Chitin and chitosan polymers: Chemistry, solubility and fiber formation

Processing-structure-functional property relationship in organic-inorganic nanostructured scaffolds for bone-tissue engineering: the response of preosteoblasts

We elucidate here for the first time the structure-processing-functional property relationship in chitosan (CS)-based scaffolds, where molecular machinery governing proliferation and growth of osteoblasts is mediated by nanostructured carbon. The interconnected network structure of organic-inorganic scaffolds was obtained by covalent linkage of carboxyl group of functionalized single-walled carbon nanohorn with the amine group of CS. The molecular-scale dispersibility of functionalized nanostructured carbon was an important physicochemical factor influencing cellular interactions and biological response. Furthermore, it was beneficial in promoting the biocompatibility and the degradation product of the scaffolds. The hydrophilicity, good water retention ability, and interconnected porous structure of organic-inorganic scaffolds enabled pronounced cell attachment and proliferation and enhanced the stability toward enzymatic degradation. The infiltration of cells and colonization of the pores of the scaffolds and cellular interactions were promoted due to covalent linkage of nanostructured carbon with CS. Additionally, the interconnectivity of porous scaffolds facilitated cells to infiltrate inside the pores of CS-nanostructured scaffolds, implying that nanostructured carbon merits consideration in tissue engineering.

Biodegradation study of microcrystalline chitosan and microcrystalline chitosan/β-TCP complex composites

Bone repair or regeneration is a common and complicated clinical problem in orthopedic surgery. The importance of natural polymers, such as microcrystalline chitosan, and minerals such as HAp and β-TCP, has grown significantly over the last two decades due to their renewable and biodegradable source, increasing the knowledge and functionality of composites in technological and biomedical applications. This study compares the biodegradation process, bioactivity, structure, morphology, and mechanical properties of microcrystalline chitosan and microcrystalline chitosan/β-TCP complex; the latter according to the new method of preparation. The complex showed a homogeneous network structure with regular pores, good bioactivity, even after 60 days of conducting the hydrolytic and enzymatic degradation process, showing a bacteriostatic and bactericidal activity. The complex indicates that it could be used successfully as a base for implants and scaffolds production in orthopedic surgery.

Chitosan, hyaluronan and chondroitin sulfate in tissue engineering for cartilage regeneration: a review

Injection of hyaluronan into osteoarthritic joints restores the viscoelasticity, augments the flow of joint fluid, normalizes endogenous hyaluronan synthesis, and improves joint function. Chitosan easily forms polyelectrolyte complexes with hyaluronan and chondroitin sulfate. Synergy of chitosan with hyaluronan develops enhanced performances in regenerating hyaline cartilage, typical results being structural integrity of the hyaline-like neocartilage, and reconstitution of the subchondral bone, with positive cartilage staining for collagen-II and GAG in the treated sites. Chitosan qualifies for the preparation of scaffolds intended for the regeneration of cartilage: it yields mesoporous cryogels; it provides a friendly environment for chondrocytes to propagate, produce typical ECM, and assume the convenient phenotype; it is a good carrier for growth factors; it inactivates metalloproteinases thus preventing collagen degradation; it is suitable for the induction of the chondrogenic differentiation of mesenchymal stem cells; it is a potent means for hemostasis and platelet delivery.

NEGATIVE VOLTAGE ELECTROSPINNING AND POSITIVE VOLTAGE ELECTROSPINNING OF TISSUE ENGINEERING SCAFFOLDS: A COMPARATIVE STUDY AND CHARGE RETENTION ON SCAFFOLDS

