Review of the Molecularly Imprinted Hydrogel In Chemical Analysis

PROCEEDING OF 3 RD INTERNATIONAL CONFERENCE ON RESEARCH, IMPLEMENTATION AND EDUCATION OF MATHEMATICS AND SCIENCE YOGYAKARTA, 16 17 MAY 2016 Review of the Molecularly Imprinted Hydrogel In Chemical Analysis C-20 Annisa Fillaeli Chemistry Education Department of Yogyakarta State University annisa_fillaeli@uny.ac.id Abstract The Molecularly Imprinted Hydrogel (MIH) is an insoluble polymer that the cavity has identical chemistry shape to the molecule target. This hydrogel is one of the Molecularly Imprinted Polymer (MIP) type commonly used in water solution. MIH is recently developed for chemical analysis needs. The MIH can give best analysis result. The analysis process should be aimed to get high accuracy and reproducibility in order to show the reliable result. It can be achieved by ensuring the supported instrument had similar character to the target molecule. The character is made by using the target molecule as an imprint in the polymer synthesis. After the extraction target molecule step, it will leave the identical cavity used to trap target molecule in the sample. The advantage of using MIH is the good result of external stimuli, such as ph, temperature, ionic strength, or electric field. Moreover, MIH can be used in various field. In pharmacy, MIH is used as carriers of drugs, proteins and glucose analysis which also show the stimuli-responsive behavior for its recognitions. Additionally, MIH is also used as separation media in particular direction such as food samples. Keywords: molecularly imprinted hydrogel (MIH), polymer, chemical analysis I. INTRODUCTION Polymer is defined as the substance that consists of molecules with one or more monomer units. A polymer is a repeating chain of atoms, formed from a binder in the form of identical molecules called monomers. Though usually an organic molecule (having a carbon chain), there are also many inorganic polymers. The use of polymers in the field of chemical analysis has been carried out. One of the goals in synthesizing polymer for this purpose is to provide material analysis support that can improve the quality of analytical results of accuracy, sensitively and reproducibility. Polymer modification to support chemical analysis can be done via imprinting techniques of molecule, common namely with Molecularly Imprinting Polymer (MIP). MIP is a polymer synthesis techniques using analyte molecules as its template. The molecule imprinting process in the polymer particles is generally carried out simultaneously with the process of monomer polymerization. Thereafter, the analyte molecules are extracted from the body of the molecule, so that part was originally imprinted the molecule into empty space with an identical shape to the imprinter molecules [1]. In the process of chemical analysis, e.g. for pretreatment separation, identical cavities can be used to trap molecules of the same/complement characters. This basic principle is also developed for polymers which have the character of swelling, such as the hydrogel. Printing molecules in hydrogel particles formed MIH is a new technique in the synthesis of MIP, which is very likely to grow rapidly. With the basic character of hydrogel is insoluble in water, the hydrogel can well interact in aqueous solvent systems. MIH which is considered safer in substance, the use of hydrogel polymer will not leave residue. In general, that usable imprinting hydrogel is already related in the polymer hydrogel body and have the same character with the hydrogel as a whole. Therefore, it is necessary to study the basic character of imprinting hydrogel, synthesis techniques and a variety of possible applications in chemical analysis. C-121

ISBN 978-602-74529-0-9 II. THE HYDROGEL Hydrogel is a polymer network that has the ability to swell in water. A hydrophilic gel that is often considered a hydrogel is a network of polymer chains that was found as a colloidal gel in which water acts as a dispersing medium. Researchers commonly define hydrogel as a substance that expands in water, have a crosslinking bond in the polymeric networks produced from the simple reaction of one or more monomers. Another definition states that polymeric materials have the ability to inflate and hold significant amounts of water in the structure, but insoluble in water. Hydrogel may be considered its usefulness performance in last 50 years based on their ability promising in various fields. Hydrogels also have a degree of flexibility that is similar to the body's tissue which also contains a lot of water [2]. The ability to absorb water in the hydrogel is derived from hydrophilic functional