to blend low molecular weight (LMW) elastic polymer during electrospinning process to increase conjugation sites and to improve the mechanical property of vascular grafts. LMW elastic polymer improved the elasticity of the scaffolds, and significantly increased the amount of heparin conjugated to the micro/nanofibrous scaffolds, which in turn increased the loading capacity of vascular endothelial growth factor (VEGF) and prolonged the release of VEGF. Vascular grafts were implanted into the carotid artery of rats to evaluate the in vivo performance. VEGF treatment significantly enhanced endothelium formation and the overall patency of vascular grafts. Heparin coating also increased cell infiltration into the electrospun grafts, thus increasing the production of collagen and elastin within the graft wall. This work demonstrates that LMW elastic polymer blending is an approach to engineer the mechanical and biological property of micro/nanofibrous vascular grafts for in situ vascular tissue engineering.

Compared to the amniotic membrane, Wharton's jelly may be a more suitable source of mesenchymal stem cells for cardiovascular tissue engineering and clinical regeneration

BACKGROUND

The success of developing cardiovascular tissue engineering (CTE) grafts greatly needs a readily available cell substitute for endothelial and interstitial cells. Perinatal annexes have been proposed as a valuable source of mesenchymal stem cells (MSCs) for tissue engineering and regenerative medicine. The objective of the present study is to evaluate the potential of human Wharton's jelly MSCs (WJ-MSCs) and amniotic membrane MSCs (AM-MSCs) as a seeding cell in CTE and cardiovascular regenerative medicine.

METHODS

WJ-MSCs/AM-MSCs were isolated and characterized in vitro according to their morphology, proliferation, self-renewal, phenotype, and multipotency. More importantly, the characteristics of hemocompatibility, extracellular matrix deposition, and gene expression and viability of both MSCs were investigated.

RESULTS

Fibroblast-like human WJ-MSCs and AM-MSCs were successfully isolated and positively expressed the characteristic markers CD73, CD90, and CD105 but were negative for CD34, CD45, and HLA-DR. Both MSCs shared trilineage differentiation toward the adipogenic, osteogenic, and chondrogenic lineages. The proliferative and self-renewal capacity of WJ-MSCs was significantly higher than that of AM-MSCs (P < 0.001). WJ-MSCs provided comparable properties of antiplatelet adhesion and did not activate the coagulation cascade to endothelial cells. However, aggregated platelets were visualized on the surface of AM-MSCs-derived cell sheets and the intrinsic pathway was activated. Furthermore, WJ-MSCs have superior properties of collagen deposition and higher viability than AM-MSCs during cell sheet formation.

CONCLUSIONS

This study highlights that WJ-MSCs could act as a functional substitute of endothelial and interstitial cells, which could serve as an appealing and practical single-cell source for CTE and regenerative therapy.

Determining the optimal protocol for preparing an acellular scaffold of tissue engineered small-diameter blood vessels

Although detergent-based decellularization protocols have been widely used to obtain a natural extracellular matrix (ECM) scaffold in tissue engineering, some key challenges still exist. To achieve an optimum natural decellularized scaffold for the construction of tissue-engineered small-diameter blood vessels (TEBV), porcine carotid arteries (PCAs) were decellularized by combining sodium dodecyl sulfate (SDS), sodium deoxycholate (SDC) and Triton X-100 (Triton) in different concentrations. Tissue samples were processed and their histological, biochemical and biomechanical characteristics were investigated. Results showed that only two methods 0.5% (SDS + SDC) and 1% (SDS + SDC) could completely remove of the cellular contents and preserve the native ECM architecture. Furthermore, 1% (SDS + SDC) based methods acquire preferable porosity and suitable mechanical strength. Residual Triton in the ECM scaffold holds intensive cytotoxity. In conclusion, 1%(SDS + SDC) based method can obtain a superior PCAs scaffold for the construction of TEBV. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 619-631, 2018.

[Tissue engineering: a multidisciplinary approach]

The prostheses have been around for thousands of years. Initially, it was substitute materials to replace members (leg, foot, hand) or for surgery (suture). The materials used have evolved, but they had never been created for medical applications. Recently, other strategies have emerged to construct or repair tissues. They are based on the use of biological components such as proteins or cells and provide a biological dimension to the term "biomaterial" and they often involve engineering. We illustrate the tissue engineering approaches using the examples of muscle and vessel regeneration strategies in the frame of restorative medicine.

