## 3 MIPs' Applications
### MIPs in Drug Delivery  
The ability of MIPs to bind strongly and selectively bioactive molecules makes these materials suitable for their potential application in biological field. The high loading capacity and the prolonged release time of the analytes, such as drugs, amounts to MIPs having a huge potential for creating suitable dosage forms [26]. In the last years, an area of great challenge in MIP technology is that of therapeutic agents, various MIPs have been used as unusual synthetic polymeric carriers to prepare drug delivery systems [175, 176]. An efficient drug delivery system should ensure that the drug is released at the right site, in the right dose and for the right period of time [177]. MIPs for drug delivery applications should have specific characteristics: the imprinted cavities should be stable to maintain the conformation in the absence of the template, but also flexible to facilitate the realization of a fast equilibrium between the release and re-uptake of the template in the cavity. To this end, the non-covalent imprinting provides faster equilibrium kinetics than the covalent imprinting approach [178, 179]. Furthermore, MIPs should be stable to resist enzymatic and chemical attacks and mechanical stress that can be found in biological fluids. Imprinted-drug delivery systems have not reached clinical applications yet because the adaptability of molecular imprinting technology for drug delivery requires important remarks on safety and toxicological concerns since the polymer devices will go into contact with biological tissues without causing toxic effects [180]. The MIPs are normally synthesized in organic solvents to improve hydrogen bonding and electrostatic interactions [178]. Nevertheless, the presence of organic solvents, commonly used in MIPs synthesis, may cause cellular damages. For this reason, in drug delivery processes, it is usually advantageous to prepare hydrophilic polymers which are compatible with biological systems. Alternatively precipitation polymerization method can be used since the polymer is usually completely immiscible with the solvent used for MIP preparation allowing easy polymer separation from the solvent [176]. Molecular imprinting water compatible is still under development and there are many problems due to the considerable weakness of hydrogen bonding and electrostatic interactions in water that decrease the selectivity of the MIP for the target molecule. However, metal coordination and hydrophobic interactions can be exploited to enhance template and functional monomer interactions [65, 181]. Recently, molecularly imprinted hydrogels for the recognition of cholesterol have been prepared by molecular design of methacrylate-based structures containing poly(ethylene glycol) in moderately and highly cross-linked networks. Swelling studies have been done to analyze the cross-linked structures of the prepared hydrogels and recognitive studies have been carried out to evaluate the influence of different reaction conditions on the ability of the systems to absorb cholesterol. The imprinted hydrogels have shown an excellent ability to recognize and release the analyte of interest [182]. In recent years, many researchers have published about the use of MIPs in drug delivery applications [179, 183] given their physicochemical properties to protect the drug from degradation by enzymes during systemic trafficking in the body. Several drugs have been used as templates to achieve polymeric devices, capable of prolonging the release profile of specific therapeutic agents with better performance as compared to more traditional drug delivery system [175]. The first report of imprinted polymers used as sustained release devices has been presented by [PERSON] and co-workers [184]. Theophylline-imprinted polymer has been prepared by a non-covalent approach for its possible application as a controlled release. The polymer obtained was able to sustain a slow drug release in pH 7.0 phosphate buffer for several hours.