PHEMA Matrix Research Articles

Tailoring the Electron Trapping Effect of a Biocompatible Triboelectric Hydrogel by Graphene Oxide Incorporation towards Self-Powered Medical Electronics.

Triboelectric nanogenerators (TENGs) are associated with several drawbacks that limit their application in the biomedical field, including toxicity, thrombogenicity, and poor performance in the presence of fluids. By proposing the use of a hemo/biocompatible hydrogel, poly(2-hydroxyethyl methacrylate) (pHEMA), this study bypasses these barriers. In contact-separation mode, using polytetrafluoroethylene (PTFE) as a reference, pHEMA generates an output of 100.0 V, under an open circuit, 4.7 μA, and 0.68 W/m2 for an internal resistance of 10 MΩ. Our findings unveil that graphene oxide (GO) can be used to tune pHEMA's triboelectric properties in a concentration-dependent manner. At the lowest measured concentration (0.2% GO), the generated outputs increase to 194.5 V, 5.3 μA, and 1.28 W/m2 due to the observed increase in pHEMA's surface roughness, which expands the contact area. Triboelectric performance starts to decrease as GO concentration increases, plateauing at 11% volumetric, where the output is 51 V, 1.76 μA, and 0.17 W/m2 less than pHEMA's. Increases in internal resistance, from 14 ΩM to greater than 470 ΩM, ζ-potential, from -7.3 to -0.4 mV, and open-circuit characteristic charge decay periods, from 90 to 120 ms, are all observed in conjunction with this phenomenon, which points to GO function as an electron trapping site in pHEMA's matrix. All of the composites can charge a 10 μF capacitor in 200 s, producing a voltage between 0.25 and 3.5 V and allowing the operation of at least 20 LEDs. The triboelectric output was largely steady throughout the 3.33 h durability test. Voltage decreases by 38% due to contact-separation frequency, whereas current increases by 77%. In terms of pressure, it appears to have little effect on voltage but boosts current output by 42%. Finally, pHEMA and pHEMA/GO extracts were cytocompatible toward fibroblasts. According to these results, pHEMA has a significant potential to function as a biomaterial to create bio/hemocompatible TENGs and GO to precisely control its triboelectric outputs.

Inverse emulsion polymerization‐assisted designing of superparamagnetic poly (2‐hydroxyethyl methacrylate) nanoparticles and magnetically triggered release of cisplatin

AbstractSuperparamagnetic nanocarriers of poly (2‐hydroxyethyl methacrylate) (PHEMA) were prepared by carrying out benzoyl peroxide (BPO) initiated inverse emulsion‐free radical polymerization of HEMA in the presence of poly (vinyl alcohol) (PVA) and subsequent in situ precipitation of magnetite within the PHEMA matrix. The as‐prepared nanoparticles were characterized by FTIR and UV–visible spectroscopy, vibrating sample magnetometry (VSM), particle size and zeta potential analysis, and transmission electron microscopy, respectively. The PHEMA nanocarriers were investigated for their blood compatibility, and cytotoxicity response to L929 cells. The superparamagnetic nanoparticles were loaded with an anticancer drug cisplatin and the release profiles of the drug were examined as a function of various experimental parameters like composition of the PHEMA nanocarriers, percentage of drug loading, and strength of the externally imposed magnetic field. The kinetics of the drug release process was also investigated, and the obtained release data were applied to different mathematical kinetic models to explore the nature of the release mechanism.

Photons Probe Entropic Potential Variation during Molecular Confinement in Nanocavities.

In thin polymeric layers, external molecular analytes may well be confined within tiny surface nano/microcavities, or they may be attached to ligand adhesion binding sites via electrical dipole forces. Even though molecular trapping is followed by a variation of the entropic potential, the experimental evidence of entropic energy variation from molecular confinement is scarce because tiny thermodynamic energy density diverseness can be tracked only by sub-nm surface strain. Here, it is shown that water confinement within photon-induced nanocavities in Poly (2-hydroxyethyl methacrylate), (PHEMA) layers could be trailed by an entropic potential variation that competes with a thermodynamic potential from electric dipole attachment of molecular adsorbates in polymeric ligands. The nano/microcavities and the ligands were fabricated on a PHEMA matrix by vacuum ultraviolet laser photons at 157 nm. The entropic energy variation during confinement of water analytes on the photon processed PHEMA layer was monitored via sub-nm surface strain by applying white light reflectance spectroscopy, nanoindentation, contact angle measurements, Atomic Force Microscopy (AFM) imaging, and surface and fractal analysis. The methodology has the potency to identify entropic energy density variations less than 1 pJm−3 and to monitor dipole and entropic fields on biosurfaces.

