Co-reporter:Ran Wang, Sihui Guan, Anna Sato, Xiao Wang, Zhe Wang, Rui Yang, Benjamin S. Hsiao, Benjamin Chu
Journal of Membrane Science 2013 446() pp: 376-382
Publication Date(Web):
DOI:10.1016/j.memsci.2013.06.020
Co-reporter:Mahati Elluru, Hongyang Ma, Michael Hadjiargyrou, Benjamin S. Hsiao, Benjamin Chu
Polymer 2013 Volume 54(Issue 8) pp:2088-2095
Publication Date(Web):3 April 2013
DOI:10.1016/j.polymer.2013.02.017
The tri-block copolymer (PEO)99-(PPO)69-(PEO)99 (commercially known as F127, with PEO and PPO representing polyethylene oxide and polypropylene oxide, respectively), a member of Pluronics copolymers, was chemically modified by introducing vinyl groups at the terminal ends of the polymer chain. With or without the addition of Pluronics or PEO chains, the modified copolymer could be cross-linked by UV irradiation to form a soft but tough gel-like scaffold. This cross-linked polymer has material properties, such as storage modulus (11–40 kPa), comparable to native human breast tissue. Swelling studies revealed that the strength of the cross-linked polymer networks could be adjusted to be comparable to human adipose tissue. Exposure of pre-adipocytes to the constituents of the Pluronics hydrogel and the cross-linked gel did not show any adverse effects on the cells, thus confirming the biocompatibility of the cross-linked hydrogel. Taken together, these findings suggest that cross-linking of modified Pluronics hydrogel can potentially yield a promising candidate scaffold for the regeneration of native tissue, such as breast tissue to repair defects resulting from lumpectomies.
Co-reporter:Ran Wang, Yang Liu, Brandon Li, Benjamin S. Hsiao, Benjamin Chu
Journal of Membrane Science 2012 Volumes 392–393() pp:167-174
Publication Date(Web):1 March 2012
DOI:10.1016/j.memsci.2011.12.019
Highly porous electrospun nanofibrous membranes have gained considerable interest in water filtration applications. To understand the effects of electrospun nanofibrous structures on the filtration performance, a series of nanofibrous membranes with different fiber diameters, diameter distributions and membrane thicknesses were prepared and studied. The results indicate a strong correlation between the physical parameters of the membrane and the filtration performance. For example, a thicker membrane with a smaller average fiber diameter greatly favors the formation of a smaller pore size and narrower pore size distribution, although the influence of the membrane thickness is relatively limited. Based on successful control of the total composite structure (electrospun polyacrylonitrile (PAN)/non-woven polyethylene terephthalate (PET)) containing the electrospun layer thickness of 200 ± 10 μm and a mean fiber diameter of 100 ± 20 nm, a high flux microfiltration (MF) membrane with a maximum pore size of 0.62 ± 0.03 μm and a mean pore size of 0.22 ± 0.01 μm was obtained. The PAN/PET nanofibrous MF membranes performed significantly better than the commercial MF membrane of the same mean pore size (0.22 μm), with two to three times higher flux (∼1.5 L/m2 h). The nanofibrous MF filter could maintain a very high rejection ratio of micro-particle and bacteria (LRV = 6). The results suggest that electrospun nanofibrous membranes are excellent materials for high-flux MF applications.Highlights► We studied the morphology of electrospun nanofibrous scaffolds. ► The morphology can affect the membrane porometry and filtration efficiency. ► Microfiltration membranes are fabricated by controlling parameters of the scaffolds. ► The membranes can remove micro-particles and bacteria with very high flux.
Co-reporter:Hongyang Ma, Benjamin S. Hsiao, and Benjamin Chu
ACS Macro Letters 2012 Volume 1(Issue 1) pp:213
Publication Date(Web):December 22, 2011
DOI:10.1021/mz200047q
Ultrafine cellulose nanofibers, 5–10 nm in diameter, were prepared from oxidation of wood pulp using the (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)/NaBr/NaClO process followed by mechanical treatment. Carboxylate groups on the surface of these nanofibers provide negative charges, which are very effective to adsorb radioactive UO22+ in water, evidenced by static adsorption and high resolution transmission electron microscopy (TEM) measurements. The UO22+ adsorption capability of ultrafine cellulose nanofibers was about 167 mg/g, which is 2–3 times higher than those of typical adsorbents such as montmorillonite, ion imprinted polymer particles, modified silica particles/fibrous membranes, and hydrogels. The high UO22+ adsorption capability can be attributed to the very high surface-to-volume ratio, high surface charge density, and hydrophilicity of ultrafine cellulose nanofibers, which can be used as effective media to remove radioactive metals from radio-nuclear wastewater.
Co-reporter:Hongyang Ma, Christian Burger, Benjamin S. Hsiao, and Benjamin Chu
ACS Macro Letters 2012 Volume 1(Issue 6) pp:723
Publication Date(Web):May 24, 2012
DOI:10.1021/mz300163h
This viewpoint describes the concept of using nanocomposite barrier layers containing directed water channels to increase membrane permeability for water purification. In one practical approach, the channels, formed at the interface between the interconnected nanofibrous scaffold and the polymer matrix, were used to guide the transport of water molecules in a directed manner and to also exclude contaminant molecules. This concept was demonstrated by embedding overlapped oxidized multiwalled carbon nanotubes into the poly(vinyl alcohol) (PVA) barrier layer for ultrafiltration (UF). We anticipate that the same approach can be extended by substituting oxidized carbon nanotubes with ultrafine cellulose nanofibers (diameter about 5 nm), which are derived from wood pulp and are environmentally friendly as well as more cost-effective, into highly cross-linked polymer barrier layers. The resulting thin-film nanofibrous composite (TFNC) membranes should exhibit a permeation flux significantly higher than those of conventional thin-film composite (TFC) membranes for nanofiltration while maintaining the same rejection capability.
Co-reporter:Hongyang Ma, Christian Burger, Benjamin S. Hsiao, and Benjamin Chu
Biomacromolecules 2012 Volume 13(Issue 1) pp:
Publication Date(Web):December 5, 2011
DOI:10.1021/bm201421g
A multilayered nanofibrous microfiltration (MF) membrane system with high flux, low pressure drop, and high retention capability against both bacteria and bacteriophages (a virus model) was developed by impregnating ultrafine cellulose nanowhiskers (diameter about 5 nm) into an electrospun polyacrylonitrile (PAN) nanofibrous scaffold (fiber diameter about 150 nm) supported by a poly(ethylene terephthalate) (PET) nonwoven substrate (fiber diameter about 20 μm). The cellulose nanowhiskers were anchored on the PAN nanofiber surface, forming a cross-linked nanostructured mesh with very high surface-to-volume ratio and a negatively charged surface. The mean pore size and pore size distribution of this MF system could be adjusted by the loading of cellulose nanowhiskers, where the resulting membrane not only possessed good mechanical properties but also high surface charge density confirmed by the conductivity titration and zeta potential measurements. The results indicated that a test cellulose nanowhisker-based MF membrane exhibited 16 times higher adsorption capacity against a positively charged dye over a commercial nitrocellulose-based MF membrane. This experimental membrane also showed full retention capability against bacteria, for example, E. coli and B. diminuta (log reduction value (LRV) larger than 6) and decent retention against bacteriophage MS2 (LRV larger than 2).
