Evaluation of the in vivo chemical reactivity of a novel copolymer insulation on cardiac leads in a single-center study

BACKGROUND

Human in vivo data on the chemical stability of different transvenous lead materials, particularly OptimTM leads, are lacking.

OBJECTIVES

The purpose of this study was to determine the chemical reactivity of insulation materials by analyzing the molar mass of extracted pacing and defibrillator leads METHODS: We collected extracted leads at Emory University Hospitals and sent the leads with thermoplastic outer insulation material for molar mass analysis, a material characteristic that informs biostability. Leads were separated based on the chemical identity of the outer insulation material, and the molar mass was measured by an independent party. The extent of chemical reaction was compared across leads having different materials: poly(ether)urethane 55D, poly(ether)urethane 80A, and Optim.

RESULTS

A total of 70 leads were extracted. The subset of extracted leads having outer insulation materials composed of PEU or Optim were analyzed for molar mass, where implant times ranged from 0.12 to 16.26 years. The rate of chemical degradation was compared by plotting the extent of reaction [Mn(t = 0)/Mn(t)] as a function of implant time. The Optim molar mass decreased to 40% of its initial value at 10 years of implant. No change in the molar mass of the PEU insulations could be resolved over the same 10-year implant time.

CONCLUSION

Because the molar mass of a polymer is directly related to its mechanical integrity, the observed decrease in molar mass of Optim likely translates into premature insulation defects and is consistent with the observed increased rate of electrical malfunction/noise in this subset of cardiac leads.

Improved in vivo stability of silicon-containing polyurethane by fluorocarbon side chain modulation of the surface structure

As a class of widely used biomedical materials, polyurethanes suffer from their insufficient stability in vivo. Although the commercialized silicone-polyetherurethanes (SiPEUs) have demonstrated excellent biostability compared with polyetherurethanes (PEUs) for long-term implantation, the usage of polydimethylsiloxane (PDMS) inevitably decreased the mechanical properties and unexpected breaches were observed. In this study, we introduced a fluorinated diol (FDO) into SiPEU to modulate the molecular interactions and micro-separated morphology. The fluorinated silicon-containing polyurethane (FSiPEU) was achieved with desirable silicone- and fluorine-enriched surfaces and mechanical properties at a low silicon content. As evidenced by in vitro culture of macrophages and in vivo hematoxylin-eosin (H&E) staining, FSiPEU demonstrated a minimized inflammatory response. After implantation in mice for 6 months, the material was devoid of significant surface degradation and had the least chain cleavage of soft segments. The results indicate that FSiPEU could be promising candidates for long-term implantation considering the combination of biostability, biocompatibility and mechanical performances.

Functional remodeling of an electrospun polydimethylsiloxane-based polyether urethane external vein graft support device in an ovine model

Saphenous vein graft (SVG) failure rates are unacceptably high, and external mechanical support may improve patency. We studied the histologic remodeling of a conformal, electrospun, polydimethylsiloxane-based polyether urethane external support device for SVGs and evaluated graft structural evolution in adult sheep to 2 years. All sheep (N = 19) survived to their intended timepoints, and angiography showed device-treated SVG geometric stability over time (30, 90, 180, 365, or 730 days), with an aggregated graft patency rate of 92%. There was minimal inflammation associated with the device material at all timepoints. By 180 days, treated SVG remodeling was characterized by minimal/nonprogressive intimal hyperplasia; polymer fragmentation and integration; as well as the development of a neointima, and a confluent endothelium. By 1-year, the graft developed a media-like layer by remodeling the neointima, and elastic fibers formed well-defined structures that subtended the neo-medial layer of the remodeled SVG. Immunohistochemistry showed that this neo-media was populated with smooth muscle cells, and the intima was lined with endothelial cells. These data suggest that treated SVGs were structurally remodeled by 180 days, and developed arterial-like features by 1 year, which continued to mature to 2 years. Device-treated SVGs remodeled into arterial-like conduits with stable long-term performance as arterial grafts in adult sheep.

In vitro oxidative stability of high strength siloxane poly(urethane-urea) elastomers based on linked-macrodiol

In vitro oxidative stability of two siloxane poly(urethane urea)s synthesized using 4,4'-methylenediphenyl diisocyanate (in SiPUU-1) and Isophorone diisocyanate (in SiPUU-2) linked soft segment was evaluated using 20% H₂ O₂ and 0.1 mol/L CoCl₂ solution at 37°C under 150% strain. Commercially available siloxane polyurethane (Elast-Eon™ 2A) and polyether polyurethane (ChronoThane P™ 80A) were used as negative and positive controls, respectively. ChronoSil™ 80A was included as another commercially available polycarbonate polyurethane. Scanning electron microscopic (SEM) examinations, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and molecular weight reduction revealed the extensive degradation of ChronoThane P™ 80A after 90 days while SiPUU-1, SiPUU-2 and Elast-Eon™ 2A showed no noticeable surface degradation. ChronoSil™ 80A showed degradation in both soft and hard segments. Tensile testing was carried out only on unstrained polyurethanes for 90 days. ChronoThane P™ 80A showed 35% loss in ultimate tensile strength and it was only 13-14% for SiPUU-1 and Elast-Eon™ 2A. However, the tensile strength of ChronoSil™ 80A was not significantly affected. The results of this study proved that SiPUU-1 possess oxidative stability comparable with Elast-Eon™ 2A. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2557-2565, 2019.

