Abstract
Cellulose, the most abundant polymer on earth, has enormous potential in developing bio-friendly, and sustainable technological products. In particular, cellulose films of nanoscale thickness (1–100 nm) are transparent, smooth (roughness <1 nm), and provide a large surface area interface for biomolecules immobilization and interactions. These attractive film properties create many possibilities for both fundamental studies and applications, especially in the biomedical field. The three liable—OH groups on the monomeric unit of the cellulose chain provide schemes to chemically modify the cellulose interface and engineer its properties. Here, the cellulose thin film serves as a substrate for biomolecules interactions and acts as a support for bio-diagnostics. This review focuses on the challenges and opportunities provided by engineering cellulose thin films for controlling biomolecules interactions. The first part reviews the methods for preparing cellulose thin films. These are by dispersing or dissolving pure cellulose or cellulose derivatives in a solvent to coat a substrate using the spin coating, Langmuir-Blodgett, or Langmuir-Schaefer method. It is shown how different cellulose sources, preparation, and coating methods and substrate surface pre-treatment affect the film thickness, roughness, morphology, crystallinity, swelling in water, and homogeneity. The second part analyses the bio-macromolecules interactions with the cellulose thin film interfaces. Biomolecules, such as antibodies and enzymes, are adsorbed at the cellulose-liquid interface, and analyzed dry and wet. This highlights the effect of film surface morphology, thickness, crystallinity, water intake capacity, and surface pre-treatment on biomolecule adsorption, conformation, coverage, longevity, and activity. Advance characterization of cellulose thin film interface morphology and adsorbed biomolecules interactions are next reviewed. X-ray and neutron scattering/reflectivity combined with atomic force microscopy (AFM), quartz crystal microbalance (QCM), microscopy, and ellipsometer allow visualizing, and quantifying the structural morphology of cellulose-biomolecule interphase and the respective biomolecules conformations, kinetics, and sorption mechanisms. This review provides a novel insight on the advantages and challenges of engineering cellulose thin films for biomedical applications. This is to foster the exploration at the molecular level of the interaction mechanisms between a cellulose interface and adsorbed biomolecules with respect to adsorbed molecules morphology, surface coverage, and quantity. This knowledge is to engineer a novel generation of efficient and functional biomedical devices.
Highlights
This review presents the methods and characterization techniques to engineer and quantify the properties of thin and smooth cellulose nanofilms
Cellulose has widely been used for 2 centuries in commodity
These properties make cellulose an attractive material for engineering advanced applications
Summary
This review presents the methods and characterization techniques to engineer and quantify the properties of thin and smooth cellulose nanofilms. The main challenge associated with using cellulose based paper bio-diagnostics is engineering functionalized surface interacting with the targeted biomolecule for a specific biomedical application. The properties of cellulose thin film interface can be optimize by: (i) functionalization of the interface by taking advantage of the 3 liable -OH groups per cellulose monomer, (ii) controlling the ratio of crystalline and amorphous phase (iii) controlling CNF/CNC assembly/organization using magnetic field (Sugiyama et al, 1992; Revol et al, 1994), shear alignment (Yoshiharu et al, 1997; Ebeling et al, 1999), and electric field alignment (Bordel et al, 2006), (iv) engineering different surface morphology, thickness, roughness, and topography. It provides insight on the best procedures for the consistent preparation of cellulose thin film of controlled structure and morphology Further it highlights on optimization of film interface properties by surface functionalization. We hope this review will provide the foundation to researchers from academics and industries for developing better biodiagnostics, sensors, coatings, and substrates
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