Immobilization of cellulase in nanofibrous PVA membranes by electrospinning

Facile chemical modification of solid alkaline lignin and chitosan via nucleophilic substitution with organohalides in the vapor phase

The reaction of solid alkaline lignin and chitosan with vapors of organohalides, namely allyl bromide and epichlorohydrin, is presented as a sustainable alternative to conventional solvent-based techniques for modifying these model nucleophilic biopolymers. This approach, which does not necessitate any catalysts or pre-treatments, exploits the inherent nucleophilicity of specific functional groups present in the biopolymers, such as sodium carboxylates, sodium phenolates, and amines, facilitating nucleophilic substitution reactions directly with the vapors of the modifying agents. Fuming with epichlorohydrin introduced 1,3-glyceryl bridges in both alkaline lignin and chitosan, resulting in their extensive crosslinking. Allyl bromide vapors, on the other hand, resulted in their O- or N-allylation. Allylated biopolymers showed promise as versatile starting materials for further reactions, while vapor-phase crosslinking with epichlorohydrin could effectively stabilize different biopolymer forms. This environmentally friendly, solvent-free approach offers several advantages over conventional solvent-based techniques, including reduced waste generation, simplified post-processing, and increased flexibility for recovering and reusing modifying agents, even in cases of contamination.

Immobilization of BoPAL3 Phenylalanine Ammonia-Lyase on Electrospun Nanofibrous Membranes of Polyvinyl Alcohol/Nylon 6/Chitosan Crosslinked with Dextran Polyaldehyde

Phenylalanine ammonia-lyase (PAL, EC 4.3.1.24) is common in plants and catalyzes the formation of trans-cinnamic acid and ammonia via phenylalanine deamination. Recombinant Bambusa oldhamii BoPAL3 protein expressed in Escherichia coli was immobilized on an electrospun nanofibrous membrane using dextran polyaldehyde as a crosslinker. The immobilized BoPAL3 protein exhibited comparable kinetic properties with the free BoPAL3 protein and could be recycled for six consecutive cycles compared with the free BoPAL3 protein. The residual activity of the immobilized BoPAL3 protein was 84% after 30 days of storage at 4 °C, whereas the free BoPAL3 protein retained 56% residual activity in the same storage conditions. Furthermore, the resistance of the immobilized BoPAL3 protein to chemical denaturants was greatly increased. Therefore, the BoPAL3 protein can be immobilized using the natural dextran polyaldehyde crosslinker in place of the conventional chemical crosslinker. Nanofibrous membranes made from polyvinyl alcohol (PVA), nylon 6, and chitosan (CS) are incredibly stable and useful for future industrial applications.

Biocompatible polyvinyl alcohol nanofibers loaded with amoxicillin and salicylic acid to prevent wound infections

Diabetic wounds are one of the most challenging clinical conditions in diabetes, necessitating the development of new treatments to foster healing and prevent microbial contamination. In this study, polyvinyl alcohol was used as a matrix polymer, and amoxicillin (AMX) and salicylic acid (SA) were selected as bioactive compounds with antimicrobial (with AMX) and anti-inflammatory action (with SA) to obtain innovative drug-loaded electrospun nanofiber patches for the management of diabetic wounds. Scanning electron microscope images revealed the uniform and beadless structure of the nanofiber patches. Mechanical tests indicated that AMX minimally increased the tensile strength, while SA significantly reduced it. The patches demonstrated effective antibacterial activity against both gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) strains. The potential of these patches in the development of novel wound dressings is highlighted by the excellent biocompatibility with fibroblast cells maintained for up to 7 d.

An Up-to-Date Review on the Remediation of Dyes and Phenolic Compounds from Wastewaters Using Enzymes Immobilized on Emerging and Nanostructured Materials: Promises and Challenges

Addressing the critical issue of water pollution, this review article emphasizes the need to remove hazardous dyes and phenolic compounds from wastewater. These pollutants pose severe risks due to their toxic, mutagenic, and carcinogenic properties. The study explores various techniques for the remediation of organic contaminants from wastewater, including an enzymatic approach. A significant challenge in enzymatic wastewater treatment is the loss of enzyme activity and difficulty in recovery post-treatment. To mitigate these issues, this review examines the strategy of immobilizing enzymes on newly developed nanostructured materials like graphene, carbon nanotubes (CNTs), and metal-organic frameworks (MOFs). These materials offer high surface areas, excellent porosity, and ample anchoring sites for effective enzyme immobilization. The review evaluates recent research on enzyme immobilization on these supports and their applications in biocatalytic nanoparticles. It also analyzes the impact of operational factors (e.g., time, pH, and temperature) on dye and phenolic compound removal from wastewater using these enzymes. Despite promising outcomes, this review acknowledges the challenges for large-scale implementation and offers recommendations for future research to tackle these obstacles. This review concludes by suggesting that enzyme immobilization on these emerging materials could present a sustainable, environmentally friendly solution to the escalating water pollution crisis.

