Networks for recognition of biomolecules: molecular imprinting and micropatterning poly(ethylene glycol)- Containing films

Thermo- and pH-Responsible Gels for Efficient Protein Adsorption and Desorption

Protein adsorption behavior was examined on poly(N-isopropylacrylamide-co-sodium methacrylate)-based hydrogels at different temperatures: 5, 20, and 37 °C, and pH: 4.5, 7, and 9.2. The hydrogels, whose covalent skeleton contains pendant anionic units due to the presence of the sodium methacrylate co-monomer, exhibited both thermo- and pH-sensitivity with different extents, which depended on the content of ionizable moieties and the cross-linker density. The hydrogel composition, temperature, and pH influenced the zeta potential of the hydrogels and their swelling properties. The proteins selected for the study, i.e., bovine serum albumin (BSA), ovalbumin (OVA), lysozyme (LYZ), and a monoclonal antibody (mAb2), differed in their aminoacidic composition and conformation, thus in isoelectric point, molecular weight, electrostatic charge, and hydrophobicity. Therefore, the response of their adsorption behavior to changes in the solution properties and the hydrogel composition was different. LYZ exhibited the strongest adsorption of all proteins with a maximum at pH 7 (189.5 mg ggel-1); adsorption of BSA and OVA reached maximum at pH 4.5 (24.4 and 23.5 mg ggel-1), whereas mAb2 was strongly adsorbed at 9.2 (21.7 mg ggel-1). This indicated the possibility of using the hydrogels for pH-mediated separation of proteins differing in charge under mild conditions in a water-rich environment of both the liquid solution and the adsorbed phase. The adsorption affinity of all proteins increased with temperature, which was attributed to the synergistic effects of attractive electrostatic and hydrophobic interactions. That effect was particularly marked for mAb2, for which the temperature change from 5 to 37 °C caused a twentyfold increase in adsorption. In all cases, the proteins could be released from the hydrogel surface by a reduction in temperature, an increase in pH, or a combination of both. This allows for the elimination of the use of salt solution as a desorbing agent, whose presence renders the recycling of buffering solutions difficult.

Temperature- and pH-responsive poly(N-isopropylacrylamide-co-methacrylic acid) microgels as a carrier for controlled protein adsorption and release

Herein, we report controlled protein adsorption and delivery of thermo- and pH-responsive poly(N-isopropylacrylamide-co-methacrylic acid) (PNIPAM-co-MAA) microgels at different temperatures, pH values and ionic strengths by employing bovine serum albumin (BSA) as a model protein. For these dual-responsive microgels, we found that the BSA adsorption was driven by several of six competing contributions, viz., physical diffusion (PD), hydrophobic interactions (HI), electrostatic attraction (EA), hydrogen bonding (HB) and temperature or pH-induced seizing action (SA_T or SA_pH), depending on the temperature and pH of the solution. Compared to the pure PNIPAM microgels, the higher swelling degree of the PNIPAM-co-MAA microgels allowed a large amount of BSA loading under any experimental conditions. A largest BSA adsorption of 45.1 μg mg^-1 was achieved at 40 °C and pH 4 due to the presence of all six contributions. The BSA adsorption and delivery could be further tuned by changing the crosslinking density within the microgels. The BSA binding onto the microgels was found to be ionic strength dependent, which could be attributed to the charge shielding of Na⁺ ions, salting out of BSA and aggregate formation of the microgels. The adsorbed BSA could be controllably released by adjusting the temperature and pH of the experiment, and with the help of sodium dodecyl sulphate (SDS) addition so as to eliminate each interaction between BSA and the microgels. Thus, this study can be useful to design a stimuli-responsive microgel-based carrier for controlled release of proteins.

