Protein immobilization on epoxy-activated thin polymer films: effect of surface wettability and enzyme loading

Experimental Analysis of the Enzymatic Degradation of Polycaprolactone: Microcrystalline Cellulose Composites and Numerical Method for the Prediction of the Degraded Geometry

The degradation rate of polycaprolactone (PCL) is a key issue when using this material in Tissue Engineering or eco-friendly packaging sectors. Although different PCL-based composite materials have been suggested in the literature and extensively tested in terms of processability by material extrusion additive manufacturing, little attention has been paid to the influence of the fillers on the mechanical properties of the material during degradation. This work analyses the possibility of tuning the degradation rate of PCL-based filaments by the introduction of microcrystalline cellulose into the polymer matrix. The enzymatic degradation of the composite and pure PCL materials were compared in terms of mass loss, mechanical properties, morphology and infrared spectra. The results showed an increased degradation rate of the composite material due to the presence of the filler (enhanced interaction with the enzymes). Additionally, a new numerical method for the prediction of the degraded geometry was developed. The method, based on the Monte Carlo Method in an iterative process, adjusts the degradation probability according to the exposure of each discretized element to the degradation media. This probability is also amplified depending on the corresponding experimental mass loss, thus allowing a good fit to the experimental data in relatively few iterations.

Protein immobilization on graphene oxide or reduced graphene oxide surface and their applications: Influence over activity, structural and thermal stability of protein

Due to the essential role of biological macromolecules in our daily life; it is important to control the stability and activity of such macromolecules. Therefore, the most promising route for enhancement in stability and activity is immobilizing proteins on different support materials. Furthermore, large surface area and surface functional groups are the important features that are required for a better support system. These features of graphene oxide (GO) and reduced graphene oxide (RGO) makes them ideal support materials for protein immobilization. Studies show the successful formation of GO/RGO-protein complexes with enhancement in structural/thermal stability due to various interactions at the nano-bio interface and their utilization in various functional applications. The present review focuses on protein immobilization using GO/RGO as solid support materials. Moreover, we also emphasized on basic underlying mechanism and interactions (hydrophilic, hydrophobic, electrostatic, local protein-protein, hydrogen bonding and van der Walls) between protein and GO/RGO which influences structural stability and activity of enzymes/proteins. Furthermore, GO/RGO-protein complexes are utilized in various applications such as biosensors, bioimaging and theranostic agent, targeted drug delivery agents, and nanovectors for drug and protein delivery.

Sustainable Solvothermal Conversion of Waste Biomass to Functional Carbon Material: Extending Its Utility as a Biocompatible Cosolvent for Lysozyme

Functional carbon material synthesis from waste biomass by a sustainable method is of prime importance and has wide variety of applications. Herein, functional carbon materials with structural variability are synthesized using a well-known solvothermal method. The leftover pulp waste biomass (PB) of citrus limetta is converted to functional carbon by treatment with a mixture of choline bitartrate (ChBt) and FeCl₃ (1:2 mol ratio) as a solvent. The biomass to solvent ratio is varied as 1:1, 0.8:1, and 0.4:1 during solvothermal treatment to obtain PB-1, PB-2, and PB-3 as functional carbon materials, respectively. On characterization, PB carbon materials were found to be rich in oxygen-containing functional groups possessing different morphologies. Furthermore, results suggested the role of solvent as a soft template and catalyst during the synthesis of carbon materials. The feasibility of synthesized carbon materials as a biocompatible cosolvent for lysozyme was evaluated. In the case of PB-2 material (synthesized using 0.8:1 biomass to solvent ratio), results show an enhancement of lysozyme activity by 150%. Besides, spectroscopic and calorimetric data confirm the preservation of thermal and structural stability of lysozyme in the PB-2 solution. Thus, this study stipulates PB-2 as an excellent cosolvent for protein studies. With this work, we aim to delve into an entirely new arena of applications of biomass in the field of biotechnology.

Tunable Polymeric Scaffolds for Enzyme Immobilization

The number of methodologies for the immobilization of enzymes using polymeric supports is continuously growing due to the developments in the fields of biotechnology, polymer chemistry, and nanotechnology in the last years. Despite being excellent catalysts, enzymes are very sensitive molecules and can undergo denaturation beyond their natural environment. For overcoming this issue, polymer chemistry offers a wealth of opportunities for the successful combination of enzymes with versatile natural or synthetic polymers. The fabrication of functional, stable, and robust biocatalytic hybrid materials (nanoparticles, capsules, hydrogels, or films) has been proven advantageous for several applications such as biomedicine, organic synthesis, biosensing, and bioremediation. In this review, supported with recent examples of enzyme-protein hybrids, we provide an overview of the methods used to combine both macromolecules, as well as the future directions and the main challenges that are currently being tackled in this field.

