Swelling Transition Temperature Research Articles

Micro 3D Printing of a Temperature-Responsive Hydrogel Using Projection Micro-Stereolithography

Stimuli-responsive hydrogels exhibiting physical or chemical changes in response to environmental conditions have attracted growing attention for the past few decades. Poly(N-isopropylacrylamide) (PNIPAAm), a temperature responsive hydrogel, has been extensively studied in various fields of science and engineering. However, manufacturing of PNIPAAm has been heavily relying on conventional methods such as molding and lithography techniques that are inherently limited to a two-dimensional (2D) space. Here we report the three-dimensional (3D) printing of PNIPAAm using a high-resolution digital additive manufacturing technique, projection micro-stereolithography (PμSL). Control of the temperature dependent deformation of 3D printed PNIPAAm is achieved by controlling manufacturing process parameters as well as polymer resin composition. Also demonstrated is a sequential deformation of a 3D printed PNIPAAm structure by selective incorporation of ionic monomer that shifts the swelling transition temperature of PNIPAAm. This fast, high resolution, and scalable 3D printing method for stimuli-responsive hydrogels may enable many new applications in diverse areas, including flexible sensors and actuators, bio-medical devices, and tissue engineering.

Effect of Block Copolymer Architecture on the Thermally Induced Swelling of Micelle-Containing Multilayer Thin Films

We investigate the effect of block copolymer (BCP) molecular weight and connectivity on the morphology and time–temperature dependent swelling of thin film hydrogels created through layer-by-layer (LbL) assembly of BCP micelles with poly(acrylic acid). BCPs of poly(N,N-dimethylaminoethyl methacrylate) (D) and poly(propylene oxide) (P), a P–D diblock, a long D–P–D triblock, and a short D–P–D triblock copolymer, were compared in terms of their temperature response in solution and within micelle–polyelectrolyte multilayers (mPEMs). The critical micellization concentration and micellization temperature of the BCPs in solution, as well as the swelling transition temperature, Tstt, of the mPEMs, decreased with increasing P block length. AFM imaging of dry mPEMs shows regular dimpled surface structures that arise from surface relaxation of micelles. When the mPEMs are cooled below Tstt in water, the thin ∼200 nm films can swell reversibly between 3 and 6 times their dry thicknesses within 2 min. The degree of sw...

Thermosensitive networks based on high molecular weight polyoxyethylene and N -isopropylacrylamide

γ- and UV-irradiation was successfully used for the preparation of mixed networks on the basis of high molecular weight polyoxyethylene (POE) and/or N-isopropylacrylamide and poly(N-isopropylacrylamide) (PNIPAAm). These gels preserve the swelling transition temperature of the pure PNIPAAm and shrink faster above this temperature due to the hydrophilic POE chains. It was found that in a collapsed state these gels retain alkaline organic salts from aqueous solutions.

Synthesis and functionalities of poly(N-vinylalkylamide). VI. A novel thermosensitive hydrogel crosslinked poly(N-vinylisobutyramide)

A novel thermosensitive poly(N-vinylisobutyramide)(polyNVIBA) hydrogel was prepared by the copolymerization of N-vinylisobutyramide (NVIBA) with butylene-bis-NVA(B-BNVA) as a crosslinker in a high yield. The swelling transition behavior was examined in comparison with poly(N-isopropylacrylamide)(polyNIPAAm) hydrogel. The resulting polyNVIBA hydrogel clearly showed a swelling transion in water at ca. 41°C. To control the transition temperature (Tt) of the gel, crosslinked copolymers of NVIBA and N-vinylacetamide (NVA) were prepared and compared with copolymers of N-isopropylacrylamide(NIPAAm) and NVA. The incorporation of NVA led to a higher swelling transition temperature. Tt of poly(NVIBA-co-NVA) gels was almost the same as those in water-soluble poly(NVIBA-co-NVA). The responses for a swelling transition of polyNVIBA and poly(NVIBA-co-NVA) gels were sharp in comparison to polyNIPAAm gels. PolyNVIBA and poly(NVIBA-co-NVA) gels desorbed 98% of water above Tt. The characteristic and the mechanism of the phase transition on the hydrogels were discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3377–3384, 1997

In vitro release of 9-β- d-arabinofuranosyladenine from thermo-responsive copoly(acryloyl- l-proline methyl ester/styrene) gels

Hydrophobic styrene (St) was copolymerized with acryloyl- l-proline methyl ester (A-ProOMe) known as a characteristic thermo-responsive gel. The thermo-responsive function of this copolymer gel perfectly disappeared by the introduction of St > 20 mol% in the gel because of a strongly hydrophobic effect owing to pendant phenyl moiety. On thermo-responsive copolymer gels ranging in St composition from 1 to 10 mol%, the deswelling process proceeded faster than swelling process. This difference was explained from the results of activation energies (| ΔE|). The swelling-temperature curve of such a thermo-responsive gel was tried to investigate by a statistical moment analysis, e.g. the area under swelling-temperature curve (AUC), mean swelling transition temperature (MSTT), and variance of swelling transition temperature (VSTT), suggesting that these values corresponds very closely to St composition in the gel. 9-β- d-arabinofuranosyladenine (Ara-A) was incorporated into the thermoresponsive copoly(A-ProOMe/St) gels and, as a result, it was found that the in vitro release of Ara-A from the gel when cycled at different temperatures at 60-min intervals shows a typical pulsatile release such as a slight amount of drug release at 10°C and a good deal of drug release at 30°C.