Adsorption dynamics of thermoresponsive microgels with incorporated short oligo(ethylene glycol) chains at the oil-water interface

Herein, we report a systematic study of the adsorption behaviour of short oligo(ethylene glycol) (OEG) chains incorporated into poly(N-isopropylaccrylamide) (PNIPAM) microgels at the dodecane-water interface as a function of the microgel concentration at two different temperatures: 298 and 313 K. The dynamic interfacial tension of the interface for the adsorption of these functional microgels is measured by means of a pendent drop method. We find that similar to pure PNIPAM microgels, the functionalized microgels initially get transported from the bulk to the interface, where they undergo the deformability dependent spreading process, and thus leading to a reduction of interfacial tension. However, the OEG chains significantly influence the dynamic processes of the microgels at the interface, enabling precise control over the interfacial activity. A tuneability of adsorption behaviour that is interpreted in terms of the diversity of structural and morphological features of the microgels, can be achieved by changing the temperature and/or the OEG chain length of the comonomer. While the temperature induced phase transition generally slows down the adsorption kinetics of the microgels, increasing the temperature from 298 to 313 K allows faster reduction of interfacial tension for the adsorption of the microgels with long OEG chains among the studied comonomers, making them a unique interfacially active functional material. Overall, incorporation of OEG chains allows tailoring the interfacial activity of microgels, thereby paving the way for the use of these microgels to act as effective Pickering emulsion stabilizers in a range of applications.

Short oligo(ethylene glycol) chain incorporated thermoresponsive microgels: from structural analysis to modulation of solution properties

Herein, we report synthesis of thermoresponsive poly(N-isopropylaccrylamide) (PNIPAM) microgels with short oligo(ethylene glycol) (OEG) chain comonomers (1 to 4/5 repeating unit) by surfactant-free precipitation copolymerization. The efficient incorporation of the comonomers was confirmed by a complete set of characterization methods viz., FTIR, 1H NMR, TEM, DLS, and viscometry. The structural heterogeneity and the distribution of the comonomers within the microgels were determined by means of 1H high-resolution transverse relaxation magnetization measurements. Interestingly, the incorporation of these short OEG chain comonomers led to the formation of a core-corona structure, in which the comonomers were mainly located in the core of the polymeric network with PNIPAM dangling chains at the microgel periphery. The experimental investigations of deswelling behaviours revealed that the OEG chains allowed precise control over the colloidal properties, including phase transition, particles size, swelling degree and polydispersity of the microgels. The tuneability of these properties that was interpreted in terms of polymeric hydrophobic/hydrophilic balance as well as structural diversity, could be achieved by changing the OEG chain length, comonomer feed and crosslinking density. Further, we found that the microgels with more hydrophilic OEG chains were able to show a higher relative swelling, and the same solid content thus led to a higher viscosity at all temperatures. The OEG chains remarkably improved the colloidal stability of the microgels in electrolyte solutions even at higher temperatures, thereby paving the way for the use of these microgels in a range of applications.

Molecular recognition with soft biomaterials

Biomacromolecules and engineered materials can achieve molecular recognition if they engage their ligand with properly oriented and chemically complementary moieties. Recently, there has been significant interest in fabricating recognitive soft materials, which possess specific affinity for biological analytes. We present a summary and evaluation of current recognitive materials for biosensing, drug delivery, and regenerative medicine applications. We highlight the impact of material composition on the extent and specificity of ligand adsorption, citing new theoretical and empirical evidence. We conclude with a guide for synthesizing and characterizing novel recognitive materials, as well as recommendations for ligand selection and experimental design.