Co-reporter:Hongyang Ma, Christian Burger, Benjamin S. Hsiao and Benjamin Chu
Journal of Materials Chemistry A 2011 vol. 21(Issue 21) pp:7507-7510
Publication Date(Web):05 Apr 2011
DOI:10.1039/C0JM04308G
The major challenges in membrane technology for water filtration are the development of new materials (e.g. high durability, low cost and low environmental concerns) and new structures (e.g. directed water channels) that can produce high permeation flux (thus low energy input) while maintaining a high selectivity or rejection rate. This highlight discusses the utilization of ultra-fine cellulose nanofibers (UCN, diameter 5–10 nm), made by TEMPO/NaBr/NaClO oxidation of natural cellulose (e.g. wood pulp), in different nanofibrous composite formats that can meet this challenge for microfiltration (MF) and ultrafiltration (UF) applications. The unique features of ultra-fine cellulose nanofibers include small diameter, high surface-to-volume ratio, easy surface functionality, good mechanical properties and good chemical resistance. The electrospun nanofibrous scaffolds with fine pore size defined by the fiber diameter could be used to remove waterborne bacteria at two to three times higher flux when compared to that of commercial MF membranes (e.g., Millipore GS9035). When UCN were used as a functionalized adsorbent infused in the asymmetric two-layered non-woven fibrous format, the membranes exhibited a high ability to remove bacteria (by size exclusion) and viruses (by adsorption) simultaneously. When UCN were used as the barrier layer in an asymmetric three-layered non-woven fibrous format containing fibers of different diameters (from 5 nm to 20 µm), the membranes exhibited a two- to ten-fold increase in permeation flux over commercial membranes for ultrafiltration of oil and water emulsions (e.g., for purification of bilge water in ships or industrially produced water).
Co-reporter:Xiaowei Li, Yimin Mao, Hongyang Ma, Feng Zuo, Benjamin S. Hsiao, Benjamin Chu
Polymer 2011 Volume 52(Issue 20) pp:4610-4618
Publication Date(Web):12 September 2011
DOI:10.1016/j.polymer.2011.07.034
An ionic liquid (IL) 1-docosanyl-3-methylimidazolium bromide was incorporated into ultra-high molecular weight polyethylene (UHMWPE) and formed IL/UHMWPE blends by solution mixing. The structure evolution of these blends during uniaxial stretching was followed by in-situ synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. During deformation at room temperature, deformation-induced phase transformation from orthorhombic to monoclinic phase was observed in both IL/UHMWPE blends and neat UHMWPE. The elongation-to-break ratios of IL/UHMWPE blends were found to increase by 2–3 times compared with that of pure UHMWPE, while the tensile strength remained about the same. In contrast, during deformation at high temperature (120 °C), no phase transformation was observed. However, the blend samples showed much better toughness, higher crystal orientation and higher tilting extent of lamellar structure at high strains.
Co-reporter:Hongyang Ma, Christian Burger, Benjamin S. Hsiao, and Benjamin Chu
Biomacromolecules 2011 Volume 12(Issue 4) pp:
Publication Date(Web):February 22, 2011
DOI:10.1021/bm1013316
Ultrafine polysaccharide nanofibers (i.e., cellulose and chitin) with 5−10 nm diameters were employed as barrier layers in a new class of thin-film nanofibrous composite (TFNC) membranes for water purification. In addition to concentration, the viscosity of the polysaccharide nanofiber coating suspension was also found to be affected by the pH value and ionic strength. When compared with two commercial UF membranes (PAN10 and PAN400), 10-fold higher permeation flux with above 99.5% rejection ratio were achieved by using ultrafine cellulose nanofibers-based TFNC membranes for ultrafiltration of oil/water emulsions. The very high surface-to-volume ratio and negatively charged surface of cellulose nanofibers, which lead to a high virus adsorption capacity as verified by MS2 bacteriophage testing, offer further opportunities in drinking water applications. The low cost of raw cellulose/chitin materials, the environmentally friendly fabrication process, and the impressive high-flux performance indicate that such ultrafine polysaccharide nanofibers-based TFNC membranes can surpass conventional membrane systems in many different water applications.
Co-reporter:Hongyang Ma, Benjamin S. Hsiao, Benjamin Chu
Polymer 2011 Volume 52(Issue 12) pp:2594-2599
Publication Date(Web):26 May 2011
DOI:10.1016/j.polymer.2011.03.051
The barrier layer of high-flux ultrafiltration (UF) thin-film nanofibrous composite (TFNC) membranes for purification of wastewater (e.g., bilge water) have been prepared by using cellulose, chitin, and a cellulose–chitin blend, regenerated from an ionic liquid. The structures and properties of regenerated cellulose, chitin, and a cellulose–chitin blend were analyzed with thermogravimetric analysis (TGA) and wide-angle X-ray diffraction (WAXD). The surface morphology, pore size and pore size distribution of TFNC membranes were determined by SEM images and molecular weight cut-off (MWCO) methods. An oil/water emulsion, a model of bilge water, was used as the feed solution, and the permeation flux and rejection ratio of the membranes were investigated. TFNC membranes based on the cellulose–chitin blend exhibited 10 times higher permeation flux when compared with a commercial UF membrane (PAN10, Sepro) with a similar rejection ratio after filtration over a time period of up to 100 h, implying the practical feasibility of such membranes for UF applications.
Co-reporter:Hongyang Ma, Kyunghwan Yoon, Lixia Rong, Yimin Mao, Zhirui Mo, Dufei Fang, Zachary Hollander, Joseph Gaiteri, Benjamin S. Hsiao and Benjamin Chu
Journal of Materials Chemistry A 2010 vol. 20(Issue 22) pp:4692-4704
Publication Date(Web):30 Apr 2010
DOI:10.1039/B922536F
A novel class of thin-film nanofibrous composite (TFNC) membrane consisting of a cellulose barrier layer, a nanofibrous mid-layer scaffold, and a melt-blown non-woven substrate was successfully fabricated and tested as an ultrafiltration (UF) filter to separate an emulsified oil and water mixture, a model bilge water for on-board ship bilge water purification. Two ionic liquids: 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate, were chosen as the solvent to dissolve cellulose under mild conditions. The regenerated cellulose barrier layer exhibited less crystallinity (determined by wide-angle X-ray diffraction, WAXD) than the original cotton linter pulps, but good thermal stability (determined by thermal gravimetric analysis, TGA). The morphology, water permeation, and mechanical stability of the chosen TFNC membranes were thoroughly investigated. The results indicated that the polyacrylonitrile (PAN) nanofibrous scaffold was partially imbedded in the cellulose barrier layer, which enhanced the mechanical strength of the top barrier layer. The permeation flux of the cellulose-based TFNC membrane was significantly higher (e.g. 10×) than comparable commercial UF membranes (PAN10 and PAN400, Sepro) with similar rejection ratios for separation of oil/water emulsions. The molecular weight cut-off (MWCO) of TFNC membranes with cellulose barrier layer was evaluated using dextran feed solutions. The rejection was found to be higher than 90% with a dextran molecular weight of 2000 KDa, implying that the nominal pore size of the membrane was less than ∼50 nm. High permeation flux was also observed in the filtration of an emulsified oil/water mixture as well as of a sodium alginate aqueous solution, while high rejection ratio (above 99.5%) was maintained after prolonged operation. A variation of the barrier layer thickness could dramatically affect the permeation flux and the rejection ratio of the TFNC membranes, while different sources of cellulose, ionic liquids, and non-woven supports did not. As ionic liquids can be recycled and reused without obvious decomposition, the chosen method also demonstrates a benign pathway to fabricate the cellulose barrier layer for other types of membranes.