A new application of statistical moment theory to evaluate the swelling behavior of thermo‐responsive gels

AbstractThe loosely cross‐linked poly(acryloyl‐L‐proline methyl ester) gel, which is known as one of the typical thermo‐responsive gels, shows a volume transition around approximately 14°C in pure water. This volume transition is shifted to higher temperature by treatment in aqueous sodium dodecyl sulfate (SDS). The analysis of the swelling‐temperature curve (frequency distribution) was performed according to a moment analysis, in which the area under the swelling‐temperature curve (AUC), mean swelling transition temperature (MSTT) and variance of swelling transition temperature (VSTT) were calculated. It is shown that the apparent volume transition temperature can be estimated from MSTT and that VSTT can be used to characterize the shape of the corresponding curves.

A New Thermo-Sensitive Hydrogel: Poly(ethylene oxide-dimethyl siloxane-ethylene oxide)/Poly(N-isopropyl acrylamide) Interpenetrating Polymer Networks I. Synthesis and Characterization

Interpenetrating polymer networks (IPNs) composed of poly(ethylene oxide-dimethyl siloxane-ethylene oxide) (PEO-PDMS-PEO) ABA triblock copolymer and poly(N-isopropyl acrylamide) (PIPAAm) were synthesized. Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) studies of bulk IPNS revealed micro phase separation with partial phase mixing between two chemically independent networks. Aqueous equilibrium swelling curves were examined as a function of temperature. DSC thermograms of the swollen IPNS exhibited the same swelling transition temperature as that of PIPAAm, although the degree of swelling of IPNS was affected by polymer composition. These observations indicate that each network in the swollen IPNs exists independently and many have different morphology than the dried bulk state. The aqueous swelling-deswelling kinetics by temperature modulation of IPNs could be controlled by gel composition nd temperatures applied.

A Thermo-Sensitive Hydrogel: Poly(ethylene oxide-dimethyl siloxane-ethylene oxide)/Poly(N-isopropyl acrylamide) Interpenetrating Polymer Networks II. On-Off Regulation of Solute Release from Thermo-Sensitive Hydrogel

Interpenetrating polymer networks (IPNs) of poly(ethylene oxide-dimethyl siloxane-ethylene oxide) (PEO-PDMS-PEO) ABA triblock copolymer and poly(N-isopropyl acrylamide) (PIPAAm) has been synthesized as thermosensitive gels. Indomethacin and ketoprofen were selected as model drugs and incorporated into thermosensitive gel. Pulsatile drug release produced from these thermosensitive gels was strongly influenced by the swelling-deswelling kinetic properties of thermosensitive gels solubility dependence of drug as a function of temperature, and the temperature applied. However, the release behavior of indomethacin and ketoprofen at several fixed temperatures from the thermosensitive gel showed similar patterns. The exact initiation temperatures for drug release of both drugs were similar and slightly below the swelling transition temperature of an unloaded gel.

Stimuli sensitive polymers for drug delivery systems

AbstractTemperature sensitive and electric field sensitive hydrogels were prepared for use in modulated drug release systems. Crosslinked poly(N‐isopropyl‐acrylamide) and its networks, modified with hydrophobic components by copolymerization or by interpenetrating polymer networks (IPNs) formation, were utilized as temperature sensitive hydrogels. Indomethacin (a model solute)‐release from polymer matrix and permeation through polymer membrane demonstrated “on‐off” regulation with temperature fluctuation. This was the result of polymer surface properties rather than bulk swelling, as temperature was changed past the swelling transition temperature range of the polymer. The on‐off regulation in an electric field was also obtained with a positively charged solute (Edrophonium chloride) release in distilled‐deionized water from a matrix of crosslinked poly(2‐acrylamido‐2‐methylpropanesulfonic acid‐co‐butyl methacrylate). This was attributed to the ion exchange between Edrophonium ion and protons produced at the anode. The swelling changes produced by local pH or ionic strength changes affected non‐charged solute release.

The possible influence of order-disorder transformations on the swelling of 85Ni-15Cr nichrome alloy

The binary alloy 85Ni-15Cr swells during neutron irradiation in a manner that is quite unrepresentative of either simple austenitic alloys or pure nickel. The nickel-chromium system is known to exhibit ordering out of reactor and this alloy was used to test the concept that alloys which develop order exhibit lower swelling rates. When the neutron irradiation data are compared to that of ion irradiations conducted by Hudson and Ashby on Ni-Cr alloys, it is shown that chromium additions appear to depress swelling in nickel initially but also appear to suppress the tendency for swelling to saturate at high exposure. Below a transition temperature near 550°C the swelling is relatively sluggish and is quite insensitive to irradiation temperature. Above the transition temperature the swelling behavior is more complex but typical of austenitic alloys. The swelling transition temperature is thought to be related to the critical temperature for order-disorder transformation.