Positive voltage electrospinning (PVES) has been mainly used for forming fibrous polymer scaffolds for different applications including tissue engineering. There is virtually no report on negative voltage electrospinning (NVES) of tissue engineering scaffolds. In this study, NVES of four biopolymers, namely, gelatin, chitosan, poly(lactic-co-glycolic acid) (PLGA), and polybutylene terephthalate (PBT), to form nanofibrous membranes was systematically investigated. For comparisons, PVES of these polymers was also conducted. It was found that chitosan fibers could not be produced using NVES. Under NVES or PVES, the fiber diameter of electrospun scaffolds generally increased with increasing needle inner diameter and polymer solution concentration but decreased with increasing working distance for all four polymers. Neither NVES nor PVES altered the chemical structure of gelatin, PLGA, and PBT. PVES and NVES resulted in fibrous membranes bearing positive charges and negative charges, respectively. PLGA and PBT fibrous membranes retained around 30% and 50%, respectively, of the initial charge one week after electrospinning. Charges on gelatin and chitosan fibrous membranes were almost completely dissipated within 60 min of electrospinning. For all four polymers, under either PVES or NVES, the retained charges on fibrous membranes increased with increasing applied electrospinning voltage. This study explored a new approach for forming fibrous scaffolds by using NVES and has opened a new area for developing negatively charged fibrous scaffolds for tissue engineering applications.

Characterization of Chitosan and Carboxymethyl Chitosan Films from Various Sources and Molecular Sizes

Carboxymethyl chitosan (CMCH) from different sources (shrimp, crab and squid) and molecular sizes (polymer and oligomer) was synthesizedviacarboxymethylation with monochloroacetic acid (MCA) in isopropyl alcohol (IPA) under alkaline condition. Next, chitosan and CMCH films were prepared and their properties were studied. Crystallinity, mechanical properties [tensile strength (TS) and percent elongation at break (EB)], water vapor transmission rate (WVTR), and color change were investigated. The crystallinity and TS value of each CMCH film was less than that of chitosan. The highest TS (28.6 MPa) was provided by chitosan film from crab oligomer (CO). The CMCH films from various types displayed the higher EB value comparing with those of chitosan films. The CMCH film from shrimp polymer (SP) exhibited the highest EB value (44%). The WVTR of each CMCH films were interestingly lower than that of chitosan, and the lowest value was obtained by the CMCH film from crab oligomer (CO) (15 g/m2day1). The CMCH films showed higher color L* and a* value but lower b* value comparing with those of chitosan films from the same type.

N-hexanoyl, N-octanoyl and N-decanoyl chitosans: Binding affinity, cell uptake, and transfection

Low transfection efficiency of chitosan limits its use as a non-viral vector for practical purposes. This study was designed to investigate the effect of fatty acyl chain length on physicochemical properties, pDNA binding affinity, cell uptake, and in vitro transfection efficiency of N-acyl chitosan (NAC). NAC polymers were synthesized by carbodiimide mediated coupling reaction of chitosan with n-hexanoic, n-octanoic, and n-decanoic acid, respectively. These NAC polymers effectively condensed pDNA resulting in the size range of 220-342 nm with net positive charge. NAC polymers also showed good pDNA binding capacity, high protection of pDNA from nuclease degradation and excellent biocompatibility. Transfection efficiency of chitosan, in HEK 293 cells, was enhanced 15-25-fold after coupling with fatty acid and increased with a decrease in fatty acyl chain length of NAC. Thus, the present study demonstrates that the NAC polymers hold great potential as novel non-viral gene delivery vector.

Preparation and characterization of biomimetic silk fibroin/chitosan composite nanofibers by electrospinning for osteoblasts culture

