The advantages of starch microemulsions, such as their thermodynamic stability, spontaneous formation, easy scale-up, large interfacial area, nanosized droplets, isotropy, and low viscosity, make them applicable to many fields of science and technology. Furthermore, the high solubilization capacities of microemulsions for both organic and inorganic compounds make them useful in extraction processes. With these characteristics, starch microemulsions can be used to coat volatile or nonpolar compounds to increase their stability or solubility in food systems or during storage and processing. Starch microemulsions have potential utility in a wide range of systems, including in pharmaceuticals, edible oil recovery, targeted delivery systems for bioactive compounds, and the protection of nutrients and nutraceuticals.
- Introduction to Starch Microemulsions
- Starch Microemulsion Preparation
- Starch Microemulsion Properties
- Application of Starch Microemulsions to Foods
Drug Delivery
Starch microemulsions can be used as a type of controlled drug delivery system. Considerable research into starch microemulsions has been conducted in the past four decades: (1) to establish the basic principles of drug release from solid matrices, (2) to develop mathematical models of controlled drug release, (3) to synthesize new biocompatible polymers for the preparation of these controlled delivery systems, (4) to identify the parameters that affect the physical and chemical properties of microemulsions, and (5) to determine the release profiles of the incorporated drugs. Many excellent reviews have been published describing the progress that has been made and the challenges that remain in microemulsion technology.
Starch microemulsions have several specific advantages over other controlled drug delivery systems, including (1) that the rate of drug release and its duration can be tailored by altering the materials and fabrication techniques used; (2) that starch microemulsions are more stable than other controlled drug delivery systems, such as liposomes; and (3) that patient compliance is greater because the dosing frequency is lower.
“Drug targeting” refers to the oriented delivery of drugs to diseased tissues by exploiting the pH sensitivity, thermal sensitivity, or magnetism of the drug carrier. The methods of targeted drug delivery can be divided into the passive delivery and active methods. The passive delivery of a drug mainly depends on changes in the hydrophilic/hydrophobic character of the carrier surface and the size of the carrier. Active delivery systems can also transfer drugs to the necessary pathological sites in the human body under the guidance of an external magnetic field or the specific affinity of coupled ligands. This method not only reduces the possible toxic side effects but also reduces the quantity of drug required. Magnetic drug microemulsions contain drugs, magnetic particles, and framework materials. Fe3O4 and γ-Fe2O3 are the main magnetic particles used in targeted drugs. Generally, the framework is made of a polymer, such as albumin, chitosan, starch, glucosan, polyethylene glycol, or PVA. These materials have high biocompatibility and biodegradation. Drugs that have already been prepared as magnetic microemulsions include hydrochloric doxorubicin, mitomycin C, actinomycin D, etc. Currently, many commercial magnetic microemulsions or nanoemulsions are used as carriers for target drugs. A magnetic nanoemulsion, with starch-coated particles of 100 nm diameter, was developed and produced by Chemicell GmbH (Berlin, Germany), and a similar material has been made by another German company, Nano-Technologies GBR. However, most studies of targeted drugs that use magnetic carriers are still in the research stage.
Metal Ion Adsorbents
Heavy metal contamination of natural waters is both an environmental hazard and a threat to human health, especially through the food chain. Therefore, it is very important to develop effective ways to remediate heavy metal contamination [60]. Starch, an agricultural biopolymer, is highly attractive for industrial use because it is renewable, biodegradable, and inexpensive. However, starch by itself cannot be used satisfactorily to chelate or adsorb heavy metal ions, because it has no inherent chelating or metal-interacting capacity. Therefore, several approaches have been developed to utilize starch as a metal scavenger. Many studies have shown that modified starch has potential utility in adsorbing heavy metal ions from aqueous solutions. Among the various modified starches tested, starch microemulsions, with their microporous structures, are potentially very useful for wastewater treatment.
Topical Hemostasis
Starch microemulsions have been approved and used as topical hemostasis agents, absorbing excess fluid from the blood and concentrating endogenous coagulation factors to maintain hemostasis. Topical hemostatic agents are a heterogeneous group of products developed to complement traditional surgical techniques and to ensure hemostasis during surgery. They are applied to bleeding tissues and maintain hemostasis through different modes of action. They can be classified according to their working mechanisms as either passive or active agents or combinations of the two. Starch microemulsions have been used for many years to induce temporary vascular occlusion during the coadministration of cytotoxic drugs in the treatment of malignancies. Since 2002, starch microemulsions have also been approved for intraoperative applications and used clinically as topical hemostatic agents.
Embolization Agents
The treatment of nonresectable primary and secondary liver tumors is still problematic. Liver metastasis is the most frequent cause of death in patients with colorectal carcinoma after curative resection. Chemoembolization combines two palliative approaches, arterial chemotherapy and local tumor ischemia, providing both local advantages and longer cytostatic retention. Starch microemulsions, such as absorbable gelatin powder and prolamine, have been used as embolizing agents.