A transparent wound dressing based on bacterial cellulose whisker and poly(2-hydroxyethyl methacrylate)

The current study was aimed to develop a transparent wound dressing comprised of bacterial cellulose (BC) and poly (2-hydroxyethyl methacrylate) (PHEMA) hydrogel coated with silver (Ag) nanoparticles. Briefly, different concentrations of BC whiskers (BCWs) were added into the HEMA solution to form PHEMA/BCWs hydrogel with volume ratio of monomer HEMA and BCWs as 7:3 and 1:1. The addition of BCWs into PHEMA matrix improved its equilibrium water content and light transmittance about 20%-40% and 10%, respectively. The Young's modulus for PHEMA was found to be 0.72MPa, which was improved to 0.57MPa and 0.50MPa for PHEMA/BCWs 7:3 and PHEMA/BCWs 1:1, respectively. Further, immersion of PHEMA/BCWs hydrogel in the AgNO3 and NaBH4 solutions bestowed it with antibacterial property and produced inhibition zones of 0.5±0.15cm and 0.25±0.15cm against Escherichia coli and Staphylococcus aureus, respectively. Similarly, PHEMA/BCWs prepared with 0.001M AgNO3 and 0.001M NaBH4 solutions showed 99% and 90% reduction in colony forming unit (CFU) for E. coli and S. aureus, respectively, after 24h. The PHEMA/BCWs/Ag hydrogel facilitated the growth of NIH3T3 fibroblast, showing their low toxicity. These results demonstrate the suitability of PHEMA/BCWs/Ag hydrogel for its application as potential transparent wound dressing material for skin repair.

Poly(2-hydroxyethylmethacrylate-graft-folic acid), synthesis, solubility enhancement, and release dynamic of folic acid

A series of poly (2-hydroxyethylmethacrylate-graft-folic acid) (FAHEMA) systems are synthesized by grafting of folic acid (FA) into poly (2–hydroxyethylmethacrylate) via an esterification reaction. The structure of these copolymers is confirmed by NMR and CHN analyses. The thermal behavior of these materials is characterized by DSC and TGA analyses. The surface morphology of FAHEMA films before and after the release process is examined by the SEM method. The cumulative FA released in different pH media from FAHEMA materials occurred via a retro-esterification reaction at body temperature during 72 h in which the influence of the swelling degree of PHEMA, the FA content and pH media on the dynamic release is widely investigated. The results obtained revealed that the solubility of FA in water deduced from the release process is widely improved compared with literature reports. It is also revealed that the diffusion of water in different pH media through the PHEMA matrix and that of FA through FAHEMA materials perfectly obeyed the Fickian models. It was deduced from the kinetic study that the release performance is obtained with the copolymers containing initially 10 and 20 wt% of FA contents.

Development of Hydrogel Lenses with Surface‐immobilized PEG Layers to Reduce Protein Adsorption

This paper describes the synthesis and characterization of a series of poly(2‐hydroxyethyl methacrylate) (pHEMA)‐based hydrogel lenses coated with poly(ethylene glycol) (PEG) chains. A novel tri‐branched PEG‐substituted hydrazide is synthesized, which imparts densely packed, covalently bound PEG layers on hydrogels, to determine whether branching provides improved coverage of the lens surface, thereby reducing protein adsorption. Surface modification of hydrogels with PEG was performed via amide‐coupling reactions between PEG‐substituted hydrazide and the pHEMA matrix. Protein adsorption, water content, optical transparency, and surface properties of the hydrogels were investigated. The hydrogels exhibited transmittance of >90% and improved surface hydrophilicity. Notably, the amount of lysozyme adsorbed on tri‐branched PEG‐coated hydrogels decreased significantly compared to the amount adsorbed onto the surface of control and linear PEG‐coated hydrogels. These results provide insight into the mechanism by which PEGs reduce lysozyme adsorption and suggest that PEG coating may offer an intriguing potential for ophthalmic biomaterials as well as protein‐resistant devices.