Nano-scale clustering of integrin-binding ligands regulates endothelial cell adhesion, migration, and endothelialization rate: novel materials for small diameter vascular graft applications

Blood contacting devices are commonly used in today's medical landscape.

Combining Electrospun Fiber Mats and Bioactive Coatings for Vascular Graft Prostheses

The patency of small-diameter (<6 mm) synthetic vascular grafts (VGs) is still limited by the absence of a confluent, blood flow-resistant monolayer of endothelial cells (ECs) on the lumen and of vascular smooth muscle cell (VSMC) growth into the media layer. In this research, electrospinning has been combined with bioactive coatings based on chondroitin sulfate (CS) to create scaffolds that possess optimal morphological and bioactive properties for subsequent cell seeding. We fabricated random and aligned electrospun poly(ethylene terephthalate), ePET, mats with small pores (3.2 ± 0.5 or 3.9 ± 0.3 μm) and then investigated the effects of topography and bioactive coatings on EC adhesion, growth, and resistance to shear stress. Bioactive coatings were found to dominate the cell behavior, which enabled creation of a near-confluent EC monolayer that resisted physiological shear-flow conditions. CS is particularly interesting since it prevents platelet adhesion, a key issue to avoid blood clot formation in case of an incomplete EC monolayer or partial cell detachment. Regarding the media layer, circumferentially oriented nanofibers with larger pores (6.3 ± 0.5 μm) allowed growth, survival, and inward penetration of VSMCs, especially when the CS was further coated with tethered, oriented epithelial growth factor (EGF). In summary, the techniques developed here can lead to adequate scaffolds for the luminal and media layers of small-diameter synthetic VGs.

A Novel Bioreactor System for the Assessment of Endothelialization on Deformable Surfaces

The generation of a living protective layer at the luminal surface of cardiovascular devices, composed of an autologous functional endothelium, represents the ideal solution to life-threatening, implant-related complications in cardiovascular patients. The initial evaluation of engineering strategies fostering endothelial cell adhesion and proliferation as well as the long-term tissue homeostasis requires in vitro testing in environmental model systems able to recapitulate the hemodynamic conditions experienced at the blood-to-device interface of implants as well as the substrate deformation. Here, we introduce the design and validation of a novel bioreactor system which enables the long-term conditioning of human endothelial cells interacting with artificial materials under dynamic combinations of flow-generated wall shear stress and wall deformation. The wall shear stress and wall deformation values obtained encompass both the physiological and supraphysiological range. They are determined through separate actuation systems which are controlled based on validated computational models. In addition, we demonstrate the good optical conductivity of the system permitting online monitoring of cell activities through live-cell imaging as well as standard biochemical post-processing. Altogether, the bioreactor system defines an unprecedented testing hub for potential strategies toward the endothelialization or re-endothelialization of target substrates.

Effects of different components of the extracellular matrix on endothelialization

The endothelialization of cardiovascular prostheses is known to improve their haemocompatibility. As such body-foreign materials often do not endothelialize spontaneously. A lot of in vitro studies are ongoing how endothelialization of biomaterials can be improved. In this study the influence of different components of a tissue-typical extracellular matrix (ECM) like laminin, fibronectin or gelatin on the formation of an endothelial cell monolayer and on the shear resistance of adherent cells on these substrates was studied.The study revealed that the density of human venous endothelial cells (HUVEC) monolayers differed markedly between cells grown on a natural ECM and cells grown on singularized components of an ECM (p < 0.001). Only HUVEC grown on laminin showed similar densities and a stress fiber pattern comparable to HUVEC grown on the ECM. HUVEC grown on gelatin- or fibronectin-coated coverslips were less firmly attached to the substrate; frequently individual HUVEC and even groups of cells detached.Concluding it seems that coating of implants with laminin supports the formation of shear resistant endothelial cell (EC) monolayer - superior to other ECM components.

The Quest for Nonthrombotic Surface Modifications to Achieve Hemocompatibility of Implantable Devices

The use of blood-contacting implantable devices is limited by surface-induced thrombosis, which has led to the development of thromboresistant surfaces. Multidisciplinary efforts have promoted the development of surface modifications to minimize thrombosis by targeting surface-induced coagulation. To this date, no material has been identified that remains irrevocably hemocompatible with time but many options are now available with their own limitations. Essential to this review is the understanding of some of the challenges in this field and newer opportunities for hemocompatibility research. This report will also briefly review many of the achievements in the development of hemocompatible biomaterial coating, including surface modifications against protein adsorption and platelet adhesion, biomimetism, and endothelialization.