Modular Fabrication of Intelligent Material-Tissue Interfaces for Bioinspired and Biomimetic Devices

One of the goals of biomaterials science is to reverse engineer aspects of human and nonhuman physiology. Similar to the body's regulatory mechanisms, such devices must transduce changes in the physiological environment or the presence of an external stimulus into a detectable or therapeutic response. This review is a comprehensive evaluation and critical analysis of the design and fabrication of environmentally responsive cell-material constructs for bioinspired machinery and biomimetic devices. In a bottom-up analysis, we begin by reviewing fundamental principles that explain materials' responses to chemical gradients, biomarkers, electromagnetic fields, light, and temperature. Strategies for fabricating highly ordered assemblies of material components at the nano to macro-scales via directed assembly, lithography, 3D printing and 4D printing are also presented. We conclude with an account of contemporary material-tissue interfaces within bioinspired and biomimetic devices for peptide delivery, cancer theranostics, biomonitoring, neuroprosthetics, soft robotics, and biological machines.

Student award for outstanding research winner in the Ph.D. category for the 2017 society for biomaterials annual meeting and exposition, april 5-8, 2017, Minneapolis, Minnesota: Characterization of protein interactions with molecularly imprinted hydrogels that possess engineered affinity for high isoelectric point biomarkers

Molecularly imprinted polymers (MIPs) with selective affinity for protein biomarkers could find extensive utility as environmentally robust, cost-efficient biomaterials for diagnostic and therapeutic applications. In order to develop recognitive, synthetic biomaterials for prohibitively expensive protein biomarkers, we have developed a molecular imprinting technique that utilizes structurally similar, analogue proteins. Hydrogel microparticles synthesized by molecular imprinting with trypsin, lysozyme, and cytochrome c possessed an increased affinity for alternate high isoelectric point biomarkers both in isolation and plasma-mimicking adsorption conditions. Imprinted and non-imprinted P(MAA-co-AAm-co-DEAEMA) microgels containing PMAO-PEGMA functionalized polycaprolactone nanoparticles were net-anionic, polydisperse, and irregularly shaped. MIPs and control non-imprinted polymers (NIPs) exhibited regions of Freundlich and BET isotherm adsorption behavior in a range of non-competitive protein solutions, where MIPs exhibited enhanced adsorption capacity in the Freundlich isotherm regions. In a competitive condition, imprinting with analogue templates (trypsin, lysozyme) increased the adsorption capacity of microgels for cytochrome c by 162% and 219%, respectively, as compared to a 122% increase provided by traditional bulk imprinting with cytochrome c. Our results suggest that molecular imprinting with analogue protein templates is a viable synthetic strategy for enhancing hydrogel-biomarker affinity and promoting specific protein adsorption behavior in biological fluids. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1565-1574, 2017.

Analyte-Responsive Hydrogels: Intelligent Materials for Biosensing and Drug Delivery

Nature has mastered the art of molecular recognition. For example, using synergistic non-covalent interactions, proteins can distinguish between molecules and bind a partner with incredible affinity and specificity. Scientists have developed, and continue to develop, techniques to investigate and better understand molecular recognition. As a consequence, analyte-responsive hydrogels that mimic these recognitive processes have emerged as a class of intelligent materials. These materials are unique not only in the type of analyte to which they respond but also in how molecular recognition is achieved and how the hydrogel responds to the analyte. Traditional intelligent hydrogels can respond to environmental cues such as pH, temperature, and ionic strength. The functional monomers used to make these hydrogels can be varied to achieve responsive behavior. For analyte-responsive hydrogels, molecular recognition can also be achieved by incorporating biomolecules with inherent molecular recognition properties (e.g., nucleic acids, peptides, enzymes, etc.) into the polymer network. Furthermore, in addition to typical swelling/syneresis responses, these materials exhibit unique responsive behaviors, such as gel assembly or disassembly, upon interaction with the target analyte. With the diverse tools available for molecular recognition and the ability to generate unique responsive behaviors, analyte-responsive hydrogels have found great utility in a wide range of applications. In this Account, we discuss strategies for making four different classes of analyte-responsive hydrogels, specifically, non-imprinted, molecularly imprinted, biomolecule-containing, and enzymatically responsive hydrogels. Then we explore how these materials have been incorporated into sensors and drug delivery systems, highlighting examples that demonstrate the versatility of these materials. For example, in addition to the molecular recognition properties of analyte-responsive hydrogels, the physicochemical changes that are induced upon analyte binding can be exploited to generate a detectable signal for sensing applications. As research in this area has grown, a number of creative approaches for improving the selectivity and sensitivity (i.e., detection limit) of these sensors have emerged. For applications in drug delivery systems, therapeutic release can be triggered by competitive molecular interactions or physicochemical changes in the network. Additionally, including degradable units within the network can enable sustained and responsive therapeutic release. Several exciting examples exploiting the analyte-responsive behavior of hydrogels for the treatment of cancer, diabetes, and irritable bowel syndrome are discussed in detail. We expect that creative and combinatorial approaches used in the design of analyte-responsive hydrogels will continue to yield materials with great potential in the fields of sensing and drug delivery.