Synthesis and characterization of novel dual environment-responsive hydrogels of Hydroxyethyl methacrylate and Methyl cellulose

The current study describes the synthesis and characterization of dual environment-responsive semi-interpenetrating hydrogels of polyhydroxyethyl methacrylate (pHEMA) and methyl cellulose (MC). HEMA was polymerized using free radical polymerization technique. Different proportions of MC were incorporated within the pHEMA matrix to induce environment-sensitive property. The microstructures of the hydrogels were studied under bright field microscopy. The hydrogels were thoroughly characterized using XRD, FTIR, swelling, mechanical and electrical studies. The micrographs of the hydrogels suggested formation of biphasic system. At lower proportions of MC, the hydrogels were oil-in-water type of formulations. An increase in the MC content resulted in the formation of bicontinuous biphasic formulations. Mechanical analysis suggested viscoelastic solid nature of the hydrogels. An increase in the MC content resulted in the increase in the viscous component. The electrical studies suggested resistive dominant behavior of the hydrogels. Thermal studies suggested better moisture retention capacity of the MC containing hydrogels. The hydrogels were found to be biocompatible in nature.

Heterogeneous patterns on block copolymer thin film via solvent annealing: Effect on protein adsorption.

Heterogeneous patterns consisting of nanometer-scaled hydrophobic/hydrophilic domains were generated by self-assembly of poly(styrene)-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) block copolymer thin film. The effect of the heterogeneity of the polymer film surface on the nonspecific adsorption of the protein human plasma fibrinogen (FBN, 5.0 × 5.0 × 47.5 nm(3)) was investigated. The kinetics of the FBN adsorption varies from a single-component Langmuir model on homogeneous hydrophilic PHEMA to a two-stage spreading relaxation model on homogeneous hydrophobic PS surface. On a heterogeneous PS-b-PHEMA surface with majority PS part, the initial FBN adsorption rate remains the same as that on the homogeneous PS surface. However, hydrophilic PHEMA microdomains on the heterogeneous surface slow down the second spreading stage of the FBN adsorption process, leading to a surface excess of adsorbed FBN molecules less than the presumed one simply calculated as adsorption onto multiple domains. Importantly, when the PS-b-PHEMA surface is annealed to form minority domelike PS domains (diameter: ∼50-100 nm) surrounded by a majority PHEMA matrix, such surface morphology proves to be strongly protein-repulsive. These interesting findings can be attributed to the enhancement of the spread FBN molecule in a mobile state by the heterogeneity of polymer film surface before irreversible adsorption occurs.

Structural and optical studies of pHEMA encapsulated ZnS:Ni2+ nanoparticles

In this study, ZnS:Ni2+ nanostructures have been synthesized through chemical precipitation method using poly (2-hydroxyethyl methacrylate) (pHEMA) as capping agent. The structural, morphological and optical properties at different pHEMA concentration of ZnS:Ni2+ were studied by using X–ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), UV–Vis Spectroscopy (UV–Vis), fourier transform infrared spectroscopy (FT-IR), Photoluminescence (PL). The Average crystalline size of the nanoparticles was found to be in the range of ∼3.59–4.36nm. The surface morphological analysis reveals that the pHEMA capped nanoparticles showed homogeneous smooth surface. HR-TEM analysis reminds the original size of pHEMA capped nanoparticles. The band gap investigation revealed the size dependent of quantum confined nanoparticles. The immobilized nanoparticles in pHEMA matrix were verified by FT-IR studies. Novel luminescence properties have been observed for uncapped and pHEMA capped ZnS nanoparticles. The optimal capping concentration was successfully determined and its influence on photoluminescence behavior has been thoroughly analyzed.