Immobilization of cellulase in the non-natural ionic liquid environments to enhance cellulase activity and functional stability

Ionic liquids (ILs) have been applied as an environmentally friendly solvent in the pretreatment of lignocellulosic biomass for more than a decade. The ILs involved pretreatment processes for cellulases mediated saccharification lead to both the breakdown of cellulose crystallinity and the decrease of lignin content, thereby improving the solubility of cellulose and the accessibility of cellulase. However, most cellulases are partially or completely inactivated in the presence of even low amount of ILs. Immobilized cellulases are found to perform improved stability and higher apparent activity in practical application compared with its free counterparts. Enzyme immobilization therefore has become a promising way to relieve the deactivation of cellulase in ILs. Various immobilization carriers and methods have been developed and achieved satisfactory results in improving the stability, activity, and recycling of cellulases in IL pretreatment systems. This review aims to provide detailed introduction of immobilization methods and carrier materials of cellulase, including natural polysaccharides, synthetic polymers, inorganic materials, magnetic materials, and newly developed composite materials, and illustrate key methodologies in improving the performance of cellulase in the presence of ILs. Especially, novel materials and concepts from the recently representative researches are focused and discussed comprehensively, and future trends in immobilization of cellulases in non-natural ILs environments are speculated in the end.

Covalent Immobilization of Cellulase Using Magnetic Poly(ionic liquid) Support: Improvement of the Enzyme Activity and Stability

A magnetic nanocomposite was prepared by entrapment of Fe₃O₄ nanoparticles into the cross-linked ionic liquid/epoxy type polymer. The resulting support was used for covalent immobilization of cellulase through the reaction with epoxy groups. The ionic surface of the support improved the adsorption of enzyme, and a large amount of enzyme (106.1 mg/g) was loaded onto the support surface. The effect of the presence of ionic monomer and covalent binding of enzyme was also investigated. The structure of support was characterized by various instruments such as FT-IR, TGA, VSM, XRD, TEM, SEM, and DLS. The activity and stability of immobilized cellulase were investigated in the prepared support. The results showed that the ionic surface and covalent binding of enzyme onto the support improved the activity, thermal stability, and reusability of cellulase compared to free cellulase.

Effect of hydrogel elasticity and ephrinB2-immobilized manner on Runx2 expression of human mesenchymal stem cells

The objective of this study is to design the manner of ephrinB2 immobilized onto polyacrylamide (PAAm) hydrogels with varied elasticity and evaluate the effect of hydrogels elasticity and the immobilized manner of ephrinB2 on the Runx2 expression of human mesenchymal stem cells (hMSC). The PAAm hydrogels were prepared by the radical polymerization of acrylamide (AAm), and N,N'-methylenebisacrylamide (BIS). By changing the BIS concentration, the elasticity of PAAm hydrogels changed from 1 to 70kPa. For the bio-specific immobilization of ephrinB2, a chimeric protein of ephrinB2 and Fc domain was immobilized onto protein A-conjugated PAAm hydrogels by making use of the bio-specific interaction between the Fc domain and protein A. When hMSC were cultured on the ephrinB2-immobilized PAAm hydrogels with varied elasticity, the morphology of hMSC was of cuboidal shape on the PAAm hydrogels immobilized with ephrinB2 compared with non-conjugated ones, irrespective of the hydrogels elasticity. The bio-specific immobilization of ephrinB2 enhanced the level of Runx2 expression. The expression level was significantly high for the hydrogels of 3.6 and 5.9kPa elasticity with bio-specific immobilization of ephrinB2 compared with other hydrogels with the same elasticity. The hydrogels showed a significantly down-regulated RhoA activity. It is concluded that the Runx2 expression of hMSC is synergistically influenced by the hydrogels elasticity and their immobilized manner of ephrinB2 immobilized.

