The haemocompatibility of polyurethane–hyaluronic acid copolymers

Design of Injectable Bioartificial Hydrogels by Green Chemistry for Mini-Invasive Applications in the Biomedical or Aesthetic Medicine Fields

Bioartificial hydrogels are hydrophilic systems extensively studied for regenerative medicine due to the synergic combination of features of synthetic and natural polymers. Injectability is another crucial property for hydrogel mini-invasive administration. This work aimed at engineering injectable bioartificial in situ cross-linkable hydrogels by implementing green and eco-friendly approaches. Specifically, the versatile poly(ether urethane) (PEU) chemistry was exploited for the development of an amphiphilic PEU, while hyaluronic acid was selected as natural component. Both polymers were functionalized to expose thiol and catechol groups through green water-based carbodiimide-mediated grafting reactions. Functionalization was optimized to maximize grafting yield while preserving group functionality. Then, polymer miscibility was studied at the macro-, micro-, and nano-scale, suggesting the formation of hydrogen bonds among polymeric chains. All hydrogels could be injected through G21 and G18 needles in a wide temperature range (4-25 °C) and underwent sol-to-gel transition at 37 °C. The addition of an oxidizing agent to polymer solutions did not improve the gelation kinetics, while it negatively affected hydrogel stability in an aqueous environment, suggesting the occurrence of oxidation-triggered polymer degradation. In the future, the bioartificial hydrogels developed herein could find application in the biomedical and aesthetic medicine fields as injectable formulations for therapeutic agent delivery.

A scope at antifouling strategies to prevent catheter-associated infections

The use of invasive medical devices is becoming more common nowadays, with catheters representing one of the most used medical devices. However, there is a risk of infection associated with the use of these devices, since they are made of materials that are prone to bacterial adhesion with biofilm formation, often requiring catheter removal as the only therapeutic option. Catheter-related urinary tract infections (CAUTIs) and central line-associated bloodstream infections (CLABSIs) are among the most common causes of healthcare-associated infections (HAIs) worldwide while endotracheal intubation is responsible for ventilator-associated pneumonia (VAP). Therefore, to avoid the use of biocides due to the potential risk of bacterial resistance development, antifouling strategies aiming at the prevention of bacterial adherence and colonization of catheter surfaces represent important alternative measures. This review is focused on the main strategies that are able to modify the physical or chemical properties of biomaterials, leading to the creation of antiadhesive surfaces. The most promising approaches include coating the surfaces with hydrophilic polymers, such as poly(ethylene glycol) (PEG), poly(acrylamide) and poly(acrylates), betaine-based zwitterionic polymers and amphiphilic polymers or the use of bulk-modified poly(urethanes). Natural polysaccharides and its modifications with heparin, have also been used to improve hemocompatibility. Recently developed bioinspired techniques yielding very promising results in the prevention of bacterial adhesion and colonization of surfaces include slippery liquid-infused porous surfaces (SLIPS) based on the superhydrophilic rim of the pitcher plant and the Sharklet topography inspired by the shark skin, which are potential candidates as surface-modifying approaches for biomedical devices. Concerning the potential application of most of these strategies in catheters, more in vivo studies and clinical trials are needed to assure their efficacy and safety for possible future use.

Development and Fabrication of Vapor Cross-Linked Hyaluronan-Polyethylene Interpenetrating Polymer Network as a Biomaterial

Flexible heart valve leaflets made from hyaluronan-enhanced linear low-density polyethylene interpenetrating polymeric network (HA-LLDPE IPN) films have been shown to provide good hemodynamics, but the resulting surfaces were not consistent; therefore, the present work tries to mitigate this problem by developing a vapor cross-linked HA-LLDPE IPN. Herein, the HA-LLDPE fabrication process is studied, and its parameters are varied to assess their effects on the IPN formation. Thermal analysis and gas chromatography-mass spectrometry were used to quantify the effects of different treatment conditions on material properties. Water contact angle goniometry, infrared spectroscopy, and toluidine blue O (TBO) staining were used to characterize the surface of the HA-LLDPE IPN. The results show that a hydrophilic surface is formed on HA-LLDPE, which is indicative of HA. HA surface density data from TBO staining show consistent HA distribution on the surface. The IPN fabrication process does not affect the tensile properties that make LLDPE an attractive material for use in flexible heart valve leaflets. The 28 day in vitro biological assays show HA-LLDPE to be noncytotoxic and resistant to enzymatic degradation. The HA-LLDPE showed less platelet adhesion and caused less platelet activation than the plain LLDPE or tissue culture polystyrene. All of the results indicate that vapor cross-linked HA-LLDPE IPN is a promising material for use as flexible leaflets for heart valve replacements.