Co-reporter:Lewis Yung, Hongyang Ma, Xiao Wang, Kyunghwan Yoon, Ran Wang, Benjamin S. Hsiao, Benjamin Chu
Journal of Membrane Science 2010 Volume 365(1–2) pp:52-58
Publication Date(Web):1 December 2010
DOI:10.1016/j.memsci.2010.08.033
A new type of thin-film nanofibrous composite membrane (TFNC) for nanofiltration (NF), prepared by interfacial polymerization (IP) of piperazine (PIP) using ionic liquids (IL) was demonstrated. A comparison was first made to illustrate the advantage of using highly porous electrospun PES nanofibrous scaffold versus typical ultrafiltration (UF) membrane as the support for the PIP-based polyamide barrier layer. Two different ILs: 1-octyl-3-methylimidazolium chloride (OMIC) and 1-butyl-3-methyl-imidazolium chloride (BMIC), were incorporated in interfacial polymerization to adjust the permeation flux and salt rejection ratio (MgSO4 and NaCl); the results were also compared with those of commercial NF membranes (i.e. NF-90 and NF-270 from Dow FILMTEC). The existence of non-reactive IL in interfacial polymerization clearly affected the structure of the barrier layer and corresponding NF properties. The smaller ion (BMIC) simultaneously reduced permeation flux and increased salt rejection rate, while the larger ion (OMIC) exhibited an increase in permeation flux but a slight reduction in salt rejection. The demonstrated TFNC membrane exhibited 2 times higher permeation flux compared to that of NF-90 with comparable salt rejection ratio, and comparable permeation flux and salt rejection performance as those of NF-270.Graphical abstractResearch highlights▶ A new TFNC NF membrane has been prepared by interfacial polymerization. ▶ Ionic liquids were used as additives. ▶ Laboratory-made TFNC membranes exhibited higher permeation flux potential.
Co-reporter:Fen Wan, Zhaohui Tang, Weidong He and Benjamin Chu
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 39) pp:12379-12389
Publication Date(Web):19 Aug 2010
DOI:10.1039/C002515A
This perspective is to introduce a new pathway for non-viral gene delivery by taking advantage of nanofibrous scaffolds as gene storage devices, gene carriers and homing devices. During gene delivery to the target, the DNA has to be protected in order to pass through a set of barriers before reaching the nucleus. The DNA can form a complex with polycations, and numerous publications exist on how to stabilize the DNA fragments by natural and synthetic materials. Electrospun nanofibrous scaffolds can be used to store the DNA, especially in the form of a more stabilized polyplex, and then to deliver the DNA (polyplex) to cells that are attached to the scaffold. While each essential step has been tested experimentally, the overall yet untested process, especially for in vivo experiments, may lead to a promising specific approach for gene/drug storage and delivery. The pathway described herein is based mainly on our understanding of the physics and chemistry of gene storage and delivery processes, in contrast to using pure biological concepts. Novel biodegradable, biocompatible nanofibrous materials with imbedded DNA (e.g., in the polyplex form) can then be designed to fabricate an intelligent scaffold for gene delivery. To achieve the above goal, the first step is to stabilize the DNA so that it can be incorporated into nanofibrous scaffolds. In this respect, we shall discuss the different methods of DNA/gene condensation and complex formation, and then explain the strategy used to incorporate DNA into electrospun nanofibers. Solvent-induced DNA condensation and then encapsulation were achieved. However, the released naked DNA was not sufficiently protected for gene transfection in cells. The objective of the current perspective is to suggest that, instead of the solvent-induced DNA condensation, one can combine the recently developed polyplex formation by using branched polyethyleneimine (bPEI). More importantly, free bPEI can be incorporated into the nanofibers separately so that during the gene delivery step, the presence of a predesigned amount of free bPEI can greatly increase the gene transfection efficiency, as has been reported recently by Chi Wu and his coworkers. Thus, a physics/chemistry-based pathway that utilizes nanofibrous scaffolds for gene delivery is within reach.
Co-reporter:Hongyang Ma, Kyunghwan Yoon, Lixia Rong, Mina Shokralla, Andrey Kopot, Xiao Wang, Dufei Fang, Benjamin S. Hsiao, and Benjamin Chu
Industrial & Engineering Chemistry Research 2010 Volume 49(Issue 23) pp:11978-11984
Publication Date(Web):June 11, 2010
DOI:10.1021/ie100545k
A new class of thin-film nanofibrous composite (TFNC) membranes, composed of a chemically cross-linked polyvinyl alcohol (PVA) barrier layer containing directional water channels through the incorporation of very fine nanofiber fillers, an electrospun polyacrylonitrile (PAN) nanofibrous scaffold midlayer, and a melt-blown polyethylene terephthalate (PET) nonwoven support, was demonstrated for ultrafiltration (UF) of oil/water emulsions. The permeation flux of TFNC membrane with a pure PVA barrier layer was already about 5 times higher than that of the commercial PAN10 (Sepro) UF membrane at low pressures (e.g., 30 psi), while maintaining a similar rejection ratio (∼ 99.7%). Two kinds of fine nanofiber fillers: oxidized multiwalled carbon nanotubes (MWCNTs) and cellulose nanofibers (CNs), were further incorporated into the PVA barrier layer to increase the permeation flux. The results indicated that permeation fluxes of MWCNT and CN filler-containing TFNC membranes were about 10-times higher than those of PAN10, while still maintaining a rejection ratio of ∼99.5%. The increase in the permeation flux could be attributed to the formation of directional water channels through the interface between the surface of MWCNT or CN fillers and that of the barrier layer and the interconnections among the fine nanofiber network.
Co-reporter:Kyunghwan Yoon, Benjamin S. Hsiao, Benjamin Chu
Journal of Membrane Science 2009 Volume 338(1–2) pp:145-152
Publication Date(Web):10 August 2009
DOI:10.1016/j.memsci.2009.04.020
In this study, we demonstrated a high flux thin film nanofibrous composite (TFNC) membrane system based on polyacrylonitrile (PAN) electrospun scaffold coupled with a thin barrier layer of cross-linked polyvinyl alcohol (PVA). With carefully chosen structural parameters (i.e., a mid-layer PAN scaffold with porosity of about 85% and cross-linked PVA top coating with thickness of about 0.5 μm), the demonstrated TFNC membrane system shall be very useful for ultrafiltration (UF) applications, exhibiting a very high flux (i.e., 12 times higher than that of conventional PAN UF membranes) and excellent rejection ratio (>99.5%) for separation of oil/water mixture (1500 ppm in water) over a long time period (tested up to 190 h) in a practical pressure range (up to 130 psig).
Co-reporter:Zhaohui Tang, Jie Wei, Lewis Yung, Bowei Ji, Hongyang Ma, Changquan Qiu, Kyunghwan Yoon, Fen Wan, Dufei Fang, Benjamin S. Hsiao, Benjamin Chu
Journal of Membrane Science 2009 Volume 328(1–2) pp:1-5
Publication Date(Web):20 February 2009
DOI:10.1016/j.memsci.2008.11.054
A novel class of high-flux thin film nanofibrous composite (TFNC) ultrafiltration membrane, consisting of UV-cured poly(vinyl alcohol) (PVA) hydro-gel barrier layer, electrospun nanofibrous PVA mid-layer scaffold and polyethylene terephthalate (PET) non-woven substrate, was investigated. The barrier layer was fabricated by photo-crosslinking of UV-reactive PVA (UV-PVA) on a chemically cross-linked nanofibrous PVA scaffold. The effects of concentration and viscosity of the UV-PVA solution on the flux and rejection rate of the TFNC membrane were studied. It was found that UV curing of a 5-wt% UV-PVA solution coating over 20-s time period yielded a high flux, high rejection UF membrane with good fouling resistance for separation of oil and water emulsion.