Orthogonally Functionalizable Polyurethane with Subsequent Modification with Heparin and Endothelium-Inducing Peptide Aiming for Vascular Reconstruction

Surface coimmobilization modifications of blood-contacting devices with both antithrombogenic moieties and endothelium-inducing biomolecules may create a synergistic effect to improve their performance. However, it is difficult to perform covalent dual-functionalization with both biomolecules on the surface of normally used synthetic polymeric substrates. Herein, we developed and characterized an orthogonally functionalizable polymer, biodegradable elastic poly(ester urethane)urea with disulfide and amino groups (PUSN), which was further fabricated into electropun fibrous scaffolds and surface modified with heparin and endothelial progenitor cells (EPC) recruiting peptide (TPS). The modification effects were assessed through platelet adhesion, EPC, and HUVEC proliferation. Results showed the dual modified PUSN scaffolds demonstrated a synergistic effect of reduced platelet deposition and improved EPC proliferation in vitro study, and demonstrated their potential application in small diameter vascular regeneration.

Stem cells: a promising source for vascular regenerative medicine

The rising and diversity of many human vascular diseases pose urgent needs for the development of novel therapeutics. Stem cell therapy represents a challenge in the medicine of the twenty-first century, an area where tissue engineering and regenerative medicine gather to provide promising treatments for a wide variety of diseases. Indeed, with their extensive regeneration potential and functional multilineage differentiation capacity, stem cells are now highlighted as promising cell sources for regenerative medicine. Their multilineage differentiation involves environmental factors such as biochemical, extracellular matrix coating, oxygen tension, and mechanical forces. In this review, we will focus on human stem cell sources and their applications in vascular regeneration. We will also discuss the different strategies used for their differentiation into both mature and functional smooth muscle and endothelial cells.

Scaffolds for hand tissue engineering: the importance of surface topography

Tissue engineering is believed to have great potential for the reconstruction of the hand after trauma, congenital absence and tumours. Due to the presence of multiple distinct tissue types, which together function in a precisely orchestrated fashion, the hand counts among the most complex structures to regenerate. As yet the achievements have been limited. More recently, the focus has shifted towards scaffolds, which provide a three-dimensional framework to mimic the natural extracellular environment for specific cell types. In particular their surface structures (or topographies) have become a key research focus to enhance tissue-specific cell attachment and growth into fully functioning units. This article reviews the current understanding in hand tissue engineering before focusing on the potential for scaffold topographical features on micro- and nanometre scales to achieve better functional regeneration of individual and composite tissues.

Development of a heart valve model surface for optimization of surface modifications

Current bioprosthetic valve replacements (BPVs) are susceptible to myriad complications, including calcification and thrombosis; however, recent research has explored surface modifications to encourage re-endothelialization of the tissue, preventing unwanted blood-tissue interactions. A bioprosthetic valve surface model (BVSM) was developed to facilitate rapid in vitro optimization of surface modification techniques for BPVs. The BVSM was manufactured by photopolymerization of PEGDA and collagen type I and subsequent addition of amine-rich peptide to provide reactive sites for surface modification. This BVSM mimics surface mechanical properties of bioprosthetic valve tissue, as measured by micropipette aspiration. The BVSM successfully mimics the latent toxic effects of glutaraldehyde fixation, as shown through MTT assay results. Amine content, assessed by XPS, was shown to be significantly lower in the BVSM than unfixed tissue. However, incubation of the surface with amine-reactive NHS-PEG-Cy5 revealed even coverage of the BVSM surface, suggesting that there exists sufficient surface reactive groups to anchor surface modifications, and that translation of the modification process to tissue will yield more complete modification of the BPV surface. These results indicate successful construction of a BVSM that mimics essential properties of bioprosthetic valve tissue and its usefulness for rapid in vitro optimization of surface modification methods for endothelialization.

STATEMENT OF SIGNIFICANCE

Current bioprosthetic valve replacements are susceptible to many complications, including calcification and thrombosis; however, recent research has explored surface modifications to encourage the integration of the replacement with the native tissue, which would prevent unwanted blood-tissue interactions. However, methods to analyze and optimize such modifications are limited by the complex surface topography, individual variability, and opacity of native tissue. Thus, we have developed a novel bioprosthetic valve tissue model (BVM) which mimics the important features of the bioprosthetic valve tissue and serves as a platform for rapid optimization and testing of surface modification strategies for tissue valves. Thus, the BVM will provide a needed platform to support rapid improvement of clinically available cardiovascular implants.

