Enzyme immobilization on electrospun polymer nanofibers: An overview

An environmentally-friendly enzyme-based nanofibrous membrane for 3,3′,5,5′-tetrabromobisphenol removal

Immobilization of HRP on NCC-incorporated CS/PVA membranes and its application in TBBPA removal.

Functional microgels assisted tryptic digestion and quantification of cytochrome c through internal standard mass spectrometry

Quantitation of cytochrome c (Cyt c) in cell lysates through surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using gold nanoparticles (Au NPs) as the matrix and GR-10 peptide as an internal standard has been demonstrated. To shorten digestion time, temperature sensitive microgels containing trypsin (TR) and Au NPs have been employed. As-prepared functional microgels (TR/Au NPs/MGs) allow digestion of Cyt c within 15 s under microwave irradiation. The internal standard SALDI-MS approach provides linearity (R(2) = 0.98) of MS signal ratio (I 1168.6/I 1067.6) of the tryptic digested peptide (m/z 1168.6) to GR-10 peptide (m/z 1067.6) against the concentration of Cyt c ranging from 25 to 200 nM, with a limit of detection (at a signal-to-noise ratio of 3) of 10 nM. This approach has been validated by the analysis of the lysates of HeLa cells, with an average concentration of 13.7 ± 3.5 μM for cytoplasmic Cyt c. Increased concentrations of Cyt c in the HeLa cells treated with etoposide (a commercial drug) or carbon dots (potential drug) have been revealed through this simple, sensitive, and rapid SALDI-MS approach, supporting the drugs induced Cyt c-mediated apoptosis of the cells. This study has shown that this internal standard SALDI-MS approach holds great potential for cell study.

Electrochemical biosensor based on functional composite nanofibers for detection of K-ras gene via multiple signal amplification strategy

An electrochemical biosensor based on functional composite nanofibers for hybridization detection of specific K-ras gene that is highly associated with colorectal cancer via multiple signal amplification strategy has been developed. The carboxylated multiwalled carbon nanotubes (MWCNTs) doped nylon 6 (PA6) composite nanofibers (MWCNTs-PA6) was prepared using electrospinning, which served as the nanosized backbone for thionine (TH) electropolymerization. The functional composite nanofibers [MWCNTs-PA6-PTH, where PTH is poly(thionine)] used as supporting scaffolds for single-stranded DNA1 (ssDNA1) immobilization can dramatically increase the amount of DNA attachment and the hybridization sensitivity. Through the hybridization reaction, a sandwich format of ssDNA1/K-ras gene/gold nanoparticle-labeled ssDNA2 (AuNPs-ssDNA2) was fabricated, and the AuNPs offered excellent electrochemical signal transduction. The signal amplification was further implemented by forming network-like thiocyanuric acid/gold nanoparticles (TA/AuNPs). A significant sensitivity enhancement was obtained; the detection limit was down to 30fM, and the discriminations were up to 54.3 and 51.9% between the K-ras gene and the one-base mismatched sequences including G/C and A/T mismatched bases, respectively. The amenability of this method to the analyses of K-ras gene from the SW480 colorectal cancer cell lysates was demonstrated. The results are basically consistent with those of the K-ras Kit (HRM: high-resolution melt). The method holds promise for the diagnosis and management of cancer.

Cross-linked polymer nanofibers for hyperthermophilic enzyme immobilization: approaches to improve enzyme performance

We report an enzyme immobilization method effective at elevated temperatures (up to 105 °C) and sufficiently robust for hyperthermophilic enzymes. Using a model hyperthermophilic enzyme, α-galactosidase from Thermotoga maritima, immobilization within chemically cross-linked poly(vinyl alcohol) (PVA) nanofibers to provide high specific surface area is achieved by (1) electrospinning a blend of a PVA and enzyme and (2) chemically cross-linking the polymer to entrap the enzyme within a water insoluble PVA fiber. The resulting enzyme-loaded nanofibers are water-insoluble at elevated temperatures, and enzyme leaching is not observed, indicating that the cross-linking effectively immobilizes the enzyme within the fibers. Upon immobilization, the enzyme retains its hyperthermophilic nature and shows improved thermal stability indicated by a 5.5-fold increase in apparent half-life at 90 °C, but with a significant decrease in apparent activity. The loss in apparent activity is attributed to enzyme deactivation and mass transfer limitations. Improvements in the apparent activity can be achieved by incorporating a cryoprotectant during immobilization to prevent enzyme deactivation. For example, immobilization in the presence of trehalose improved the apparent activity by 10-fold. Minimizing the mat thickness to reduce interfiber diffusion was a simple and effective method to further improve the performance of the immobilized enzyme.