groups attached to the polymer backbone. As for why the water-insoluble hydrogel derived from crosslinking bonds between the polymer chains within the network. Many materials, both natural and synthetic polymer have the same definition with hydrogel. III. HYDROGEL CLASSIFICATION Hydrogel is classified in several groups. That is based on the origin, the composition of the polymer, the configuration of the structure, the type of cross-linker networks, the physical nature, and its electrical charges network. The origin of hydrogel consists of natural and artificial hydrogel. Additionally, the composition of the polymer is actually influenced by the method of preparation, so hydrogel is grouped into hydrogel homo-polymer, copolymer hydrogel and hydrogel multi-polymer. Homo-polymer hydrogel is a network polymer derived from a monomer having basic structure consisting of any polymer network. Homo-polymers may have crosslinking at the chain structure depend mainly on the basic character of the polymer and polymerization techniques. Hydrogel copolymers consisted of two or more different species of monomer with at least one hydrophilic component, composed of random, block or alternate configuration along the polymer chain. Multi-polymer Interpenetrating Polymeric Hydrogel (IPN), one type of important hydrogel, is made of two independent synthetic crosslinking or polymers in the form of a network. Based on the configuration of physical structure and chemical compositions, hydrogel is classified into an amorphous (non-crystalline), semi-crystalline (a complex mixture of amorphous and crystalline phases), and crystalline. While from the type of cross-linking bond, hydrogel is divided into the origin of the intersection of physical, or chemical crosslinking. Chemical crosslinking network has a permanent junction, although a network of physics intersections has a well-formed polymer chain involved or of physical interaction such as ionic interactions, hydrogen bonding or hydrophobic interactions. Furthermore, based on their physical appearance, hydrogen recognized as a matrix, thin layer films or microspheres depending on the polymerization technique used in the preparation stage. Other classification is based on electric charge network, hydrogel is divided into four categories based on the presence or absence of electrical charge that is located on a chain crosslinking non-ionic (neutral), ionic (including anion or cation), electrolyte amphoteric (ampholytic) contain both acid groups and base, or zwitter-ion, ion containing both anionic and cationic groups at each repeat unit structure [3]. IV. HYDROGEL AND IMPRINTED HYDROGEL POLYMERIZATION TECHNIQUES Hydrogels have adequate network crosslinking polymers with three dimensional hydrophilic bonding to constrict reversibly expands in water and leaving a large volume of fluid in the form of deployment. Hydrogel can be designed with a response that can be controlled to shrink and swell with changes in the external environment. Hydrogel can show the dramatics volume in transition response to various stimuli physics and chemistry where physical stimuli are temperature, electric charge or magnetism, light, pressure, and sound while chemical stimuli include ph, solvent composition, ionic strength and the molecular species. Further expand or shrink response to change in the external environment can be very drastic for hydrogel as a known phenomenon which is called volume collapse or transition phase. Generally, three main parts in the synthesis of hydrogel is the monomer, initiator and cross-linker. To control the heat of polymerization reaction, and the final properties of hydrogel, solvent can use, for example, water, or other aqueous solutions. Then, the hydrogel mass is washed to clean impurities or residual constituents. C-122

C-123 PROCEEDING OF 3 RD INTERNATIONAL CONFERENCE ON RESEARCH, IMPLEMENTATION AND EDUCATION OF MATHEMATICS AND SCIENCE YOGYAKARTA, 16 17 MAY 2016 Synthesis hydrogel using acrylamide, acrylic acid or salt thereof by suspense and dissolution polymerization were more choosen. Hydrogel is generally made from polar monomer. Based on the basic material, hydrogel polymer can be classified as natural, synthetic polymer hydrogel and a combination of both types. Based on the preparation method, hydrogel can be obtained by graft polymerization, cross-linking polymerization, formation of a water-soluble polymer, and the formation of crosslinking by radiation. Polymerization techniques used are bulk polymerization, solution polymerization, suspension polymerization, polymerization with grafting technique/ coating, and radiation polymerization [2]. Most vinyl monomers