Temperature-sensitive system

An alternative approach utilizes temperature-sensitive systems. Poloxamer FI27 undergoes phase transition induced by changes in temperature. At room temperature the poloxamer remains a solution. When the solution is instilled onto the eye surface (34 °C) the elevated temperature causes the solution to become a gel, thereby prolonging its contact with the ocular surface. One of the disadvantages of such a system is that it is characterized by a high polymer concentration (25% poloxamer), and the surfactant properties of poloxamer may be detrimental to ocular tolerability. 

Ruel-Gariepy, E., and Leroux, J. C. (2004), In situ-forming hydrogels—Review of temperature-sensitive systems, Eur. J. Pharm. Biopharm., 58,409-426. 

In an effort to obtain a less temperature-sensitive system, lower nickel content catalysts were prepared on an alumina support and tested for demethylation activity. The first, Preparation A, with a nominal nickel content of 50 wt % was activated at 700°F in a slow stream of hydrogen at atmospheric pressure for 16 hours. This catalyst was tested at conditions similar to those employed with the nickel-kieselguhr catalyst reported above. The results are given in Table II. 

Sterilisation by the use of gases usually involves either ethylene oxide or formaldehyde. Both are broad spectrum biocides but neither is as effective as heat. Both may be used for temperature sensitive systems. Both must be used under the correct conditions as they are toxic, and ethylene oxide is explosive when mixed with air. Ethylene oxide is highly penetrative, but formaldehyde is not and is generally used where surface sterility is required. 

Ruel-Gariepy, E. Leronx, J.C. 2004, In iim-forming hydrogels - review of temperature-sensitive systems , European Journal of Pharmaceutics and Biopharmaceutics, vol. 58, no. 2, pp. 409-426. 

A pH/temperature sensitive system was also reported as an injectable system. The pH sensitive imits can complex with a protein drug with opposite charges to reduce the initial burst release of an incorporated drug. Thermogelling PEG/ PCGA, PEG/PCL, and PEG/PCLA were eoupled to pH sensitive amine containing blocks to prepare pH/temperature sensitive gelling system. ... 

Gariepy, ER Leroux, JC. In situ-forming hydrogels— review of temperature-sensitive systems. EurJPharm Biopharm, 2004, 58, 409-426. 

Gariepy ER, Leroux JC (2004) In situ-forming hydrogels -review of temperature-sensitive systems. Eur J Pharm Biopharm 58 409 26... 

All the samples exhibited higher release rates at higher temperatures. These results are in correspondence with the temperature-dependent swelling behaviours of PVA/PAAc IPN hydrogels. All IPN samples showed positive temperature-sensitive systems before they reached the equilibrated state. The... 

PNIPAm-based systems are the most extensively reported temperature-responsive polymers in literature. Other temperature sensitive systems incorporate analogues of NIPAm such as A-( -propyl)acrylamide (nPAm), AW-diethylacrylamide (DEA), and A-ethylmethylacrylamide (EMA) as well as derivatives of the amino acid L-proline A-acryloyl-L-proline methyl ester (A-Pro-OMe) and A-acryloyl-4-trans-L-proline... 

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