Osteoblast biocompatibility of novel chitosan crosslinker, hexamethylene-1,6-diaminocarboxysulfonate.

Chitosan is a naturally occurring polysaccharide, which has proven to be an attractive candidate for bone tissue engineering, due to its ability to promote osteoblast mineralization. Electrospinning has become a well-established cell scaffold processing technique, as it produces a high surface area to volume fibrous material that can mimic the three dimensionality of the extracellular matrix of a cell. In this study, we have investigated the osteoblast response to two different chemically crosslinked (hexamethylene-1,6-diaminocarboxysulfonate (HDACS) and genipin) electrospun chitosan scaffolds and their film counterparts in order to determine how material chemistry influences cellular behavior in conjunction with material topology. In addition, material properties of each fiber scaffold such as porosity and tensile strength were considered. MLO-A5 osteoblast cells grown on chitosan-HDACS scaffolds were found to display a more organized cellular network, along with significantly more filopodia extensions, compared to those grown on chitosan-genipin scaffolds. After 2 days of growth on chitosan-HDACS fibers, a higher level of alkaline phosphatase expression in MLO-A5 cells was reported compared to that of either chitosan-genipin fibers or films. These results indicate that not only chemistry, but also surface topology is an important effecter of cellular behavior. Ultimately, chitosan-HDACS fiber scaffolds provided an adequate substrate for osteoblast attachment and proliferation.

Osteoblast biocompatibility of premineralized, hexamethylene-1,6-diaminocarboxysulfonate crosslinked chitosan fibers.

Biopolymer-ceramic composites are thought to be particularly promising materials for bone tissue engineering as they more closely mimic natural bone. Here, we demonstrate the fabrication by electrospinning of fibrous chitosan-hydroxyapatite composite scaffolds with low (1 wt %) and high (10 wt %) mineral contents. Scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and unidirectional tensile testing were performed to determine fiber surface morphology, elemental composition, and tensile Young's modulus (E) and ultimate tensile strength (σUTS ), respectively. EDS scans of the scaffolds indicated that the fibers, crosslinked with either hexamethylene-1,6-diaminocarboxysulfonate (HDACS) or genipin, have a crystalline hydroxyapatite mineral content at 10 wt % additive. Moreover, FESEM micrographs showed that all electrospun fibers have diameters (122-249 nm), which fall within the range of those of fibrous collagen found in the extracellular matrix of bone. Young's modulus and ultimate tensile strength of the various crosslinked composite compositions were in the range of 116-329 MPa and 2-15 MPa, respectively. Osteocytes seeded onto the mineralized fibers were able to demonstrate good biocompatibility enhancing the potential use for this material in future bone tissue engineering applications.

Various-sourced pectin and polyethylene oxide electrospun fibers.

Pectin, a naturally occurring and biorenewable polysaccharide, is derived from plant cell wall tissue and used in applications ranging from food processing to biomedical engineering. Due to extraction methods and source variation, there is currently no consensus in literature as to the exact structure of pectin. Here, we have studied key material properties of electrospun pectin blends with polyethylene oxide (PEO) (1:1, v/v) in order to demonstrate the fabrication of a fibrous and less toxic material system, as well as to understand the effects of source variability on the resulting fibrous mats. The bulk pectin degree of esterification (DE) estimated using FTIR (bulk apple pomace (AP)=28%, bulk citrus peel (CP)=86% and bulk sugar beet pulp (SBP)=91%) was shown to inversely correlate with electrospun fiber crystallinity determined using XRD (PEO-AP=37%, PEO-CP=28% and PEO-SBP=23%). This in turn affected the trend observed for the mean fiber diameter (n=50) (PEO-AP=124 ± 26 nm, PEO-CP=493 ± 254 nm and PEO-SBP=581 ± 178 nm) and elastic tensile moduli (1.6 ± 0.2 MPa, 4.37 ± 0.64 MPa and 2.49 ± 1.46 MPa, respectively) of the fibrous mats. Electrospun fibers containing bulk AP had the lowest DE, highest crystallinity, smallest mean fiber diameter, and lowest tensile modulus compared to either the bulk CP or bulk SBP. Bound water in PEO-CP fiber and bulk pectin impurities in PEO-SPB were observed to influence fiber branching and mean diameter distributions, which in turn influenced the fiber tensile properties. These results indicate that pectin, when blended with PEO in water, produces submicron fibrous mats with pectin influencing the blend fiber properties. Moreover, the source of pectin is an important variable in creating electrospun blend fibrous mats with desired material properties.

Non-covalent crosslinkers for electrospun chitosan fibers.

Electrospun chitosan fibers have numerous potential in biomedical, food, and pharmaceutical applications. However, the mats formed are often not chemically stable in a wide range of pHs unless crosslinked. Here, we report on the use of glycerol phosphate (GP), tripolyphosphate (TPP) and tannic acid (TA) as a new set of non-covalent crosslinkers for electrospun chitosan fibers. Crosslinking with or without heat or base activation were performed either prior to (one-step or activated one-step) or after (two-step or activated two-step) electrospinning with either GP or TA. TPP crosslinking was performed in two-step and activated two-step. FESEM, FTIR and UV-vis transmittance at 600 nm were used to determine fiber surface morphology, chemical interactions and solubility in 1M AA (pH 3), water (~pH 6) and 1 M NaOH (pH 13), respectively. Crosslinking of chitosan with GP and TA yields fibers with a mean diameter range of 145-334 nm and 143-5554 nm, respectively. TPP crosslinking produced branched fibers with mean diameters of 117-462 nm range. Two-step chitosan-TA did not dissolve in 1M AA even after 72 h while all chitosan-TPP, activated two-step chitosan-TA and two-step heat activated chitosan-GP fibers survived in water after 72 h.

New crosslinkers for electrospun chitosan fibre mats. Part II: mechanical properties.

Few studies exist on the mechanical performance of crosslinked electrospun chitosan (CS) fibre mats. In this study, we show that the mat structure and mechanical performance depend on the different crosslinking agents genipin, epichlorohydrin (ECH), and hexamethylene-1,6-diaminocarboxysulphonate (HDACS), as well as the post-electrospinning heat and base activation treatments. The mat structure was imaged by field emission scanning electron microscopy and the mechanical performance was tested in tension. The elastic modulus, tensile strength, strain at failure and work to failure were found to range from 52 to 592 MPa, 2 to 30 MPa, 2 to 31 per cent and 0.041 to 3.26 MJ m(-3), respectively. In general, neat CS mats were found to be the stiffest and the strongest, though least ductile, while CS-ECH mats were the least stiff, weakest, but the most ductile, and CS-HDACS fibre mats exhibited intermediary mechanical properties. The mechanical performance of the mats is shown to reflect differences in the fibre diameter, number of fibre-fibre contacts formed within the mat, as well as varying intermolecular bonding and moisture content. The findings reported here complement the chemical properties of the mats, described in part I of this study.