6 Molecularly Imprinted Polymers—Preparation, Biomedical Applications and Technical Challenges

Advances in Molecularly Imprinted Polymers as Drug Delivery Systems

Despite the tremendous efforts made in the past decades, severe side/toxic effects and poor bioavailability still represent the main challenges that hinder the clinical translation of drug molecules. This has turned the attention of investigators towards drug delivery vehicles that provide a localized and controlled drug delivery. Molecularly imprinted polymers (MIPs) as novel and versatile drug delivery vehicles have been widely studied in recent years due to the advantages of selective recognition, enhanced drug loading, sustained release, and robustness in harsh conditions. This review highlights the design and development of strategies undertaken for MIPs used as drug delivery vehicles involving different drug delivery mechanisms, such as rate-programmed, stimuli-responsive and active targeting, published during the course of the past five years.

Separation and determination of trace environmental estrogen through molecularly imprinted solid phase extraction coupled to high performance liquid chromatography

In recent years, there has been an increasing demand on the determination of trace environmental estrogen. In this study, a new 17β-estradiol molecularly imprinted polymer was successfully synthesized on the surface of activated silica gel. This prepared molecularly imprinted polymer was characterized, and found to exhibit good recognition, high selectivity, and a rapid adsorption-desorption dynamic toward 17β-estradiol. Using the molecularly imprinted polymer as a sorbent, an effective method of solid phase extraction coupled to high performance liquid chromatography for the separation and determination of 17β-estradiol was developed. Under optimal conditions, the detection limit (S/N = 3) of 17β-estradiol was 12.0 ng L(-1). The enrichment factor was 198, and the linear range of the calibration graph was 0.05-300 mg L(-1). Blank water samples spiked with 17β-estradiol at three different levels were analyzed by the developed method to afford recoveries ranging from 82.7% to 103.0%. Moreover, this presented method was applied to the quantitative detection of 17β-estradiol in a polluted water sample with a level of 0.024 mg L(-1).

Molecularly imprinted polymers: present and future prospective

Molecular Imprinting Technology (MIT) is a technique to design artificial receptors with a predetermined selectivity and specificity for a given analyte, which can be used as ideal materials in various application fields. Molecularly Imprinted Polymers (MIPs), the polymeric matrices obtained using the imprinting technology, are robust molecular recognition elements able to mimic natural recognition entities, such as antibodies and biological receptors, useful to separate and analyze complicated samples such as biological fluids and environmental samples. The scope of this review is to provide a general overview on MIPs field discussing first general aspects in MIP preparation and then dealing with various application aspects. This review aims to outline the molecularly imprinted process and present a summary of principal application fields of molecularly imprinted polymers, focusing on chemical sensing, separation science, drug delivery and catalysis. Some significant aspects about preparation and application of the molecular imprinting polymers with examples taken from the recent literature will be discussed. Theoretical and experimental parameters for MIPs design in terms of the interaction between template and polymer functionalities will be considered and synthesis methods for the improvement of MIP recognition properties will also be presented.

The biomimetic immunoassay based on molecularly imprinted polymer: a comprehensive review of recent progress and future prospects

Immunoassay, based on a selective affinity of the biological antibody for its antigen, is one of the most usual analytical methods in food safety and environmental chemistry. However, it presents several drawbacks because of the nature of the antibody. Molecular imprinting technique, due to its high selectivity and stability, ease of preparation and low cost, has shown great potential in producing artificial antibodies in biomimetic immunoassays. This article focuses on the recent states, advantages, current problems and outlooks of molecularly imprinted radio, fluoro, enzyme-linked and chemiluminescent immunoassays, and biomimetic immunosensor, with special emphasis on the challenges in developing biomimetic enzyme-linked immunosorbent assays (BELISAs). The biomimetic immunoassay method will provide an important new analysis platform in food safety, although the sensitivity and specificity is relatively low.

PRACTICAL APPLICATION

As a new simple analysis method, the biomimetic immunoassay has attractive prospect, although some limitations were existed in real-sample assay. In this critical review, some promising solutions for overcoming its drawbacks were put forward, which may promote the more quick development and extensive application of this method in food safety.

Novel biphasic separations utilising highly selective molecularly imprinted polymers as biorecognition solvent extraction agents

Molecularly imprinted polymers (MIPs) represent a class of artificial receptors that promise an environmentally robust alternative to naturally occurring biorecognition elements of biosensing devices and systems. However, in general, the performance of conventional MIPs in aqueous environments is poor. In the study reported here, this limitation has been addressed by the novel application of MIPs as a solvent extraction solid phase in a biphasic solvent system. This paper describes a previously unreported use of MIPs as solvent extraction reagents, their successful application to aqueous sample media and the opportunities for utilisation of this unique system in novel biosensing and separation procedures. This study demonstrates the development of a novel biphasic solvent system utilising MIP in the extracting phase to enhance both efficiency and selectivity of a simple two phase liquid extraction. Monodisperse propranolol imprinted polymer microspheres [p(divinylbenzene-co-methacrylic acid)] were prepared by precipitation polymerisation. Initially, the affinity of the polymers for (R,S)-propranolol was assessed by established techniques whereby the MIP demonstrated greater affinity for the template than did the non-imprinted control polymer (NIP). Importantly, MIP performance was also assessed using the novel dual solvent system. The depletion of (R,S)-propranolol from the aqueous phase into the polymer containing organic phase was determined. When compared to control extractions containing no polymer the presence of MIP in the extracting solvent phase resulted in an increased extraction of (R,S)-propranolol from the aqueous phase. Importantly, this extraction was significantly greater in the presence of MIP when compared to NIP. This unique principle generates opportunities for MIP based extractions and chemical enrichments in industrial applications, offering commercial, ecological and practical advantages to traditional solvent extraction techniques. The technique is readily transferable to analytical microsystems utilising MIP recognition elements generating promising opportunities for MIP based sensing of aqueous sample media.