Self-Assembly of Amyloid Fibrils That Display Active Enzymes

Enzyme immobilization is an important strategy to enhance the stability and recoverability of enzymes and to facilitate the separation of enzymes from reaction products. However, enzyme purification followed by separate chemical steps to allow immobilization on a solid support reduces the efficiency and yield of the active enzyme. Here we describe polypeptide constructs that self-assemble spontaneously into nanofibrils with fused active enzyme subunits displayed on the amyloid fibril surface. We measured the steady-state kinetic parameters for the appended enzymes in situ within fibrils and compare these with the identical protein constructs in solution. Finally, we demonstrated that the fibrils can be recycled and reused in functional assays both in conventional batch processes and in a continuous-flow microreactor.

Biodegradable polymers for electrospinning: towards biomedical applications

Electrospinning has received much attention recently due to the growing interest in nano-technologies and the unique material properties. This review focuses on recent progress in applying electrospinning technique in production of biodegradable nanofibers to the emerging field of biomedical. It first introduces the basic theory and parameters of nanofibers fabrication, with focus on factors affecting the morphology and fiber diameter of biodegradable nanofibers. Next, commonly electrospun biodegradable nanofibers are discussed, and the comparison of the degradation rate of nanoscale materials with macroscale materials are highlighted. The article also assesses the recent advancement of biodegradable nanofibers in different biomedical applications, including tissue engineering, drug delivery, biosensor and immunoassay. Future perspectives of biodegradable nanofibers are discussed in the last section, which emphasizes on the innovation and development in electrospinning of hydrogels nanofibers, pore size control and scale-up productions.

Recent advances in electrospinning technology and biomedical applications of electrospun fibers

Electrospinning technology underwent rapid development in recent years, which can be used for fabricating electrospun fibers with different morphologies and multidimensional structures. These fibers are widely applied in medical diagnosis, tissue engineering, replica molding and other applications. Here we review the recent advances in the electrospinning technology, especially technical progress in fabricating electrospun fibers and assemblies with multidimensional structures, and the biomedical applications of these fibers.

Laccase immobilized on a PAN/adsorbents composite nanofibrous membrane for catechol treatment by a biocatalysis/adsorption process

The treatment of catechol via biocatalysis and adsorption with a commercial laccase immobilized on polyacrylonitrile/montmorillonite/graphene oxide (PAN/MMT/GO) composite nanofibers was evaluated with a homemade nanofibrous membrane reactor. The properties in this process of the immobilized laccase on PAN, PAN/MMT as well as PAN/MMT/GO with different weight ratios of MMT and GO were investigated. These membranes were successfully applied for removal of catechol from an aqueous solution. Scanning electron microscope images revealed different morphologies of the enzyme aggregates on different supports. After incorporation of MMT or MMT/GO, the optimum pH showed an alkaline shift to 4, compared to 3.5 for laccase immobilized on pure PAN nanofibers. The optimum temperature was at 55 °C for all the immobilized enzymes. Besides, the addition of GO improved the operational stability and storage stability. A 39% ± 2.23% chemical oxygen demand (COD) removal from the catechol aqueous solution was achieved. Experimental results suggested that laccase, PAN, adsorbent nanoparticles (MMT/GO) can be combined together for catechol treatment in industrial applications.

In Situ Deposition of PLGA Nanofibers via Solution Blow Spinning

Nanofiber mats and scaffolds have been widely investigated for biomedical applications. Commonly fabricated using electrospinning, nanofibers are generated ex situ using an apparatus that requires high voltages and an electrically conductive target. We report the use of solution blow spinning to generate conformal nanofiber mats/meshes on any surface in situ, utilizing only a commercial airbrush and compressed CO₂. Solution and deposition conditions of PLGA nanofibers were optimized and mechanical properties characterized with dynamic mechanical analysis. Nanofiber mat degradation was monitored for morphologic and molecular weight changes in vitro. Biocompatibility of the direct deposition of nanofibers onto two cell lines was demonstrated in vitro and interaction with blood was qualitatively assessed with scanning electron microscopy. A pilot animal study illustrated the wide potential of this technique across multiple surgical applications, including its use as a surgical sealant, hemostatic, and buttress for tissue repair.

