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Vasculoprotective endothelium glycocalyx (GCX) shedding plays a critical role in vascular disease. Previous work demonstrated that GCX degradation disrupts endothelial cell (EC) gap junction connexin (Cx) proteins, likely blocking interendothelial molecular transport that maintains EC and vascular tissue homeostasis to resist disease. Here, we focused on GCX regeneration and tested the hypothesis that vasculoprotective EC function can be stimulated via replacement of GCX when it is shed. We used EC with [i] intact heparan sulfate (HS), the most abundant GCX component; [ii] degraded HS; or [iii] HS that was restored after enzyme degradation, by cellular self-recovery or artificially. Artificial HS restoration was achieved via treatment with exogenous HS, with or without the GCX regenerator and protector sphingosine 1- phosphate (S1P). In these cells we immunocytochemically examined expression of Cx isotype 43 (Cx43) at EC borders and characterized Cx-containing gap junction activity by measuring interendothelial spread of gap junction permeable Lucifer Yellow dye. With intact HS, 60% of EC borders expressed Cx43 and dye spread to 2.88 ± 0.09 neighboring cells. HS degradation decreased Cx43 expression to 30% and reduced dye spread to 1.87± 0.06 cells. Cellular self-recovery of HS restored baseline levels of Cx43 and dye transfer. Artificial HS recovery with exogenous HS partially restored Cx43 expression to 46% and yielded dye spread to only 1.03 ± 0.07 cells. Treatment with both HS and S1P, recovered HS and restored Cx43 to 56% with significant dye transfer to 3.96 ± 0.23 cells. This is the first evidence of GCX regeneration in a manner that effectively restores vasculoprotective EC communication.

In this article, an expansive interpretation of "Tissue Engineering" is proposed which is in congruence with classical and recent published definitions. I further simplify the definition of tissue engineering as: "Exerting systematic control of the body's cells, matrices and fluids." As a consequence, many medical therapies not commonly considered tissue engineering are placed in this category because of their effect on the body's responses. While the progress of tissue engineering strategies is inexorable and generally positive, it has been subject to setbacks as have many important medical therapies. Medical practice is currently undergoing a transition on several fronts (academics, start-up companies, going concerns) from the era of "replacement medicine" where body parts and functions are replaced by mechanical, electrical or chemical therapies to the era of tissue engineering where health is restored by regeneration generation or limitation of the body's tissues and functions by exploiting our expanding knowledge of the body's biological processes to produce natural, healthy outcomes.

The treatment of diseased vasculature remains challenging, in part because of the difficulty in implanting drug-eluting devices without subjecting vessels to damaging mechanical forces. Implanting materials using adhesive forces could overcome this challenge, but materials have previously not been shown to durably adhere to intact endothelium under blood flow. Marine mussels secrete strong underwater adhesives that have been mimicked in synthetic systems. Here we develop a drug-eluting bioadhesive gel that can be locally and durably glued onto the inside surface of blood vessels. In a mouse model of atherosclerosis, inflamed plaques treated with steroid-eluting adhesive gels had reduced macrophage content and developed protective fibrous caps covering the plaque core. Treatment also lowered plasma cytokine levels and biomarkers of inflammation in the plaque. The drug-eluting devices developed here provide a general strategy for implanting therapeutics in the vasculature using adhesive forces and could potentially be used to stabilize rupture-prone plaques.

A series of poly(ethylene glycol)-co-poly(lactide) diacrylate macromers was synthesized with variable PEG molecular weights (10 or 20 kDa) and lactate contents (0 or 6 lactates per end group). These macromers were polymerized to form hydrogels by free radical polymerization using either redox or photochemical initiators. The extent of polymerization was determined by monitoring the compressive modulus of the resulting hydrogels and by quantitative determination of unreacted acrylate after exhaustive hydrolysis of the gel. Polymerization efficiency was found to depend on the lactate content of the macromer, with higher lactate macromers giving more efficient polymerization. For redox-initiated polymerization using ferrous gluconate/t-butyl hydroperoxide initiator, macromers containing approximately six lactate repeats per end group required lower concentrations of initiator to reach high conversion than lactate-free macromers. Photochemical polymerization with α,α-dimethoxy-α-phenylacetophenone (Irgacure 651(®)) was found to be less efficient than redox polymerization, requiring the addition of N-vinyl-2- pyrrolidone (NVP) as a co-monomer to achieve conversions comparable with redox polymerization. When conditions were optimized to provide near complete conversion for all gels, the presence of lactate repeat units in the hydrogel was generally found to reduce swelling and increase the compressive modulus. Calculated values of molecular weight between cross-links (M(c)) and mesh size using Flory-Rehner theory showed that macromer molecular weight had the greatest impact on the network structure of the gel., (Copyright © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Polymers used in implantable devices, although relatively unreactive, may degrade in vivo through unknown mechanisms. For example, polyetherurethane elastomers used as cardiac pacemaker lead insulation have developed surface defects after implantation. This phenomenon, termed "environmental stress cracking," requires intimate contact between polymer and host phagocytic cells, suggesting that phagocyte-generated oxidants might be involved. Indeed, brief exposure of polyetherurethane to activated human neutrophils, hypochlorous acid, or peroxynitrite produces modifications of the polymer similar to those found in vivo. Damage to the polymer appears to arise predominantly from oxidation of the urethane-aliphatic ester and aliphatic ether groups. There are substantial increases in the solid phase surface oxygen content of samples treated with hypochlorous acid, peroxynitrite or activated human neutrophils, resembling those observed in explanted polyetherurethane. Furthermore, both explanted and hypochlorous acid-treated polyetherurethane show marked reductions in polymer molecular weight. Interestingly, hypochlorous acid and peroxynitrite appear to attack polyetherurethane at different sites. Hypochlorous acid or activated neutrophils cause decreases in the urethane-aliphatic ester stretch peak relative to the aliphatic ether stretch peak (as determined by infrared spectroscopy) whereas peroxynitrite causes selective loss of the aliphatic ether. In vivo degradation may involve both hypohalous and nitric oxide-based oxidants because, after long-term implantation, both stretch peaks are diminished. These results suggest that in vivo destruction of implanted polyetherurethane involves attack by phagocyte-derived oxidants.