Characterization and Evaluation of Carboxymethyl Cellulose-Based Films for Healing of Full-Thickness Wounds in Normal and Diabetic Rats

Artificial skin substitute made of polymeric films are of great demand in the field of skin tissue engineering. We report here the fabrication of carboxymethyl cellulose (CMC) and poly(ethylene glycol) (PEG) blend films by solution casting method for wound healing applications. The physicochemical characteristics and the thermal stability of the films were analyzed. The surface morphology shows crystalline structures with large hexagonal-like platelet crystals of CMC on the surface of the films. Pure CMC films exhibited higher tensile strength than the CMC/PEG blend films. The swelling ratio (SR) of the films was influenced by the pH of Tris-HCL buffer (2.0, 5.0, and 7.0), which increased with increase in pH. The hemocompatibility assay and cytotoxicity test using NIH 3T3 fibroblast cells showed that the films were biocompatible. To evaluate the wound healing efficacy, the films were applied in full-thickness wounds created in normal and diabetic Wistar albino rats. The wounds healed faster with pure CMC film compared to blend films in both normal and diabetic rats, evidenced by intensive collagen formation in histopathological analysis. Thus, the films have potential application in skin regeneration, thereby to restore the structural and functional characteristics of the skin.

Novel triphosphorylation polyurethane nanoparticles for blood-contacting biomaterials' coating

Improving hemocompatibility of biomaterials and devices contacting the human blood has been the subject of intensive research. In this study, we synthesized a novel excellent blood compatible polyurethane/sodium triphosphate nanoparticle (PU/STPP). Characterization of polyurethane/sodium triphosphate (PU/STPP) nanoparticles was carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic light scattering (DLS), nuclear magnetic resonance (NMR), and energy dispersive spectroscopy (EDS). Blood compatibility assessment of PU/STPP nanoparticles was performed by in vitro coagulation time, plasma clotting time, hemolysis rate, and red blood cell morphology tests. Cell compatibility evaluations of PU/STPP nanoparticles were obtained by MTT cell viability tests. The PU/STPP nanoparticles also were used to modify vascular prostheses with cosedimentation. Platelet adhesion tests showed that blood compatibility of vascular prostheses coated with PU/STPP nanoparticles is better than that of pure vascular prostheses.

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.

Nylon-3 polymers that enable selective culture of endothelial cells

Substrates that selectively encourage the growth of specific cell types are valuable for the engineering of complex tissues. Some cell-selective peptides have been identified from extracellular matrix proteins; these peptides have proven useful for biomaterials-based approaches to tissue repair or regeneration. However, there are very few examples of synthetic materials that display selectivity in supporting cell growth. We describe nylon-3 polymers that support in vitro culture of endothelial cells but do not support the culture of smooth muscle cells or fibroblasts. These materials may be promising for vascular biomaterials applications.

Effect of hyaluronic acid incorporation method on the stability and biological properties of polyurethane-hyaluronic acid biomaterials

