Combinational Hydrogel and Xerogel Actuators Showing NIR Manipulating Complex Actions.

Near-infrared (NIR)-driven shape memory hydrogels are synthesized with a one-pot polymerization of N,N-dimethylacrylamide in the inorganic clay and graphene oxide (GO) suspension. The hydrogel consists of only a physically crosslinked network, which is partially thermoreversible. With the efficient photothermal energy transformation of GO in the hydrogels, the shape recovery from the temporal shape is achieved by NIR irradiation. The optimal shape fixing percentage and recovery rate are found at moderate monomer and crosslinker contents. Meanwhile, the xerogel dried from the hydrogel also shows a fast NIR response shape change. The NIR manipulating combinational hydrogel-xerogel actuators are prepared by combining the wet and soft hydrogel and its dry and rigid xerogel together. The actuators achieve complex actions of turning and lifting under sequential NIR irradiation to carry an object up- and downward and around obstacles, or to transfer an object to a target position. This work provides a new idea for designing combinational actuators to fulfil complex actions.

Nanozeolites doped photopolymer layers with reduced shrinkage.

An acrylamide based photopolymer doped with pure silica MFI-type zeolite (silicalite-1) nanoparticles has been characterized for holographic recording purposes. The concentrations of the silicalite-1 nanoparticles in the photopolymer layers were 1, 2.5, 5 and 7.5 wt. %. The inclusion of silicalite-1 nanoparticle in the photopolymer has resulted in an increase of the diffraction efficiency by up to 40%, and decrease of the shrinkage from 1.32% to 0.57%. The best results were obtained in layers doped with 5 wt. % silicalite-1 nanoparticles.

Retrieval of rat aortic smooth muscle cells as intact cell sheet for regenerative medicine: a cost effective approach using photo polymerization.

Cell-based therapeutics are promising routes for the regeneration of damaged cells and organs. The recovery of cells cultured in vitro for such applications requires the use of proteolytic enzymes which deteriorate its property by disruption of cell-cell and cell-matrix interactions. Intact cell sheets can be retrieved with the use of thermo responsive polymer grafted on to the culture plates. Our study presents the use of photo-polymerization as a simple and inexpensive way to create thermo-responsive culture surfaces for the detachment of intact cell sheet. Poly (N-isopropyl acrylamide) (PNIPAAm) was synthesized by photo-polymerization and characterized by NMR spectroscopy, differential scanning calorimetry and gel permeation chromatography. Thermo-responsive culture dishes were prepared by the coating method and characterized for its thermo-responsive efficacy using FTIR spectroscopy and water contact angle measurements. Atomic force microscopy depicted the thin coating achieved with this method is similar to the conventional grafting method. Suitability for cell culture and cell sheet retrieval was assessed by culturing rat aortic smooth muscle cells in the PNIPAAm coated tissue culture plates. The cells remained viable as evident from the live dead assay and the cell sheet was detached by low temperature treatment. The results demonstrate a versatile method for creating thermo responsive culture surfaces while eliminating the use of expensive radiation sources for the conventional grafting method.

Evaluation of thermosensitive microspheres as potential components for sun-protectors.

In this study thermosensitive polymeric microspheres obtained in former research were evaluated in vitro for their photoprotective activity. The UVA/UVB ratio was assessed at so called shelf temperature, i.e., at 25 degrees C, and at elevated temperature of 45 degrees C. The evaluated polymers absorb higher levels of UV radiation, when heated from 25 degrees C to 45 degrees C. The MS1 polymer may be defined as polymer with high efficiency in the terms of gaining protection against UVA radiation, when heated. The MS2 absorbs both UVA and UVB radiation, and may be considered, as most protective, when heated to 45 degrees C. The equalized and less strong activity has the polymer MS3 when heated, with lipophilic radical implemented during synthesis.

Removal of bovine serum albumin using solid-phase extraction with in-situ polymerized stationary phase in a microfluidic device.