Macroporous 2-hydroxyethyl methacrylate hydrogels of dual porosity for cell cultivation: morphology, swelling, permeability, and mechanical behavior

Macroporous hydrogels of dual porosity based on cross-linked poly(2-hydroxyethyl methacrylate) (pHEMA) were prepared, and their swelling, mechanical responses, and hydraulic permeability, as well as cell adhesion and proliferation, were examined on gel-based scaffolds. Large pores on the order of tens and hundreds of microns were generated by adding a solid porogen (fractionated particles of sodium chloride) to the polymerization mixture, which was subsequently washed out of the gel. Small pores on the order of a few microns were formed by the reaction-induced phase separation mechanism caused by addition of a diluent (1-dodecanol), which is a poor solvent for pHEMA. Morphological studies using light and electron microscopy techniques revealed that the large pores were embedded in the pHEMA matrix containing small fused spherical pores. Mechanical behavior of the dual-porosity hydrogels characterized by oscillatory shear measurements revealed that despite very high pore volume, the hydrogels were sufficiently stiff and self-supportive. The cell cultivation pilot experiment showed that the morphology (dual porosity) demonstrated marked effects on the promotion of cell adhesion, growth, and proliferation, not only on the gel surface but in the large pores within the gel bulk as well.

The biocompatibility and water uptake behavior of superparamagnetic poly(2-Hydroxyethyl methacrylate) - magnetite nanocomposites as possible nanocarriers for magnetically mediated drug delivery system

The present study aims at formulating a novel multifunctional biocompatible superparamagnetic nanocarriers system comprising of magnetic material in solid polymer matrix of poly (2-hydroxyethyl methacrylate) (PHEMA). To design these nanocarriers PHEMA nanoparticles were prepared by modified suspension polymerization method followed by co-precipitation of iron oxide within the PHEMA matrix. The so prepared superparamagnetic nanocomposite (mPHEMA) was characterized by Fourier transform Infrared spectroscopy (FTIR), and Energy dispersive X-ray spectroscopy (EDAX) confirming the presence of Fe3O4 in the PHEMA nanoparticles. The vibrating sample magnetometer (VSM) studies and Mossbauer spectral analysis confirmed the superparamagnetic character of materials having saturation magnetization (Ms) of 23 emu/g at 5 kOe applied magnetic field and room temperature. Biocompatible nature was ascertained by in vitro cytotoxicity test following an extract method based on (ISO10993-5, 2009), anti-haemolytic activity, and bovine serum albumin (blood protein) adsorption test. The water sorption behaviour of superparamagnetic mPHEMA nanocomposites was studied as a function of various factors such as chemical composition of nanoparticles, pH and temperature of the swelling bath, simulated biological fluids and applied magnetic field. The results revealed that the superparamagnetic mPHEMA nanocomposite could prove to be an excellent option for controlled and targeted delivery of anticancer drugs by application of an external magnetic field.

Extended Release of Timolol from Nanoparticle-Loaded Fornix Insert for Glaucoma Therapy

We have developed a cylindrical insert that can be inserted in the fornix for extended release of glaucoma drug timolol. The insert is prepared by incorporating timolol-loaded nanoparticles into a poly hydroxyl ethyl methacrylate (p-HEMA) matrix. A 1-mm diameter, 7.5-mm long insert with 25% (w/w) particles can release timolol for about 10 days at an average rate of about 15 μg/day, which may be therapeutically effective. The increase in particle fraction increases drug loading, but also increases the release duration. The net effect of increasing the particle fraction is a significant increase in release duration, but a decrease in daily drug release rates, in the first few weeks. The release duration increases to about 1 and 3 months on increasing the particle fraction to 50% and 75%, respectively. The average daily release rates in the first 3 weeks are 15, 9, and 3 μg/day for the inserts with 50%, 75%, and 100% (w/w) particles, respectively. The mechanism of release is hydrolysis of the ester bond that links timolol to the propoxylated glyceryl triacrylate matrix, and thus the release profiles fit a first order reaction model. The water content of the inserts decreases from 31% to almost zero on increasing the particle loading from 25% to 100%. The rate constant for the hydrolysis decreases with an increase in particle loading in the insert most likely due to the reduction in the water content. The inserts can be packaged in wet conditions and stored in a refrigerator, but the inserts will exhibit a burst release caused by release of the drug from the particles into the p-HEMA matrix during the shelf life. Also, the magnitude of drug release after the initial burst is reduced due to the storage. The burst effect could potentially be avoided by packaging the inserts in a dry state, with hydration before insertion.