Fabrication of zeolite-polymer composite nanofibers for removal of uremic toxins from kidney failure patients

There is a need to develop a simple, cheap, and accessible method of treating patients with kidney failure, especially in resource-limited environments such as disaster areas and the developing world due to the inaccessibility of conventional hemodialysis treatments. In this study, we develop a zeolite-polymer composite nanofiber mesh to remove uremic toxins for blood purification. The nanofiber is composed of blood compatible poly(ethylene-co-vinyl alcohol) (EVOH) as the primary matrix polymer and zeolites which are capable of selectively adsorbing uremic toxins such as creatinine. The composite fiber meshes were produced by a cost-effective electrospinning method: electrospinning composite solutions of EVOH and zeolites. Scanning electron microscope (SEM) images revealed that the 7 w/v% EVOH solution produced non-woven fibers with a continuous and smooth morphology. The SEM also showed that over 90% of zeolites in the solution were successfully incorporated into the EVOH nanofibers. Although the barrier properties of the EVOH matrix lowered the creatinine adsorption capacity of the zeolites in the fiber when compared with adsorption to free zeolites, their adsorption capacity was still 67% of the free zeolites. The proposed composite fibers have the potential to be utilized as a new approach to removing nitrogenous waste products from the bloodstream without the requirement of specialized equipment.

Design and development of papain–urea loaded PVA nanofibers for wound debridement

Nanofiber based delivery of enzyme for wound debridement with sustained functional integrity.

Effective encapsulation of laccase in an aluminium silicate nanotube hydrogel

Laccase was encapsulated during aluminium silicate nanotube (ASNT) hydrogel formation. This encapsulation method has fewer negative effects on the relatively unstable enzyme because of the milder conditions used compared to sol–gel silica formation.

“Ready-to-use” hollow nanofiber membrane-based glucose testing strips

Fabrication and application of a hollow nanofiber membrane-based test strip for glucose detection.

Laccase-polyacrylonitrile nanofibrous membrane: highly immobilized, stable, reusable, and efficacious for 2,4,6-trichlorophenol removal

Increasing attention has been given to nanobiocatalysis for commercial applications. In this study, laccase was immobilized on polyacrylonitrile (PAN) nanofibrous membranes through ethanol/HCl method of amidination reaction and successfully applied for removal of 2,4,6-trichlorophenol (TCP) from water. PAN membranes with fiber diameters from 200 nm to 300 nm were fabricated via electrospinning and provided a large surface area for enzyme immobilization and catalytic reactions. Images of scanning electron microscope demonstrated the enzyme molecules were aggregated on the nanofiber surface. The immobilized laccase exhibited 72% of the free enzyme activity and kept 60% of its initial activity after 10 operation cycles. Moreover, the storage stability of the immobilized laccase was considered excellent because they maintained more than 92% of the initial activity after 18 days of storage, whereas the free laccase retained only 20%. The laccase-PAN nanofibrous membranes exhibited high removal efficiency of TCP under the combined actions of biodegradation and adsorption. More than 85% of the TCP was removed under optimum conditions. Effects of various factors on TCP removal efficiency of the immobilized laccase were analyzed. Results suggest that laccase-PAN nanofibrous membranes can be used in removing TCP from aqueous sources and have potential for use in other commercial applications.