potential to be synthesized as a hydrogel. Bulk hydrogels can be formed with one or more types of monomers. There are a wide variety of vinyl monomers to prepare a hydrogel with the desired physical properties. A small amount of crosslinking agent need to be added in the right formula. The polymerization reaction is generally initiated by radiation, ultraviolet light or chemical catalyst. Selection of the appropriate initiator based on the considerations in monomer and solvent used. The resulting hydrogel can be a membrane, rod, granular particles and emulsified. Bulk polymerization technique is a way of easiest hydrogel synthesis. The result is a homogeneous hydrogel, clear like glass, has a transparent matrix and very hard texture. However, when immersed in water, the glassy matrix swell to become soft and flexible [4]. In solution polymerization, or known as cross-linking polymerization, the solvent served as a hot reducer becomes a major advantages of the synthesis technique compared to bulk polymerization. Certain solvents used for the hydrogel polymerization such as water, ethanol, a mixture of water-ethanol and benzyl alcohol. Suspension polymerization or dispersion polymerization has its own advantages because the resulted particle are shaped in beads, so it does not require grinding step. Generally, the hydrogel from bulk polymerization techniques have an inherent weak structure. To improve mechanical properties, a mixture essentially can be deposited on a surface area supporting more robust / stable. So it can be said directly over the polymerization process that supported solids with generally covalent bonded have interaction between polymers and surfaces. The last of hydrogel polymerization techniques is irradiation with high energy. Gamma rays and electron beams are used as initiator. The irradiation charged on aqueous polymer solution produce radicals on the polymeric chains. The combination of radicals from different chain will form a cross-linking structure in the polymer network. Reviewing of the hydrogel polymerization techniques, it can be built the imprinting polymer that the molecule template must become a member of supporting polymer pore along polymerization process. From all of polymerization techniques, the template molecule should be added initially together with the monomer, initiator/catalyst, and cross-linker agent. After the imprinted polymer has been resulted, the template directly extracted from the polymer networks. Thereafter, the complement pore that have identical shape with the template molecule are established. After all, the final polymer are known as molecularly imprinted hydrogel (MIH). Synthesizing the imprinting molecules into organic polymer is first reported by Wulff and Sarhan (1972 in [4]), which recently become a technique widely used in the preparation of polymeric materials with molecular recognition side. The material is applied as a separation media, the sensor element and the catalyst. Step through molecular imprinting techniques polymerization is overcoming between monomers and the molecular imprinter (templates). Complex formation spontaneously happen with a porogenic solvent which sterically set during crosslinking polymerization. The density of crosslinking is determined by the number/amount of crosslinking agent (stoichiometry). After releasing of imprinter molecules from the polymer matrix, artificial identifier will be formed. The template-monomer complex can be formed either by covalent or weak non-covalent interactions (e.g. hydrophobic interaction, ionic and hydrogen bonding [4]. The type of polymerization is selected in addition to the main predictions result considered a functional monomer selection. For example, polymerization of monomer polyvinyl alcohol can be determined in the form of addition polymerization, Vinyl alcohol has a bond that will form a series of polymers with the aid of crosslinking agents and an intermediate form of radical anion or cation. The results of the polymerization will not contain side products, besides the remaining of excess solvent. Cationic addition polymerization is initiated by the acid added to the compound of the double bond to form a cation. These cations play a role in the propagation stage to form a polymeric chain. The acid used is phosphoric acid or sulfuric acid as a catalyst / initiator. MIH can be prepared in various ways for this type of selected polymerization. It can be bulk polymerization (bulk polymerization) or suspension polymerization (suspension polymerization) [5]. Each method has its advantages and limitations. Bulk polymerization method has an advantage in terms of the simplest polymerization technique, does not require special skills and special instrumentation. However, the limited ability of bulk polymerization in terms of the product is not uniform in size, which automatically requires a stage pulverization and particle size selection for specific needs (such as column chromatography material). Furthermore,

