Microsponges, a patented technology for chronotherapeutic topical drug delivery, has evolved for oral, pulmonary, and parenteral drug delivery. Various advances have been made with this carrier particle resulting in the development of novel carrier particles, namely nanosponges, nanoferrosponges, and porous microbeads. This chapter deals with the application for topical delivery of pharmaceuticals and for cosmetic purpose; potential of the delivery system for oral drug delivery, pulmonary, and parenteral purpose; and also provides an insight on the recent advances made in this field and future prospect. While many commercial products are available for topical purpose, the use of the technology for sustained/controlled/targeted delivery of pharmaceuticals/biopharmaceuticals via alternative routes is still in infancy. Extensive research inputs are required to resolve preclinical and clinical intricacies before the technology can be put into use for alternative administrative routes and for tissue engineering.
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Multiparticulate systems can control the drug release via temporal control or spatial control or both. These offer the advantages of ease of fabrication, high degree of dispersion in gastrointestinal tract (Asghar & Chandran 2006), reduced risk of dose dumping (Solanki, Patel, Barot, Parijiya, & Shelat, 2012), leading to less inter- and intra-subject variability (Goyel, Prajapati, Purohit, & Mehta, 2010), and efficient drug loading. Due to their advantages these have been widely explored as drug carriers and sequentially this has led to the development of microsponges in 1988. These porous microspheres were exclusively designed for chronotherapeutic topical drug delivery but attempts to utilize them for oral, pulmonary and parenteral drug delivery were also made (Smith, Morhenn, & Webster, 2006). Various advances have been made with this carrier particle resulting in the development of various novel developments.
The microsponge technology was introduced for topical delivery of drug products to facilitate the controlled release of active drug into the skin in order to reduce systemic exposure and minimize local cutaneous reactions to active drugs. Also known as solid phase porous microsphere (Figure 1); is a patented microparticulate system, comprising of highly cross-linked, polymeric porous microspheres having numerous interconnected voids in the particle, loaded with active agent within a collapsible structure (Embil & Nacht 1996) with large porous surface to entrap wide range of active agents with varying pharmacological activities administered in different doses that can be released at the desired site of absorption (Sharma & Pathak 2006).
The pores in the microparticle form a continuous arrangement open to the exterior surface of particles which permits the outward diffusion of the entrapped drug molecule at a controlled rate depending on the pore size (Nacht & Kantz, 1992). High degree of polymeric cross-linking results in insoluble, inert microparticles with satisfactory strength to withstand high shear. These microparticles were once visualized to consist of several nanoparticles enclosed in a porous polymeric outer surface (Katz, Cheng, & Nacht, 1999). A microsponge of size approximating 25 μm can have up to 3000 mm/g of pore length with a pore volume of about 1 ml/g (Gans, 1999). In addition to efficient entrapment of active ingredients, the technology is predicted to minimize side effects, improve stability, increase elegance and enhance formulation flexibility (Srivastava & Pathak 2012).
Primarily the products lined up for commercial purpose include those intended for topical applications due to the favourable features namely- The microsponge system can prevent excessive accumulation of ingredients within the epidermis and the dermis. It can absorb oil up to 6 times its weight without drying and extends drug release for up to 12 h. The microsponge system can significantly reduce the irritation of effective drugs without reducing their efficacy. The microsponges are then washed away with the next cleansing (Kaity, Maiti, Ghosh, Pal, Ghosh, & Banerjee, 2010). The characteristics of microsponges and the active pharmaceutical ingredient to be incorporated therein are listed in Table 1.
The microsponges may be prepared using any one of the following methods (1) Liquid-liquid suspension polymerization [Bottom-up approach] (Tansel et al 1992) ; (2) Quasi-Emulsion Solvent diffusion[Top down approach] (Kawashima, Niwa, Handa, Takeuchi, Iwamoto, & Itoh, 1989); (3) Water in oil in water (w/o/w) emulsion solvent diffusion (Rawat, Majumder, & Ahsan, 2008); Oil in oil emulsion solvent diffusion (Mandal, Bostanian, Graves, Chapman, & Idodo, 2001); (4) Addition of porogen (Bae, Son, Park, & Han, 2009); Lyophilization (Liu, Liu, Ng, Froix, Ohno, & Heller, 1997) and Electrohydrodynamic atomization (Pancholi, Ahras, Stride, Edirisinghe, & Samarasinghe, 2009). Table 2 lists the evaluation parameters of microsponges along with the determination method/equipment.