Co-reporter:Kyunghwan Yoon, Benjamin S. Hsiao, Benjamin Chu
Journal of Membrane Science 2009 Volume 326(Issue 2) pp:484-492
Publication Date(Web):20 January 2009
DOI:10.1016/j.memsci.2008.10.023
Electrospun polyacrylonitrile (PAN) nanofibrous scaffold was used as a mid-layer support in a new kind of high flux thin film nanofibrous composite (TFNC) membranes for nanofiltration (NF) applications. The top barrier layer was produced by interfacial polymerization of polyamides containing different ratios of piperazine and bipiperidine. The filtration performance (i.e., permeate flux and rejection) of TFNC membranes based on electrospun PAN nanofibrous scaffold was compared with those of conventional thin film composite (TFC) membranes consisting of (1) a commercial PAN ultrafiltration (UF) support with the same barrier layer coating and (2) two kinds of commercial NF membranes (i.e., NF90 and NF270 from Dow Filmtec). The nanofiltration test was carried out by using a divalent salt solution (MgSO4, 2000 ppm) and a cross-flow filtration cell. The results indicated that TFNC membranes exhibited over 2.4 times more permeate flux than TFC membranes with the same chemical compositions, while maintaining the same rejection rate (ca. 98%). In addition, the permeate flux of hand-cast TFNC membranes was about 38% higher than commercial NF270 membrane with the similar rejection rate.
Co-reporter:Benjamin Chu;Benjamin S. Hsiao
Journal of Polymer Science Part B: Polymer Physics 2009 Volume 47( Issue 24) pp:2431-2435
Publication Date(Web):
DOI:10.1002/polb.21854
Co-reporter:Kyunghwan Yoon, Benjamin S. Hsiao, Benjamin Chu
Polymer 2009 50(13) pp: 2893-2899
Publication Date(Web):
DOI:10.1016/j.polymer.2009.04.047
Co-reporter:Rafael Muñoz-Espí, Christian Burger, Chirakkal V. Krishnan and Benjamin Chu
Chemistry of Materials 2008 Volume 20(Issue 23) pp:7301
Publication Date(Web):November 14, 2008
DOI:10.1021/cm802193t
The influence of polyoxyethylene-containing polymers on the crystal structure and habit of molybdenum-oxide-based products crystallized from peroxomolybdate solutions was investigated. Polyoxyethylene homopolymers of various molar masses were compared with a polyoxyethylene alkyl ether and a triblock copolymer of polyoxyethylene and polypropylene. Conventional hydrothermal synthesis at temperatures between 70 and 180 °C was compared with an ultrasonic pathway at 70 °C. The structure of the products was investigated by small- and wide-angle X-ray scattering. Different crystal phases were obtained depending on the polymer concentration and the preparation methods. At 70 °C, a compound with tentative formula MoO3−x(O2)x·nH2O (n ≈ 1), showing X-ray diffraction patterns matching those of triclinic monohydrate molybdenum trioxide, was the product found in the absence of any polymer. However, small concentrations of any polyoxyethylene-containing polymer led to a monoclinic hemihydrate phase under the same conditions and temperature. At temperatures above 90 °C, the patterns of the resulting products could be indexed according to orthorhombic anhydrous MoO3, although the blue color of certain samples indicated an oxygen deficiency. At high polymer concentrations and temperatures under 90 °C, the material crystallized in an unusual primitive cubic structure, independent of the exact type of polyoxyethylene polymer used, with a very large cubic lattice constant of ∼5 nm. However, the molar mass and the structure of the polymer do influence the lattice constants of the final crystal leading to a slight decrease with increasing molar mass. At high polymer concentrations and 180 °C, the product was identified as MoO2. The polymer acts not only as a structure-directing agent but also as a mild reducing agent, as judged from the nontrivial redox behavior of the molybdenum ions when the crystallization occurs in the presence of polymer. The excellent catalytic properties of representative types of the synthesized materials were demonstrated for the epoxidation of cyclohexene and cyclooctene by tert-butyl hydroperoxide.
Co-reporter:Kyunghwan Yoon, Benjamin S. Hsiao and Benjamin Chu
Journal of Materials Chemistry A 2008 vol. 18(Issue 44) pp:5326-5334
Publication Date(Web):10 Sep 2008
DOI:10.1039/B804128H
Nanofibers, mainly fabricated by electrospinning, have exhibited great potential for many emerging environmental applications. They can be considered as one of the safest nanomaterials due to their extremely long length (can be up to hundreds of kilometers) and their ability to be embedded within other media. Their high surface-to-volume ratio, large porosity (up to over 80%) and adjustable functionality are also much more effective than conventional non-woven and polymeric membranes in particulate separation and liquid filtration. Technology advances such as multiple-jet electrospinning and electroblowing for mass production of nanofibers have made it practical to use nanofibrous scaffolds as a unique and breakthrough component in separation media for both gas and liquid filtration. In this review, the opportunities and challenges of using functional nanofibers for several representative environmental applications are reviewed.