NahAa can convert naphthalene and reduce chromate simultaneously and immobilized on functional multiwall carbon nanotubes for wastewater treatment

Pseudomonas brassicacearum LZ-4 is a facultative anaerobic bacterium, can efficiently degrade naphthalene and reduce chromate simultaneously. In this study, we showed that the naphthalene degradation enzyme NahAa from P. brassicacearum LZ-4 can reduce Cr(VI). Heterologous expression in E. coli S17-1 along with RNA interference of NahAa in strain LZ-4 showed the enzyme can reduce chromate in vivo. In vitro, purified NahAa was identified and can catalyze Cr(VI) reduction by 64.2%. Flavin adenine dinucleotide (FAD) was identified as a cofactor of NahAa, which Cr(VI) could obtain electrons from NADH through NahAa-associated FAD for reduction. Immobilized NahAa on functional multi walled carbon nanotubes via physical adsorption method to produce a stable, high efficient composite MWCNT-NahAa. The maximum efficiency of MWCNT-NahAa composite was obtained in enzyme concentrations of 6 mg/mL and 20 min immobilization time. The optical reaction conditions for MWCNT-NahAa were pH 7.0 and 30 °C, still retaining 50% of its initial activities after five consecutive cycles. Application of composites in wastewater can reduce 90.4% Cr(VI), higher than free NahAa that was 63.5%. To our best knowledge, this is the first report immobilized enzyme in polycyclic aromatic hydrocarbons-degradation pathway for Cr(VI) wastewater treatment, providing a new insights on combined pollution remediation.

Protein Nanoparticles: Uniting the Power of Proteins with Engineering Design Approaches

Protein nanoparticles, PNPs, have played a long-standing role in food and industrial applications. More recently, their potential in nanomedicine has been more widely pursued. This review summarizes recent trends related to the preparation, application, and chemical construction of nanoparticles that use proteins as major building blocks. A particular focus has been given to emerging trends related to applications in nanomedicine, an area of research where PNPs are poised for major breakthroughs as drug delivery carriers, particle-based therapeutics or for non-viral gene therapy.

Nanofibrous Membrane with Encapsulated Glucose Oxidase for Self-Sustained Antimicrobial Applications

Polyvinyl alcohol (PVA) nanofibrous membrane, consisting of separately encapsulated glucose oxidase (GOx) and glucose (Glu) nanofibers, was prepared via simultaneously electrospinning PVA/GOx and PVA/Glu dopes. The as-prepared pristine membrane could self-sustainably generate hydrogen peroxide (H2O2) only in contact with an aqueous solution. The H2O2 production level was well maintained even after storing the dry membrane at room temperature for 7 days. Cross-linking the membrane via reaction with glutaraldehyde (GA) vapor could not only prevent the nanofibrous membrane from dissolving in water but also prolonged the release of H2O2. The sustained release of H2O2 from the membrane achieved antimicrobial capability equivalent to that of 1% H2O2 against both Escherichia coli and Staphylococcus aureus. Gram(+) S. aureus cells were more susceptible to H2O2 than Gram(-) E. coli and >99% of S. aureus were killed after 1 h incubation with the membrane. Pristine and GA-crosslinked nanofibrous membrane with in situ production of H2O2 were self-sterilized in which no microorganism contamination on the membrane could be detected after 2 weeks incubation on an agar plate. The GOx/Glu membrane may find potential application as versatile antimicrobial materials in the field of biomedicine, in the food and health industries, and especially challenges related to wound healing in diabetic patients.

Design of 3D Scaffolds for Hard Tissue Engineering: From Apatites to Silicon Mesoporous Materials

Advanced bioceramics for bone regeneration constitutes one of the pivotal interests in the multidisciplinary and far-sighted scientific trajectory of Prof. Vallet Regí. The different pathologies that affect osseous tissue substitution are considered to be one of the most important challenges from the health, social and economic point of view. 3D scaffolds based on bioceramics that mimic the composition, environment, microstructure and pore architecture of hard tissues is a consolidated response to such concerns. This review describes not only the different types of materials utilized: from apatite-type to silicon mesoporous materials, but also the fabrication techniques employed to design and adequate microstructure, a hierarchical porosity (from nano to macro scale), a cell-friendly surface; the inclusion of different type of biomolecules, drugs or cells within these scaffolds and the influence on their successful performance is thoughtfully reviewed.

