Use Of Thermosensitive Polymer Research Articles

Electrochemical dopamine sensor based on the use of a thermosensitive polymer and an nanocompositeprepared from multiwalled carbon nanotubes and graphene oxide.

An electrochemical dopamine sensor with a temperature-controlled switch was constructed by using a mixture of thermo-sensitive block copolymers (type tBA-PDEA-tBA), graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs). If the temperature is below 26°C, the polymer on the glassy carbon electrode (GCE) is stretched, the distance between the MWCNTs is large, and the charge transfer resistance (Rct) of the composite also is large. In the presence of dopamine, the electron transfer at theelectrode is strongly retarded and in the "off" state. At above 38°C, the polymer is shrunk and the Rct is much smaller. The presence of dopamine results in a rapid electron transfer at the GCE, and this is referred to as the "on" state. At temperatures between 26 and 38°C, the polymer shrinks slightly and has a "spring-like" state. There is a linear relationship between the response current (typically measured at a potential as low as 0.16V vs. Ag/AgCl) and temperature. The response to dopamine is linear in the 0.06 to 4.2μM and 4.2 to 18.2μM concentration range, and the detection limit is 42nM. Conceivably, this approach provides a novel approach towards the design of electrochemical sensors based on the use of thermo-sensitive polymers. Graphical abstract Schematic presentation of reversible and temperature-controlled electrochemical response of dopamine on the thermo-sensitive block copolymers (tBA-PDEA-tBA) / multi-walled carbon nanotubes (MWCNTs) / graphene oxide (GO) / glassy carbon electrode (GCE).

Preparation and evaluation of radioiodinated thermoresponsive polymer based on poly(N‐isopropyl acrylamide) for radiotherapy

A thermoresponsive polymer based on poly N‐isopropylacrylamide (PNIPAM) was synthesized and radioiodinated to explore its potential use in localized radiotherapy. The synthesized PNIPAM polymer was functionalized with L‐tyrosinamide to facilitate radioiodination. The content of tyrosinamide groups in the polymer was assayed spectrophotometrically (λ = 275nm). The functionalized polymer showed a cloud point temperature of 29–31°C and phase separation at 35°C, as revealed by Differential Scanning Calorimetry (DSC) and Dynamic Light Scattering (DLS). The phase transition temperature is conducive for preferential localization of the polymer at the site of injection due to changes in the polymer conformation at body temperature. For in vivo demonstration, the biodistribution studies of radioiodinated polymer were carried out in Swiss mice bearing fibrosarcoma tumor. Biodistribution studies showed a retention of 30% of the injected labeled polymer, PNIPAM‐125I‐tyrosinamide, in the solid tumor tissues after 2 h of intratumoral injection. Although the activity decreased with time, 3–4% of the injected dose (i.d) was found to be retained in the tumor on 5 d post injection. The results suggest the potential use of thermosensitive polymer based on poly N‐isopropylacrylamide for locoregional radionuclide therapy. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 860‐868, 2013

Preparation of thermosensitive gelatin-pluronic copolymer for cartilage tissue engineering

In this study, a gelatin conjugated Pluronic® thermosensitive polymer(Gelatin-Pluronic, GP) was synthesized by the direct coupling of gelatin to monocarboxylated Pluronic®(MP) and characterized. The use of thermosensitive polymers has recently been proposed for many applications including tissue engineering, gene therapy, novel drug delivery systems, implantable devices, such as scaffolds for cartilage regeneration and nanotechnology. Water soluble thermosensitive GP was developed as an injectable scaffold using EDC/NHS as a coupling reagent for catilage regeneration. 1H NMR, and FTIR were used to characterize the chemical structure of the modified gelatins. The GP solution showed a reversible sol-gel transition behavior around body temperature. The cell viability was evaluated using methylthiazolyldiphenyl tetrazolium bromide (MTT) assay. The optical density (O.D.) of GP was significantly higher than that of Pluronic® at 1, 3 and 5 days, indicating that the cell viability on GP was better than on Pluronic®. Therefore, the GP copolymer can be used as an injectable cell-containing scaffold owing to its thermally reversible properties and good biocompatibility.

Surfactant induced drug delivery based on the use of thermosensitive polymers

A novel approach of controlled drug delivery using thermosensitive polymers is developed in this paper. The drug release occurs at physiological temperature, at which the polymer is normally not soluble, and no medium temperature changes are required to bring about the delivery. For this purpose benefit is taken from the specific binding properties of some anionic surfactants and poly( N-isopropylacrylamide) (PNIPAAm) in order to modify the dissolution properties of PNIPAAm and of a copolymer with N-vinyl-acetamide (NVA), and so to induce the release of a drug contained in compression coated tablets. The influence of surfactant type and amount on the drug release rates and lag times from tablets coated with PNIPAAm or with the copolymer are discussed. It was found that the lag time is influenced by the surfactant species and amount. When use is made of a copolymer as coating agent, it is possible to bring about the release of the drug by incorporating only a very small amount (as low as 2%) of sodium dodecyl sulfate (SDS) in the coating.

Synthesis and functionality of poly(N-vinylalkylamide). X. A novel aqueous two-phase system based on thermosensitive polymers and dextran

The use of thermosensitive polymers in an aqueous two-phase system was studied. Poly(N-isopropylacrylamide) (PNIPAAm) and poly(N-vinylisobutyramide) (PNVIBA) were used as thermosensitive polymers. Both polymers could form aqueous two-phase with dextran, respectively. The phase diagrams of each system were successfully obtained. Using myoglobin as a model protein, a preliminary separation study was performed. The separation ability of both polymers was higher than that from the poly(ethylene glycol)-dextran system. Protein separation ability appeared to be related to the hydrophilic/hydrophobic balance of the polymers. Both PNVIBA and PNIPAAm rich phases maintained their thermosensitivity after two-phase formation. PNVIBA and PNIPAAm are useful as polymers for a functional aqueous two-phase system.

Application of thermosensitive polymers as a new embolic material for intravascular neurosurgery.

Application of thermosensitive polymers as an embolic material for intravascular neurosurgery was investigated. We intended to use thermosensitive polymers to occlude vessels by precipitation in response to body temperature. Copolymers of N-isopropylacrylamide (NIPAM) and N-n-propylacrylamide (NPAM) were selected as thermosensitive polymers. To determine the optimal lower critical soluble temperature (LCST) for the embolic material, we developed an in vitro flow model. In this study the copolymers with an LCST of 24-26 degrees C showed appropriate precipitation. To prove the occlusion of vessels in vivo, we injected the copolymers into a rabbit kidney through a microcatheter. The extent of embolization was judged by angiography and histological examination. An acute toxicity test of the copolymer of NIPAM and NPAM was performed in comparison with that of the NIPAM monomer. The copolymer used in this paper showed no acute toxicity in mice. Water solubility, non-adhesiveness, and non-toxicity are the advantages of the use of thermosensitive polymers as an embolic material. By changing the LCST, various embolic materials can be designed. Based on our results, we believe that the application of thermosensitive polymers as a new embolic material is very promising.