Reducing the thrombogenicity of ion-selective electrode membranes through the use of a silicone-modified segmented polyurethane

Wearable Potentiometric Sensors for Medical Applications

Wearable potentiometric sensors have received considerable attention owing to their great potential in a wide range of physiological and clinical applications, particularly involving ion detection in sweat. Despite the significant progress in the manner that potentiometric sensors are integrated in wearable devices, in terms of materials and fabrication approaches, there is yet plenty of room for improvement in the strategy adopted for the sample collection. Essentially, this involves a fluidic sampling cell for continuous sweat analysis during sport performance or sweat accumulation via iontophoresis induction for one-spot measurements in medical settings. Even though the majority of the reported papers from the last five years describe on-body tests of wearable potentiometric sensors while the individual is practicing a physical activity, the medical utilization of these devices has been demonstrated on very few occasions and only in the context of cystic fibrosis diagnosis. In this sense, it may be important to explore the implementation of wearable potentiometric sensors into the analysis of other biofluids, such as saliva, tears and urine, as herein discussed. While the fabrication and uses of wearable potentiometric sensors vary widely, there are many common issues related to the analytical characterization of such devices that must be consciously addressed, especially in terms of sensor calibration and the validation of on-body measurements. After the assessment of key wearable potentiometric sensors reported over the last five years, with particular attention paid to those for medical applications, the present review offers tentative guidance regarding the characterization of analytical performance as well as analytical and clinical validations, thereby aiming at generating debate in the scientific community to allow for the establishment of well-conceived protocols.

Reduction of thrombogenicity of PVC-based sodium selective membrane electrodes using heparin-modified chitosan

Heparin-modified chitosan (H-chitosan) membrane was utilized to enhance biocompatibility of sodium selective membrane electrode based on the highly thrombogenic polyvinyl chloride (PVC). Sodium ion sensing film was prepared using PVC, sodium ionophore-X, potassium tetrakis(chlorophenyl)-borate, and o-nitrophenyloctylether. The PVC-based sensing film was sandwiched to chitosan or H-chitosan to prevent platelet adhesion on the surface of PVC. Potentiometric response characteristics of PVC-chitosan and PVC-H-chitosan membrane electrodes were found to be comparable to that of a control PVC based sodium-selective electrode. This indicates that chitosan and H-chitosan layers do not alter the response behaviour of the PVC-based sensing film. Biocompatibility of H-chitosan was confirmed by in vitro platelet adhesion study. The platelet adhesion investigations indicated that H-chitosan film is less thrombogenic compared to PVC, which could result in enhancement of biocompatibility of sodium selective membrane electrodes based on PVC, while maintaining the overall electrochemical performance of the PVC-based sensing film.

Properties evaluation of a new MRI contrast agent based on Gd-loaded nanoparticles

Nanosized materials of gadolinium oxide can provide high-contrast enhancement in magnetic resonance imaging (MRI). The aim of this research was to characterize a novel emulsion composed of a silicon-based nanocomposite polymer (NCP) and gadolinium (III) oxide (Gd₂O₃) nanoparticles. The size and morphological structure of this nanoparticle are determined by particle size analysis device (zeta sizer) and transmission electronic microscope. We determined composition of Gd₂O₃ nanoparticles with energy dispersive X-ray analysis (EDXA) and magnetic resonance signal by T₁-weighted MRI. Cytotoxicity of Gd₂O₃ nanoparticles in SK-MEL-3 cancer cells was evaluated. Zeta sizer showed Gd₂O₃ nanoparticles to be 75 nm in size. EDXA indicated the two main chemical components of gadolinium-nanocomposite polymer emulsion: gadolinium and silicon and MRI also showed a significantly higher incremental relaxivity for Gd₂O₃ nanoparticles compared to Magnevist (conventional contrast agent). In such concentrations, the slope of R₁ relaxivity (1/T₁) vs. concentration curve of Magnevist and Gd₂O₃ were 4.33, 7.98 s⁻¹ mM⁻¹. The slope of R₂ relaxivity (1/T₂) vs. concentration curve of Magnevist and Gd₂O₃ were 5.06, 13.75 s⁻¹ mM⁻¹. No appreciable toxicity was observed with Gd₂O₃ nanoparticles. Gadolinium-nanocomposite polymer emulsion is well characterized and has potential as a useful contrast agent for magnetic resonance molecular imaging.