Preparation of carboxymethyl starch/polyvinyl-alcohol electrospun composite nanofibers from a green approach

A green approach for the preparation of starch-based composite nanofibers using electrospinning was developed. The water-soluble sodium carboxymethyl starch (CMS) with DS 0.31 was prepared. The addition of co-blending polymer polyvinyl-alcohol (PVA) was attempted to improve the CMS solution spinnability, which blends from aqueous solution were prepared at different CMS/PVA weight ratios. The solution parameters including viscosity, surface tension and conductivity were measured and the morphologies of nanofibers were observed by SEM. Smooth, continuous, and defect-free nanofibers were successfully obtained range from the blend of CMS/PVA weight ratios of 10:90 to 80:20. Diameter distribution diagrams suggested that the diameter of the nanofibers reduced with the concentration of CMS increasing. This is the first report that the thin nanofiber (135.29 nm) with bead-free was obtained at the maximal CMS content of 50.0 wt% in the CMS/PVA blend. This study provided a green approach to produce starch-based nano-scale fibers.

Overview on immobilization of enzymes on synthetic polymeric nanofibers fabricated by electrospinning

The arrangement and type of support has a significant impact on the efficiency of immobilized enzymes. 1-dimensional fibrous materials can be one of the most desirable supports for enzyme immobilization. This is due to their high surface area to volume ratio, internal porosity, ease of handling, and high mechanical stability, all of which allow a higher enzyme loading, release and finally lead to better catalytic efficiency. Fortunately, the enzymes can reside inside individual nanofibers to remain encapsulated and retain their three-dimensional structure. These properties can protect the enzyme's tolerance against harsh conditions such as pH variations and high temperature, and this can probably enhance the enzyme's stability. This review article will discuss the immobilization of enzymes on synthetic polymers, which are fabricated into nanofibers by electrospinning. This technique is rapidly gaining popularity as one of the most practical ways to fibricate polymer, metal oxide, and composite micro or nanofibers. As a result, there is interest in using nanofibers to immobilize enzymes. Furthermore, present research on electrospun nanofibers for enzyme immobilization is primarily limited to the lab scale and industrial scale is still challanging. The primary future research objectives of this paper is to investigate the use of electrospun nanofibers for enzyme immobilization, which includes increasing yield to transfer biological products into commercial applications.

Production of Trans-Cinnamic Acid by Immobilization of the Bambusa oldhamii BoPAL1 and BoPAL2 Phenylalanine Ammonia-Lyases on Electrospun Nanofibers

Phenylalanine ammonia-lyase (PAL) catalyzes the nonoxidative deamination of phenylalanine to yield trans-cinnamic acid and ammonia. Recombinant Bambusa oldhamii BoPAL1/2 proteins were immobilized onto electrospun nanofibers by dextran polyaldehyde as a cross-linking agent. A central composite design (CCD)-response surface methodology (RSM) was utilized to optimize the electrospinning parameters. Escherichia coli expressed eBoPAL2 exhibited the highest catalytic efficiency among four enzymes. The optimum conditions for fabricating nanofibers were determined as follows: flow rate of 0.10 mL/h, voltage of 13.8 kV, and distance of 13 cm. The response surface models were used to obtain the smaller the fiber diameters as well as the highest PAL activity in the enzyme immobilization. Compared with free BoPALs, immobilized BoPALs can be reused for at least 6 consecutive cycles. The remained activity of the immobilized BoPAL proteins after storage at 4 °C for 30 days were between 75 and 83%. In addition, the tolerance against denaturants of the immobilized BoPAL proteins were significantly enhanced. As a result, the dextran polyaldehyde natural cross-linking agent can effectively replace traditional chemical cross-linking agents for the immobilization of the BoPAL enzymes. The PAL/nylon 6/polyvinyl alcohol (PVA)/chitosan (CS) nanofibers made are extremely stable and are practical for industrial applications in the future.

