Microgels in drug delivery

Vinogradov, S. V. (2006), Colloidal microgels in drug delivery applications, Curr. Pharm. Des., 12,4703-4712. 

Mahnsten M (2011) Microgels in drug delivery. In Femandez-Nieves A, Wyss HM, Mattsson J, Weitz DA (eds) Microgel suspensions fimdamditals and applications. Wiley-VCH, Weinheim, pp 375-405... 

Lopez, V.C. and Snowden, M.J., The role of colloidal microgels in drug delivery. Drug Deliv. Syst. Sci.,3,19, 2003. 

Such microgel nanoparticles with varying gelatin concentration and crosslinking density have a high potential for use in drug delivery applications. The gelatin nanoparticles can also be used as template particles for the formulation of apatite... 

As mentioned above, the preparation of nanogels by addition reactions of functional macromolecular precursors is mainly used for biomedical applications. Thus, the choice of synthetic precursors for microgel formation is restricted to biocompatible materials. Moreover, as most applications are in drug delivery, the molecular weight of the gel precursors should be below the threshold for renal clearance, a value that depends on the molecular architecture and chemical nature of the polymer but that is usually smaller than 30kDa, which is set as the limit for linear PEG [97], Polymers that are mostly used and thus presented in more detail here are PEG, poly(glycidol) (PG), and polyethylene imine) (PEI). 

Thermally sensitive polymers under colloidal nano and microgels are also started to be used in drug delivery and the most examined polymers are poly(A-alkylacrylamide) derivatives. Unfortunately, such polymers are biocompatible but not biodegradable, and they are mainly used... 

Hollow silica gels were prepared using PNlPAAm by Liu et al. Rhodamine B was taken as the model drug, it was observed that the LCST of the PNlPAAm was increased to 40.6°C, which indicates a good performance of temperature-dependent phase transition. To further confirm the temperature responsiveness of the system, the release study was carried out at 25°C and 40°C. it was observed that 82.5% of the RHB was released for 12 h at 25°C while 86.5% was released at 40°C in 12 h. Thus, this indicates the prepared microgels achieve thermoresponsive controlled release behavior and were also found to be biocompatible [36]. Some of the applications of thermoresponsive polymers in drug delivery are summarised in Table 20.1. 

In general, microgels obtained by radiation methods can be used in various applications in the same way as conventional synthesized systems, e.g., as drug delivery templates, for encapsulation, or as microreactors [29, 30], PAAm for example can be used as template material to synthesize hollow cadmium selenide nanospheres [24], and PVP can be used for the incorporation of ferromagnetic nanoparticles to obtain magnetic hydrogel microspheres [13],... 

Oh, J. K., Lee, D. I., and J. M. Park. 2009. Biopolymer-based microgels/nanogels for drug delivery applications. Progress in Polymer Science 34 1261-1282. 

Mahnsten, M. Bysell, H. Hansson, P. Biomacromolecules in microgels—Opportunities and challenges for drug delivery. Curr. Opin. Colloid Interface Sci. 2010,15 (6), 435-444. 

FIGURE 54.23 A schematic representation of inverse miniemulsion or microemulsion polymerization for the preparation of nanometer-sized particles of water-soluble and water-swellable polymers as well as cross-linked particles in the presence of cross-linkers. (Reprinted from Polymer, 50(19), Oh, J.K., Bencherif, S.A., and Matyjaszewski, K., Atom transfer radical polymerization in inverse miniemulsion A versatile route toward preparation and functionalization of microgels/nanogels for targeted drug delivery applications, 4407-4423. Copyright 2009, with permission from Elsevier.)... 

Oh, J.K. Bencherif, S.A. Matyjaszewski, K. Atom transfer radical polymerization in inverse miniemulsion A versatile route toward preparation and funetionalization of microgels/nanogels for targeted drug delivery applications. Polymer 2009,50 (19), 4407-4423. 

Since Pelton and Chibante reported the synthesis of the first temperature-sensitive microgel from iV-isopropylacrylamide (NIPAM) and crosslinker in 1986 [74], responsive microgels have attracted numerous attempts to explore their potential application in many fields, such as sensing and drug delivery [75]. Now the most extensively studied respruisive microgels are prepared with poly(fV-isopropyla-crylamide) (PNIPAM) [2], It is weU known that the phase transition temperature of PNIPAM is about 32°C [76], When r< LCST, the PNIPAM chain is soluble in water as a random cod. When r LCST, the subtle balance between PNIPAM and water is broken and phase transition occurs [77]. However, the single-molecule level mechanism of the phase transition of PNIPAM had not been proposed until very recently. 

---