Immunosensors for C‑Reactive Protein Based on Ultrathin Films of Carboxylated Cellulose Nanofibrils

C-reactive protein (CRP) is an acute phase protein that has been widely used as a predictor of cardiovascular diseases. We report herein the synthesis of immunosensors based on carboxylated cellulose nanofibrils (CNF) for CRP detection, as demonstrated by quartz crystal microgravimetry (QCM). QCM sensors carrying ultrathin films of carboxylated CNF were prepared by using two protocols: (i) spin coating of CNF on the sensors followed by carboxylation via in situ oxidation with 2,2,6,6-tetramethylpiperidine 1-oxyl and (ii) carboxymethylation of CNF in aqueous dispersion followed by spin coating deposition on the sensors. Protein A was conjugated to the carboxylated CNF via <i>N</i>-(3-(Dimethylamino)­propyl)-<i>N</i>′-ethylcarbodiimide hydrochloride/<i>N</i>-hydroxysuccinimide and used as a ligand for oriented immobilization of anti C-reactive protein (anti-CRP). The different carboxyl group density of the two oxidized CNF surfaces influenced Protein A binding and, subsequently, the available immobilized anti-CRP molecules. The detection efficiency for CRP, specificity, and concentration range displayed by the carboxylated CNF-based immunosensors coupled with oriented and unoriented anti-CRP were determined and compared

Bioactive Cellulose Nanofibrils for Specific Human IgG Binding

Bioactive films were produced by conjugation of a short peptide onto modified cellulose nanofibrils (CNF). Specifically, a hydrophilic copolymer, poly­(2-aminoethyl methacrylate hydrochloride-<i>co</i>-2-hydroxyethylmethacrylate) (poly­(AMA-<i>co</i>-HEMA)), was grafted via surface initiated polymerization from an initiator coupled to CNF. The poly­(AMA-<i>co</i>-HEMA) was used as a spacer and support layer for immobilization of the peptide, acetylated-HWRGWVA, which has specific affinity with human immunoglobulin G (hIgG). Two methods for peptide grafting were compared: modification of CNF in aqueous suspension followed by assembly into a bioactive film and peptide grafting on a preformed CNF film. The CNF-based networks were examined on solid supports via atomic force microscopy (AFM) and extreme resolution imaging with ultralow electron landing energies (scanning low energy electron microscopy). The specific binding capability of hIgG and nonspecific protein resistance of the resultant peptide-modified CNF were evaluated by using quartz crystal microgravimetry (QCM). The effects of initiator concentration and thickness of poly­(AMA-<i>co</i>-HEMA) layer on hIgG adsorption were investigated in the developed systems, which exhibited high signal-to-noise response

Formation and Antifouling Properties of Amphiphilic Coatings on Polypropylene Fibers

We describe the formation of amphiphilic polymeric assemblies via a three-step functionalization process applied to polypropylene (PP) nonwovens and to reference hydrophobic self-assembled <i>n</i>-octadecyltrichlorosilane (ODTS) monolayer surfaces. In the first step, denatured proteins (lysozyme or fibrinogen) are adsorbed onto the hydrophobic PP or the ODTS surfaces, followed by cross-linking with glutaraldehyde in the presence of sodium borohydride (NaBH₄). The hydroxyl and amine functional groups of the proteins permit the attachment of initiator molecules, from which poly (2-hydroxyethyl methacrylate) (PHEMA) polymer grafts are grown directly through “grafting from” atom transfer radical polymerization. The terminal hydroxyls of HEMA’s pendent groups are modified with fluorinating moieties of different chain lengths, resulting in amphiphilic brushes. A palette of analytical tools, including ellipsometry, contact angle goniometry, Fourier transform infrared spectroscopy in the attenuated total reflection mode, and X-ray photoelectron spectroscopy is employed to determine the changes in physicochemical properties of the functionalized surfaces after each modification step. Antifouling properties of the resultant amphiphilic coatings on PP are analyzed by following the adsorption of fluorescein isothiocyanate-labeled bovine serum albumin as a model fouling protein. Our results suggest that amphiphilic coatings suppress significantly adsorption of proteins as compared with PP fibers or PP surfaces coated with PHEMA brushes. The type of fluorinated chain grafted to PHEMA allows modulation of the surface composition of the topmost layer of the amphiphilic coating and its antifouling capability

Formation and Antifouling Properties of Amphiphilic Coatings on Polypropylene Fibers