Robust nanocarriers to engineer nanobiocatalysts for bioprocessing applications

The synergistic integration of bio-catalysis engineering with nanostructured materials, as unique multifunctional carrier matrices, has emerged as a new interface of nanobiocatalysis (NBC). NBC is an emerging innovation that offers significant considerations to expand the designing and fabrication of robust catalysts at the nanoscale with improved catalytic characteristics for multipurpose bioprocessing applications. In addition, nanostructured materials with unique structural, physical, chemical, and functional entities have manifested significant contributions in mimicking the enzyme microenvironment. A fine-tuned enzyme microenvironment with an added-value of NBC offers chemo- regio- and stereo- selectivities and specificities. Furthermore, NBC is growing rapidly and will become a powerful norm in bio-catalysis with much controlled features, such as selectivity, specificity, stability, resistivity, induce activity, reaction efficacy, multi-usability, improved mass transfer efficiency, high catalytic turnover, optimal yield, ease in recovery, and cost-effectiveness. Considering the above critics and unique structural, physicochemical, and functional attributes, herein, we present and discuss advances in NBC and its bioprocessing applications in different fields. Briefly, this review is focused on four parts, i.e., (1) NBC as a drive towards applied nanobiocatalysts (as an introduction with opportunities), (2) promising nanocarriers to develop nanobiocatalysts, (3) applications in the fields of biotransformation, biofuel production, carbohydrate hydrolysis, bio-/nanosensing, detergent formulations, and extraction and purification of value-added compounds, and (4) current challenges, concluding remarks, and future trends.

Self-Assembly and Mechanical Properties of Engineered Protein Based Multifunctional Nanofiber for Accelerated Wound Healing

The present work reports a new route for preparing tunable multifunctional biomaterials through the combination of synthetic biology and material chemistry. Genetically encoded catechol moiety is evolved in a nanofiber mat with defined surface and secondary reactive functional chemistry, which promotes self-assembly and wet adhesion property of the protein. The catechol moiety is further exploited for the controlled release of boric acid that provides a congenial cellular microenvironment for accelerated wound healing. The presence of 3,4-dihydroxyphenylalanine in the nanofiber mat act as a stimulus to trigger cell proliferation, migration, and vascularization to accelerate wound healing. Electron paramagnetic resonance, NMR, FTIR, and circular dichroism spectroscopy confirm the structural integrity, antioxidant property, and controlled release of boric acid. Fluorescent and scanning electron microscopy reveals the 3D architecture of nanofiber mat, which favors fibroblast growth, endothelial cell attachment, and tube formation, which are the desirable properties of a wound-healing material. Animal studies in the murine wound healing model assert that the multifunctional biomaterial significantly improve re-epithelialization and accelerate wound closure.

Spherical vs rod-like cellulose nanocrystals from enzymolysis: A comparative study as reinforcing agents on polyvinyl alcohol

In this paper, we have isolated cellulose nanocrystallines (CNCs) with different morphologies by enzymatic hydrolysis, and prepared flexible and transparent nanocomposite films with PVA matrix via solution casting. By means of SEM, UV-vis, XRD, DTG, FT-IR and mechanical methods, the effects of rod-shaped cellulose nanocrystallines (RCNCs) and spherical cellulose nanocrystallines (SCNCs) on PVA nanocomposite films were compared systematically. The results showed CNCs with different morphologies had little effect on the transparency of the composite films, and the crystallinity fluctuated with the change of CNCs additive amount. Compared with the RCNCs, SCNCs had a better improve ability to the thermal stability of the composite films by promoting pyrolysis temperature 60-80 °C. On the contrary, the maximum mechanical properties of the composite films of RCNCs were much higher than those of SCNCs, and the Young's modulus of the PVA/RCNCs composite film were increased by 120.97 % in comparison with the pure PVA.

A Comprehensive Review of the Covalent Immobilization of Biomolecules onto Electrospun Nanofibers

Biomolecule immobilization has attracted the attention of various fields such as fine chemistry and biomedicine for their use in several applications such as wastewater, immunosensors, biofuels, et cetera. The performance of immobilized biomolecules depends on the substrate and the immobilization method utilized. Electrospun nanofibers act as an excellent substrate for immobilization due to their large surface area to volume ratio and interconnectivity. While biomolecules can be immobilized using adsorption and encapsulation, covalent immobilization offers a way to permanently fix the material to the fiber surface resulting in high efficiency, good specificity, and excellent stability. This review aims to highlight the various covalent immobilization techniques being utilized and their benefits and drawbacks. These methods typically fall into two categories: (1) direct immobilization and (2) use of crosslinkers. Direct immobilization techniques are usually simple and utilize the strong electrophilic functional groups on the nanofiber. While crosslinkers are used as an intermediary between the nanofiber substrate and the biomolecule, with some crosslinkers being present in the final product and others simply facilitating the reactions. We aim to provide an explanation of each immobilization technique, biomolecules commonly paired with said technique and the benefit of immobilization over the free biomolecule.