Serum albumin, one of the most abundant serum proteins, blocks the expression of other important biomarkers. The objective of this study is to remove serum albumin effectively by using solid-phase extraction (SPE) in microfluidic devices. Photo-polymerized adsorbent as a stationary phase of SPE was used to remove bovine serum albumin (BSA). The adsorption capacity was examined with the effect of pH and concentration in BSA solution, and adjustment of monomer concentration such as hydrophilic 2-acrylamido-2-methyl-1-propanesulfonic acid and acrylamide in the adsorbent. The effect of hydrophobic butyl methacylate on BSA adsorption was also studied. Selective removal in a bicomponent with BSA and bovine gamma-globulin was performed by adjusting the pH as required.

On the development of a VIPARnd radiotherapy 3D polymer gel dosimeter.

This work presents an improvement of the VIPARnd ('nd' stands for 'normoxic, double', or VIP) polymer gel dosimeter. The gel composition was altered by increasing the concentration of the monomeric components, N-vinylpyrrolidone (NVP) and N,N'-methylenebisacrylamide (MBA), in co-solvent solutions. The optimal composition (VIPARCT, where 'CT' stands for computed tomography, or VIC) comprised: 17% NVP, 8% MBA, 12% t-BuOH, 7.5% gelatine, 0.007% ascorbic acid, 0.0008% CuSO4 × 5H2O and 0.02% hydroquinone. The following characteristics of VIC were achieved: (i) linear dose range of 0.9_30 Gy, (ii) saturation for radiation doses of over 50 Gy, (iii) threshold dose of about 0.5 Gy, (iv) dose sensitivity of 0.171 Gy-1 s-1, which is roughly 2.2 times higher than that of VIP (for nuclear magnetic resonance measurements). It was also found that VIC is dose- rate-independent, and its dose response does not alter if the radiation source is changed from electrons to photons for external beam radiotherapy. The gel responded similarly to irradiation with small changes in radiation energy but was sensitive to larger energy changes. The VIC gel retained temporal stability from 20 h until at least 10 d after irradiation, whereas spatial stability was retained from 20 h until at least 6 d after irradiation. The scheme adopted for VIC manufacturing yields repeatable gels in terms of radiation dose response. The VIC was also shown to perform better than VIP using x-ray computed tomography as a readout method; the dose sensitivity of VIC (0.397 HU Gy-1) was 1.5 times higher than that of VIP. Also, the dose resolution of VIC was better than that of VIP in the whole dose range examined.

Dynamic swelling behavior of gamma-radiation induced polyelectrolyte poly(AAm-co-CA) hydrogels in urea solutions.

The aim of this study was to investigate the equilibrium swelling properties in urea solutions of gamma-radiation induced polyelectrolyte copolymeric hydrogels consisting of acrylamide (AAm) and crotonic acid (CA). Poly(acrylamide-co-crotonic acid), poly(AAm-co-CA) hydrogels containing different amounts of CA were obtained in the form of rods after radiation. Swelling experiments were performed in aqueous urea solutions at 25 degrees C, gravimetrically. The hydrogels showed large extents of swelling in aqueous (urea/water) media the swelling being highly dependent on the chemical composition of the hydrogels and irradiation dose. The percentage swelling of poly(AAm-co-CA) hydrogels was between 1160 and 4250%, while that of the AAm hydrogels was between 670 and 900%. The diffusional exponent values (n) are between 0.51 and 0.66, hence the diffusion of urea/water into the hydrogels is non-Fickian. Equilibrium urea/water contents of the hydrogel systems were changed between 0.870 and 0.977.

Visible light induced radical cyclization of o-iodophenylacrylamides: a concise synthesis of indolin-2-one.

A [Ir(ppy)2(dtb-bpy)]PF6-catalyzed intramolecular radical cyclization of o-iodophenylacrylamides affording indolin-2-ones in moderate to excellent yields via 5-exo-trig radical cyclization under visible light is presented. This method provides new access to the synthesis of indolin-2-ones under mild reaction conditions.

Highly robust hydrogels via a fast, simple and cytocompatible dual crosslinking-based process.

A highly robust hydrogel device made from a single biopolymer formulation is reported. Owing to the presence of covalent and non-covalent crosslinks, these engineered systems were able to (i) sustain a compressive strength of ca. 20 MPa, (ii) quickly recover upon unloading, and (iii) encapsulate cells with high viability rates.