Molecular imprinting polymers and their composites: a promising material for diverse applications

Molecular imprinted polymerization is considered one of the most useful preparation strategies to obtain highly selective polymeric materials called molecular imprinted polymers (MIPs).

Role of Mechanical Factors in Applications of Stimuli-Responsive Polymer Gels - Status and Prospects

Due to their unique characteristics such as multifold change of volume in response to minute change in the environment, resemblance of soft biological tissues, ability to operate in wet environments, and chemical tailorability, stimuli responsive gels represent a versatile and very promising class of materials for sensors, muscle-type actuators, biomedical applications, and autonomous intelligent structures. Success of these materials in practical applications largely depends on their ability to fulfill application-specific mechanical requirements. This article provides an overview of recent application-driven development of covalent polymer gels with special emphasis on the relevant mechanical factors and properties. A short account of mechanisms of gel swelling and mechanical characteristics of importance to stimuli-responsive gels is presented. The review highlights major barriers for wider application of these materials and discusses latest advances and potential future directions toward overcoming these barriers, including interpenetrating networks, homogeneous networks, nanocomposites, and nanofilamentary gels.

The challenge to improve the response of biomaterials to the physiological environment

New applications of biomaterials often require advanced structures containing synthetic and natural components that are tuned to provide properties unique to a specific application. We discuss how structural characteristics of biomaterials, especially hydrophilic ones, can be used in conjunction with non-ideal thermodynamics to develop advanced medical systems. We show a number of examples of biocompatible, intelligent biomaterials that can be used for organ replacement, biosensors, precise drug delivery over days or weeks, and regenerative medicine.

Latest trends in molecular imprinted polymer based drug delivery systems

Molecular imprinted polymers (MIP) are promising and versatile materials that have been used for the determination of many different analytes.

Recognition and selective adsorption of pesticides by superparamagnetic molecularly imprinted polymer nanospheres

Selective adsorption of pesticides phosalone, diazinon, and chlorpyrifos from aqueous solution by superparamagnetic molecularly imprinted polymer nanosphere.

Bio-mimetic sensors based on molecularly imprinted membranes

An important challenge for scientific research is the production of artificial systems able to mimic the recognition mechanisms occurring at the molecular level in living systems. A valid contribution in this direction resulted from the development of molecular imprinting. By means of this technology, selective molecular recognition sites are introduced in a polymer, thus conferring it bio-mimetic properties. The potential applications of these systems include affinity separations, medical diagnostics, drug delivery, catalysis, etc. Recently, bio-sensing systems using molecularly imprinted membranes, a special form of imprinted polymers, have received the attention of scientists in various fields. In these systems imprinted membranes are used as bio-mimetic recognition elements which are integrated with a transducer component. The direct and rapid determination of an interaction between the recognition element and the target analyte (template) was an encouraging factor for the development of such systems as alternatives to traditional bio-assay methods. Due to their high stability, sensitivity and specificity, bio-mimetic sensors-based membranes are used for environmental, food, and clinical uses. This review deals with the development of molecularly imprinted polymers and their different preparation methods. Referring to the last decades, the application of these membranes as bio-mimetic sensor devices will be also reported.