A Facile Method for the Fabrication of Silver Nanoparticles Surface Decorated Polyvinyl Alcohol Electrospun Nanofibers and Controllable Antibacterial Activities

Polyvinyl alcohol (PVA) electrospun nanofibers (NFs) are ideal carriers for loading silver nanoparticles (Ag NPs) serving as antibacterial materials. However, it is still a challenge to adjust the particles size, distribution, and loading density via a convenient and facile method in order to obtain tunable structure and antimicrobial activities. In this study, Ag NPs surface decorated PVA composite nanofibers (Ag/PVA CNFs) were fabricated by the solvothermal method in ethylene glycol, which plays the roles of both reductant and solvent. The morphology and structure of the as-fabricated Ag/PVA CNFs were characterized by scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, X-ray diffraction, UV-visible spectroscopy, and Fourier transform infrared spectroscopy. Ag NPs had an average diameter of 30 nm, the narrowest size distribution and the highest loading density were successfully decorated on the surfaces of PVA NFs, at the AgNO3 concentration of 0.066 mol/L. The antibacterial properties were evaluated by the methods of absorption, turbidity, and growth curves. The as-fabricated Ag/PVA hybrid CNFs exhibit excellent antimicrobial activities with antibacterial rates over 98%, especially for the sample prepared with AgNO3 concentration of 0.066 mol/L. Meanwhile, the antibacterial effects are more significant in the Gram-positive bacteria of Staphylococcus aureus (S. aureus) than the Gram-negative bacteria of Escherichia coli (E. coli), since PVA is more susceptive to S. aureus. In summary, the most important contribution of this paper is the discovery that the particles size, distribution, and loading density of Ag NPs on PVA NFs can be easily controlled by adjusting AgNO3 concentrations, which has a significant impact on the antibacterial activities of Ag/PVA CNFs.

Application of blocking and immobilization of electrospun fiber in the biomedical field

The fiber obtained by electrospinning technology is a kind of biomaterial with excellent properties, which not only has a unique micro-nanostructure that gives it a large specific surface area and porosity, but also has satisfactory biocompatibility and degradability (if the spinning material used is a degradable polymer). These biomaterials provide a suitable place for cell attachment and proliferation, and can also achieve immobilization. On the other hand, its large porosity and three-dimensional spatial structure show unique blocking properties in drug delivery applications in order to achieve the purpose of slow release or even controlled release. The immobilization effect or blocking effect of these materials is mainly reflected in the hollow or core-shell structure. The purpose of this paper is to understand the application of the electrospun fiber based on biodegradable polymers (aliphatic polyesters) in the biomedical field, especially the immobilization or blocking effect of the electrospun fiber membrane on cells, drugs or enzymes. This paper focuses on the performance of these materials in tissue engineering, wound dressing, drug delivery system, and enzyme immobilization technology. Finally, based on the existing research basis of the electrospun fiber in the biomedical field, a potential research direction in the future is put forward, and few suggestions are also given for the technical problems that urgently need to be solved.

Extreme-Pressure Superlubricity of Polymer Solution Enhanced with Hydrated Salt Ions

The development of new routes or materials to realize superlubricity under high contact pressure can result in energy-saving and reduction of emissions. In this study, superlubricity (μ = 0.0017) under extreme pressure (717 MPa, more than twice the previously reported liquid superlubricity) between the frictional pair of Si₃N₄/sapphire was achieved by prerunning-in with a H₃PO₄ (HP) solution followed by lubrication with an aqueous solution consisting of poly(vinyl alcohol) (PVA) and sodium chloride (NaCl). Under the same test condition, the aqueous PVA lubricant did not show superlubricity. Results of X-ray photoelectron spectroscopy and Raman spectroscopy indicate the formation of a PVA-adsorbed film at the frictional interface after lubrication with PVA but not after lubrication with PVA/NaCl, indicating competitive adsorption between hydrated Na⁺ ions and PVA molecules. The hydrated Na⁺ ions adsorbed preferentially to the solid surfaces, causing the transformation of the shear interface from a polymer film/polymer film to a solid/polymer film. Meanwhile, the hydrated Na⁺ ions also produced hydration repulsion force and induced low shear stress between the solid surfaces. Furthermore, NaCl increased the viscosity of the polymer lubricant, enhanced the hydrodynamic effect between interfaces, and decreased direct contact between the friction pair, causing a further reduction in friction. Thus, the superlubricity of the PVA/NaCl mixture is attributed to the combination of hydration and hydrodynamic effects. This study provides a novel route and mechanism for achieving extreme-pressure superlubricity at the macroscale, through the synergistic lubricating effect of hydrated ions and a polymer solution, propelling the industrial application of superlubricity.