Simultaneous Improvement of Oxidative and Hydrolytic Resistance of Polycarbonate Urethanes Based on Polydimethylsiloxane/Poly(hexamethylene carbonate) Mixed Macrodiols

The degradation behaviors including oxidation and hydrolysis of silicone modified polycarbonate urethanes were thoroughly investigated. These polyurethanes were based on polyhexamethylene carbonate (PHMC)/polydimethylsiloxane (PDMS) mixed macrodiols with molar ratio of PDMS ranging from 5% to 30%. It was proved that PDMS tended to migrate toward surface and even a small amount of PDMS could form a silicone-like surface. Macrophages-mediated oxidation process indicated that the PDMS surface layer was desirable to protect the fragile soft PHMC from the attack of degradative species. Hydrolysis process was probed in detail after immersing in boiling buffered water using combined analytical tools. Hydrolytically stable PDMS could act as protective shields for the bulk to hinder the chain scission of polycarbonate carbonyls whereas the hydrolysis of urethane linkages was less affected. Although the promoted phase separation at higher PDMS fractions lead to possible physical defects and mechanical compromise after degradation, simultaneously enhanced oxidation and hydrolysis resistance could be achieved for the polyurethanes with proper PDMS incorporation.

Morphology and surface properties of high strength siloxane poly(urethane-urea)s developed for heart valve application

A series of siloxane poly(urethane-urea) (SiPUU) were developed by incorporating a macrodiol linked with a diisocyanate to enhance mixing of hard and soft segments (SS). The effect of this modification on morphology, surface properties, surface elemental composition, and creep resistance was investigated. The linked macrodiol was prepared by reacting α,ω-bis(6-hydroxyethoxypropyl) poly(dimethylsiloxane)(PDMS) or poly(hexamethylene oxide) (PHMO) with either 4,4'-methylenediphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), or isophorone diisocyanate (IPDI). SiPUU with PHMO-MDI-PHMO and PHMO-IPDI-PHMO linked macrodiols showed enhanced creep resistance and recovery when compared with a commercial biostable polyurethane, Elast-Eon™ 2A. Small and wide-angle X-ray scattering data were consistent with significant increase of hydrogen bonding between hard and SS with linked-macrodiols, which improved SiPUU's tensile stress and tear strengths. These SiPUU were hydrophobic with contact angle higher than 101° and they had low water uptake (0.7%·w/w of dry mass). They also had much higher siloxane concentration on the surface compared to that in the bulk. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 112-121, 2019.

Development of high strength siloxane poly(urethane-urea) elastomers based on linked macrodiols for heart valve application

Mixed macrodiol based siloxane poly(urethane-urea)s (SiPUU) having number average molecular weights in the range 87-129 kDa/mol were synthesized to give elastomers with high tensile and tear strengths required to fabricate artificial heart valves. Polar functional groups were introduced into the soft segment to improve the poor segmental compatibility of siloxane polyurethanes. This was achieved by linking α,ω-bis(6-hydroxyethoxypropyl) poly(dimethylsiloxane) (PDMS) or poly(hexamethylene oxide) (PHMO) macrodiols with either 4,4'-methylenediphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) prior to polyurethane synthesis. The hard segment was composed of MDI, and a 1:1 mixture of 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane and 1,2-ethylene diamine. We report the effect of urethane linkers in soft segments on properties of the SiPUU. PHMO linked with either MDI or IPDI produced SiPUU with the highest tensile and tear strengths. Linking PDMS hardly affected the tensile strength; however, the tear strength was improved. The stress-strain curves showed no plastic deformation region typically observed for conventional polyurethanes indicating good creep resistance. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1712-1720, 2018.

Fabrication of macromolecular gradients in aligned fiber scaffolds using a combination of in-line blending and air-gap electrospinning

Although a variety of fabrication methods have been developed to generate electrospun meshes with gradient properties, no platform has yet to achieve fiber alignment in the direction of the gradient that mimics the native tendon-bone interface. In this study, we present a method combining in-line blending and air-gap electrospinning to address this limitation in the field. A custom collector with synced rotation permitted fiber collection with uniform mesh thickness and periodic copper wires were used to induce fiber alignment. Two poly(ester urethane ureas) with different hard segment contents (BPUR 50, BPUR 10) were used to generate compositional gradient meshes with and without fiber alignment. The compositional gradient across the length of the mesh was characterized using a fluorescent dye and the results indicated a continuous transition from the BPUR 50 to the BPUR 10. As expected, the fiber alignment of the gradient meshes induced a corresponding alignment of adherent cells in static culture. Tensile testing of the sectioned meshes confirmed a graded transition in mechanical properties and an increase in anisotropy with fiber alignment. Finite element modeling was utilized to illustrate the gradient mechanical properties across the full length of the mesh and lay the foundation for future computational development work. Overall, these results indicate that this electrospinning method permits the fabrication of macromolecular gradients in the direction of fiber alignment and demonstrate its potential for use in interfacial tissue engineering.

STATEMENT OF SIGNIFICANCE

The native tendon-bone interface contains a gradient of properties that ensures stability of the joint. Without this transition, failure can occur due to stress concentration at the bone insertion site. Electrospinning is a method commonly used to produce fibrous grafts with gradient properties; however, no current method allows for gradients in the direction of fiber alignment. This work details a novel electrospinning method to produce gradients in the direction of fiber alignment in order to better mimic transitional zones and improve regeneration of the tendon-bone interface. In addition to the biomechanical gradients demonstrated here, this method may also be used to generate gradients of macromolecular, biochemical, and cellular cues with broad potential utility in tissue engineering.