Co-reporter:Jun Wu;Xuefen Wang;Jong Kahk Keum;Hongwen Zhou;Mikhail Gelfer;Carlos-Alberto Avila-Orta;Hui Pan;Weiliam Chen;Shu-Min Chiao;Benjamin S. Hsiao
Journal of Biomedical Materials Research Part A 2007 Volume 80A(Issue 4) pp:800-812
Publication Date(Web):20 OCT 2006
DOI:10.1002/jbm.a.30972
Novel water soluble, biocompatible, and highly viscoelastic polyelectrolyte complexes were prepared by mixing of positively charged chitosan grafted with poly (ethylene glycol) monomethyl ether (CS-g-MPEG) and negatively charged hyaluronic acid (HA). CS-g-MPEGs having different degrees of substitution were synthesized by reacting chitosan with MPEG-aldehyde. The molecular structure, thermal and rheological properties, as well as biocompatibility of CS-g-MPEG/HA complexes were characterized. Rheological results showed that a small amount of HA could greatly enhance the viscosity of CS-g-MPEG solution. The highest viscosity was obtained when the charge ratio of CS-g-MPEG/HA was close to 1.0. Small-angle X-ray scattering measurements provided some insights into the lamellar structure of the CS-g-MPEG/HA complex. The CS-g-MPEG/HA complex system offers promising potentials in pharmaceutical, cosmetic, and biotechnology applications (e.g., cell scaffold, artificial synovial fluid, and drug/gene delivery medium). © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Co-reporter:Jonathan B. Chiu;Cheng Liu;Benjamin S. Hsiao;Michael Hadjiargyrou
Journal of Biomedical Materials Research Part A 2007 Volume 83A(Issue 4) pp:1117-1127
Publication Date(Web):25 JUN 2007
DOI:10.1002/jbm.a.31279
The utilization of electrospun biodegradable scaffolds by fine-tuning their biofunctionalities through a simple mixing method was demonstrated in this study. Poly(L-lactide) (PLLA)-based scaffolds containing small amounts of bioactive collagen type I molecules were investigated for enhancements in cellular behavior. Electron microscopy revealed no topological alterations of the fibers in the collagen/PLLA scaffolds when compared with pure PLLA scaffolds. Cell attachment after 24 h was robust on collagen/PLLA scaffolds, with cytoskeletal analysis showing that the attached cells were aligned along the fibers assuming a spindle-shape appearance. Despite these morphological differences, gene expression analyses revealed no apparent alterations in mRNA levels of four genes involved in cell attachment across the various scaffolds. Although cell proliferation was not adversely affected, there were clear differences in cell penetration; after 1 week, cells migrated through 32 and 85% of PLLA and collagen/PLLA scaffolds, respectively. Mineralization of primary calvaria osteoblasts provided further evidence that collagen-containing electrospun PLLA scaffolds could sustain cell differentiation. Overall, the inclusion of collagen type I in even miniscule amounts (<1 wt %) within electrospun PLLA scaffolds could effectively modulate certain aspects of cellular behavior. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Co-reporter:Jun Zhang, Marcus Gassmann, Weidong He, Fen Wan and Benjamin Chu
Lab on a Chip 2006 vol. 6(Issue 4) pp:526-533
Publication Date(Web):02 Mar 2006
DOI:10.1039/B515557F
A reversible thermo-responsive gel system, consisting of Pluronic copolymer mixture of F87 and F127, has been used to successfully carry out the separation of oligonucleotides, for the first time, by microchip-based capillary electrophoresis. Pluronic triblock copolymers F87 (E61P40E61) and F127 (E99P69E99), with E, P, and subscript denoting oxyethylene, oxypropylene, and segment length respectively, have a unique temperature dependent viscosity-adjustable property and a dynamic coating ability in aqueous solution, including 1 × TBE buffer. The mixture solution has a reversible thermo-responsive property and its sol–gel transition temperature can be adjusted ranging from about 17 °C to 38 °C by varying the relative weight ratio of F87 and F127 at an optimized concentration of ∼30% (w/v) for oligonucleotide separations. Oligonucleotide sizing markers ranging from 8 to 32 base could be successfully separated in a 1.5 cm long separation channel by the mixture solution in its gel-like state. A 30% (w/v) with a F87/F127 weight ratio of 1 ∶ 2 which has a “sol–gel” transition point of about 26 °C shows the best sieving ability. The sieving ability of the mixture solution was further confirmed in an Agilent Bioanalyzer 2100 system. Fast separation of oligonucleotides has been achieved within 40 s with one base resolution.
Co-reporter:Jun Zhang, Weidong He, Dehai Liang, Dufei Fang, Benjamin Chu, Marcus Gassmann
Journal of Chromatography A 2006 Volume 1117(Issue 2) pp:219-227
Publication Date(Web):9 June 2006
DOI:10.1016/j.chroma.2006.03.106
Polyacrylamide (PAM) was used as a model polymer to build up an empirical model that relates polymer molecular weight, polymer concentration and solution viscosity. The desired random copolymers of acrylamide (AM) and N,N-dimethylacrylamide (DMA) used as DNA separation media for different specifications were synthesized under the guidance of the empirical model. The separation performances of rationally designed copolymers were tested in a 1.2 cm long separation channel, simulating microchip-based capillary electrophoresis. pBR322/HaeIII digest was successfully separated with good separation resolution and fast speed. Validation of the sieving ability of our polymers was performed in the Agilent 2100 Bioanalyzer. The results of the 10 bp (base pair) DNA ladder separation demonstrate the potential of our approach for the sieving matrix in microchip-based electrophoresis.
Co-reporter:Jinglu Chen;Benjamin S. Hsiao
Journal of Biomedical Materials Research Part A 2006 Volume 79A(Issue 2) pp:307-317
Publication Date(Web):30 JUN 2006
DOI:10.1002/jbm.a.30799
A highly porous electrospun poly(L-lactic acid) (PLLA) nanofibrous scaffold was used as a matrix for mineralization of hydroxyapatite. The mineralization process could be initiated by immersing the electrospun scaffold in the simulated body fluids (SBF) at 37°C for varying periods of time. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), wide-angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR), and Raman spectroscopy were used to characterize the composition and the structure of the deposited mineral on the nanofiber surface. Results indicated that the mineral phase was a carbonated apatite with thin flake-like nanostructures. The effects of functional groups on the scaffold surface and anionic additives in the incubation fluids on the nucleation and growth of the mineral were investigated. It was found that a minuscule amount of anionic additives (e.g., citric acid and poly-L-aspartic acid) in the SBF could effectively inhibit the mineral growth. Surface modification of the scaffold was carried out by hydrolysis of PLLA scaffold in NaOH aqueous solution, where carboxylic acid groups were produced without compromising the scaffold integrity. The mineralization process from modified PLLA electrospun scaffolds was significantly enhanced because the calcium ions can bind to the carboxylate groups on the fiber surface. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Co-reporter:Dehai Liang, Benjamin S. Hsiao, Michael Hadjiargyrou, Benjamin Chu
Journal of Non-Crystalline Solids 2006 Volume 352(42–49) pp:4394-4399
Publication Date(Web):15 November 2006
DOI:10.1016/j.jnoncrysol.2006.01.139
A novel approach to create a biodegradable scaffold containing a condensed DNA core and a biodegradable polymer shell has been demonstrated. In this approach, the extended DNA chains were first collapsed into compact globules in a poor solvent, containing 94% DMF + 6%TE buffer, where the shrinkage in the radius of gyration was by a factor of about 9. The condensed DNA globule was then encapsulated by using a tri-block copolymer of polylactide–poly(ethylene glycol)–polylactide (LEL). The encapsulated DNA protected it from degradation during the electro-spinning process, which also removed the undesirable DMF solvent, preserving the DNA in the dry nanofibrous scaffold. An enhanced transfection activity was observed when the scaffold was used to deliver the embedded DNA to cells adhered to the scaffold.
Co-reporter:Jinglu Chen;Christian Burger;Chirakkal V. Krishnan;Benjamin S. Hsiao;Melvin J. Glimcher
Macromolecular Chemistry and Physics 2005 Volume 206(Issue 1) pp:
Publication Date(Web):27 DEC 2004
DOI:10.1002/macp.200400066
Summary: Simultaneous small- and wide-angle X-ray diffraction of in vitro calcified highly ordered decalcified shad fish bone collagen have identified the calcium phosphate (Ca-P) crystals, formed as poorly crystalline apatite, and their highly ordered spatial, axial distribution with respect to the supramolecular packing of collagen fibrils. The extent of in vitro calcification was significantly diminished when the supramolecular collagen packing was disrupted. These findings are similar to both electron microscopic and small angle X-ray scattering (SAXS) studies of native shad and other species of fish bone and other animal species and of in vitro experiments of the calcification of purified and reconstituted native type collagen fibrils. The results emphasize the important role of the supramolecular packing of collagen fibrils in the heterogeneous nucleation of apatite crystals initiating calcification. The exquisite spatial relationships of the inorganic crystal and the supramolecular packing of native collagen fibrils also form a two-phase composite substance, providing distinct mechanical properties and other physiological functions to bone substance and tissue.
