Ramiz Boy

Fabrication and Characterization of Poly(ε-caprolactone)/α-Cyclodextrin Pseudorotaxane Nanofibers.

Multifunctional scaffolds comprising neat poly(ε-caprolactone) (PCL) and α-cyclodextrin pseudorotaxanated in α-cyclodextrin form have been fabricated using a conventional electrospinning process. Thorough in-depth characterizations were performed on the pseudorotaxane nanofibers prepared from chloroform (CFM) and CFM/dimethylformamide (DMF) utilizing scanning electron microscopy (SEM), transmission electron microscopy (TEM), rheology, differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), wide-angle X-ray diffraction (WAXD), and Instron tensile testing. The results indicate the nanofibers obtained from chloroform retain the rotaxanated structure; while those obtained from CFM/DMF had significantly dethreaded during electrospinning. As a consequence, the nanowebs obtained from CFM showed higher moduli and lower elongations at break compared to neat PCL nanowebs and PCL/α-CD nanowebs electrospun from CFM/DMF.

Correlation of the stoichiometries of poly(ε-caprolactone) and α-cyclodextrin pseudorotaxanes with their solution rheology and the molecular orientation, crystallite size, and thermomechanical properties of their nanofibers

Pseudorotaxane nanofibers based on biomedical polymers, such as poly(e-caprolactone) (PCL), and α-cyclodextrins (α-CD) open new horizons for a variety of biomedical applications. From our recent report on pseudorotaxane suspensions and nanofibers, we inferred several unique characteristics, such as improvements in mechanical properties and a several-fold increase in viscosity values at low concentrations. In this report, through in-depth characterization employing techniques, such as rheological measurements, we investigate the reasons behind the unusual viscosity values observed in their suspensions. Additionally, combining rheology and TEM, we examine the phenomena responsible for the fiber diameter variation within a single nanofiber. Although, both 2D-wide angle X-ray diffraction patterns and selected area electron microscopy showed poor molecular orientation of the polymer chains along the fiber axis in the pseudorotaxanes, we attribute the observed higher modulus values to the denser nature and crystal packing of the PCL chains emanating from the surfaces of the columnar host α-CD crystals in the pseudorotaxanes, which was evidenced by crystallite size analyses. Finally, dynamic mechanical analyses illustrated that the interlacing of polymer chains protruding from the columnar α-CD cavities have a profound impact on the mechanical properties of these composites.

A Review of Cellulose and Cellulose Blends for Preparation of Bio-derived and Conventional Membranes, Nanostructured Thin Films, and Composites

ABSTRACT Cellulose has been used as a raw material for the manufacture of membranes and fibers for many years. This review gives the background of the most recent methods of treating or dissolving cellulose, and its derivatives to form polymer films or membranes for a variety of applications. Indeed, some potential applications of bacterial cellulose, nanofibrillar cellulose (NFC) for films showing enhanced barrier characteristics are reviewed as well as the utilization of cellulose nanonocrystals (CNC) for production of highly oriented super strong films or thin films is discussed. Because of the success of the Lyocell process as well as the amine/metal thiocyanate solvent blends of cellulose and other polysaccharides like starch, chitosan, and other natural polymers. Consequently, the use of cellulose (or its derivatives) and another polysaccharide dissolved as a blend is also elaborated. It is our hope that the reader will want to follow up and investigate these new systems and use them to develop end use materials for all sorts of applications, from medical to water filtration, or electrogels for use in batteries.

Properties of chitosan/soy protein blended films with added plasticizing agent as a function of solvent type at acidic pH

ABSTRACT Pure and blend films from chitosan (CH) and soy protein isolate (SPI) were produced in varying compositions (CH/SPI 75/25, 50/50, 25/75 w/w) based on the solvent type (acetic and formic acids). Glycerol was used as a plasticizer. The interactions between the two biopolymers was confirmed by FTIR and TGA, indicating miscibility and compatibility. Increasing the amount of soy protein decreased the tensile strength and absorptive properties, but improved the ability of the film to withstand thermal degradation. Blend films cast using acetic acid gave higher hydrophobicity, better internal blend miscibility, and better tensile properties than blend films cast from formic acid. GRAPHICAL ABSTRACT

Aliphatic Polyester Nanofibers Functionalized with Cyclodextrins and Cyclodextrin-Guest Inclusion Complexes