Immobilization of horseradish peroxidase on electrospun microfibrous membranes for biodegradation and adsorption of bisphenol A

Horseradish peroxidase (HRP) from roots of horseradish (Amoracia rusticana) was successfully immobilized on novel enzyme carriers, poly(methyl methacrylate-co-ethyl acrylate) (PMMA CEA) microfibrous membranes, and used for removal of bisphenol A from water. PMMA CEA fibrous membranes (PFM) with fiber diameters of 300-500 nm, were fabricated by electrospinning. HRP was covalently immobilized on the surface of microfibers previously activated by polyethylenimine and glutaraldehyde. HRP loading reached 285 mg/g, and enzyme activity was 70% of free HRP after immobilization. Both stabilities and reusability of HRP were greatly improved after immobilization. After six repeated runs, immobilized HRP retained about 50% of its initial activity. Immobilized HRP exhibited significantly higher removal efficiency for bisphenol A (BPA) in 3h (93%) compared with free HRP (61%) and PFM alone (42%). The high BPA removal can be resulted by improvement of catalytic activity of immobilized HPR with adsorption on modified PMMA CEA support.

Surface modification of halloysite nanotubes with dopamine for enzyme immobilization

Halloysite nanotubes (HNTs) have been proposed as a potential support to immobilize enzymes. Improving enzyme loading on HNTs is critical to their practical applications. Herein, we reported a simple method on the preparation of high-enzyme-loading support by modification with dopamine on the surface of HNTs. The modified HNTs were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses. The results showed that dopamine could self-polymerize to adhere to the surface of HNTs and form a thin active coating. While the prepared hybrid nanotubes were used to immobilize enzyme of laccase, they exhibited high loading ability of 168.8 mg/g support, which was greatly higher than that on the pristine HNTs (11.6 mg/g support). The immobilized laccase could retain more than 90% initial activity after 30 days of storage and the free laccase only 32%. The immobilized laccase could also maintain more than 90% initial activity after five repeated uses. In addition, the immobilized laccase exhibited a rapid degradation rate and high degradation efficiency for removal of phenol compounds. These advantages indicated that the new hybrid material can be used as a low-cost and effective support to immobilize enzymes.

Preservation of cell viability and protein conformation on immobilization within nanofibers via electrospinning functionalized yeast

We investigate the immobilization of a model system of functionalized yeast that surface-display enhanced green fluorescent protein (eGFP) within chemically crosslinked polyvinyl alcohol (PVA) nanofibers. Yeast is incorporated into water insoluble nanofibrous materials by direct electrospinning with PVA followed by vapor phase chemical crosslinking of the polymer. Incorporation of yeast into the fibers is confirmed by elemental analysis and the viability is indicated by live/dead staining. Following electrospinning and crosslinking, we confirm that the yeast maintains its viability as well as the ability to express eGFP in the correct conformation. This method of processing functionalized yeast may thus be a powerful tool in the direct immobilization of properly folded, active enzymes within electrospun nanofibers with potential applications in biocatalysis.

Microencapsulation of chemotherapeutics into monodisperse and tunable biodegradable polymers via electrified liquid jets: control of size, shape, and drug release

This paper describes microencapsulation of antitumor agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU, Carmustine) into biodegradable polymer poly(lactic-co-glycolic) acid (PLGA) using an electrojetting technique. The resulting BCNU-loaded PLGA microcapsules have significantly higher drug encapsulation efficiency, more tunable drug loading capacity, and (3) narrower size distribution than those generated using other encapsulation methods.

Adsorption and transformation of PAHs from water by a laccase-loading spider-type reactor

The remediation of polycyclic aromatic hydrocarbons (PAHs) polluted waters has become a concern as a result of the widespread use of PAHs and their adverse impacts on water ecosystems and human health. To remove PAHs rapidly and efficiently in situ, an active fibrous membrane, laccase-loading spider-type reactor (LSTR) was fabricated by electrospinning a poly(D,L-lactide-co-glycolide) (PDLGA)/laccase emulsion. The LSTR is composed of beads-in-string structural core-shell fibers, with active laccase encapsulated inside the beads and nanoscale pores on the surface of the beads. This structure can load more laccase and retains higher activity than do linear structural core-shell fibers. The LSTR achieves the efficient removal/degradation of PAHs in water, which is attributed to not only the protection of the laccase activity by the core-shell structure but also the pre-concentration (adsorption) of PAHs on the surface of the LSTR and the concentration of laccase in the beads. Moreover, the effects of pH, temperature and dissolved organic matter (DOM) concentration on the removal of PAHs by the LSTR, in comparison with that by free laccase, have been taken into account. A synergetic mechanism including adsorption, directional migration and degradation for PAH removal is proposed.