Preparation and characterization of carbon nanotube filled poly (2-hydroxyethylmethacrylate) nanocomposites

Poly(2-hydroxyethylmethacrylate) (PHEMA)/multiwalled carbon nanotubes (MWNTs) nanocomposites were prepared by solvent casting using dimethyl formamide (DMF) solvent via sonication process. Effect of addition of MWNTs on the properties of nanocomposites was investigated at different nanofiller contents. Uniform dispersion and distrubution of nanotubes in PHEMA matrix is obtained within the studied composition range. The electrical resistivity, dielectric permittivity and the loss factor of dry PHEMA and PHEMA/MWNT nanocomposites were studied by varying the MWNT concentration in the frequency range of 30 Hz to 1 MHz. The obtained results indicated that the addition MWNTs to PHEMA matrix decreases the electrical resistivity and increases the dielectric constant at low dielectric loss. The thermal properties of the PHEMA/MWNT nanocomposites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermal behavior of these nanocomposites was also compared with PHEMA homopolymer. The glass transition temperature ( Tg) of PHEMA homopolymer was found to increase with nanotube concentration. Experimental results also demonstrated that the incorporation of the MWNTs into the PHEMA matrix not only enhanced the mechanical property but also increased and the thermal stability of the PHEMA/MWNT nanocomposites increases with increase in MWNT concentration.

Two Dimensional Nanoarrays of Individual Protein Molecules

Protein molecules on solid surfaces are essential to a number of applications, such as biosensors, biomaterials, and drug delivery. In most approaches for protein immobilization, inter-molecular distances on the solid surface are not controlled and this may lead to aggregation and crowding. Here, a simple approach to immobilize individual protein molecules in a well-ordered 2D array is shown, using nanopatterns obtained from a polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) diblock copolymer thin film. This water-stable and protein-resistant polymer film contains hexagonally ordered PS cylindrical domains in a PHEMA matrix. The PS domains are activated by incorporating alkyne-functionalized PS and immobilizing azide-tagged proteins specifically onto each PS domain using "Click" chemistry. The nanometer size of the PS domain dictates that each domain can accommodate no more than one protein molecule, as verified by atomic force microscopy imaging. Immunoassay shows that the amount of specifically bound antibody scales with the number density of individual protein molecules on the 2D nanoarrays.

Polymer Composites Reinforced by Locking-In a Liquid-Crystalline Assembly of Cellulose Nanocrystallites

An attempt was made to synthesize novel composites comprising poly(2-hydroxyethyl methacrylate) (PHEMA) and cellulose nanocrystallites (CNC) (acid-treated cotton microfibrils) from suspensions of CNC in an aqueous 2-hydroxyethyl methacrylate (HEMA) monomer solution. The starting suspensions (∼5 wt % CNC) separated into an isotropic upper phase and an anisotropic bottom one in the course of quiescent standing. By way of polymerization of HEMA in different phase situations of the suspensions, we obtained films of three polymer composites, PHEMA-CNC(iso), PHEMA-CNC(aniso), and PHEMA-CNC(mix), coming from the isotropic phase, anisotropic phase, and embryonic nonseparating mixture, respectively. All the composites were transparent and, more or less, birefringent under a polarized optical microscope. A fingerprint texture typical of cholesteric liquid crystals of longer pitch spread widely in PHEMA-CNC(aniso) but rather locally appeared in PHEMA-CNC(iso). Any of the CNC incorporations into the PHEMA matrix improved the original thermal and mechanical properties of this amorphous polymer material. In dynamic mechanical measurements, the locking-in of the respective CNC assemblies gave rise to an increase in the glass-state modulus E' of PHEMA as well as a marked suppression of the E'-falling at temperatures higher than T(g) (≈ 110 °C) of the vinyl polymer. It was also observed for the composites that their modulus E' rerose in a range of about 150-190 °C, which was attributable to a secondary cross-linking formation between PHEMA chains mediated by the acidic CNC filler. The mechanical reinforcement effect of the CNC dispersions was ensured in a tensile test, whereby PHEMA-CNC(aniso) was found to surpass the other two composites in stiffness and strength.