Hybrid integrated label-free chemical and biological sensors

Label-free sensors based on electrical, mechanical and optical transduction methods have potential applications in numerous areas of society, ranging from healthcare to environmental monitoring. Initial research in the field focused on the development and optimization of various sensor platforms fabricated from a single material system, such as fiber-based optical sensors and silicon nanowire-based electrical sensors. However, more recent research efforts have explored designing sensors fabricated from multiple materials. For example, synthetic materials and/or biomaterials can also be added to the sensor to improve its response toward analytes of interest. By leveraging the properties of the different material systems, these hybrid sensing devices can have significantly improved performance over their single-material counterparts (better sensitivity, specificity, signal to noise, and/or detection limits). This review will briefly discuss some of the methods for creating these multi-material sensor platforms and the advances enabled by this design approach.

Photolithographic boronate affinity molecular imprinting: a general and facile approach for glycoprotein imprinting

Better than expected: With a regular boronic acid as the functional monomer, a general and facile approach for glycoprotein imprinting exhibited several highly favorable features that are beyond normal expectation, which make the prepared MIPs feasible for the recognition of trace glycoproteins in complicated real samples.

Stimuli-sensitive hydrogels: ideal carriers for chronobiology and chronotherapy

The development of solid-phase peptide synthesis in the early 1960s and recombinant DNA technology in the early 1970s boosted the scientific interest of utilizing proteins and peptides as potential therapeutic agents to battle poorly controlled diseases. While there has been rapid progress in the development and synthesis of new proteins and peptides as potential therapeutic agents, the formulation and development of the associated delivery systems is lacking. The development of delivery systems is equally important due to the problems of stability, low bioavailability and short half-life of proteins and peptides. The main problem in this field is that low stability leads to low bioavailability. In this review we draw attention to chrono-pharmacological drug-delivery systems, which can be used to match the delivery of therapeutic agents with the biological rhythm. They are very important especially in endocrinology and in vaccine therapy. We show that the treatment of hypopituitary dwarfism by administration of human growth-hormone-releasing hormone (GHRH) is more effective when GHRH is administered in a pulsatile manner that exhibits a period characteristic of the patient's circadian rhythm. Here we examine how to design novel chrono-pharmacological drug-delivery systems that should be able to release the therapeutic agents at predetermined intervals.

Photopolymerization and photostructuring of molecularly imprinted polymers for sensor applications--a review

Biosensors are already well established in modern analytical chemistry, and have become important tools for clinical diagnostics, environmental analysis, production monitoring, drug detection or screening. They are based on the specific molecular recognition of a target molecule by a biological receptor such as an antibody or an enzyme. Synthetic biomimetic receptors like molecularly imprinted polymers (MIPs) have been shown to be a potential alternative to biomolecules as recognition element for biosensing. Produced by a templating process at the molecular level, MIPs are capable of recognizing and binding target molecules with similar specificity and selectivity to their natural analogues. One of the main challenges in MIP sensor development is the miniaturization of MIP structures and their interfacing with the transducer or with a microchip. Photostructuring appears thereby as one of the most suitable methods for patterning MIPs at the micro and nano scale, directly on the transducer surface. In the present review, a general overview on MIPs in biosensing applications is given, and the photopolymerization and photopatterning of MIPs are particularly described.

Immuno-like assays and biomimetic microchips

Biomimetic assays with molecularly imprinted polymers (MIPs) are bound to be an alternative to the traditional immuno-analytical methods based on antibodies. This is due to the unique combination of advantages displayed by the artificial materials including the absence of animal inoculation and sacrifice, unnecessary hapten conjugation to a carrier protein for stimulated production, the possibility of manufacturing MIPs against toxic substances, excellent physicochemical stability, reusability, ease of storage, and recognition in organic media. If the selectivity and affinity of MIPs are increased, many more immuno-like assays will be developed using radioactive, enzymatic, colorimetric, fluorescent, chemiluminescent, or electrochemical interrogation methods. This chapter provides a comprehensive comparison between the bio- and biomimetic entities and their usage.