Co-reporter:Xinhua Zong, Harold Bien, Chiung-Yin Chung, Lihong Yin, Dufei Fang, Benjamin S. Hsiao, Benjamin Chu, Emilia Entcheva
Biomaterials 2005 Volume 26(Issue 26) pp:5330-5338
Publication Date(Web):September 2005
DOI:10.1016/j.biomaterials.2005.01.052
The structural and functional effects of fine-textured matrices with sub-micron features on the growth of cardiac myocytes were examined. Electrospinning was used to fabricate biodegradable non-woven poly(lactide)- and poly(glycolide)-based (PLGA) scaffolds for cardiac tissue engineering applications. Post-processing was applied to achieve macro-scale fiber orientation (anisotropy). In vitro studies confirmed a dose–response effect of the poly(glycolide) concentration on the degradation rate and the pH value changes. Different formulations were examined to assess scaffold effects on cell attachment, structure and function. Primary cardiomyocytes (CMs) were cultured on the electrospun scaffolds to form tissue-like constructs. Scanning electron microscopy (SEM) revealed that the fine fiber architecture of the non-woven matrix allowed the cardiomyocytes to make extensive use of provided external cues for isotropic or anisotropic growth, and to some extent to crawl inside and pull on fibers. Structural analysis by confocal microscopy indicated that cardiomyocytes had a preference for relatively hydrophobic surfaces. CMs on electrospun poly(l-lactide) (PLLA) scaffolds developed mature contractile machinery (sarcomeres). Functionality (excitability) of the engineered constructs was confirmed by optical imaging of electrical activity using voltage-sensitive dyes. We conclude that engineered cardiac tissue structure and function can be modulated by the chemistry and geometry of the provided nano- and micro-textured surfaces. Electrospinning is a versatile manufacturing technique for design of biomaterials with potentially reorganizable architecture for cell and tissue growth.
Co-reporter:Kwangsok Kim, Yen K. Luu, Charles Chang, Dufei Fang, Benjamin S. Hsiao, Benjamin Chu, Michael Hadjiargyrou
Journal of Controlled Release 2004 Volume 98(Issue 1) pp:47-56
Publication Date(Web):23 July 2004
DOI:10.1016/j.jconrel.2004.04.009
The successful incorporation and sustained release of a hydrophilic antibiotic drug (Mefoxin®, cefoxitin sodium) from electrospun poly(lactide-co-glycolide) (PLGA)-based nanofibrous scaffolds without the loss of structure and bioactivity was demonstrated. The morphology and density of the electrospun scaffold was found to be dependent on the drug concentration, which could be attributed to the effect of ionic salt on the electrospinning process. The drug release behavior from the electrospun scaffolds and its antimicrobial effects on Staphylococcus aureus cultures were also investigated. In all tested scaffolds, the maximum dosage of drug was released after 1 h of incubation in water at 37 °C. The usage of the amphiphilic block copolymer (PEG-b-PLA) reduced the cumulative amount of the released drug at earlier time points and prolonged the drug release rate at longer times (up to a 1-week period). The antibiotic drug released from these electrospun scaffolds was effective in their ability to inhibit Staphylococcus aureus growth (>90%). The combination of mechanical barriers based on non-woven nanofibrous biodegradable scaffolds and their capability for local delivery of antibiotics increases their desired utility in biomedical applications, particularly in the prevention of post-surgical adhesions and infections.
Co-reporter:Christian Burger, Jingcheng Hao, Qicong Ying, Hiroyuki Isobe, Masaya Sawamura, Eiichi Nakamura, Benjamin Chu
Journal of Colloid and Interface Science 2004 Volume 275(Issue 2) pp:632-641
Publication Date(Web):15 July 2004
DOI:10.1016/j.jcis.2004.02.048
The self-assembly behavior of a fullerene-based surfactant, C60(CH3)5K, in water was studied using a combination of static and dynamic light scattering, as well as transmission electron microscopy, and compared to that of the compound C60(C6H5)5K. Both fullerene surfactant systems spontaneously assemble into large vesicles consisting of closed spherical shells formed by bilayers, with critical aggregation concentrations (CAC) lower than 10−6 g ml−1. At low concentrations, the aggregate sizes of C60(CH3)5K (radius R∼26.8 nm) and C60(C6H5)5K (R∼17.0 nm) were found to be substantially different from each other, showing that the change of the substituents surrounding the polar cyclopentadienide head group makes it possible to control the size of the resulting aggregates. Furthermore, the C60(CH3)5K vesicles were found to exist in two qualitatively different types of aggregation with a critical reaggregation concentration (CRC) located at 3.30×10−6 g ml−1. Above the CRC, larger aggregates were observed (R∼37.6 nm), showing a more complex form of supramolecular aggregation, e.g., in terms of multi-bilayer vesicles and/or of clusters of bilayer vesicles.
Co-reporter:Tianbo Liu, Christian Burger, Benjamin Chu
Progress in Polymer Science 2003 Volume 28(Issue 1) pp:5-26
Publication Date(Web):January 2003
DOI:10.1016/S0079-6700(02)00077-1
Polymeric systems have played important roles as templates for nanofabrication since they can offer nanotemplates with different morphologies and tunable sizes, can be easily removed after reactions, and can be further modified with different functional groups to enhance the interactions. This review covers recent advances in polymer-assisted fabrication of nanomaterials with emphasis on ordered polymeric nanostructures. Examples could include self-assembled amphiphilic block co-polymers/surfactants, cross-linkable polymers, dendrimers, microemulsions, latex particles, biomacromolecules, electric- or shear-induced structures as templates to fabricate inorganic, organic/inorganic composites and polymeric materials with nanoscale modifications. The phase behavior of block co-polymers in water and the use of templates to form ordered nanostructures are reviewed in detail. Modern physical techniques for nanoscale characterization are briefly discussed.
Co-reporter:Kwangsok Kim, Meiki Yu, Xinhua Zong, Jonathan Chiu, Dufei Fang, Young-Soo Seo, Benjamin S. Hsiao, Benjamin Chu, Michael Hadjiargyrou
Biomaterials 2003 Volume 24(Issue 27) pp:4977-4985
Publication Date(Web):December 2003
DOI:10.1016/S0142-9612(03)00407-1
Typical properties of poly(d,l-lactide) (PLA)-based scaffolds (films and foams), such as long degradation time, mechanical stiffness and hydrophobicity, are sometimes not suitable for biomedical applications. These properties can be substantially altered by electrospinning of PLA blends with miscible poly(lactide-co-glycolide) (PLGA) random copolymers, poly(lactide-b-ethylene glycol-b-lactide) (PLA-b-PEG-b-PLA) triblock copolymers, and a lactide (used as a hydrolytic catalyst). Electrospun scaffolds based on the multi-component PLA blends, comprised of randomly interconnected webs of sub-micron sized fibers, have a bulk density of 0.3–0.4 g/cm3. In this study, the concentration effects of PLA-b-PEG-b-PLA triblock copolymer and lactide on the cell proliferation and the hydrophilicity of electrospun scaffolds were investigated. Based on in vitro degradation study, we found that the electrospun scaffold having PLA (40 wt%), PLGA (LA/GA=50/50, 25 wt%), PLA-b-PEG-b-PLA (20 wt%), and lactide (15 wt%) underwent a rapid weight loss of ∼65% in 7 weeks. The hydrophobicity of this membrane, as determined by contact angle measurements in a cell buffer solution, decreased by ∼50% from 105° (of an electrospun PLA scaffold) to 50°. The selection of suitable chemical compositions in conjunction with the non-invasive electrospinning process is useful in the production of a new kind of biodegradable scaffolds suitable for different biomedical applications such as cell storage and delivery as well as prevention of post-surgical adhesion because of their porosity, mechanical flexibility and tunable biodegradability.