STATEMENT OF SIGNIFICANCE

Differentiation fate of mesenchymal stem cells (MSC) is modified by biochemical and biophysical factors, such as elasticity and signal proteins. However, there are few experiments about combinations of them. In this study, to evaluate the synergistic effect of them on cell properties of MSC, we established to design the manner of Eph signal ligand, ephrinB2, immobilized onto polyacrylamide hydrogels with varied elasticity. The gene expression level of an osteogenic maker, Runx2, was enhanced by the immobilized manner, and significantly enhanced for the hydrogels of around 4kPa elasticity with bio-specific immobilization of ephrinB2. This is the novel report describing to demonstrate that the Runx2 expression of MSC is synergistically influenced by the hydrogels elasticity and their manner of ephrinB2 immobilized.

Immobilization of laccase from Aspergillus oryzae on graphene nanosheets

Laccase enzymes of Aspergillus oryzae were immobilized on graphene nanosheets by physical adsorption and covalent bonding. Morphological features of the graphene sheets were characterized via microscopy techniques. The immobilization by adsorption was carried out through contact between graphene and solution of laccase enzyme dissolved in deionized water. The adsorption process followed a Freundlich model, showing no tendency to saturation within the range of values used. The process of immobilization by covalent bonding was carried out by nitration of graphene, followed by reduction of sodium borohydride and crosslinking with glutaraldehyde. The process of immobilization by both techniques increased the pH range of activity of the laccase enzyme compared to the free enzyme and increased its operating temperature. On operational stability, the enzyme quickly loses its activity after the second reaction cycle when immobilized via physical adsorption, while the technique by covalent bonding retained around 80% activity after six cycles.

Display of fungal hydrophobin on the Pichia pastoris cell surface and its influence on Candida antarctica lipase B

To modify the Pichia pastoris cell surface, two classes of hydrophobins, SC3 from Schizophyllum commune and HFBI from Trichoderma reesei, were separately displayed on the cell wall. There was an observable increase in the hydrophobicity of recombinant strains. Candida antarctica lipase B (CALB) was then co-displayed on the modified cells, generating strains GS115/SC3-61/CALB-51 and GS115/HFBI-61/CALB-51. Interestingly, the hydrolytic and synthetic activities of strain GS115/HFBI-61/CALB-51 increased by 37 and 109 %, respectively, but decreased by 26 and 43 %, respectively, in strain GS115/SC3-61/CALB-51 compared with the hydrophobin-minus recombinant strain GS115/CALB-GCW51. The amount of glycerol by-product from the transesterification reaction adsorbed on the cell surface was significantly decreased following hydrophobin modification, removing the glycerol barrier and allowing substrates to access the active sites of lipases. Electron micrographs indicated that the cell wall structures of both recombinant strains appeared altered, including changes to the inner glucan layer and outer mannan layer. These results suggest that the display of hydrophobins can change the surface structure and hydrophobic properties of P. pastoris and affect the catalytic activities of CALB displayed on the surface of P. pastoris cells.

Bioinspired polymer vesicles and membranes for biological and medical applications

Biological membranes play an essential role in living organisms by providing stable and functional compartments, supporting signalling and selective transport. Combining synthetic polymer membranes with biological molecules promises to be an effective strategy to mimic the functions of cell membranes and apply them in artificial systems.

Chemoenzymatic method for glycomics: Isolation, identification, and quantitation

Over the past decade, considerable progress has been made with respect to the analytical methods for analysis of glycans from biological sources. Regardless of the specific methods that are used, glycan analysis includes isolation, identification, and quantitation. Derivatization is indispensable to increase their identification. Derivatization of glycans can be performed by permethylation or carbodiimide coupling/esterification. By introducing a fluorophore or chromophore at their reducing end, glycans can be separated by electrophoresis or chromatography. The fluorogenically labeled glycans can be quantitated using fluorescent detection. The recently developed approaches using solid-phase such as glycoprotein immobilization for glycan extraction and on-tissue glycan mass spectrometry imaging demonstrate advantages over methods performed in solution. Derivatization of sialic acids is favorably implemented on the solid support using carbodiimide coupling, and the released glycans can be further modified at the reducing end or permethylated for quantitative analysis. In this review, methods for glycan isolation, identification, and quantitation are discussed.