Concentration dependent atrazine–atrazine complex formation promotes selectivity in atrazine imprinted polymers

An atrazine (ATR) molecularly imprinted polymer (MIP) was prepared using a non-covalent strategy. The affinity and selectivity of the polymer was initially evaluated under non-equilibrium conditions and the polymer was shown to possess good template selectivity. The selectivity of the polymer was further investigated under equilibrium conditions and over a range of concentrations using Scatchard plots and Hill plots and by assessing distribution coefficients and normalised selectivity values. It was observed that both selectivity and affinity were dependent on the concentration of the ligand and that unusually selectivity and affinity were better at higher atrazine concentrations. It was concluded that this phenomenon resulted from the formation of atrazine-atrazine complexes during the pre-polymerisation stage and during rebinding and that the polymer demonstrated improved atrazine affinity when the conditions favoured complex formation.

Enthalpy changes associated with protein binding to thin films

Molecularly imprinted thin films consisting of proteins embedded in polymerised aminophenyl boronic acid have been made on glass supports. The protein contents of the films have been optimised to achieve a maximum energy of interaction between the film and the native template. The fabrication of the films and the subsequent removal from their surfaces of the imprint proteins has been shown to be a facile and easily reproduced process. The enthalpy changes associated with the rebinding of the films with their original templates (lysozyme and cytochrome c) and with non-native templates has been examined by micro-calorimetry. The results demonstrate that thin films can be successfully imprinted as shown by the significant reduction in the enthalpy (DeltaH) observed when the films were rebound with proteins other than the original templates. Additionally, it was shown that after binding, non-template proteins could be removed by washing and a greater enthalpy again observed when the films were rebound with the native protein compared to that which had been found with the non-native protein.

Molecularly imprinted polymers for drug delivery

Molecular imprinting technology has an enormous potential for creating satisfactory drug dosage forms. Although its application in this field is just at an incipient stage, the use of MIPs in the design of new drug delivery systems (DDS) and devices useful in closely related fields, such as diagnostic sensors, is receiving increasing attention. Examples of MIP-based DDS can be found for the three main approaches developed to control the moment at which delivery should begin and/or the drug release rate, i.e. rate-programmed, activation-modulated, or feedback-regulated drug delivery. The utility of these systems for administering drugs by different routes (e.g. oral, ocular or transdermal) or trapping undesired substances under in vivo conditions is discussed. This review seeks to highlight the more remarkable advantages of the imprinting technique in the development of new efficient DDS as well as pointing out some possibilities to adapt the synthesis procedures to create systems compatible with both the relative instable drug molecules, especially of peptide nature, and the sensitive physiological tissues with which MIP-based DDS would enter into contact when administered. The prospects for future development are also analysed.

Spectroscopic anatomy of molecular-imprinting of cyclodextrin. Evidence for preferential formation of ordered cyclodextrin assemblies

The processes of molecular-imprinting of beta-cyclodextrin (beta-CyD) with cholesterol and stigmasterol (cross-linking agent = diisocyanate) have been analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy. These templates enormously promote the formation of dimers and trimers of beta-CyD, which are only inefficiently formed in their absence. These ordered assemblies are the guest-binding sites, in which two or three beta-CyD molecules cooperate to bind large steroids. Ordered assemblies are also formed when 2,6-di-O-methyl-beta-cyclodextrin is used in place of beta-CyD. Direct spectroscopic evidence for molecular-imprinting effect has been obtained. Molecular imprinting of CyDs is potent for tailor-made preparation of synthetic receptors for nanometer-scaled guests.

Synthesis and evaluation of molecularly imprinted polymers for extracting hydrolysis products of organophosphate flame retardants

A molecularly imprinted polymer (MIP) that selectively retains diphenyl phosphate was prepared using a structural analogue, ditolyl phosphate, as a template. Diphenyl phosphate is a degradation product of the flame retardant additive, triphenyl phosphate. The latter has been shown to be a common airborne contaminant in indoor environments and to be emitted from various goods such as video display units. Triphenyl phosphate induces several documented biological responses, including allergenic effects. Two different polymers, one prepared from methacrylic acid and the other from 2-vinylpyridine (2-Vpy), were investigated for their ability to recognise diphenyl phosphate. The polymers were used in solid-phase extraction cartridges (MISPE) and evaluated by comparing their recovery and breakthrough parameters with those of corresponding non-imprinted polymers (NIPs). The polymer made from the basic monomer showed the most selective recognition to the acidic analyte. Diphenyl phosphate was adsorbed to the basic MIP (2-Vpy-MIP) when methanol was used as mobile phase, and approximately 80% of the analyte was recovered when eluted from this polymer using a mixture of methanol and trifluoroacetic acid. There was a clear difference in the retention strengths of 2-Vpy-MIP and the corresponding 2-Vpy-NIP. The selectivity of the investigated 2-Vpy-MIP polymer towards a structural analogue of diphenyl phosphate, di(2-ethylhexyl) phosphate was also assessed. This compound was less strongly retained using the same experimental conditions. The results indicate that the prepared 2Vpy-MIP strongly recognises diphenyl phosphate due to the imprinting effect. This interaction probably arises mostly from an ionic interaction between the basic monomers and the acidic analyte. An LC-electrospray ionisation multiple MS method, using negative ion detection and ion-pair chromatography, was developed for separation and quantification of the strongly acidic dialkylated phosphate esters. The instrumental limit of detection was below 50 pg for all investigated compounds and the MS method was shown to be linear in the investigated range of 0.05-85 ng.