Nanostructure of polystyrene-b-poly(2-hydroxyethyl methacrylate) and derivatives with phosphonic diacid groups

Surface engineering for precise positioning of biomolecules is of particular interest for controlled fabrication of biochips. In this study, a novel approach for the preparation of nanodomains with phosphonic diacid groups that were previously shown to reversibly bind to a family of proteins (annexins) in a calcium-dependent manner is described. The strategy makes use of polystyrene-b-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) precursors prepared by atom transfer radical polymerization (ATRP) to obtain hexagonally packed PS cylinders (fPS = 0.25-0.27) in a PHEMA matrix. The pendant hydroxyl groups of PHEMA are then partially (ca. 20%) converted into phosphonic diacid groups via sequential reactions involving phosphorylation, silylation and methanolysis. This process produces PS-b-P(HEMA-co-PEMA) derivatives that still retain the hexagonal morphology, but their degree of structural organization is reduced comparatively to the precursors.

Prepolymerized organic–inorganic hybrid nanoparticles as fillers for light-cured methacrylate monomers

Poly(hydroxyethyl methacrylate)/silica (PHEMA/SiO2) hybrid organic–inorganic nanocomposites were prepared through the simultaneous polymerization of 2-hydroxyethyl methacrylate and tetraethoxysilane. PHEMA/SiO2 materials were obtained as monolithic and transparent films consisting of silica nanoparticles (diameter below 100 nm) surrounded by the PHEMA matrix. The films were crushed into fine powder and the PHEMA/SiO2 particles were used as filler of methacrylate monomers. The polymeric methacrylate present in the PHEMA/SiO2 hybrid particles improves the compatibility of the filler with the methacrylate monomer to be photopolymerized, resulting in enhanced wetting capabilities. The composites prepared from PHEMA/SiO2-prepolymerized particles offer the possibility of reduced polymerization shrinkage without severe reductions in flow characteristics of the precured polymers. The monomer conversions of composites prepared with either 30 or 60 wt% PHEMA/SiO2 particles were similar. This indicates that the penetration of visible radiation into the sample is not reduced significantly by the presence of the filler.

Influence of matrices on oxygen sensing of three sensing films with chemically conjugated platinum porphyrin probes and preliminary application for monitoring of oxygen consumption of Escherichia coli ( E. coli)

Oxygen sensing films were synthesized by a chemical conjugation of functional platinum porphyrin probes in silica gel, polystyrene (PS), and poly(2-hydroxyethyl methacrylate) (PHEMA) matrices. Responses of the sensing films to gaseous oxygen and dissolved oxygen were studied and the influence of the matrices on the sensing behaviors was investigated. Silica gel films had the highest fluorescence intensity ratio from deoxygenated to oxygenated environments and the fastest response time to oxygen. PHEMA films had no response to gaseous oxygen, but had greater sensitivity and a faster response time for dissolved oxygen than those of PS films. The influence of matrices on oxygen response, sensitivity and response time was discussed. The influence is most likely attributed to the oxygen diffusion abilities of the matrices. Since the probes were chemically immobilized in the matrices, no leaching of the probes was observed from the sensing films when applied in aqueous environment. One sensing film made from the PHEMA matrix was used to preliminarily monitor the oxygen consumption of Escherichia coli ( E. coli) bacteria. E. coli cell density and antibiotics ampicillin concentration dependent oxygen consumption was observed, indicating the potential application of the oxygen sensing film for biological application.

A New Crosslinkable Oxygen Sensor Covalently Bonded into Poly(2-hydroxyethyl methacrylate)-CO-Polyacrylamide Thin Film for Dissolved Oxygen Sensing.