Thrombogenicity was assessed by measuring the amount of 111In-platelets and 125I-fibrinogen deposited on the inner luminal surface of six polyurethanes for up to 60 min of blood contact in a canine ex-vivo shunt model. Commercial and laboratory synthesized polymers were examined. Two of the commercially synthesized polyurethanes (Biostable PURs) do not contain ether linkages in the polymer backbone and have previously shown resistance to oxidative and hydrolytic degradation. Static contact angle measurements, dynamic contact angle measurements, and ESCA were used to characterize the surfaces of these polyurethanes. The effectiveness of an acetone extraction used to remove extrusion waxes from Pellethane 2363-80A was similarly studied. Both Pellethane 2363-80A and the ether-free materials had relatively nonthrombogenic surfaces, as indicated by low platelet and fibrinogen deposition, making them potentially good candidates for biomedical applications.

A series of segmented polyurethanes (SPUs) with various polyol soft segments was prepared and their hydrolytic degradation and degradation due to lipid sorption was investigated. The hydrolytic degradation of the SPUs was investigated in a papain solution, where it was shown that the SPU based on poly(ethyleneoxide) (PEO) soft segment was susceptible to hydrolytic degradation. X-ray photoelectron spectroscopic (XPS) data suggest dissociation of the urethane linkage by enzymatic degradation. Degradation by lipid sorption was observed for the SPU based on a poly(dimethylsiloxane) (PDMS) soft segment. This is ascribed to the high solubility of lipid in the PDMS segment of the SPU.

The relationship between surface, bulk and ex vivo blood-contacting properties of segmented polyurethanes with various polyol soft segment was investigated. The polyols used in this study were poly(ethylene oxide), poly(tetramethylene oxide), hydrogenated poly(butadiene), poly(butadiene) and poly(dimethylsiloxane). The hard segment of these segmented polyurethanes was composed of 4,4' diphenylmethane diisocyanate and 1,4 butanediol, present at 50 wt%. An experimental polyurethane, Biostable PUR, which has shown excellent biostability, was used in this study. The segmented polyurethanes based on the hydrophobic polyols such as poly(dimethylsiloxane) and hydrogenated poly(butadiene) showed distinct microphase separation between hard and soft segments. X-ray photoelectron spectroscopy revealed the surface enrichment of the hydrophobic component at the air-solid interface. Dynamic contact angle measurements indicated that the poly(dimethylsiloxane)-based segmented polyurethane possessed a hydrophobic surface in water. The poly(dimethylsiloxane)-based segmented polyurethane had the lowest platelet adhesion among the segmented polyurethanes investigated in this study, whilst the platelet deposition on the poly(ethylene oxide)-based polymer increased with time.

A series of segmented polyurethanes (SPUs) containing various polyol soft segments was prepared and their resistance to oxidative degradation was investigated after aging in AgNO3 solution. The SPU with the polyether soft segment showed a large reduction in mechanical strength after exposure to the oxidative environment. Surface cracking was often observed for these specimens. XPS measurements revealed that scission of the ether linkage occurs upon oxidation. The oxidative resistance of SPUs containing aliphatic hydrocarbon soft segments was significantly improved over the poly(tetramethylene oxide) (PTMO) based polyurethane.

Polyurethanes offer the greatest versatility in compositions and properties of any family of polymers. For implantable medical devices, a few specific elastomeric polyurethane compositions have demonstrated a combination of toughness, durability, biocompatibility and biostability not achieved by any other available material. Because of the complex behavior of implantable polyurethanes in the body environment, designers and fabricators of polyurethane-containing devices must pay particular attention to the choice of composition and design of components. Subsequent treatment during qualification, fabrication, sterilization, storage, implantation, in vivo operation and explantation also determine the performance and provide the means for assessing the efficacy of the polyurethane in the implanted device.

We have developed a simple method for detecting high concentrations of chloride in sweat from ambulatory subjects, a measurement useful in the detection of cystic fibrosis. The method is based on the standard approach of stimulating sweat generation through iontophoresis of pilocarpine nitrate into the skin, followed by collection and analysis of the sweat for chloride concentration. The sweat-stimulating reagents are contained in polymeric gel pads, which are used in conjunction with a small battery-powered stimulator. The chloride analysis is subsequently done on the stimulated site by use of a thin test patch that picks up a fixed amount of sweat and changes color if the chloride concentration is higher than a predetermined value. The successful completion of a test is indicated by a fill tab, which changes color when the appropriate amount of sweat has been picked up by the chloride test patch.

Polyurethanes have become the most valuable implantable elastomers for uses requiring toughness, durability, biocompatibility and biostability. They are inherently stable in the body environment. However, physical and chemical changes may be effected by conditions of processing, fabrication, use or interactions with other device components. Most prominent modes of polyurethane degradation include mineralization, environmental stress-cracking and oxidation. While the mechanisms of these forms of degradation are not fully understood, an awareness of their causes and effects can lead to procedures that provide all of the long-term functionality required for the sophisticated polyurethane-based devices of today and tomorrow.