We describe the formation of amphiphilic polymeric assemblies via a three-step functionalization process applied to polypropylene (PP) nonwovens and to reference hydrophobic self-assembled <i>n</i>-octadecyltrichlorosilane (ODTS) monolayer surfaces. In the first step, denatured proteins (lysozyme or fibrinogen) are adsorbed onto the hydrophobic PP or the ODTS surfaces, followed by cross-linking with glutaraldehyde in the presence of sodium borohydride (NaBH₄). The hydroxyl and amine functional groups of the proteins permit the attachment of initiator molecules, from which poly (2-hydroxyethyl methacrylate) (PHEMA) polymer grafts are grown directly through “grafting from” atom transfer radical polymerization. The terminal hydroxyls of HEMA’s pendent groups are modified with fluorinating moieties of different chain lengths, resulting in amphiphilic brushes. A palette of analytical tools, including ellipsometry, contact angle goniometry, Fourier transform infrared spectroscopy in the attenuated total reflection mode, and X-ray photoelectron spectroscopy is employed to determine the changes in physicochemical properties of the functionalized surfaces after each modification step. Antifouling properties of the resultant amphiphilic coatings on PP are analyzed by following the adsorption of fluorescein isothiocyanate-labeled bovine serum albumin as a model fouling protein. Our results suggest that amphiphilic coatings suppress significantly adsorption of proteins as compared with PP fibers or PP surfaces coated with PHEMA brushes. The type of fluorinated chain grafted to PHEMA allows modulation of the surface composition of the topmost layer of the amphiphilic coating and its antifouling capability

Solid-State Synthesis of Metal Nanoparticles Supported on Cellulose Nanocrystals and Their Catalytic Activity

Heterogeneous catalysis has played a critical role in environmental remediation, for example, in processes that generate toxic streams. Thus, there is an ever-increasing need for green, cost-effective routes to synthesize highly active catalysts. In this study, a cellulose nanomaterial (cellulose nanocrystals, CNC) was employed as solid support for the nucleation of silver and gold nanoparticles via solid-state synthesis. The process involved solvent-free reduction in ambient conditions of metal precursors on the surface of CNC and in the presence of ascorbic acid. Surface plasmon resonance and X-ray diffraction indicated the successful formation of the metal nanoparticles, in the form of organic–inorganic hybrids. A strong hydrogen bonding was observed between CNC and the metal nanoparticles owing to the high density of hydroxyl groups in CNC, as determined by Fourier transform infrared spectroscopy. Electron microscopies indicated that the silver and gold precursors formed nanoparticles of hexagonal and spherical shape, respectively. The organic–inorganic hybrids were demonstrated as the potential catalyst for the reduction of 4-nitrophenol to 4-aminophenol. Overall, we introduce a green, solvent-free, and facile method for the production of noble metal nanoparticles supported on CNC, which offer promise in the scalable synthesis and for application in heterogeneous catalysis

Hollow Filaments from Coaxial Dry–Jet Wet Spinning of a Cellulose Solution in an Ionic Liquid: Wet-Strength and Water Interactions

Hollow tubing and tubular filaments are highly relevant to membrane technologies, vascular tissue engineering, and others. In this context, we introduce hollow filaments (HF) produced through coaxial dry–jet wet spinning of cellulose dissolved in an ionic liquid ([emim][OAc]). The HF, developed upon regeneration in water (23 °C), displays superior mechanical performance (168 MPa stiffness and 60% stretchability) compared to biobased counterparts, such as those based on collagen. The results are rationalized by the effects of crystallinity, polymer orientation, and other factors associated with rheology, thermal stability, and dynamic vapor sorption. The tensile strength and strain of the HF (dry and wet) are enhanced by drying and wetting cycles (water vapor sorption and desorption experiments). Overall, we unveil the role of water molecules in the wet performance of HF produced by cellulose regeneration from [emim][OAc], which offers a basis for selecting suitable applications

Generation of Functional Coatings on Hydrophobic Surfaces through Deposition of Denatured Proteins Followed by Grafting from Polymerization

Hydrophilic coatings were produced on flat hydrophobic substrates featuring <i>n</i>-octadecyltrichlorosilane (ODTS) and synthetic polypropylene (PP) nonwoven surfaces through the adsorption of denatured proteins. Specifically, physisorption from aqueous solutions of α-lactalbumin, lysozyme, fibrinogen, and two soy globulin proteins (glycinin and β-conglycinin) after chemical (urea) and thermal denaturation endowed the hydrophobic surfaces with amino and hydroxyl functionalities, yielding enhanced wettability. Proteins adsorbed strongly onto ODTS and PP through nonspecific interactions. The thickness of adsorbed heat-denatured proteins was adjusted by varying the pH, protein concentration in solution, and adsorption time. In addition, the stability of the immobilized protein layer was improved significantly after interfacial cross-linking with glutaraldehyde in the presence of sodium borohydride. The amino and hydroxyl groups present on the protein-modified surfaces served as reactive sites for the attachment of polymerization initiators from which polymer brushes were grown by surface-initiated atom-transfer radical polymerization of 2-hydroxyethyl methacrylate. Protein denaturation and adsorption as well as the grafting of polymeric brushes were characterized by circular dichroism, ellipsometry, contact angle, and Fourier transform infrared spectroscopy in the attenuated total reflection mode