The fabrication of nanofibers by electrospinning has gained popularity in the past two decades; however, only in this decade, have polymeric nanofibers been functionalized using cyclodextrins (CDs) or their inclusion complexes (ICs). By combining electrospinning of polymers with free CDs, nanofibers can be fabricated that are capable of capturing small molecules, such as wound odors or environmental toxins in water and air. Likewise, combining polymers with cyclodextrin-inclusion complexes (CD-ICs), has shown promise in enhancing or controlling the delivery of small molecule guests, by minor tweaking in the technique utilized in fabricating these nanofibers, for example, by forming core–shell or multilayered structures and conventional electrospinning, for controlled and rapid delivery, respectively. In addition to small molecule delivery, the thermomechanical properties of the polymers can be significantly improved, as our group has shown recently, by adding non-stoichiometric inclusion complexes to the polymeric nanofibers. We recently reported and thoroughly characterized the fabrication of polypseudorotaxane (PpR) nanofibers without a polymeric carrier. These PpR nanofibers show unusual rheological and thermomechanical properties, even when the coverage of those polymer chains is relatively sparse (~3%). A key advantage of these PpR nanofibers is the presence of relatively stable hydroxyl groups on the outer surface of the nanofibers, which can subsequently be taken advantage of for bioconjugation, making them suitable for biomedical applications. Although the number of studies in this area is limited, initial results suggest significant potential for bone tissue engineering, and with additional bioconjugation in other areas of tissue engineering. In addition, the behaviors and uses of aliphatic polyester nanofibers functionalized with CDs and CD-ICs are briefly described and summarized. Based on these observations, we attempt to draw conclusions for each of these combinations, and the relationships that exist between their presence and the functional behaviors of their nanofibers.

Novel cellulose-collagen blend biofibers prepared from an amine/salt solvent system

Cellulose/collagen biofibers were produced from ethylene diamine/potassium thiocyanate binary solvent system, with methanol as a coagulant. The dynamic viscosity of the solutions decreased with the gradual increase in the collagen content up to 40%. The elemental analysis showed incorporation of collagen into cellulose matrix, thereby demonstrating some degree of interaction with the cellulose matrix. The chemical and thermal analysis further revealed an intermolecular interaction between cellulose and the protein and improved thermal stability, respectively. Furthermore, the electron microscopy images mostly exhibited fibrillar morphology with no visible phase separation, indicating compatibility between the two phases. Moreover, biofibers containing higher cellulose content showed higher crystallinity, tensile, and birefringence properties of the composite fibers.

Functional Nanofibers Containing Cyclodextrins

The process of obtaining nanofibers from polymer solutions has been reported in the literature for the past two decades. However, only in the past few years, have nanofibers containing cyclodextrins (CDs) or their inclusion compounds (ICs) with low or high molecular weight compounds been extensively reported. These nanofibers exhibit superior properties compared to those of their neat polymer nanofibers. It has been observed that with the simple addition of CDs, marked increases in crystallinity, crystallizability, small molecule encapsulation capability, lowered hydrophobicity, and other surface functionalities can be achieved. In this chapter, an in-depth discussion of cyclodextrins, their structures, and inclusion complexes will be provided. Various strategies utilized to obtain those nanofibers functionalized with CDs or their ICs will be discussed. CD based technologies offer green alternatives for designing scaffolds with specific improved properties for growing cells and tissues. For example, increased small molecule encapsulation or release capability can be achieved, as well stronger nanofibers can be produced. Due to their excellent biocompatibility, biodegradability, and abundant availability, CDs and their ICs, offer excellent opportunities for producing functionalized nanofibers, which have not yet been extensively reported. For this reason, much of our focus in this chapter will concentrate on various strategies for future research in nanofibers functionalized with CDs and their ICs.

Formation of Cellulose and Protein Blend Biofibers

Cellulose and proteins are potential polymers for developing biodegradable materials for high value-added applications. A combination with these natural polymers could be useful to enhance the properties of final materials and to extend their application areas. In particular, blend biofibers that are degradable and sustainable can be engineered from a mixture of cellulose and proteins, such as soy protein, silk fibroin, collagen, etc. In a binary polymeric blend, the compatibility of cellulose and proteins is influenced by the characteristics of each polymer in the employed solvent system as well as processing conditions. Therefore, utilizing solvents that can dissolve cellulose and proteins, and coagulants that are non-solvents for both polymers is of importance. In this book chapter, the formation and characteristics of blend biofibers from these polymers will be discussed.