Micro- and nanotechnologies for intelligent and responsive biomaterial-based medical systems

Advances in medical treatments of a wide variety of pathophysiological conditions require the development of better therapeutic agents, as well as a combination of the required therapeutic agents with device-integrated biomaterials that can serve as sensors and carriers. Combination of micro- and nano-fabricated systems with intelligent biomaterials that have the ability to sense and respond is a promising avenue for the development of better diagnostic and therapeutic medical systems. Micro- and nano-electromechanical systems (MEMs and NEMs) are now becoming a family of potentially powerful new technologies for drug delivery, diagnostic tools, and tissue engineering. Improvements in micro- and nano-fabrication technologies have enhanced the ability to create better performing therapeutic systems for numerous pathophysiological applications. More importantly, MEMS- and NEMS-based tissue regeneration scaffolds, biosensors, and drug delivery devices provide new opportunities to mimic the natural intelligence and response of biological systems.

Micro- and nanofabrication methods in nanotechnological medical and pharmaceutical devices

Micro- and nanofabrication techniques have revolutionized the pharmaceutical and medical fields as they offer the possibility for highly reproducible mass-fabrication of systems with complex geometries and functionalities, including novel drug delivery systems and bionsensors. The principal micro- and nanofabrication techniques are described, including photolithography, soft lithography, film deposition, etching, bonding, molecular self assembly, electrically induced nanopatterning, rapid prototyping, and electron, X-ray, colloidal monolayer, and focused ion beam lithography. Application of these techniques for the fabrication of drug delivery and biosensing systems including injectable, implantable, transdermal, and mucoadhesive devices is described.

[New intelligent and targetted drug delivery systems. Pharmaceutical and biomedical applications]

Biomaterials are widely used in numerous medical applications. Chemical engineering has played a central role in this research and development. We review herein polymers as biomaterials, materials and approaches used in drug and protein delivery systems, materials used as scaffolds in tissue engineering, and nanotechnology and microfabrication techniques applied to biomaterials.

Flocculation behavior of temperature-sensitive poly(N-isopropylacrylamide) microgels containing polar side chains with OH groups

The flocculation behavior of poly(N-isopropylacrylamide) (pNIPAM) microgels containing polar -(OCH(2)CH(2))(3)OH chains, incorporated by the copolymeric components (triethyleneglycol methacrylate, TREGMA), in aqueous NaCl solution was investigated. Determination of the critical flocculation temperatures (CFTs) and the critical flocculation concentrations (CFCs) of the microgels at 45 degrees C shows that polar -(OCH(2)CH(2))(3)OH chains have different influence on the flocculation behavior of the microgels at temperatures below and above their volume phase transition temperatures (VPTTs). The flocculation of the microgels becomes more difficult with the increase of -(OCH(2)CH(2))(3)OH chains below the VPTT. In contrast, the microgels flocculate more easily with more -(OCH(2)CH(2))(3)OH chains above the VPTT. Preliminary investigation on the flocculation kinetics of the microgels further shows that -(OCH(2)CH(2))(3)OH chains have different effects on the flocculation rate at temperatures below and above the VPTT. The flocculating rate of the microgels at 25 degrees C decreases with the increase of -(OCH(2)CH(2))(3)OH chains. While the flocculation rate at 45 degrees C increases with the increase of -(OCH(2)CH(2))(3)OH chains due to their enrichment on the surface of the microgels as a result of the temperature-induced volume-phase transition, which was verified by variable temperature (1)H NMR spectroscopy. The polar -(OCH(2)CH(2))(3)OH chains rich in the surface increase the attractive force between the microgels, promoting the flocculation.