Enhanced Catalytic Performance of Trichoderma reesei Cellulase Immobilized on Magnetic Hierarchical Porous Carbon Nanoparticles

Cellulase from Trichoderma reesei was immobilized by covalent or non-covalent binding onto magnetic hierarchical porous carbon (MHPC) nanomaterials. The immobilization yield and the enzyme activity were higher when covalent immobilization approach was followed. The covalent immobilization approach leads to higher immobilization yield (up to 96%) and enzyme activity (up to 1.35 U mg^-1) compared to the non-covalent cellulase binding. The overall results showed that the thermal, storage and operational stability of the immobilized cellulase was considerably improved compared to the free enzyme. The immobilized cellulose catalyzed the hydrolysis of microcrystalline cellulose up to 6 consecutive successive reaction cycles, with a total operation time of 144 h at 50 °C. The half-life time of the immobilized enzyme in deep eutectic solvents-based media was up to threefold higher compared to the soluble enzyme. The increased pH and temperature tolerance of the immobilized cellulase, as well as the increased operational stability in aqueous and deep eutectic solvents-based media indicate that the use of MHPCs as immobilization nanosupport could expand the catalytic performance of cellulolytic enzymes in various reaction conditions.

Enzyme Immobilization on Nanomaterials for Biosensor and Biocatalyst in Food and Biomedical Industry

Enzymes exhibit a great catalytic activity for several physiological processes. Utilization of immobilized enzymes has a great potential in several food industries due to their excellent functional properties, simple processing and cost effectiveness during the past decades. Though they have several applications, they still exhibit some challenges. To overcome the challenges, nanoparticles with their unique physicochemical properties act as very attractive carriers for enzyme immobilization. The enzyme immobilization method is not only widely used in the food industry but is also a component methodology in the pharmaceutical industry. Compared to the free enzymes, immobilized forms are more robust and resistant to environmental changes. In this method, the mobility of enzymes is artificially restricted to changing their structure and properties. Due to their sensitive nature, the classical immobilization methods are still limited as a result of the reduction of enzyme activity. In order to improve the enzyme activity and their properties, nanomaterials are used as a carrier for enzyme immobilization. Recently, much attention has been directed towards the research on the potentiality of the immobilized enzymes in the food industry. Hence, the present review emphasizes the different types of immobilization methods that is presently used in the food industry and other applications. Various types of nanomaterials such as nanofibers, nanoflowers and magnetic nanoparticles are significantly used as a support material in the immobilization methods. However, several numbers of immobilized enzymes are used in the food industries to improve the processing methods which not only reduce the production cost but also the effluents from the industry.

Silicon substituted hydroxyapatite/VEGF scaffolds stimulate bone regeneration in osteoporotic sheep

Silicon-substituted hydroxyapatite (SiHA) macroporous scaffolds have been prepared by robocasting. In order to optimize their bone regeneration properties, we have manufactured these scaffolds presenting different microstructures: nanocrystalline and crystalline. Moreover, their surfaces have been decorated with vascular endothelial growth factor (VEGF) to evaluate the potential coupling between vascularization and bone regeneration. In vitro cell culture tests evidence that nanocrystalline SiHA hinders pre-osteblast proliferation, whereas the presence of VEGF enhances the biological functions of both endothelial cells and pre-osteoblasts. The bone regeneration capability has been evaluated using an osteoporotic sheep model. In vivo observations strongly correlate with in vitro cell culture tests. Those scaffolds made of nanocrystalline SiHA were colonized by fibrous tissue, promoted inflammatory response and fostered osteoclast recruitment. These observations discard nanocystalline SiHA as a suitable material for bone regeneration purposes. On the contrary, those scaffolds made of crystalline SiHA and decorated with VEGF exhibited bone regeneration properties, with high ossification degree, thicker trabeculae and higher presence of osteoblasts and blood vessels. Considering these results, macroporous scaffolds made of SiHA and decorated with VEGF are suitable bone grafts for regeneration purposes, even in adverse pathological scenarios such as osteoporosis. STATEMENT OF SIGNIFICANCE: For the first time, the in vivo behavior of scaffolds made of silicon substituted hydroxyapatites (SiHA) has been evaluated under osteoporosis conditions. In order to optimize the bone regeneration properties of these bioceramics, 3D macroporous scaffolds have been manufactured by robocasting and implanted in osteoporotic sheep. Our experimental design shed light on the important issue of the biological response of nano-sized bioceramics vs highly crystalline bioceramics, as well as on the importance of coupling vascularization and bone growth processes by decorating SiHA scaffolds with vascular endothelial growth factor.

