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Use of a Microsponge in Drug Delivery Systems
Geeta Patel* (M Pharm) and Dr.J K Patel (M Pharm, Ph.D)
Abstract
The Microsponge Delivery System is a unique technology for the controlled release of topical agents and consists of macroporous beads, typically 10-25 microns in diameter, loaded with active agent. When applied to the skin, the microsponge releases its active ingredient on a time mode and also in response to other stimuli (rubbing, temperature, pH, etc). Microsponge technology offers entrapment of ingredients and is believed to contribute towards reduced side effects, improved stability, increased elegance, and enhanced formulation flexibility. In addition, numerous studies have confirmed that Microsponge systems are non-irritating, non-mutagenic, non-allergenic, and non-toxic. MDS technology is being used currently in cosmetics, over-the-counter (OTC) skin care, sunscreens and prescription products.
Introduction
Microsponges are porous microspheres having myriad of interconnected voids of particle size range 5-300µm. These microsponges have the capacity to entrap a wide range of active ingredients such as emollients, fragrances, essential oils, sunscreens and anti-infective, etc. are used as a topical carrier system (S P Vyas et al. 2002).
Microsponges are microscopic spheres capable of absorbing skin secretions, therefore reducing oiliness and shine from the skin. Spherical particles composed of clusters of even tinier spheres are capable of holding four times their weight in skin secretions. Clinical studies demonstrated that the use of microsponges in a lotion reduced perceived oiliness on the skin by 50%; shine was reduced by 20%.
Microspheres, averaging 25µm in diameter (Embil K et al.1996) and embedded in the vehicle, act like microscopic sponges, storing the active drug until its release is triggered by application to the skin surface. Micropores within the spheres comprise a total pore density of approximately 1mL/g, for extensive drug retention. Release of drug into the skin is initiated by a variety of triggers, including rubbing and higher than-ambient skin temperature.
Microsponge particles are extremely small, inert, indestructible spheres that do not pass through the skin. Rather, they collect in the tiny nooks and crannies of skin and slowly release the entrapped Retinol, as the skin needs it. The empty spheres are then washed away with the next cleansing.
Conventional formulations of topical drugs are intended to work on the outer layers of the skin. Typically, such products release their active ingredients upon application, producing a highly concentrated layer of active ingredient that is rapidly absorbed (S Natch et al. 1990).
The Microsponge system can prevent excessive accumulation of ingredients within the epidermis and the dermis. Potentially, the Microsponge system can reduce significantly the irritation of effective drugs without reducing their efficacy.
Further these porous microspheres with active ingredients can be incorporated in to formulations such as creams, lotions and powders. Microsponges consisting of non-collapsible structures with porous surface through active ingredients are released in a controlled manner (Nacths and Martin, 1990). Depending upon the size the total pore length may range up to 10 ft and pore volume up to 1 ml/g.
By delivering the active gradually to the skin an example like MDS-benzoyl peroxide formulations have excellent efficacy with minimal irritation. These are typical benefits from the use of the MDS (Wester RC et al. 1991,C Omog et al. 2000). This delivery system can be incorporated into conventional dosage forms such as creams, lotions, gels, ointments, and powder and share a broad package of benefits.
Method of preparation
1) Polymerization
The porous microspheres are prepared by suspension polymerization method in liquid-liquid systems (D'Souza et al. 2005). In their preparation, the monomers are first dissolved along with active ingredients in a suitable solvent solution of monomer and are then dispersed in the aqueous phase, which consist of additives (surfactant, suspending agents, etc. to aid in formation of suspension). The polymerization is then initiated by adding catalyst or by increasing temperature or irradiation. The various steps in the preparation of microsponges are summarized as: (S P Vyas et al. 2002)
- Selection of monomer or combination of monomers
- Formation of chain monomers as polymerization begins
- Formation of ladders as a result of cross linking between chain monomers
- Folding of monomer ladder to form spherical particles
- Agglomeration of microspheres, which give rise to formation of bunches of microspheres
- Binding of bunches to form microsponges
The polymerization process leads to the formation of a reservoir type of system, which opens at the surface through pores. In some cases an inert liquid immiscible with water but completely miscible with monomer is used during the polymerization to form the pore network. After the polymerization the liquid is removed leaving the porous microspheres, i.e., microsponges. Impregnating them within preformed microsponges then incorporates the functional substances. Some times solvent may be used for faster and efficient incorporation of the active substances. The microsponges act as a topical carriers for variety of functional substances, e.g. anti acne, anti inflammatory, anti purities, anti fungal, rubefacients, etc.
2) Quasi-Emulsion solvent diffusion method
All microsponges were prepared by a quasi-emulsion solvent diffusion method using an external phase of containing 200 ml distilled water and 40 mg polyvinyl alcohol (PVA) 72 000 (Tansel et al. 2003). The internal phase consisted of ketoprofen, ethyl alcohol, polymer and triethylcitrate (TEC), which was added at an amount of 20% of the polymer in order to facilitate the plasticity (Y Kawasima et al. 1993).
At first, the internal phase was prepared at 60°C and added to the external phase at room temperature. After emulsification, the mixture was continuously stirred for 2 hours. Then the mixture was filtered to separate the microsponges. The product was washed and dried by vacuum oven at 40°C for 24 hours.
Evaluation Parameters (D'Souza et al. 2005,Tansel et al. 2003)
Prepared Microsponges are generally evaluated for:
• Polymer composition
• Particle size (Microscopy)
• Surface topography (SEM)
• Pore Diameter
• Drug content
Offerings
• Advanced oil control
• Extended release
• Reduced irritation formulas
• Allows novel product form
• Improved product aesthetics
Benefits
• Advanced oil control - absorb up to 6 times its weight without drying
• Extended release - continuous action up to 12 hours
• Reduced irritation - getter tolerance means broader consumer acceptance
• Improved product aesthetics - gives product an elegant feel
Flexibility Benefits
• Improves stability - thermal, physical and chemical
• Allows incorporation of immiscible
• Improves material processing - liquid can be converted to powders
• Allows for novel product forms
Drugs explored in Microsponge delivery system (MDS) (Y Kawashima et al. 1992,D'Souza et al. 2005,Wster RC et al. 1991,Tansel et al. 2003)
• Kotoprofen
• Benzyl peroxide
• Retinol
• Fluconazole
• Ibuprofen
• Tretinoin
• Trolamine
About the Authors:
Geeta Patel* (M Pharm) and Dr.J K Patel (M Pharm, Ph.D)
Department of Pharmaceutics & Pharmaceutical Technology,
S. K. Patel College of Pharmaceutical Education and Research, Ganpat University, Kherva-382711. Gujarat, India.
*Corresponding Author: Geeta M Patel, Lecturer
Department of Pharmaceutics & Pharmaceutical Technology,
S. K. Patel College of Pharmaceutical Education and Research, Ganpat University, Kherva-382711. Gujarat, India. E-mail - geekhappy2002@yahoo.co.in
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