pH-induced shrinking and swelling of hydrogels based on copolymers of acrylic acid and acrylamide

Hydrogels are three-dimensional polymeric networks that can absorb and retain large quantities of water in relation to their physical size. By incorporating stimuli-responsive units into the gel structure, hydrogel materials can be actuated by external stimuli such as photo, thermal, electro and chemical (e.g. pH). In this paper, we demonstrate that the size and volume of a pH sensitive hydrogel based on acrylic acid (AA) and acrylamide (Am) can change when exposed to different pH environments. The pH responsive hydrogels that were developed used copolymers of AA and Am in different molar ratios 30:70, 50:50 and 70:30, respectively. At a pH value above the pKa of AA (pH > 4.5) the AA dissociates to the more hydrophilic acrylate anion (A-) triggering swelling of the hydrogel. In contrast, at pH < 4.5, the hydrogel contracts due to the formation of the less hydrophilic AA form in the polymer backbone, which triggers the release of water from the gel causing it to physically contract. The hydrogel samples were photo-polymerised using a photo-mask with 1mm diameter circles exposed. Each of the hydrogel samples was placed in pH solutions varying from pH 1-14. The hydrogels with 50:50 molar ratio of Am:AA in the polymer backbone produced hydrogels with the highest relative pH response when compared with the other molar ratios, having a large diameter increase from pH 2 (~0.57mm) to pH 10 (~3.27mm). Successive changes of the solution pH showed that the pH-induced actuation is a reversible process with no detectable hysteresis

Stimuli-responsive hydrogels based on acrylic acid and acrylamide

Hydrogels are three-dimensional polymeric networks that can absorb and retain large quantities of water in relation to their physical size. By incorporating stimuli-responsive units into the gel structure, hydrogels can be actuated by external stimuli such as light[1], temperature[2] and pH[3], among others. In this study pH responsive hydrogels were developed using copolymers of acrylic acid (AA) and acrylamide (Am) in different molar ratios (30:70, 50:50 and 70:30, respectively). In order to turn this pH response into a photo-response, a reversible photo-acid generator, namely spiropyran acrylate (SP-A), was copolymerised in the polymer backbone

pH and photo-responsive hydrogels based on acrylic acid and acrylamide

Hydrogels are three-dimensional polymeric networks that can absorb and retain large quantities of water in relation to their physical size. By incorporating stimuli-responsive units into the gel structure, hydrogel materials can be actuated by external stimuli such as photo, thermal, electro and pH, respectively. In this study, pH responsive hydrogels were developed by using copolymers of acrylic acid (AA) and acrylamide (Am) in different molar ratios (30:70, 50:50 and 70:30, respectively). At pH above the pKa of AA (pH>4.5) the AA dissociates to the more hydrophilic acrylate (A-) form triggering swelling of the hydrogel. In contrast, at pH < 4.5, the hydrogel contracts due to the formation of the hydrophilic AA form in the polymer backbone, which triggers release of water from the gel. In order to turn this pH response into a photo-response, a reversible photo-acid generator, spiropyran acrylate (SP-A), was copolymerised in the polymer backbone. In acidic environments, the SP-A will spontaneously convert to the protonated hydrophilic merocyanine (MC-H+) form and switch back to the hydrophobic SP-A when exposed to white light, expelling a proton in the process. The switching between these two forms can be used to trigger LCST behaviour in the gel, leading to photo-controlled swelling/contraction due to water uptake and release. The composition used for the photo responsive hydrogel was AA: Am: SP-A in a 10:10:1 molar ratio. When the hydrogel is immersed in water, in the dark, the AA dissociates and the proton is taken by the SP-A to form MC-H+, which gives the hydrogel a yellow colour. Under these conditions (A-, MC-H+) the polymer chains are more hydrophilic causing the hydrogel to expand (Fig. 1, initial point). However, when exposed to white light, the MC-H+ is converted back to the SP-A form (colourless) expelling a proton, decreasing the local pH, and protonating the AA. This makes the polymer chain less hydrophilic and the hydrogel contracts (Fig. 1, 0-10 min). As seen in Fig. 1, this process is reversible and with the initial photo-contraction complete in seconds. After ca. 10 min, the white light is switched off, and the hydrogel reswells to about 95% of its fully hydrated size after ca. 15 min in the dark