In this study, we have successfully fabricated electrospun bead-free silk fibroin [SF]/chitosan [CS] composite nanofibers [NFs] covering the whole range of CS content (0%, 25%, 50%, 75%, and 100%). SF/CS spinning solutions were prepared in a mixed solvent system of trifluoroacetic acid [TFA] and dichloromethane. The morphology of the NFs was observed by scanning electron microscope, and the average fiber diameter ranges from 215 to 478 nm. Confocal laser scanning microscopy confirms the uniform distribution of SF and CS within the composite NFs. To increase biocompatibility and preserve nanostructure when seeded with cells in culture medium, NFs were treated with an ethanol/ammonia aqueous solution to remove residual TFA and to change SF protein conformation. After the chemical treatment, SF/CS NFs could maintain the original structure for up to 54 days in culture medium. Properties of pristine and chemically treated SF/CS NFs were investigated by Fourier transform infrared spectroscopy [FT-IR], X-ray diffraction [XRD], and thermogravimetry/differential scanning calorimetry [TG/DSC]. Shift of absorption peaks in FT-IR spectra confirms the conformation change of SF from random coil to β-sheet by the action of ethanol, which is also consistent with the SF crystalline diffraction patterns measured by XRD. From TG/DSC analysis, the decomposition temperature peaks due to salt formation from TFA and protonated amines disappeared after chemical treatment, indicating complete removal of TFA by binding with ammonium ions during the treatment. This was also confirmed with the disappearance of F1s peak in X-ray photoelectron spectroscopy spectra and disappearance of TFA salt peaks in FT-IR spectra. The composite NFs could support the growth and osteogenic differentiation of human fetal osteoblastic [hFOB] cells, but each component in the composite NF shows distinct effect on cell behavior. SF promotes hFOB proliferation while CS enhances hFOB differentiation. The composite SF/CS NFs will be suitable for bone tissue engineering applications by choosing a suitable blend composition.PACS: 87.85.jf; 87.85.Rs; 68.37.Hk.

Investigation of self-assembling proline- and glycine-rich recombinant proteins and peptides inspired by proteins from a symbiotic fungus using atomic force microscopy and circular dichroism spectroscopy

Fiber-forming proteins and peptides are being scrutinized as a promising source of building blocks for new nanomaterials. Arabinogalactan-like (AGL) proteins expressed at the symbiotic interface between plant roots and arbuscular mycorrhizal fungi have novel sequences, hypothesized to form polyproline II (PPII) helix structures. The functional nature of these proteins is unknown but they may form structures for the establishment and maintenance of fungal hyphae. Here we show that recombinant AGL1 (rAGL1) and recombinant AGL3 (rAGL3) are extended proteins based upon secondary structural characteristics determined by electronic circular dichroism (CD) spectroscopy and can self-assemble into fibers and microtubes as observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). CD spectroscopy results of synthetic peptides based on repeat regions in AGL1, AGL2 and AGL3 suggest that the synthetic peptides contain significant amounts of extended PPII helices and that these structures are influenced by ionic strength and, at least in one case, by concentration. Point mutations of a single residue of the repeat region of AGL3 resulted in altered secondary structures. Self-assembly of these repeats was observed by means of AFM and optical microscopy. Peptide (APADGK)(6) forms structures with similar morphology to rAGL1 suggesting that these repeats are crucial for the morphology of rAGL1 fibers. These novel self-assembling sequences may find applications as precursors for bioinspired nanomaterials.

Transient charge-masking effect of applied voltage on electrospinning of pure chitosan nanofibers from aqueous solutions

The processing of a polyelectrolyte (whose functionality is derived from its ionized functional groups) into a nanofiber may improve its functionality and yield multiple functionalities. However, the electrospinning of nanofibers from polyelectrolytes is imperfect because polyelectrolytes differ considerably from neutral polymers in their rheological properties. In our study, we attempt to solve this problem by applying a voltage of opposite polarity to charges on a polyelectrolyte. The application of this 'countervoltage' can temporarily mask or screen a specific rheological property of the polyelectrolyte, making it behave as a neutral polymer. This approach can significantly contribute to the development of new functional nanofiber materials.

pH- and voltage-responsive chitosan hydrogel through covalent cross-linking with catechol

A new method for covalently cross-linking chitosan is developed by chemically oxidizing catechol to o-quinone which subsequently reacts with and cross-links chitosan through Michael addition and Schiff base formation. The cross-linked chitosan film shows a pH-responsive, switchlike behavior toward the negatively charged redox probe, Fe(CN)(6)(3-/4-), and withstands harsh acidic conditions. The negative Fe(CN)(6)(3-/4-) is found to be trapped and enriched in the catechol-cross-linked chitosan film under acidic conditions and released into solution by either increasing pH or applying a negative voltage. Chitosan films made with different techniques, i.e., solvent evaporation (simple deposition), electrodeposition, and covalent cross-linking, are examined using cyclic voltammetry and electrochemical impedance spectroscopy (EIS), and the results demonstrate that fabrication methods greatly affect the properties of the chitosan films.