Layered Co-Immobilization of β-Glucosidase and Cellulase on Polymer Film by Visible-Light-Induced Graft Polymerization

Exploring a suitable immobilization strategy to improve catalytic efficiency and reusability of cellulase is of great importance to lowering the cost and promoting the industrialization of cellulose-derived bioethanol. In this work, a layered structure with a thin PEG hydrogel as the inner layer and sodium polyacrylate (PAANa) brush as the outer layer was fabricated on low density polyethylene (LDPE) film by visible-light-induced graft polymerization. Two enzymes, β-glucosidase (BG) and cellulase, were separately coimmobilized onto this hierarchical film. As supplementary to cellulase for improving catalytic efficiency, BG was in situ entrapped into the inner PEG hydrogel layer during the graft polymerization from the LDPE surface. After graft polymerization of sodium acrylate on the PEG hydrogel layer was reinitiated, cellulase was covalently attached on the outer PAANa brush layer. Owing to the mild reaction condition (visible-light irradiation and room temperature), the immobilized BG could retain a high activity after the graft polymerization. The immobilization did not alter the optimal pH and temperature of BG or the optimal temperature of cellulase. However, the optimal pH of cellulase shifts to 5.0 after immobilization. Compared with the original activity of single cellulase system and isolated BG/cellulase immobilization system, the dual-enzyme system exhibited 82% and 20% increase in catalytic activity, respectively. The dual-enzyme system could maintain 93% of carboxymethylcellulose sodium salt (CMC) activity after repeating 10 cycles of hydrolysis and 89% of filter paper activity after 6 cycles relative to original activity, exhibiting excellent reusability. This layer coimmobilization system of BG and cellulase on the polymer film displays tremendous potential for practical application in a biorefinery.

Production of glutaric acid from 5-aminovaleric acid by robust whole-cell immobilized with polyvinyl alcohol and polyethylene glycol

Glutaric acid is an attractive C5 dicarboxylic acid with wide applications in the biochemical industry. Glutaric acid can be produced by fermentation and bioconversion, and several of its biosynthesis pathways have been well characterized, especially the simple pathway involving glutaric acid from l-lysine using 5-aminovaleric acid. We previously reported the production of glutaric acid using 5-aminovaleric acid and α-ketoglutaric acid by a whole-cell reaction, resulting in a high conversion yield. In this study, we sought to enhance the stability and reusability of this whole-cell system for realizing the efficient production of glutaric acid under harsh reaction conditions. To this end, various matrices were screened to immobilize Escherichia coli whole-cell overexpressing 4-aminobutyrate aminotransferase (GabT), succinate semi-aldehyde dehydrogenase (GabD), and NAD(P)H oxidase (NOX). We ultimately selected a PVA-PEG gel (LentiKats^®) for cell entrapment, and several factors of the reaction were optimized. The optimal temperature and pH were 35 °C and 8.5, respectively. Treatment with Tween 80 as a surfactant, as well as additional NOX, was found to be effective. Under the optimized conditions, an immobilized cell retained 55% of its initial activity even after the eighth cycle, achieving 995.2 mM accumulated glutaric acid, whereas free cell lost most of their activity after only two cycles. This optimized whole-cell system can be used in the large-scale production of glutaric acid.

Investigation of nanoparticle immobilized cellulase: nanoparticle identity, linker length and polyphenol hydrolysis

Cellulase containing nanobiocatalysts have been useful as an extraction tool based on their ability to disrupt plant cell walls. In this work, we investigate the effect of nanoparticle composition and chemical linkage towards immobilized cellulase activity. Cellulase nanoconstructs have been prepared, characterized and compared for their loading efficiencies with standard assays and enzyme kinetics and correlate well with the cognate loading efficiencies. Application of the cellulase-immobilized nanoparticles on onion skins results in release of a distinctive composition of polyphenols. The aglycosidic form of quercetin is the dominant product of onion skin hydrolysis affected by cellulase nanobiocatalysts. Chitosan-coated iron oxide nanoparticles with APTES-conjugated cellulase are found to be most effective for polyphenol release and for transformation of glycosidic to aglycosidic form of quercetin. These results shed light on the activity of immobilized cellulase beyond their role in cell wall disruption and are important for the practical application of cellulase nanobiocatalysts.

Anisotropic Cellulose Nanofibers/Polyvinyl Alcohol/Graphene Aerogels Fabricated by Directional Freeze-drying as Effective Oil Adsorbents

Under the current situation of frequent oil spills, the development of green and recyclable high-efficiency oil-absorbing aerogel materials has attracted wide attention from researchers. In this study, we report a high-strength, three-dimensional hydrophobic cellulose nanofiber (CNF)/polyvinyl alcohol (PVA)/graphene oxide (GO) composite aerogel with an anisotropic porous structure, which was fabricated by directional freeze-drying technology using anisotropically grown ice crystals as a template, followed by hydrophobic treatment with a simple dip coating process. The prepared composite aerogel presented anisotropic multi-level pore microstructures, low density (17.95 mg/cm3) and high porosity (98.8%), good hydrophobicity (water contact angle of 142°) and great adsorption capacity (oil absorption reaching 96 times its own weight). More importantly, the oriented aerogel had high strength, whose compressive stress at 80% strain reached 0.22 MPa and could bear more than 22,123 times its own weight without deformation. Therefore, the CNF/PVA/GO composite aerogel prepared by a simple and easy-to-operate directional freeze-drying method is a promising absorbent for oil-water separation.