Radiation grafting of hydrophilic monomers onto poly[bis(trifluoroethoxy)phosphazene].

The hydrophilic monomers dimethylacrylamide (DMAA) and acrylamide (AAm) were radiation grafted onto poly[bis-(trifluoroethoxy)phosphazene] (PTFP) for biocompatibility enhancement through direct irradiation of the polymer films immersed in monomer-solvent mixtures, and the progress of grafting was followed up to a large monomer depletion. The water absorption of the samples was found to increase as the amount of the grafted chains increased. The grafted chains, mainly confined in the film surface at high dose rates, progressively extend to the interior of the sample as the dose rate decreases. In the grafted samples the ultimate mechanical properties epsilon r and sigma r were essentially preserved. The in vivo tests indicated an enhancement of surface biocompatibility in the PTFP-g-AAm samples and not in the PTFP-g-DMAA samples.

Improving calibration accuracy in gel dosimetry.

A new method of calibrating gel dosimeters (applicable to both Fricke and polyacrylamide gels) is presented which has intrinsically higher accuracy than current methods, and requires less gel. Two test-tubes of gel (inner diameter 2.5 cm, length 20 cm) are irradiated separately with a 10 x 10 cm2 field end-on in a water bath, such that the characteristic depth-dose curve is recorded in the gel. The calibration is then determined by fitting the depth-dose measured in water, against the measured change in relaxivity with depth in the gel. Increased accuracy is achieved in this simple depth-dose geometry by averaging the relaxivity at each depth. A large number of calibration data points, each with relatively high accuracy, are obtained. Calibration data over the full range of dose (1.6-10 Gy) is obtained by irradiating one test-tube to 10 Gy at dose maximum (Dmax), and the other to 4.5 Gy at Dmax. The new calibration method is compared with a 'standard method' where five identical test-tubes of gel were irradiated to different known doses between 2 and 10 Gy. The percentage uncertainties in the slope and intercept of the calibration fit are found to be lower with the new method by a factor of about 4 and 10 respectively, when compared with the standard method and with published values. The gel was found to respond linearly within the error bars up to doses of 7 Gy, with a slope of 0.233 +/- 0.001 s(-1) Gy(-1) and an intercept of 1.106 +/- 0.005 Gy. For higher doses, nonlinear behaviour was observed.

Photosensitization by drugs.

UV irradiation (365 nm) of air-saturated methanol solutions of 20 drugs absorbing in the 300--400 nm region gave rise to oxygen uptake, as determined with a polarographic oxygen electrode. The drugs were tested for photosensitizing capability by either a Type I (free radical) or a Type II (single molecular oxygen) mechanism. This testing was done by the inclusion of either acrylamide or 2,5-dimethylfuran in the irradiated drug solution, with observation of the subsequent polymerization or oxidation, respectively. Phenothiazine and thiazide derivatives appear capable of photosensitization by both mechanisms; promethazine, trifluoperazine, and furosemide show relatively high reactivity. Diazepam (weak), hexachlorophene, aminacrine, pyrilamine, tetracycline, demeclocycline, quinine, and anthracene (strong) react only by a Type II mechanism, with a photosensitizing efficiency increasing in the order given. A correlation appears to exist with reports of in vivo photosensitivity.

NMR relaxation enhancement in gels polymerized and cross-linked by ionizing radiation: a new approach to 3D dosimetry by MRI.

A new type of tissue-equivalent medium for magnetic resonance imaging of the dose distributions produced by ionizing radiation has been developed. Agarose gel is infused with acrylamide and N,N'-methylene-bis-acrylamide (Bis) comonomers, which are readily polymerized by free radical initiators in de-aerated aqueous solutions. Polymerization and cross-linking induced locally by free radical products of water radiolysis increase the rate of water proton spin relaxation gradually up to doses of about 15 Gy. The slopes of the dose-response curves at 64 MHz are 0.015 and 0.28 s-1 Gy-1 for R1 and R2, respectively. The agarose matrix as well as the high (50% by weight) relative concentration of the cross-linker (Bis) per total comonomer limit the spread of polymerization so that the spatial distribution of the radiation dose is faithfully represented in the resultant spatial distribution of relaxation rates. The gel can be imaged with conventional magnetic resonance imaging devices with high spatial resolution and accuracy. In addition, due to the well established effect of the precipitation of insoluble agglomerates of highly cross-linked acrylamide, the optical turbidity of the gel increases gradually with the absorbed dose. This may provide an additional means of visualizing the dose distribution in three dimensions. The major advantage of the acrylamide-Bis-agarose gels over those that depend on ionic chemical dosimeters, for example, Fricke-infused gels, lies in the lack of diffusion of radiation-induced chemical changes subsequent to or concurrent with irradiation.