A new oxygen sensor, compound 2, was synthesized through a chemical modification of a popularly used oxygen sensor of platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP). The new sensor compound 2 possesses four crosslinkable methacrylate functional moieties, enabling it to be polymerized and crosslinked with other monomers for polymer sensing film (also called membrane) preparation. Using this characteristic, compound 2 was covalently bonded to hydrophilic poly(2-hydroxyethyl methacrylate)-co-polyacrylamide (referred to as PHEMA to simplify) and hydrophobic polystyrene (PS) films. To better understand the advantages and disadvantages of chemical crosslinking approaches and the influence of polymer matrices on sensing performance, PtTFPP was physically incorporated into the same PHEMA and PS matrices to compare. Response to dissolved oxygen (DO), leaching of the sensor molecules from their matrices, photostability of the sensors, and response time to DO changes were studied. It was concluded that the chemical crosslinking of the sensor compound 2 in polymer matrices: (i) alleviated the leaching problem of sensor molecules which usually occurred in the physically doped sensing systems and (ii) significantly improved sensors' photostability. The PHEMA matrix was demonstrated to be more suitable for oxygen sensing than PS, because for the same sensor molecule, the oxygen sensitivity in PHEMA film was higher than that in PS and response time to DO change in the PHEMA film was faster than that in PS. It was the first time oxygen sensing films were successfully prepared using biocompatible hydrophilic PHEMA as a matrix, which does not allow leaching of the sensor molecules from the polymer matrix, has a faster response to DO changes than that of PS, and does not present cytotoxicity to human lung adenocarcinoma epithelial cells (A549). It is expected that the new sensor compound 2 and its similar compounds with chemically crosslinking characteristics can be widely applied to generate many interesting oxygen sensing materials for studying biological phenomena.

On the Role of Water Molecules in the Interface between Biological Systems and Polymers

The excellent biocompatibility of PMEA was ascribed by Tanaka to the predominant population of intermediate water in the hydrated polymer matrix. The intermediate water concept was examined using the 'nano-plate model' on the basis of new results (by Morita) of a time-resolved IR study on the water sorption process into PMEA. The examination showed that the image picture proposed by Tanaka concerning the role of intermediate water was in consistent with experimental results so far obtained. Morita showed that the intermediate water exhibited a strong peak at 3400 cm−1 in its IR spectrum. Water sorption profiles of MMA, PEG and PMVE were found to be similar to that of PMEA. It was shown that the biocompatibility of these polymers could be explained by the intermediate water concept. It was also pointed out that PVP and PDMAA have a considerable amount of intermediate water under appropriate circumstances. The PHEMA–water system showed neither clear peak for cold crystallization in DSC chart, nor the strong peak at 3400 cm−1 in its IR spectrum, because the PHEMA system did not contain enough intermediate water to show similar behavior to PMEA. The hydrated PHEMA matrix contains a stable network structure of water molecules including the nodes of OH groups of its side-chains. In the stable network system, most water molecules should be hydrogen bonded strongly to form non-freezing water, but not intermediate water. The inferior biocompatibility of PHEMA was ascribed to the stable network structure of water molecules. Some of the PHEMA co-polymers, on the other hand, were found to have highly improved biocompatibility. Mechanism for the improvement was discussed in terms of loosening the network structure, which could be brought about by introducing ionic groups or branching to the polymer chains through co-polymerization with appropriate 'key monomers'. The mobility of polymer chains, as well as the population of three kinds of water in polysaccharide molecules in aqueous medium could change in response to their chemical structure such as nature of ionic groups, the degree of branching, etc. Polysaccharides located at the utmost-outer layer of blood cells probably possess a loosened network structure to form soft biological surface where intermediate water predominates. Cellulose, on the other hand, has a common feature with PHEMA in the sense of predominance of the non-freezing water in its hydrated system. Note: The word 'biocompatibility' is used in general as the term evaluating properties of materials which do not cause adverse effect when the materials come into contact with living organisms, such as proteins, biological cells and tissues. This review paper primarily deals with 'biocompatibility' of polymer materials against various biological elements in blood flow system.