Design and implementation of two-dimensional polymer adsorption models: evaluating the stability of Candida antarctica lipase B/solid-support interfaces by QCM-D

A two-dimensional model of a solid-supported enzyme catalyst bead is fabricated on a quartz crystal microbalance with dissipation monitoring (QCM-D) sensor to measure in situ interfacial stability and mechanical properties of Candida antarctica Lipase B (CAL B) under varied conditions relating to ring-opening polymerization. The model was fabricated using a dual photochemical approach, where poly(methyl methacrylate) (PMMA) thin films were cross-linked by a photoactive benzophenone monolayer and blended cross-linking agent. This process produces two-dimensional, homogeneous, rigid PMMA layers, which mimic commercial acrylic resins in a QCM-D experiment. Adsorption of CAL B to PMMA in QCM-D under varied buffer ionic strengths produces a viscoelastic enzyme surface that becomes more rigid as ionic strength increases. The rigid CAL B/PMMA interface demonstrates up to 20% desorption of enzyme with increasing trace water content. Increased polycaprolactone (PCL) binding at the enzyme surface was also observed, indicating greater PCL affinity for a more hydrated enzyme surface. The enzyme layer destabilized with increasing temperature, yielding near complete reversible catalyst desorption in the model.

Immobilization of biocatalysts for enzymatic polymerizations: possibilities, advantages, applications

Biotechnology also holds tremendous opportunities for realizing functional polymeric materials. Biocatalytic pathways to polymeric materials are an emerging research area with not only enormous scientific and technological promise, but also a tremendous impact on environmental issues. Many of the enzymatic polymerizations reported proceed in organic solvents. However, enzymes mostly show none of their profound characteristics in organic solvents and can easily denature under industrial conditions. Therefore, natural enzymes seldom have the features adequate to be used as industrial catalysts in organic synthesis. The productivity of enzymatic processes is often low due to substrate and/or product inhibition. An important route to improving enzyme performance in non-natural environments is to immobilize them. In this review we will first summarize some of the most prominent examples of enzymatic polymerizations and will subsequently review the most important immobilization routes that are used for the immobilization of biocatalysts relevant to the field of enzymatic polymerizations.

Immobilization-stabilization of proteins on nanofibrillated cellulose derivatives and their bioactive film formation

In a number of different applications for enzymes and specific binding proteins a key technology is the immobilization of these proteins to different types of supports. In this work we describe a concept for protein immobilization that is based on nanofibrillated cellulose (NFC). NFC is a form of cellulose where fibers have been disintegrated into fibrils that are only a few nanometers in diameter and have a very large aspect ratio. Proteins were conjugated through three different strategies using amine, epoxy, and carboxylic acid functionalized NFC. The conjugation chemistries were chosen according to the reactive groups on the NFC derivatives; epoxy amination, heterobifunctional modification of amino groups, and EDC/s-NHS activation of carboxylic acid groups. The conjugation reactions were performed in solution and immobilization was performed by spin coating the protein-NCF conjugates. The structure of NFC was shown to be advantageous for both protein performance and stability. The use of NFC allows all covalent chemistry to be performed in solution, while the immobilization is achieved by a simple spin coating or spreading of the protein-NFC conjugates on a support. This allows more scalable methods and better control of conditions compared to the traditional methods that depend on surface reactions.

Effect of substrate (ZnO) morphology on enzyme immobilization and its catalytic activity

In this study, zinc oxide (ZnO) nanocrystals with different morphologies were synthesized and used as substrates for enzyme immobilization. The effects of morphology of ZnO nanocrystals on enzyme immobilization and their catalytic activities were investigated. The ZnO nanocrystals were prepared through a hydrothermal procedure using tetramethylammonium hydroxide as a mineralizing agent. The control on the morphology of ZnO nanocrystals was achieved by varying the ratio of CH3OH to H2O, which were used as solvents in the hydrothermal reaction system. The surface of as-prepared ZnO nanoparticles was functionalized with amino groups using 3-aminopropyltriethoxysilane and tetraethyl orthosilicate, and the amino groups on the surface were identified and calculated by FT-IR and the Kaiser assay. Horseradish peroxidase was immobilized on as-modified ZnO nanostructures with glutaraldehyde as a crosslinker. The results showed that three-dimensional nanomultipod is more appropriate for the immobilization of enzyme used further in catalytic reaction.

