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M. de Fátima Júlio, A. Soares, L. M. Ilharco, I. Flores-Colen and J. de Brito, Silica-based aerogels as aggregates for cement-based thermal renders, Cem. Concr. Compos., 2016, 72, 309–318 CrossRef.
K. Kanamori, M. Aizawa, K. Nakanishi and T. Hanada, New transparent methylsilsesquioxane aerogels and xerogels with improved mechanical properties, Adv. Mater., 2007, 19(12), 1589–1593 CrossRef CAS. Through analysis of nitrogen sorption isotherms (adsorption/desorption), obtained from a Surface Area and Porosity Analyzer (Micromeritics TriStar II), specific surface area (SSA), pore size, and cumulative pore volume of aerogel/cryogel specimens are determined. Pre-treatment of previously sintered samples (to 600 °C) is performed by heating these to 250 °C during approximately 3 hours of degassing of a flowing gas used to remove any form of moisture, impurities, and contaminants. As next step, the degassed samples are cooled to cryogenic temperatures (−195 °C) under vacuum conditions, during which data in relation to the quantity of the absorbent gas adhering to the solid adsorbate for different values of relative pressure ( P/ P o) is collected. Calculation of the specific surface area (SSA) of the adsorbate is then performed from the data given by the adsorption isotherm plot at relative pressure ( P/ P o) from 0.003 to 0.3, which is based on the Brunauer–Emmett–Teller (BET) theory. The Barrett, Joyner, and Halenda (BJH) method, based on the Kelvin model of pore filling, is used for calculation of the pore size and pore volume of the samples, by analyzing the data from the desorption branch of the isotherm curve. The afore-mentioned test is also employed to establish nanoparticle size of the aerogel/cryogel samples.T. Y. Wei, T. F. Chang, S. Y. Lu and Y. C. Chang, Preparation of monolithic silica aerogel of low thermal conductivity by ambient pressure drying, J. Am. Ceram. Soc., 2007, 90(7), 2003–2007 CrossRef CAS. However, after reviewing these areas of interest there is room for further investigation. For example, cryogels used in injectable gels for DDS is currently an emerging field. In the examples given previously there were no two methods that were similar and when authors compared the use of cryogels, there was mostly comparison to hydrogels rather than previously reported work involving cryogels. In the field of cryogels for drug delivery and wound healing there are several examples of systems that have demonstrated proof of principle. However, there are limited efforts dedicated to testing these on human test subjects which is required to learn the effects these potential drugs can have on humans whether long term or short term. Bessonov, I.V.; Rochev, Y.A.; Arkhipova, A.Y.; Kopitsyna, M.N.; Bagrov, D.V.; Karpushkin, E.A.; Bibikova, T.N.; Moysenovich, A.M.; Soldatenko, A.S.; Nikishin, I.I. Fabrication of hydrogel scaffolds via photocrosslinking of methacrylated silk fibroin. Biomed. Mater. 2019, 14, 034102. [ Google Scholar] [ CrossRef]
Kornblith, L.Z.; Moore, H.B.; Cohen, M.J. Trauma-induced coagulopathy: The past, present, and future. J. Thromb. Haemost. 2019, 17, 852–862. [ Google Scholar] [ CrossRef]Cheng, N.; Ren, C.; Yang, M.; Wu, Y.; Zhang, H.; Wei, S.; Wang, R. Injectable Cryogels Associate with Adipose-Derived Stem Cells for Cardiac Healing After Acute Myocardial Infarctions. J. Biomed. Nanotech. 2021, 17, 981–988. [ Google Scholar] [ CrossRef] Macroporous polymeric gels with their unique heterogeneous open-porous structure open new perspectives for the development of innovative systems for biomedical and pharmaceutical applications. Cryotropic gelation is an efficient method for the preparation of super-macroporous polymer hydrogels. They have large pore sizes which can easily contain samples and additives whilst also retaining biocompatible structures [ 86]. Some reports focus on the use of model drug compounds [ 87– 89], or newly synthesised antimicrobial compounds [ 90], for example. Here, we highlight recent examples whereby a drug of clinical relevance has been investigated using cryogels for delivery.
