Multiwalled carbon nanotube (MWCNT) reinforced cellulose fibers by electrospinning

Multiwalled carbon nanotubes (MWCNTs) were successfully incorporated in ultrafine cellulose fibers by electrospinning MWCNT-loaded cellulose acetate (CA) solutions, followed by deacetylation of CA to cellulose (cell). The mean fiber diameter reduced from 321 nm of the as-spun fibers to 257 and 228 nm of those with 0.11 and 0.55 wt % MWCNTs, respectively, and became more uniform. Hydrolysis of CA to cell further reduced the mean fiber sizes by another 8-16%. The MWCNTs were observed to be well-aligned along the fiber axes. The MWCNT/cell composite fibers had increased specific surface, from 4.27 m(2)/g to 5.07 and 7.69 m(2)/g at 0.11 and 0.55 wt % MWCNTs, respectively, and much improved water wettability. The mechanical properties of the fibers were also greatly enhanced with increased MWCNT loading levels. The fact that MWCNTs were observed in only about a third of the fibers at a very low 0.55 wt % loading suggests significantly higher tensile strength may be achieved by a further increase in MWCNT loadings.

Fluorescent polyurethane nanofabrics: a source of singlet oxygen and oxygen sensing

Polyurethane (PUR) nanofabrics based on nanofibers of average diameters in the range of 250-110 nm with different meso-tetraphenylporphyrin (TPP) loading (0.01-5 wt %) were prepared by an electrospinning process. The oxygen quenching of excited states and singlet oxygen-sensitized delayed fluorescence (SODF) of TPP were studied at different oxygen pressures. We found that TPP in PUR matrix is present in monomeric state, and it is easily accessed by oxygen. Analysis of the kinetics of the TPP triplet, singlet oxygen, and SODF indicates that repopulation of TPP fluorescent state includes reaction of singlet oxygen with TPP triplets. The integrated SODF achieved more than 20% of the prompt fluorescence for nanofabric loaded with 5 wt % TPP. The dependence of SODF intensity on the TPP concentration in nanofibers is nearly quadratic.

Exploring molecular changes at the surface of polypropylene after accelerated thermomolecular adhesion treatments

A central composite rotatable design (CCRD) method was used to investigate the performance of the accelerated thermomolecular adhesion process (ATmaP), at different operating conditions. ATmaP is a modified flame-treatment process that features the injection of a coupling agent into the flame to impart a tailored molecular surface chemistry on the work piece. In this study, the surface properties of treated polypropylene were evaluated using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). All samples showed a significant increase in the relative concentration of oxygen (up to 12.2%) and nitrogen (up to 2.4%) at the surface in comparison with the untreated sample (0.7% oxygen and no detectable nitrogen) as measured by XPS. ToF-SIMS and principal components analysis (PCA) showed that ATmaP induced multiple reactions at the polypropylene surface such as chain scission, oxidation, nitration, condensation, and molecular loss, as indicated by changes in the relative intensities of the hydrocarbon (C(3)H(7)(+), C(3)H(5)(+), C(4)H(7)(+), and C(5)H(9)(+)), nitrogen and oxygen-containing secondary ions (C(2)H(3)O(+), C(3)H(8)N(+), C(2)H(5)NO(+), C(3)H(6)NO(+), and C(3)H(7)NO(+)). The increase in relative intensity of the nitrogen oxide ions (C(2)H(5)NO(+) and C(3)H(7)NO(+)) correlates with the process of incorporating oxides of nitrogen into the surface as a result of the injection of the ATmaP coupling agent.

The development of genipin-crosslinked poly(caprolactone) (PCL)/gelatin nanofibers for tissue engineering applications

Composite nanofibers of poly(caprolactone) (PCL) and gelatin crosslinked with genipin are prepared. The contact angles and mechanical properties of crosslinked PCL-gelatin nanofibers decrease as the gelatin content increases. The proliferation of myoblasts is higher in the crosslinked PCL-gelatin nanofibers than in the PCL nanofibers, and the formation of myotubes is only observed on the crosslinked PCL-gelatin nanofibers. The expression level of myogenin, myosin heavy chain, and troponin T genes is increased as the gelatin content is increased. The results suggest that PCL-gelatin nanofibers crosslinked with genipin can be used as a substrate to modulate proliferation and differentiation of myoblasts, presenting potential applications in muscle tissue engineering.

Lipase immobilization on smectite nanoclays: characterization and application to the epoxidation of alpha-pinene

The immobilization of lipase B from Candida antarctica on smectite group nanoclays (Laponite, SWy-2 and Kunipia), as well as on their organically modified derivatives, was investigated. A combination of techniques, namely X-ray diffraction, thermal analysis, X-ray photoelectron and FT-IR spectroscopy, was used for characterization of the novel immobilized biocatalyst. Structural and biochemical characterization have revealed that the hydrophobic microenvironment created by the organo-modified clays induces minor changes on the secondary structure of the enzyme, resulting in enhanced catalytic behaviour in hydrophobic media. The immobilized lipase on such modified nanoclays can be effectively applied for the indirect epoxidation of alpha-pinene using hydrogen peroxide as substrate. The amount of alpha-pinene epoxide produced in a single-step biocatalytic process is up to 3-fold higher than that of free enzyme or enzyme immobilized in non-modified clays. Moreover, lipase immobilized in modified clays retains up to 90% of its initial activity, even after 48h of incubation in the presence of oxidant, and up to 60% after four reaction cycles, while other forms of the enzyme retain less than 10%.