The high failure rate of small diameter vascular grafts continues to drive the development of new materials and modification strategies that address this clinical problem, with biomolecule incorporation typically achieved via surface-based modification of various biomaterials. In this work, we examined whether the method of biomolecule incorporation (i.e., bulk versus surface modification) into a polyurethane (PU) polymer impacted biomaterial performance in the context of vascular applications. Specifically, hyaluronic acid (HA) was incorporated into a poly(ether urethane) via bulk copolymerization or covalent surface tethering, and the resulting PU-HA materials characterized with respect to both physical and biological properties. Modification of PU with HA by either surface or bulk methods yielded materials that, when tested under static conditions, possessed no significant differences in their ability to resist protein adsorption, platelet adhesion, and bacterial adhesion, while supporting endothelial cell culture. However, only bulk-modified PU-HA materials were able to fully retain these characteristics following material exposure to flow, demonstrating a superior ability to retain the incorporated HA and minimize enzymatic degradation, protein adsorption, platelet adhesion, and bacterial adhesion. Thus, despite bulk methods rarely being implemented in the context of biomolecule attachment, these results demonstrate improved performance of PU-HA upon bulk, rather than surface, incorporation of HA. Although explored only in the context of PU-HA, the findings revealed by these experiments have broader implications for the design and evaluation of vascular graft modification strategies.

Biological evaluation of polyvinyl alcohol hydrogel crosslinked by polyurethane chain for cartilage tissue engineering in rabbit model

Polyvinyl alcohol (PVA) hydrogel chains were crosslinked by urethane pre-polymer (PPU) in order to fabricate a new substitute for cartilage lesions. The microscopy images showed that the cultured chondrocytes had spherical morphology on PVA-PPU sample after 4 weeks of isolation in vitro. The alcian blue and safranin O staining proved the presence of proteoglycan on the surface of PVA-PPU sample secreted by cultured chondrocytes. This was confirmed by the detection of sulfate ions in the wavelength dispersive X-ray (WDX) analysis. In addition, the expression of collagen type II and aggrecan were observed in chondrocytes cultured on PVA-PPU by RT-PCR. Moreover, the implantation of the PVA-PPU sample with autologous cultured chondrocytes revealed the formation of neocartilage tissue in a rabbit model during 12 weeks follow up. In conclusion, the results verified that isolated chondrocytes cultured on PVA-PPU retain their original phenotype and this composition can be considered as promising substrate for cartilage tissue engineering.

Enhancement of fatty acid-based polyurethanes cytocompatibility by non-covalent anchoring of chondroitin sulfate

For tissue engineering purpose biopolymer chondroitin sulfate (CS), one of the major components of cartilage and bone extracellular matrix, was immobilized onto the surface of amino-functionalized polyurethane (PU) films derived from naturally occurring oleic and 10-undecenoic acids. The amino-functionalized PUs were prepared by aminolysis with 1,6-hexamethylenediamine of synthesized PUs containing methyl ester groups. FTIR-ATR, XPS, SEM, and water contact angle measurements were used to confirm the surface changes at each step of treatment, both in morphologies and chemical composition. Cytotoxicity and cell morphology analysis using osteoblast cell line MG63 showed that PU-CS films are suitable materials for cell growth, spreading, and differentiation.

A Hybrid Coil/Polymer Device for Occlusion of Cerebral Aneurysms

The treatment of cerebral aneurysms is frequently accomplished via endovascular delivery of metal coils in order to occlude the aneurysm and prevent rupture. This procedure involves imprecise packing of large lengths of wire into the aneurysm and often results in high rates of aneurysm recanalization. Over time, this incomplete aneurysm occlusion can lead to aneurysm enlargement, which may have fatal consequences. This report describes the fabrication and preliminary testing of a novel aneurysm occlusion device composed of a single metal coil surrounded by a biocompatible polymer shell. These coil-in-shell devices were tested under flow conditions in synthetic in vitro models of saccular aneurysms and deployed in vivo in a short-term porcine aneurysm model to study occlusion efficacy. A single nickel titanium shape memory wire was used to deploy a biocompatible, elastic polymeric shell, leading to aneurysmal sac filling in both in vitro and in vivo aneurysm models. The deployment of this coil-in-shell device in synthetic aneurysm models in vitro resulted in varying degrees of aneurysm occlusion, with less than 2% of trials resulting in significant leakage of fluid into the aneurysm. Meanwhile, in vivo coil-in-shell device implantation in a porcine aneurysm model provided proof-of-concept for successful occlusion, as both aneurysms were completely occluded by the devices. Both in vitro and in vivo studies demonstrated that this coil-in-shell device may be attractive as an alternative to traditional coil embolization methods in some cases, allowing for a more precise and controlled aneurysm occlusion.