Co-reporter:S.-Q. Zhou;Q. Wan;D.-H. Liang;B. Chu;P. Xu;J. Lai
Journal of Applied Polymer Science 2000 Volume 77(Issue 4) pp:733-739
Publication Date(Web):25 MAY 2000
DOI:10.1002/(SICI)1097-4628(20000725)77:4<733::AID-APP3>3.0.CO;2-K
Static and dynamic light scattering experiments were performed to characterize the copolymer of tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE). Solvents of perfluoro-2-butyltetrahydrofuran (FC-75) and Flutec PP11 (PP11) were used to dissolve the TFE-PMVE copolymer. By taking advantage of the solvent properties of FC-75 and PP11, homogeneous TFE-PMVE copolymer solutions were specially prepared in a FC-75/PP11 mixed solvent. Such prepared solutions could provide a strong enough scattered intensity for light scattering studies. The molecular weight, molecular weight distribution, chain dimensions, and conformation were determined for the TFE-PMVE copolymer in the FC-75/PP11 mixed solvent. A combination of viscosity and molecular weight measurements enabled the calculation of the k value in the relation of η0 = k (Mw)3.4 and thus the prediction of the molecular weight of a given TFE-PMVE copolymer with the same composition by using only the simpler and more readily available rheological measurements. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 733–739, 2000
Co-reporter:Li-Zhi Liu;J. P. Penning;R. St. John Manley
Journal of Polymer Science Part B: Polymer Physics 2000 Volume 38(Issue 17) pp:2296-2308
Publication Date(Web):19 JUL 2000
DOI:10.1002/1099-0488(20000901)38:17<2296::AID-POLB100>3.0.CO;2-M
The incorporation of poly(1,4-butylene adipate) (PBA) and its crystallization behavior within poly(vinylidenefluoride) (PVF2) spherulites in miscible PVF2/PBA blends have been further studied with small-angle X-ray synchrotron scattering (SAXS). The incorporation of PBA into the PVF2 interlamellar region was found to be dependent on the PVF2 crystallization conditions. In our previous work, where the blends were crystallized by a one-step quenching process directly from 190 (a single-phase region) to 20 °C (a three-phase region), the transition from PBA inclusion in the PVF2 interlamellar region to interlamellar exclusion occurred at a PBA weight fraction of ∼ 0.5. In this case, where the blends were first quenched from 190 (a single-phase region) to 130 °C (a two-phase region) and then further quenched to 20 °C (a three-phase region), the transition occurred at a PBA weight fraction of less than 0.3. That is, when a blend is crystallized under different conditions, different amounts of the PBA component are incorporated into the PVF2 interlamellar phase. The thickness of the PVF2 interlamellar phase, in turn, may affect the PBA crystalline structure in the interlamellar region. Time-resolved SAXS was used to probe the crystallization dynamics of both PVF2 and PBA components in a blend containing 60 wt % PBA. The blend was quenched from the single-phase region at 190 to 130 °C to crystallize the PVF2 component and was then further quenched to 20 °C to crystallize the PBA component. This study, together with our earlier results, shows that the time dependence of the PVF2 crystallization rate and crystalline lamellar thickness is a function of the PBA content in the blend. The glass-transition temperature of the blend and the PBA diffusion process are the two dominant factors that control the PVF2 crystallization dynamics. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2296–2308, 2000
Co-reporter:Fengji Yeh;Christian Burger;Shuiqin Zhou
Journal of Polymer Science Part B: Polymer Physics 1999 Volume 37(Issue 16) pp:2165-2172
Publication Date(Web):19 JUL 1999
DOI:10.1002/(SICI)1099-0488(19990815)37:16<2165::AID-POLB18>3.0.CO;2-F
Small-angle X-ray scattering was used to investigate the nanostructures of complexes formed by slightly crosslinked anionic copolymer gels of poly(sodium methacrylate-co-N-isopropylacrylamide) [P(MAA/NIPAM)] with cetyltrimethylammonium bromide (CTAB), and didodecyldimethylammonium bromide (DDAB), respectively, at room temperature (∼ 23°C). Several highly ordered supramolecular structures were observed in the polyelectrolyte gel–surfactant complexes. In P(MAA/NIPAM)–CTA systems, in sequence with decreasing charge density of the P(MAA/NIPAM) copolymer chains, structures of the Pm3n space group cubic, face-centered cubic close packing of spheres, and hexagonal close packing of spheres were determined at a charge content of ≥ 75, 67, and 50%, respectively. The spheres and rods in these structures were the spherical and cylindrical micelles formed by the self-assembly of CTA cations with their paraffin chains inside. Both the aggregation number and the size of the micelles decreased with a decreasing charge density of the copolymer chains. In the P(MAA/NIPAM)–DDA systems, the bilayer lamellar structures formed at charge contents ≥ 75% transferred to bicontinuous cubic structures of the Ia3d space group at charge contents of 50–67%. The rods in the Ia3d cubic structures were formed by the self-assembly of double-tailed DDA cations with polar moieties inside. The formation of these highly ordered structures were driven by both electrostatic and hydrophobic interactions of the charged copolymer chains/surfactants and the surfactants/surfactants inside the charged gels. The structures became less ordered by further decreasing the charge content of the P(MAA/NIPAM) chains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2165–2172, 1999
Co-reporter:Christian Burger, Hong-wen Zhou, Hao Wang, Igors Sics, Benjamin S. Hsiao, Benjamin Chu, Lila Graham, Melvin J. Glimcher
Biophysical Journal (15 August 2008) Volume 95(Issue 4) pp:
Publication Date(Web):15 August 2008
DOI:10.1529/biophysj.107.128355
Combined small-angle x-ray scattering and transmission electron microscopy studies of intramuscular fish bone (shad and herring) indicate that the lateral packing of nanoscale calcium-phosphate crystals in collagen fibrils can be represented by irregular stacks of platelet-shaped crystals, intercalated with organic layers of collagen molecules. The scattering intensity distribution in this system can be described by a modified Zernike-Prins model, taking preferred orientation effects into account. Using the model, the diffuse fan-shaped small-angle x-ray scattering intensity profile, dominating the equatorial region of the scattering pattern, could be quantitatively analyzed as a function of the degree of mineralization. The mineral platelets were found to be very thin (1.5 nm ∼ 2.0 nm), having a narrow thickness distribution. The thickness of the organic layers between adjacent mineral platelets within a stack is more broadly distributed with the average value varying from 6 nm to 10 nm, depending on the extent of mineralization. The two-dimensional analytical scheme also leads to quantitative information about the preferred orientation of mineral stacks and the average height of crystals along the crystallographic c axis.
Co-reporter:Dehai Liang, Benjamin S. Hsiao, Benjamin Chu
Advanced Drug Delivery Reviews (10 December 2007) Volume 59(Issue 14) pp:1392-1412
Publication Date(Web):10 December 2007
DOI:10.1016/j.addr.2007.04.021
Functional nanofibrous scaffolds produced by electrospinning have great potential in many biomedical applications, such as tissue engineering, wound dressing, enzyme immobilization and drug (gene) delivery. For a specific successful application, the chemical, physical and biological properties of electrospun scaffolds should be adjusted to match the environment by using a combination of multi-component compositions and fabrication techniques where electrospinning has often become a pivotal tool. The property of the nanofibrous scaffold can be further improved with innovative development in electrospinning processes, such as two-component electrospinning and in-situ mixing electrospinning. Post modifications of electrospun membranes also provide effective means to render the electrospun scaffolds with controlled anisotropy and porosity. In this article, we review the materials, techniques and post modification methods to functionalize electrospun nanofibrous scaffolds suitable for biomedical applications.