Immobilization of heparin on polysulfone surface for selective adsorption of low-density lipoprotein (LDL)

A versatile method was developed to immobilize heparin covalently on polysulfone sheets (PSu) to achieve selective adsorption of low-density lipoprotein (LDL). This was achieved by activation of PSu with successive treatments of chlorodimethyl ether and ethylenediamine, and subsequent chemical binding of heparin with bifunctional linker molecules. A heparin density up to 0.86 microg cm(-2) on a dense PSu film was achieved. The modified PSu films were characterized by attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The hydrophilicity of the PSu film was improved greatly by covalent immobilization of heparin. The water contact angle of PSu film was decreased from 86.6 + or - 3.7 degrees to 50.5 + or - 3.2 degrees after binding of 0.36 microg cm(-2) heparin. An enzyme-linked immunosorbent assay was used to measure the binding of LDL on plain and modified PSu films. It was found that the heparin-modified PSu film could selectively recognize LDL from binary protein solutions. Furthermore, it was possible to desorb LDL from heparinized PSu, but not from plain PSu, with heparin, sodium chloride or urea solution, which indicates a selective but reversible binding of LDL to heparin. The results suggest that heparin-modified PSu membranes are promising for application in simultaneous hemodialysis and LDL apheresis therapy.

Role of alpha-fetoprotein in hepatocellular carcinoma: prognostication, treatment monitoring or both?

Despite recent breakthroughs in the treatment for both early and advanced hepatocellular carcinoma, the development of markers for prognostication and treatment monitoring remains to be explored. Serum alpha-fetoprotein has been frequently measured at diagnosis and serially during treatment by clinicians for decades, with an aim for prognostication of disease and monitoring of treatment response. In this review, the evidence regarding the prognostic value of serum alpha-fetoprotein and the value of serial alpha-fetoprotein in the monitoring of treatment efficacy will be discussed, with emphasis on recent data.

Electrospun Polyacrylonitrile Nanofibrous Membranes Tailored for Acetylcholinesterase Immobilization

Nanofibrous polyacrylonitrile membranes (PANNFM) were obtained by electrospinning and then prepared for immobilizing acetylcholinesterase (AChE). Initially, the chemical modification of PANNFM with ethylenediamine produced reactive groups to overcome their inertness and hydrophobicity. The natural polymer, chitosan, was then tethered on the nanofibrous membranes to improve their biocompatibility. Scanning electron microscopy (SEM) and cross-section SEM were used to determine morphological and porosity changes of the membranes. The immobilized AChE had greater relative activity as well as thermal and storage stability compared to the free enzyme. The bound AChE showed excellent reusability. Chitosan-modified PANNFM was shown to be a suitable strategy for facile immobilization of AChE to produce a promising system that effectively supports biocatalysts.

Surface Engineered Polymeric Biomaterials with Improved Biocontact Properties

We present many examples of surface engineered polymeric biomaterials with nanosize modified layers, controlled protein adsorption, and cellular interactions potentially applicable for tissue and/or blood contacting devices, scaffolds for cell culture and tissue engineering, biosensors, biological microchips as well as approaches to their preparation.

Immobilization of Candida antarctica lipase B on Polystyrene Nanoparticles

Polystyrene (PS) nanoparticles were prepared via a nanoprecipitation process. The influence of the pH of the buffer solution used during the immobilization process on the loading of Candida antarctica lipase B (Cal-B) and on the hydrolytic activity (hydrolysis of p-nitrophenyl acetate) of the immobilized Cal-B was studied. The pH of the buffer solution has no influence on enzyme loading, while immobilized enzyme activity is very dependent on the pH of adsorption. Cal-B immobilized on PS nanoparticles in buffer solution pH 6.8 performed higher hydrolytic activity than crude enzyme powder and Novozyme 435.

Immobilization of poly (ethylene imine) on poly (L-lactide) promotes MG63 cell proliferation and function

Poly (ethylene imine) (PEI) is a polycation widely used for DNA transfection to cells but also applied as primary polycation for layer-by-layer (LBL) assembly of polyelectrolytes. The aim of the present study was to investigate the effect of modification with PEI on the biocompatibility of poly (L-lactide) (PLLA) films. PEI with different molecular weight was immobilized on PLLA by either adsorption or covalent binding. Cell morphologies, immuno-fluorescence staining, cell proliferation by lactate dehydrogenase assay and cell differentiation by alkaline phosphatase assay were utilized to assess the biocompatibility of the modified PLLA using osteoblast cell line MG63. Results revealed that PEI modification remarkably improved cell adhesion, viability, proliferation and function compared with plain PLLA. Hence, PEI-modified PLLA is acceptable as transfection vehicle for engineering of bone and other tissues, or as primary layer to allow LBL assembly to generate biomimetic surface coatings.

Surface-functionalized electrospun nanofibers for tissue engineering and drug delivery

Electrospun nanofibers with a high surface area to volume ratio have received much attention because of their potential applications for biomedical devices, tissue engineering scaffolds, and drug delivery carriers. In order to develop electrospun nanofibers as useful nanobiomaterials, surfaces of electrospun nanofibers have been chemically functionalized for achieving sustained delivery through physical adsorption of diverse bioactive molecules. Surface modification of nanofibers includes plasma treatment, wet chemical method, surface graft polymerization, and co-electrospinning of surface active agents and polymers. A variety of bioactive molecules including anti-cancer drugs, enzymes, cytokines, and polysaccharides were entrapped within the interior or physically immobilized on the surface for controlled drug delivery. Surfaces of electrospun nanofibers were also chemically modified with immobilizing cell specific bioactive ligands to enhance cell adhesion, proliferation, and differentiation by mimicking morphology and biological functions of extracellular matrix. This review summarizes surface modification strategies of electrospun polymeric nanofibers for controlled drug delivery and tissue engineering.