In-Plane Compression and Biopolymer Permeation Enable Super-stretchable Fiber Webs for Thermoforming toward 3‑D Structures

The typically poor ductility of cellulosic fibers and ensuing bonded networks and paper webs set limits on any effort to produce associated three-dimensional structures without relying on chemical, often unsustainable, approaches. To address this challenge, we report on a facile and green method that combines mechanical and biopolymer treatment: in-plane compression and aqueous solution permeation via spraying. The first enabled network extensibility while the second, which relied on the use of either food-grade gelatin, guar gum, or polylactic acid, improved network strength and stiffness. As a result, an unprecedented elongation of ∼30% was achieved after unrestrained drying of the fiber web. At the same time, the structures experienced a significant increase in tensile strength and stiffness (by ∼306% and ∼690%, respectively). Such simultaneous property improvement, otherwise very difficult to achieve, represents a substantial gain in the material’s toughness, which results from the synergistic effects associated with the mechanical response of the network under load, fiber intrinsic strength, and interfiber bonding. The level of plasticity developed in fiber webs upon biaxial compaction (longitudinal followed by lateral compaction), which was performed to reduce property anisotropy, allowed the synthesis of 3-D packaging materials via direct thermoforming. Moreover, the formability was found to be temperature and humidity dependent (strain and creep compliance after creep/recovery cycles in dynamic mechanical analyses). Overall, an inexpensive, green, and scalable approach is introduced to expand the properties spaces for paper and related non-wovens that allows 2-D and 3-D formability of in-plane compacted fiber networks

Filaments with Affinity Binding and Wet Strength Can Be Achieved by Spinning Bifunctional Cellulose Nanofibrils

We demonstrate benzophenone (BP) conjugation via amine-reactive esters onto oxidized cellulosic fibers that were used as precursors, after microfluidization, of photoactive cellulose nanofibrils (CNF). From these fibrils, cellulose I filaments were synthesized by hydrogel spinning in an antisolvent followed by fast biradical UV cross-linking. As a result, the wet BP-CNF filaments retained extensively the original dry strength (a remarkable ∼80% retention). Thus, the principal limitation of these emerging materials was overcome (the wet tensile strength is typically <0.5% of the value measured in dry conditions). Subsequently, antihuman hemoglobin (anti-Hb) antibodies were conjugated onto residual surface carboxyl groups, making the filaments bifunctional for their active groups and properties (wet strength and bioactivity). Optical (surface plasmon resonance) and electroacoustic (quartz crystal microgravimetry) measurements conducted with the bifunctional CNF indicated effective anti-Hb conjugation (2.4 mg m^–2), endowing an excellent sensitivity toward Hb targets (1.7 ± 0.12 mg m^–2) and negligible nonspecific binding. Thus, the anti-Hb biointerface was deployed on filaments that captured Hb efficiently from aqueous matrices (confocal laser microscopy of FITC-labeled antibodies). Significantly, the anti-Hb biointerface was suitable for regeneration, while its sensitivity and selectivity in affinity binding can be tailored by application of blocking copolymers. The developed bifunctional filaments based on nanocellulose offer great promise in detection and affinity binding built upon 1D systems, which can be engineered into other structures for rational use of material and space

Solid Wood Modification toward Anisotropic Elastic and Insulative Foam-Like Materials

The methods used to date to produce compressible wood foam by top-down approaches generally involve the removal of lignin and hemicelluloses. Herein, we introduce a route to convert solid wood into a super elastic and insulative foam-like material. The process uses sequential oxidation and reduction with partial removal of lignin but high hemicellulose retention (process yield of 72.8%), revealing fibril nanostructures from the wood’s cell walls. The elasticity of the material is shown to result from a lamellar structure, which provides reversible shape recovery along the transverse direction at compression strains of up to 60% with no significant axial deformation. The compressibility is readily modulated by the oxidation degree, which changes the crystallinity and mobility of the solid phase around the lumina. The performance of the highly resilient foam-like material is also ascribed to the amorphization of cellulosic fibrils, confirmed by experimental and computational (molecular dynamics) methods that highlight the role of secondary interactions. The foam-like wood is optionally hydrophobized by chemical vapor deposition of short-chained organosilanes, which also provides flame retardancy. Overall, we introduce a foam-like material derived from wood based on multifunctional nanostructures (anisotropically compressible, thermally insulative, hydrophobic, and flame retardant) that are relevant to cushioning, protection, and packaging