Blood compatibility of tubular polymeric materials studied by biological surface interactions.

Tubular polymeric materials modified by radiation techniques can be used as vascular prosthesis and components of prosthetic devices. The biological interaction between these materials and blood was studied by in vitro and ex vivo methods. Silicone rubber tubes were copolymerized with acrylamide and N-vinylpyrrolidone by radiation-grafting techniques. The irradiation was performed with gamma-rays from a 60Co source at a constant dose rate (0.2 kGy/h) for various time intervals (4-15 h). To evaluate the antithrombogenicity of the grafted tubes, the surface adsorption of 125I-albumin and 125I-fibrinogen was studied. All graft copolymers show a preference for albumin, and the degree of preference appears to correlate with antithrombogenic tendency. In the ex vivo experiment with animals, tubes were implanted in the carotid artery of dogs and the blood flow in the graft copolymers was detected with an ultrasonic flow meter. The blood flow rate in the ungrafted implants decreased more rapidly (stopped completely after 15 to 210 min) compared to the flow rate in the grafted ones (decreased slowly from 38 to 35 ml/min and 70 to 60 ml/min). There was a direct relationship between both methods in the study of blood compatibility of the materials. The results suggest that the graft copolymers can be used as biomaterials for long-term use in cardiovascular systems.

Determination of acrylamide monomer in polyacrylamide degradation studies by high-performance liquid chromatography.

A high-performance liquid chromatography method using C18 and ion-exchange columns in series is developed for the determination of acrylamide and acrylic acid monomers in polymeric samples. The C18 column acts as a guard column, trapping surfactants and impurities and retaining the nonionic species. The ion-exchange column then separates the monomers according to their respective ionic strengths. This method has been proven in the laboratory to work successfully for all types of acrylamide/acrylic acid polymers and matrices. Detection limits for both monomers can be achieved in the parts-per-billion range. The method is used to study the possible degradation of polyacrylamide to acrylamide monomer in the presence of glyphosate (a herbicide) and sunlight. Polyacrylamide is used as a spray drift reduction aid in combination with glyphosate. In normal applications, the polymer and herbicide are in contact with each other in the presence of sunlight. The results show that the polymer does not degrade to acrylamide in the presence of glyphosate or sunlight or any combination of the two. It is also observed that glyphosate influences the solubility of polyacrylamide, and care must be used when combining the two.

[Polymer materials for biomedical purposes obtained by radiological methods. II. Radiation polymerization of acrylamides and N-vinylpyrrolidone]. / Materialy polimerowe do celów biomedycznych otrzymywane metodami radiacyjnymi. II. Polimeryzacja radiacyjna akryloamidu i N-winylopirolidonu.

The radiation polymerization of acrylamide and N-vinylpyrrolidin-2-one in aqueous solutions has been investigated. The effect of the monomer concentration as well as the dose rate of the ionizing radiation on the process has been determined. The radical mechanism of the polymerization process has been confirmed experimentally. The effect of the individual transient species of the water radiolysis on the initiation of the polymerization process as well as the changes of the molecular weights of the arising polymers have been investigated. The dependence of the galation dose of the system on the monomer concentration has been determined.

[Polymer materials for biomedical use obtained by radiation methods. III. Radiation cross-linking of acrylamide and N-vinylpyrrolidone]. / Materialy polimerowe do celów biomedycznych otrzymywane metodami radiacyjnymi. III. Sieciowanie radiacyjne akryloamidu i N-winylopirolidonu.

