The barrel is often manufactured in sections in order to shorten the residence time of molten materials. The extruder generally consists of one or two rotating screws (either corotating or counter rotating) inside a stationary cylindrical barrel. However, the theoretical approach to understanding the melt extrusion process (Figure 1) can be summarized by classifying the whole procedure of HME compaction into the following : (1) feeding of the extruder through a hopper, (2) mixing, grinding, reducing the particle size, venting, and kneading, (3) flow through the die, and (4) extrusion from the die and further downstream processing. During this process, polymers are melted and formed into products of different shapes and sizes such as plastic bags, sheets, and pipes by forcing polymeric components and active substances including any additives or plasticisers through an orifice or die under controlled temperature, pressure, feeding rate, and screw speed.

HME involves the compaction and conversion of blends from a powder or a granular mix into a product of uniform shape. Breitenbach first introduced the development of melt extrusion process in pharmaceutical manufacturing operations however, Follonier and his coworkers first examined the hot-melt technology to manufacture sustained release polymer-based pellets of various freely soluble drugs. Extrusion is the process of pumping raw materials at elevated controlled temperature and pressure through a heated barrel into a product of uniform shape and density. The technology (HME) has proven to be a robust method of producing numerous drug delivery systems and therefore it has been found to be useful in the pharmaceutical industry as well. With the advent of high throughput screening, currently more than half of all plastic products including bags, sheets, and pipes are manufactured my HME and therefore various polymers have been used to melt and form different shapes for a variety of industrial and domestic applications. Since then, it has been used in the plastic, rubber, and food manufacturing industry to produce items ranging from pipes to sheets and bags. Hot-melt extrusion technique was first invented for the manufacturing of lead pipes at the end of the eighteenth century. Process Technology of Hot-Melt Extrusion (HME) In this chapter, the hot-melt extrusion technique is reviewed based on a holistic perspective of its various components, processing technologies, and the materials and novel formulation design and developments in its varied applications in oral drug delivery systems. In addition to being a proven manufacturing process, HME meets the goal of the US Food and Drug AdministrationвЂ™s (FDA) process analytical technology (PAT) scheme for designing, analyzing, and controlling the manufacturing process via quality control measurements during active extrusion process. This makes HME an excellent alternative to other conventionally available techniques such as roll spinning and spray drying. Since the industrial application of the extrusion process back in the 1930вЂ™s, HME has received considerable attention from both the pharmaceutical industry and academia in a range of applications for pharmaceutical dosage forms, such as tablets, capsules, films, and implants for drug delivery via oral, transdermal, and transmucosal routes. HME has now provided opportunity for use of materials in order to mask the bitter taste of active substances.

To date HME has emerged as a novel processing technology in developing molecular dispersions of active pharmaceutical ingredients (APIs) into various polymer or/and lipid matrices which has led this technique to demonstrate time controlled, modified, extended, and targeted drug delivery. This paper reviews the innumerable benefits of HME, based on a holistic perspective of the equipment, processing technologies to the materials, novel formulation design and developments, and its varied applications in oral drug delivery systems. HME has already been demonstrated as a robust, novel technique to make solid dispersions in order to provide time controlled, modified, extended, and targeted drug delivery resulting in improved bioavailability as well as taste masking of bitter active pharmaceutical ingredients (APIs).

Over the last three decades industrial adaptability has allowed hot-melt extrusion (HME) to gain wide acceptance and has already established its place in the broad spectrum of manufacturing operations and pharmaceutical research developments.

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