ISBN 978-602-74529-0-9 bulk polymerization also has low performance. Suspension polymerization is more likely done to overcome the polymer particle size uniformity. The resulting particles has spherical granules, high reproducibility, and can be produced on a large scale [6]. V. APPLICATION OF MOLECULARLY IMPRINTED HYDROGEL Hydrogel, a water insoluble material, has a crosslinking polymer network consisting of homo or hetero hydrophilic polymer, which has ability to absorb significant amounts of water. From the biological point of view, these properties are important because this character is very similar with natural tissue that minimizes possible irritation of the membranes or tissues nearby. Based on this reason, the imprinting hydrogel is widely used in pharmaceutical field, such as delivery agent of various drugs, peptides or proteins. Recently, most of the gel that sensitive to analyte is not completely synthetic, but it is used the proteins in a polymer matrix as a sensor or activating mechanism. The use of a protein, lectin and other component were incorporated into immunogenic targets along the gel during the synthesis process procedures for the good analyte identification system, which is actually similar, and has a specific cluster included to bind the analyte and demonstrated cross-reactivity to bind the other similar analyte. In other words, it is showing immunogenicity at a higher level. In this section, molecular imprinting bridging it, and so it produces architectural chemical precision that can bind the analyte and distinguish isomers [2]. The design of molecularly imprinted hydrogel for controlled release of cisplatin has been studied [7]. The cisplatin, a widely used metal-based antineoplastic drug that able to have therapeutic activity against several solid tumors along with testicular cancer, ovarian cancer, lymphoma and glioma, becomes the template molecule that together with methacrylic acid (MAAc), 2-hydroxyethylmetacrylate (HEMA) as based hydrogel and NN - metylenebisacrylamide (NN-MBA) as cross-linker, develops MIP hydrogels. The schematic reaction is shown below. Figure 1. The formation of MIH with cisplatin as a template [7] Both molecular imprinted and non-imprinted polymers that were synthesized has been used to study the swelling character and the in vitro dynamics release of drug. This hydrogels product is hoped for tumor therapy through slow release of cisplatin with the specified time according to the particular dosage. The research results showed that the C-124

PROCEEDING OF 3 RD INTERNATIONAL CONFERENCE ON RESEARCH, IMPLEMENTATION AND EDUCATION OF MATHEMATICS AND SCIENCE YOGYAKARTA, 16 17 MAY 2016 swelling parameter was reduced by increasing amount of NN-MBA. Both in the MIH and NIH (non-imprinted hydrogel) in terms of releasing the drug will be lower with the higher NN - MBA because crosslinking density is higher and smaller particle size. Because of its supramolecular interactions, MIP can be used for the development of biomimic drug delivery devices. Of course this should be supported by the application of this MIH-cisplatin in vivo environments. Other hydrogel imprinting products in pharmaceutical development as drug delivery device is the synthesis of molecularly imprinted stimuli-reponsive hydrogel for protein recognition [8]. By using acrylamide based hydrogel via in situ photo-initiated crosslinking polymerization, MAAc and NN-MBA were synthesized with lysozyme as a template to produce MIH protein recognition. The results showed that MIH was higher than NIH in terms of protein binding capacity and selectivity towards lysozyme and the temperature-responsive swelling-deswelling of the materials modulated the binding ability. The introduction of proteins and signal transduction can be combined in one material for selective protein to MIP hydrogel. This also leads to deswelling ability. Reached such great effects made possible by the combination of hydrogel imprinting matrix. It showed the critical phase transition. Responding to the protein recognition / binding, this result will allow to the additional functions of the hydrogel, for example the development of protein (micro) sensor based measurement swelling and pressure. Furthermore, the new release of MIH that display isomerically resolved glucose is also proposed by combining poly(allylamine