Photo-responsive hydrogels with enhanced volume changes due to local pH alterations

Photo-responsive hydrogels of varying compositions containing spiropyran photochromic units have been widely studied in recent years due to their many potential applications, including photo-actuated micro-valves for microfluidic devices [1,2]. In this study two hydrogel formulations were employed to produce reversible photo-responsive hydrogel actuators operative in neutral pH. Both compositions contain the photochromic unit spiropyran acrylate (SP) and acrylic acid (AA) copolymerised in the main polymer backbone, together with N-isopropylacrylamide (NIPAAm) or acrylamide (AAm), respectively. At neutral pH, the AA comonomer dissociates to the acrylate anion (A-) and the proton transfers to the SP unit to give the more hydrophilic protonated merocyanine (MC-H+) form, which triggers water uptake and hydrogel expansion. Under white light irradiation, the MC-H+ reverts to the more hydrophobic SP isomer, with simultaneous reformation of acrylic acid, and hydrogel contraction. In the case of p(NIPAAm-co-AA-co-SP) hydrogel, an area contraction of up to 45% of its fully hydrated size was achieved after 4 min of white light exposure followed by reswelling to up to 85% of the initial size after 11 min in the dark. In the case of p(AAm-co-AA-co-SP) hydrogel, the SP unit serves also as a reversible photo-acid generator changing the local pH which in turn determines the ratio of AA/A-, and therefore the hydrophilic character of the polymer backbone. In this case, photo-contraction of ~15% in diameter is achieved within 90 seconds of white light irradiation followed by reswelling to ~95% of its fully hydrated size after further ~30 seconds in the dark. In both cases the photo-induced contraction/reswelling processes were reversible and repeatable over at least 3 cycles with no detectable hysteresis

Clinical characteristics of Kawasaki disease with sterile pyuria

PurposeKawasaki disease (KD) is a systemic vasculitis and affects many organ systems. It often presents sterile pyuria, microscopic hematuria, and proteinuria due to renal involvement. The aims of this study were to define clinical characteristics of acute KD patients with pyuria and to analyze meaning of pyuria in KD.MethodsThe medical records and laboratory findings including serum and urine test of 133 patients with KD admitted to Yeungnam University Hospital from March 2006 to December 2010 were reviewed retrospectively.ResultsForty patients had sterile pyuria and their clinical characteristics including age, gender and body weight were not significantly different with those who did not have pyuria. Fever duration after treatment was significantly longer in KD patients with pyuria. Erythrocyte sedimentation rate, C-reactive protein and serum concentration of alanine aminotransferase were significantly higher in patients with pyuria. Hyponatremia and coronary artery lesion were seen more often in patients with pyuria but there was no significant difference. Also serum blood urea nitrogen was significantly higher in KD patients with pyuria. Urine β2-microglobulin was elevated in both patients groups and showed no difference between two groups.ConclusionWe found more severe inflammatory reaction in KD patients with pyuria. We also found elevation of some useful parameters like β2-microglobulin that indicate renal involvement of KD through the urine test. Careful management and follow up will need for KD patients with pyuria and it is necessary in the future to study the specific parameters for renal involvement of KD

Medium-size-vessel vasculitis

Medium-size-artery vasculitides do occur in childhood and manifest, in the main, as polyarteritis nodosa (PAN), cutaneous PAN and Kawasaki disease. Of these, PAN is the most serious, with high morbidity and not inconsequential mortality rates. New classification criteria for PAN have been validated that will have value in epidemiological studies and clinical trials. Renal involvement is common and recent therapeutic advances may result in improved treatment options. Cutaneous PAN is a milder disease characterised by periodic exacerbations and often associated with streptococcal infection. There is controversy as to whether this is a separate entity or part of the systemic PAN spectrum. Kawasaki disease is an acute self-limiting systemic vasculitis, the second commonest vasculitis in childhood and the commonest cause of childhood-acquired heart disease. Renal manifestations occur and include tubulointerstitial nephritis and renal failure. An infectious trigger and a genetic predisposition seem likely. Intravenous immunoglobulin (IV-Ig) and aspirin are effective therapeutically, but in resistant cases, either steroid or infliximab have a role. Greater understanding of the pathogenetic mechanisms involved in these three types of vasculitis and better long-term follow-up data will lead to improved therapy and prediction of prognosis

Tin and organotin

NRC publication: Ye