Functionalized kaolin as support for endoglucanase immobilization

Endoglucanases are an enzyme of cellulases complex that has a great potential for many technological applications. One of the issues of its use concerns the recovery and reuse of this enzyme. Thus, in this study, the use of a surface-modified kaolin was evaluated to immobilize endoglucanase and evaluate the enzyme activity for its reuse. Kaolin was surface modified with 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde (GA). In addition, the properties of the immobilized enzyme were investigated and compared with those of the free enzyme. Results showed that the optimal pH value of endoglucanase was not affected by the immobilization process but showed a broader range of optimal temperature compared to free enzyme. Immobilization on kaolin allowed fast and easy cellulase recovery with a loss of enzyme activity of only 20% after eight cycles of use. These results indicate that kaolin is a promising substitute to the currently synthetic supports studied for cellulases immobilization with the advantage of being abundant in nature, resistant to microbial attack, chemically and mechanically stable.

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.

Effective quorum quenching with a conformation-stable recombinant lactonase possessing a hydrophilic polymeric shell fabricated via electrospinning

Quorum sensing (QS) in Gram-negative bacteria is frequently regulated by the diffusible signal N-acylhomoserine lactone (AHL) along with the production of virulence factors in pathogens. To inhibit QS, we fabricated heat-resistant, long-term-stable AHL-lactonase AiiM by electrospinning (ES) aqueous polyvinyl alcohol (PVA) solution containing genetically engineered AiiM with a maltose-binding protein (MBP) tag. MBP-AiiM was immobilized via its inclusion within a dense PVA shell formed during the drying process of ES, followed by cross-linking between hydroxyl groups on PVA. Secondary structure analysis via circular dichroism suggested no conformational change in the MBP-AiiM during ES. Even after pre-heating of MBP-AiiM/PVA fiber mats at 70 °C for 24 h, QS-dependent prodigiosin production in the model pathogen Serratia marcescens AS-1 was effectively inhibited to 0.13% that of the control. Additionally, relative prodigiosin production was reduced to ~20% that of the control after 5-month storage in buffer solution. These results suggest that a shear-thinning process using an entangled PVA aggregate during elongational changes to fibrous domains and a drying process during ES contributes not to enzymatic inactivation caused by conformational changes, but rather to the fabrication of a dense PVA shell around the MBP-AiiM molecules to protect them from disruptors including heating. The developed quorum-quenching enzyme has high potential to inhibit AHL-mediated QS frequently appearing in various Gram-negative bacteria.

"Smart" chemistry and its application in peroxidase immobilization using different support materials

In the past few decades, the enzyme immobilization technology has been exploited a lot and thus became a matter of rational design. Immobilization is an alternative approach to bio-catalysis with the added benefits, adaptability to automation and high-throughput applications. Immobilization-based approaches represent simple but effective routes for engineering enzyme catalysts with higher activities than wild-type or pristine counterparts. From the chemistry viewpoint, the concept of stabilization via manipulation of functional entities, the enzyme surfaces have been an important driving force for immobilizing purposes. In addition, the unique physiochemical and structural functionalities of pristine or engineered cues, or insoluble support matrices (carrier) such as mean particle diameter, swelling behavior, mechanical strength, and compression behavior are of supreme interest and importance for the performance of the immobilized systems. Immobilization of peroxidases into/onto insoluble support matrices is advantageous for practical applications due to convenience in handling, ease separation of enzymes from a reaction mixture and the reusability. A plethora of literature is available explaining individual immobilization system. However, current literature lacks the chemistry viewpoint of immobilization. This review work presents state-of-the-art "Smart" chemistry of immobilization and novel potentialities of several materials-based cues with different geometries including microspheres, hydrogels and polymeric membranes, nanoparticles, nanofibers, composite and hybrid or blended support materials. The involvement of various functional groups including amino, thiol, carboxylic, hydroxyl, and epoxy groups via "click" chemistry, amine chemistry, thiol chemistry, carboxyl chemistry, and epoxy chemistry over the protein surfaces is discussed.