Orientation-regulated immobilization of Jagged1 on glass substrates for ex vivo proliferation of a bone marrow cell population containing hematopoietic stem cells

Notch signaling has been recognized as a key pathway to regulate the proliferation and differentiation of hematopoietic stem cells (HSC). In this study, the orientation-regulated immobilization of a Notch ligand was designed to achieve the efficient Notch ligand-receptor recognition for the ex vivo proliferation of a bone marrow cell population containing HSC. Protein A was chemically conjugated onto aminated glass substrates, followed by immobilizing a recombinant chimeric protein of Jagged1 and Fc domain (Jagged1-Fc) through the biospecific binding between protein A and Fc domain. Protein A adsorption was suppressed for the Jagged1-Fc-immobilized substrates, in contrast to the Jagged1-Fc-coated ones, indicating the orientation-regulated immobilization of Jagged1-Fc for the substrates. Mouse lineage negative cells (Lin(-)) were cultured on the Jagged1-Fc-immobilized substrates. Flow cytometric analyses demonstrated that c-Kit(+), Sca-1(+), Lin(-), and CD34(-) cells of an HSC population was significantly proliferated on the Jagged1-Fc-immobilized substrates 6 days after culture, whereas no proliferation was observed for the Jagged1-Fc-coated substrates in a random manner or Jagged1-Fc-immobilized ones with a Notch signaling inhibitor. It is concluded that the orientation-regulated immobilization of Jagged1-Fc increased the efficiency of Jagged1 to recognize the Notch receptors, resulting in the promoted ex vivo proliferation of the HSC population.

Graphene oxide as a matrix for enzyme immobilization

Graphene oxide (GO), having a large specific surface area and abundant functional groups, provides an ideal substrate for study enzyme immobilization. We demonstrated that the enzyme immobilization on the GO sheets could take place readily without using any cross-linking reagents and additional surface modification. The atomically flat surface enabled us to observe the immobilized enzyme in the native state directly using atomic force microscopy (AFM). Combining the AFM imaging results of the immobilized enzyme molecules and their catalytic activity, we illustrated that the conformation of the immobilized enzyme is mainly determined by interactions of enzyme molecules with the functional groups of GO.

Reactive surface coatings based on polysilsesquioxanes: controlled functionalization for specific protein immobilization

The key designing in reliable biosensors is the preparation of thin films in which biomolecular functions may be immobilized and addressed in a controlled and reproducible manner. This requires the controlled preparation of specific binding sites on planar surfaces. Poly(methylsilsesquioxane)-poly(pentafluorophenyl acrylates) (PMSSQ-PFPA) are promising materials to produce stable and adherent thin reactive coatings on various substrates. Those reactive surface coatings could be applied onto various materials, for example, gold, polycarbonate (PC), poly(tetrafluoroethylene) (PTFE), and glass. By dipping those substrates in a solution of a desired amine, specific binding sites for protein adsorption could be immobilized on the surface. The versatile strategy allowed the attachment of various linkers, for example, biotin, l-thyroxine, and folic acid. The adsorption processes of streptavidin, pre-albumin, and folate-binding protein were monitored using surface plasmon resonance (SPR), Fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy, and atomic force microscopy (AFM). The presented protein immobilization strategy, consisting of four steps (a) spin-coating of PMSSQ-PFPA hybrid polymer from tetrahydrofuran (THF) solution, (b) annealing at 130 degrees C for 2 h to induce thermal cross-linking of the PMSSQ part, (c) surface analogues reaction with different amino-functionalized specific binding sites for proteins, and (d) controlled assembly of proteins on the surface, may find various applications in future biosensor design.

A conventional route to scalable morphology-controlled regular structures and their superhydrophobic/hydrophilic properties for biochips application

We use a conventional and straightforward route to fabricate scalable morphology-controlled regular structures. This route is based on the etching of PDMS microlens array in CF4 and CF4/O2 plasma. PDMS microlens array can be changed to regularly isolated microdot structures array in CF4 plasma. Microbowl shaped structures array can be reached in CF4/O2 plasma. Moreover, a set of structures after CF4 plasma treatment display superhydrophobicity, while a set of structures after CF4/O2 plasma treatment present hydrophilicity. DNA molecules can be readily enriched on the hydrophilic surface. We believe that the regular structure array surfaces provide a useful inspiration towards biomolecular detection and transportation in biochips.

Imaging surface charges of individual biomolecules

Surface charges play a key role in determining the structure and function of proteins, DNA, and larger biomolecular structures. Here we report on the measurement of the electrostatic surface potential of individual DNA and avidin molecules with nanometer resolution using Kelvin probe force microscopy. We also show, for the first time, the surface potential of buffer salts shielding individual DNA molecules, which would not be possible with conventional ensemble techniques.