Co-reporter:Hongyang Ma, Kyunghwan Yoon, Lixia Rong, Yimin Mao, Zhirui Mo, Dufei Fang, Zachary Hollander, Joseph Gaiteri, Benjamin S. Hsiao and Benjamin Chu
Journal of Materials Chemistry A 2010 - vol. 20(Issue 22) pp:NaN4704-4704
Publication Date(Web):2010/04/30
DOI:10.1039/B922536F
A novel class of thin-film nanofibrous composite (TFNC) membrane consisting of a cellulose barrier layer, a nanofibrous mid-layer scaffold, and a melt-blown non-woven substrate was successfully fabricated and tested as an ultrafiltration (UF) filter to separate an emulsified oil and water mixture, a model bilge water for on-board ship bilge water purification. Two ionic liquids: 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate, were chosen as the solvent to dissolve cellulose under mild conditions. The regenerated cellulose barrier layer exhibited less crystallinity (determined by wide-angle X-ray diffraction, WAXD) than the original cotton linter pulps, but good thermal stability (determined by thermal gravimetric analysis, TGA). The morphology, water permeation, and mechanical stability of the chosen TFNC membranes were thoroughly investigated. The results indicated that the polyacrylonitrile (PAN) nanofibrous scaffold was partially imbedded in the cellulose barrier layer, which enhanced the mechanical strength of the top barrier layer. The permeation flux of the cellulose-based TFNC membrane was significantly higher (e.g. 10×) than comparable commercial UF membranes (PAN10 and PAN400, Sepro) with similar rejection ratios for separation of oil/water emulsions. The molecular weight cut-off (MWCO) of TFNC membranes with cellulose barrier layer was evaluated using dextran feed solutions. The rejection was found to be higher than 90% with a dextran molecular weight of 2000 KDa, implying that the nominal pore size of the membrane was less than ∼50 nm. High permeation flux was also observed in the filtration of an emulsified oil/water mixture as well as of a sodium alginate aqueous solution, while high rejection ratio (above 99.5%) was maintained after prolonged operation. A variation of the barrier layer thickness could dramatically affect the permeation flux and the rejection ratio of the TFNC membranes, while different sources of cellulose, ionic liquids, and non-woven supports did not. As ionic liquids can be recycled and reused without obvious decomposition, the chosen method also demonstrates a benign pathway to fabricate the cellulose barrier layer for other types of membranes.
Co-reporter:Hongyang Ma, Christian Burger, Benjamin S. Hsiao and Benjamin Chu
Journal of Materials Chemistry A 2011 - vol. 21(Issue 21) pp:NaN7510-7510
Publication Date(Web):2011/04/05
DOI:10.1039/C0JM04308G
The major challenges in membrane technology for water filtration are the development of new materials (e.g. high durability, low cost and low environmental concerns) and new structures (e.g. directed water channels) that can produce high permeation flux (thus low energy input) while maintaining a high selectivity or rejection rate. This highlight discusses the utilization of ultra-fine cellulose nanofibers (UCN, diameter 5–10 nm), made by TEMPO/NaBr/NaClO oxidation of natural cellulose (e.g. wood pulp), in different nanofibrous composite formats that can meet this challenge for microfiltration (MF) and ultrafiltration (UF) applications. The unique features of ultra-fine cellulose nanofibers include small diameter, high surface-to-volume ratio, easy surface functionality, good mechanical properties and good chemical resistance. The electrospun nanofibrous scaffolds with fine pore size defined by the fiber diameter could be used to remove waterborne bacteria at two to three times higher flux when compared to that of commercial MF membranes (e.g., Millipore GS9035). When UCN were used as a functionalized adsorbent infused in the asymmetric two-layered non-woven fibrous format, the membranes exhibited a high ability to remove bacteria (by size exclusion) and viruses (by adsorption) simultaneously. When UCN were used as the barrier layer in an asymmetric three-layered non-woven fibrous format containing fibers of different diameters (from 5 nm to 20 µm), the membranes exhibited a two- to ten-fold increase in permeation flux over commercial membranes for ultrafiltration of oil and water emulsions (e.g., for purification of bilge water in ships or industrially produced water).
Co-reporter:Fen Wan, Zhaohui Tang, Weidong He and Benjamin Chu
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 39) pp:NaN12389-12389
Publication Date(Web):2010/08/19
DOI:10.1039/C002515A
This perspective is to introduce a new pathway for non-viral gene delivery by taking advantage of nanofibrous scaffolds as gene storage devices, gene carriers and homing devices. During gene delivery to the target, the DNA has to be protected in order to pass through a set of barriers before reaching the nucleus. The DNA can form a complex with polycations, and numerous publications exist on how to stabilize the DNA fragments by natural and synthetic materials. Electrospun nanofibrous scaffolds can be used to store the DNA, especially in the form of a more stabilized polyplex, and then to deliver the DNA (polyplex) to cells that are attached to the scaffold. While each essential step has been tested experimentally, the overall yet untested process, especially for in vivo experiments, may lead to a promising specific approach for gene/drug storage and delivery. The pathway described herein is based mainly on our understanding of the physics and chemistry of gene storage and delivery processes, in contrast to using pure biological concepts. Novel biodegradable, biocompatible nanofibrous materials with imbedded DNA (e.g., in the polyplex form) can then be designed to fabricate an intelligent scaffold for gene delivery. To achieve the above goal, the first step is to stabilize the DNA so that it can be incorporated into nanofibrous scaffolds. In this respect, we shall discuss the different methods of DNA/gene condensation and complex formation, and then explain the strategy used to incorporate DNA into electrospun nanofibers. Solvent-induced DNA condensation and then encapsulation were achieved. However, the released naked DNA was not sufficiently protected for gene transfection in cells. The objective of the current perspective is to suggest that, instead of the solvent-induced DNA condensation, one can combine the recently developed polyplex formation by using branched polyethyleneimine (bPEI). More importantly, free bPEI can be incorporated into the nanofibers separately so that during the gene delivery step, the presence of a predesigned amount of free bPEI can greatly increase the gene transfection efficiency, as has been reported recently by Chi Wu and his coworkers. Thus, a physics/chemistry-based pathway that utilizes nanofibrous scaffolds for gene delivery is within reach.
Co-reporter:Kyunghwan Yoon, Benjamin S. Hsiao and Benjamin Chu
Journal of Materials Chemistry A 2008 - vol. 18(Issue 44) pp:NaN5334-5334
Publication Date(Web):2008/09/10
DOI:10.1039/B804128H
Nanofibers, mainly fabricated by electrospinning, have exhibited great potential for many emerging environmental applications. They can be considered as one of the safest nanomaterials due to their extremely long length (can be up to hundreds of kilometers) and their ability to be embedded within other media. Their high surface-to-volume ratio, large porosity (up to over 80%) and adjustable functionality are also much more effective than conventional non-woven and polymeric membranes in particulate separation and liquid filtration. Technology advances such as multiple-jet electrospinning and electroblowing for mass production of nanofibers have made it practical to use nanofibrous scaffolds as a unique and breakthrough component in separation media for both gas and liquid filtration. In this review, the opportunities and challenges of using functional nanofibers for several representative environmental applications are reviewed.
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