Imparting electroactivity to polycaprolactone fibers with heparin-doped polypyrrole: Modulation of hemocompatibility and inflammatory responses

Hemocompatibility, anti-inflammation and anti-thrombogenicity of acellular synthetic vascular grafts remains a challenge in biomaterials design. Using electrospun polycaprolactone (PCL) fibers as a template, a coating of polypyrrole (PPy) was successfully polymerized onto the fiber surface. The fibers coated with heparin-doped PPy (PPy-HEP) demonstrated better electroactivity, lower surface resistivity (9-10-fold) and better anti-coagulation response (non-observable plasma recalcification after 30min vs. recalcification at 8-9min) as compared to fibers coated with pristine PPy. Red blood cell compatibility, measured by% hemolysis, was greatly improved on PPy-HEP-coated PCL in comparison to uncoated PCL (3.9±2.1% vs. 22.1±4.1%). PPy-HEP-coated PCL fibers also exhibited higher stiffness values (6.8±0.9MPa vs. 4.2±0.8MPa) as compared to PCL fibers, but similar tensile strengths. It was also observed that the application of a low alternating current led to a 4-fold reduction of platelet activation (as quantitated by CD62p expression) for the PPy-HEP-coated fibers as compared to non-stimulated conditions. In parallel, a reduction in the leukocyte adhesion to both pristine PPy-coated and PPy-HEP-coated fibers was observable with AC stimulation. Overall, a new strategy involving the use of hemocompatible conducting polymers and electrical stimulation to control thrombogenicity and inflammatory responses for synthetic vascular graft designs was demonstrated.

Oligonucleotide biofunctionalization enhances endothelial progenitor cell adhesion on cobalt/chromium stents

As the endothelium still represents the ideal surface for cardiovascular devices, different endothelialization strategies have been attempted for biocompatibility and nonthrombogenicity enhancement. Since endothelial progenitor cells (EPCs) could accelerate endothelialization, preventing thrombosis and restenosis, the aim of this study was to use oligonucleotides (ONs) to biofunctionalize stents for EPC binding. In order to optimize the functionalization procedure before its application to cobalt-chromium (Co/Cr) stents, discs of the same material were preliminarily used. Surface aminosilanization was assessed by infrared spectroscopy and scanning electron microscopy. A fluorescent endothelial-specific ON was immobilized on aminosilanized surfaces and its presence was visualized by confocal microscopy. Fluorescent ON binding to porcine blood EPCs was assessed by flow cytometry. Viability assay was performed on EPCs cultured on unmodified, nontargeting ON or specific ON-coated discs; fluorescent staining of nuclei and F-actin was then performed on EPCs cultured on unmodified or specific ON-coated discs and stents. Disc biofunctionalization significantly increased EPC viability as compared to both unmodified and nontargeting ON-coated surfaces; cell adhesion was also significantly increased. Stents were successfully functionalized with the specific ON, and EPC binding was confirmed by confocal microscopy. In conclusion, stent biofunctionalization for EPC binding was successfully achieved in vitro, suggesting its use to obtain in vivo endothelialization, exploiting the natural regenerative potential of the human body.

Neutron reflectometry from poly (ethylene-glycol) brushes binding anti-PEG antibodies: evidence of ternary adsorption

Neutron reflectometry provides evidence of ternary protein adsorption within polyethylene glycol (PEG) brushes. Anti-PEG Immunoglobulin G antibodies (Abs) binding the methoxy terminated PEG chain segment specifically adsorb onto PEG brushes grafted to lipid monolayers on a solid support. The Abs adsorb at the outer edge of the brush. The thickness and density of the adsorbed Ab layer, as well as its distance from the grafting surface grow with increasing brush density. At high densities most of the protein is excluded from the brush. The results are consistent with an inverted "Y" configuration with the two FAB segments facing the brush. They suggest that increasing the grafting density favors narrowing of the angle between the FAB segments as well as overall orientation of the bound Abs perpendicular to the surface.

Surface modification and endothelialization of biomaterials as potential scaffolds for vascular tissue engineering applications

This review highlights the recent developments of surface modification and endothelialization of biomaterials in vascular tissue engineering applications.