Conformational Changes of Fibrinogen after Adsorption

The adsorption behavior of fibrinogen to two biomedical polyurethanes and a perfluorinated polymer has been investigated. Changes in the secondary structure of adsorbed fibrinogen were monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and sum frequency generation vibrational spectroscopy (SFG). SFG measurements were performed in the amide I range as well as in the C-H/N-H stretching range. Amide I signals from SFG demonstrate that fibrinogen has post-adsorption conformational changes that are dependent upon the polymer surface properties. For example, strong attenuation of the amide I and N-H stretching signals with increasing residence time was observed for fibrinogen adsorbed to poly(ether urethane) but not for the other two polymers. This change is not readily observed by ATR-FTIR. Differences in the observed spectral changes for fibrinogen adsorbed to each polymer are explained by different initial binding mechanisms and post-adsorption conformational changes.

Enhancing the blood compatibility of ion-selective electrodes

In vivo monitoring of various analytes is important for many bioanalytical and biomedical applications. The crucial challenge in this type of applications is the interaction of the sensor with the host environment, which is qualitatively described by the term biocompatibility. This review discusses recent advances in methods and materials used for the improvement of the biocompatibility of ion-selective electrodes especially as it relates to their interaction with blood components.

Sum Frequency Generation Studies on the Surface Structures of Plasticized and Unplasticized Polyurethane in Air and in Water

This study characterizes the molecular surface structures of polyurethane (PU) and plasticized PU films in air, in water, and in albumin solution in situ using a nonlinear optical technique, sum frequency generation (SFG) vibrational spectroscopy. Two different plasticizers are investigated: dioctyl sebacate (DOS) and o-nitrophenyl octyl ether (NPOE). Plasticization of PU is common for biosensors to achieve better adhesion, malleability, elasticity, and permeability; however, this can adversely affect biocompatibility. Our research indicates that plasticizers can segregate to the PU surface not only in air but also in water. In addition, plasticizer content can affect protein adsorption behaviors of PU surfaces. This is the first time surface-sensitive SFG has been applied to deduce plasticizer surface behavior in situ. More specifically, we found that DOS dominates the surface of the film with DOS surface concentrations higher than DOS bulk concentrations both in air and in contact with an aqueous environment. NPOE has a reduced effect at the surface compared to DOS in both air and aqueous environments. Addition of either DOS or NPOE to PU was also found to cause a change in albumin adsorption.

Ionophore-based ion-selective potentiometric and optical sensors

This paper describes ion-selective electrodes (ISEs) and optodes with a focus on the fundamental mechanisms, response characteristics, and recognition elements (ionophores) described to date for these sensors. The topics covered review the most frequently encountered ideas about ionophore-based sensors, including the theoretical and experimental parameters that influence response, typical ionophore structures, useful membrane compositions, and applications. Since these sensors are applicable in a number of fields, such as clinical, environmental, and process monitoring, as well as more novel approaches such as microfluidic-based systems and micro/nanoprobes, this article provides descriptions that are oriented toward a more general audience. Furthermore, a large portion of this review describes the ionophore component itself in hopes of inspiring ideas in readers of how novel molecular architectures with new ionic targets or improved selectivity can be developed.

Implantable chemical sensors for real-time clinical monitoring: progress and challenges

Recently, progress has been made in the development of implantable chemical sensors capable of real-time monitoring of clinically important species such as PO(2), PCO(2), pH, glucose and lactate. The need for developing truly biocompatible materials for sensor fabrication remains the most significant challenge for achieving robust and reliable sensors capable of monitoring the real-time physiological status of patients.

Improving the blood compatibility of ion-selective electrodes by employing poly(MPC-co-BMA), a copolymer containing phosphorylcholine, as a membrane coating

The hydrogelpoly(2-methacryloyloxyethylphosphorylcholine-co-butyl methacrylate), or poly(MPC-co-BMA), was used as a coating for polyurethane- and poly(vinyl chloride)-based membranes to develop ion-selective electrodes (ISEs) with enhanced blood compatibility. Adverse interactions of poly(MPC-co-BMA) with blood were diminished due to the phosphorylcholine functionalities of the hydrogel, which mimic the phospholipid polar groups present on the surface of many cell membranes. As demonstrated by immunostaining, hydrogel-coated PVC membranes soaked in platelet-rich plasma showed less adhesion and activation of platelets than uncoated PVC membranes, indicating an improvement in biocompatibility owing to the hydrogel. Furthermore, little differences in the potentiometric response characteristics, e.g., slope, detection limit, and selectivity, of ISEs employing uncoated and coated membranes were observed.