hydrochloride)(paa-hcl) with glucose phosphate mono-sodium salt binding [9]. This hydrogel is synthesize in order to provide biosensor quantitatively glucose in monitoring diabetic blood. In this study, epichlorohydrin (EPI), ethylene glycol diglycidyl ether (EDGE) and glycerol diglycidyl ether (GDE) were used as cross-linker. The last three of cross-linker has their own type of crosslinking type within polymer networks. Researcher sure that there are relation between polymer binding capacity to the analyte and the cross-linking amount in the polymeric network. And so, these crosslinking models are shown in figure 2. Figure 2. The crosslinking reaction and cross-linker used in MIH synthesis [9] The results showed that MIH using EPI decrease the glucose binding capacity as increasing the amount of imprint. As the smaller crosslinking than EDGE, it could be expected that EDGE will give quite the same data. But the EDGE data showed that the binding capacity has linier pattern to the increasing of imprint present. Others, the GDE gives different result. The trend observed that as the concentration of imprint increase, both the glucose and fructose binding capacity decrease. But the mechanical integrity of using GDE was very poor when compared to the used of EPI and EDGE. Approximately 25% of each polymer was lost because it has excessive fracture, giving the C-125

ISBN 978-602-74529-0-9 hydrogel was so inconsistency. So much efforts to be made of optimizing the MIH capability and the factors that affect its properties. The next step is to make MIH-fructose in enhancing the bonding capacity and selectivity for recognition alike glucose hydrogel. Beside the pharmaceutical applications, the MIH is also used in the food field research. One of this application is the use of Caffeine molecularly imprinted poly(vinyl alcohol) hydrogel in selectivity study to separate contained caffeine in some commodity. It is developed by using polyvinyl alcohol as the monomer, glutaraldehyde as crosslinker and sulphuric acid as the catalyst. This hydrogel is made for environmental reason due to the last caffeine imprinted polymer has the toxic monomer. So it was very worry to apply the hydrogel in the food samples [10]. This recently hydrogel produce in membrane separation by reacting of monomer and cross-linker in the gaseous state to decrease poisonous potency from its nature. The result indicated that the imprinted hydrogel was successful made. The caffeine imprinted hydrogel absorbs a higher amount of caffeine than non-imprinted ones. The hydrogel was in the membrane form, with transparent, homogenous and have good resistance to solvent action, owing to crosslinking. VI. CONCLUSION Molecularly imprinted hydrogel can be synthesized with availability of the monomer, cross-linker and initiator/catalyst via several polymerization techniques. Most of synthesized hydrogel give the good result in pharmaceutical field as drug delivery and also in protein and glucose recognitions. The imprinted hydrogel is also used in food samples as caffeine media separation. VII. REFERENCES [1] Börje Sellergren (2001). Molecularly Imprinted Polymers: Man-made mimics of antibodies and their applications in analytical chemistry. Amsterdam: Elsevier. [2] Ahmed EM. Hydrogel: Preparation, characterization, and applications. J Adv Res (2013), http://dx.doi.org/10.1016/j.jare.2013.07.006. [3] Byrne ME, Park K, and Peppas NA. Molecular Imprinting within Hydrogels. Advanced Drug Delivery Reviews 54 (2002) 149-161. [4] Walach Anna K. Molecularly Imprinted Hydrogels for Application in Aqueous Environment. Polym. Bull. (2013) 70:1647-1657. [5] Pérez-Moral,N dan Mayes, A.G. Comparative study of imprinted polymer particles prepared by different polymerization methods. Analytica Chimica Acta 504 (2004) 15 21. [6] Pena EB, Vallejo VG, Yuste AR, Pereira LB, Cruz JM, Bilbao A, Lorenzo CA and Bondi MCM. Molecularly Imprinted Hydrogels as Functional Active Packaging Materials. Food Chemistry 190 (2016) 487-494. [7] Singh B, Chauhan, and Sharma V. Design of molecular imprinted hydrogel for controlled release of cisplatin: evaluation of network density of hydrogels. Ind. Eng. Chem. Res. 20011, 50, 13742-13751. [8] Adrus N and Ulbricht M. Molecularly imprinted stimuli-responsive hydrogels for protein recognition. Polymer 53 (2012) 4359-4366. [9] Wizeman and Kofinas. Molecularly imprinted polymer hydrogels displaying isomerically resolved glucose binding. Biomaterials 22 (2001) 1485-1491. [10] Patachia S, Croitoru C and Scarneciu I. Selectivity studies of molecularly imprinted poly(vinyl alcohol) hydrogels. Environmental Engineering and Management Journal 10 (2011), 2, 175-179. C-126