The course of the radiation formation of hydrogels in aqueous solutions of acrylamide and N-vinylpyrrolidone was investigated on the base of gel-sol analysis. Using relations from Inokuti's equation as a test of crosslinking mechanism it was pointed out that creation of gels takes place according to classical mechanism e.g. through four-functional joining points. In the systems containing oxygen gel formation results from simultaneous crosslinking and degradation. On the base of swelling measurements of gels (ROCH method) the yields of radiation processes were calculated. Using a method of pulse radiolysis the absorption spectra of macroradicals were recorded, their structures discussed and the rate constants of crosslinking estimated.

N-isopropylacrylamide gel dosimeter to evaluate clinical photon beam characteristics.

The introduction of beam intensity control concept in current radiotherapy techniques has increased treatment planning complexity. Thus, small-field dose measurement has become increasingly vital. Polymer gel dosimetry method is widely studied. It is the only dose measurement tool that provides 3D dose distribution. This study aims to use an N-isopropylacrylamide (NIPAM) gel dosimeter to conduct beam performance measurements of percentage depth dose (PDD), beam flatness, and symmetry for photon beams with field sizes of 3×3 and 4×4 cm(2). Computed tomography scans were used to readout the gel dosimeters. In the PDD measurement, the NIPAM gel dosimeter and Gafchromic™ EBT3 radiochromic film displayed high consistency in the region deeper than the build-up region. The gel dosimeter dose profile had 3% lower flatness and symmetry measurement at 5 cm depth for different fields compared with that of the Gafchromic™ EBT3 film. During gamma evaluation under 3%/3 mm dose difference/distance-to-agreement standard, the pass rates of the polymer gel dosimeter to the TPS and EBT3 film were both higher than 96%. Given that the gel is tissue equivalent, it did not exhibit the energy dependence problems of radiochromic films. Therefore, the practical use of NIPAM polymer gel dosimeters is enhanced in clinical dose verification.

Fast self-healing of graphene oxide-hectorite clay-poly(N,N-dimethylacrylamide) hybrid hydrogels realized by near-infrared irradiation.

Self-healing hydrogels were proposed to be used as biomaterials, because of the capability of spontaneously healing injury, but most of the reported self-healing hydrogels do not possess high mechanical strength and fast self-healing at the same time. Herein, we prepared graphene oxide (GO)-hectorite clay-poly(N,N-dimethylacrylamide) (PDMAA) hybrid hydrogels with enhanced mechanical properties and fast self-healing capability realized by near-infrared (NIR) irradiation. The physical cross-linking between clay sheets and PDMAA chains provided the hydrogel with mechanical strength to maintain its stability in shape and architecture. GO sheets in the hybrid hydrogels acted as not only a collaborative cross-linking agent but also as a NIR absorber to absorb the NIR irradiation energy and transform it to thermal energy rapidly and efficiently, resulting in a rapid temperature increase of the GO containing gels. The chain mutual diffusion and the reformation of physical cross-linking occurred more quickly at higher temperature; consequently, the damaged hydrogel was almost completely recovered in a few minutes upon irradiation. We also demonstrated a potential application of the hybrid hydrogel as a self-healing surgical dressing.

A simple strategy for in situ fabrication of a smart hydrogel microvalve within microchannels for thermostatic control.

Self-regulation of temperature in microchip systems is crucial for their applications in biomedical fields such as cell culture and biomolecule synthesis as well as those cases that require constant temperature conditions. Here we report on a simple and versatile approach for in situ fabrication of a smart hydrogel microvalve within a microchip for thermostatic control. The thermo-responsive hydrogel microvalve enables the "on-off" switch by sensing temperature fluctuations to control the fluid flux as well as the fluid heat exchange for self-regulation of the temperature at a constant range. Such temperature self-regulation is demonstrated by integrating the microvalve-incorporated microchip into the flow circulation loop of a micro-heat-exchanging system for thermostatic control. Moreover, the microvalve-incorporated microchip is employed for culturing cells under temperature self-regulation. The smart microvalve shows great potential as a temperature controller for applications that require thermostatic conditions. This approach offers a facile and flexible strategy for in situ fabricating hydrogel microvalves within microchips as chemostats and microreactors for biomedical applications.