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To create a scaffold that is suitable for the construction of tissue-engineered skin, a novel asymmetric porous scaffold with different pore sizes on either side was prepared by combining a collagen-chitosan porous membrane with fibrin glue. Tissue-engineered skin was fabricated using this asymmetric scaffold, fibroblasts, and a human keratinocyte line (HaCaT). Epidermal cells could be seen growing easily and achieved confluence on the fibrin glue on the upper surface of the scaffold. Scanning electron microscopy showed typical shuttle-like fibroblasts adhering to the wall of the scaffold and fluorescence microscopy showed them growing in the dermal layer of the scaffold. The constructed composite skin substitute had a histological structure similar to that of normal skin tissue after three weeks of culture. The results of our study suggest that the asymmetric scaffold is a promising biologically functional material for skin tissue engineering, with prospects for clinical applications.

Physical patterns were created on hydrated PSS/PDADMAC multilayers without using external force. A typical process was to put a PDMS stamp onto the wet and swollen multilayers, which were then put into an oven and maintained for a period of time to micromold the multilayers. The influence of molding temperature and time, multilayer thickness, solvent quality, and multilayer compositions on pattern formation were elucidated. Evolution of the patterns from double lines, double strips, and meniscus-shaped ridges to high ridges was observed under all conditions, revealing that this is a universal principle for this process. Finally, patterns on PAA/PAH and PSS/PAH multilayers were also prepared at the optimal conditions, highlighting its wide generality on the multilayer patterning.

This paper proposes a new constitutive model to describe the dynamic plasticity of FCC metals using the thermal activation mechanism of dislocation motion. In the model development, the constitutive parameters were directly linked with the characteristics of microstructures of materials. As an example of its application, the model was used to describe the behavior of OFHC copper. To determine the globally optimized parameters of the constitutive model for OFHC copper, an improved multi-variable optimization method of constrained nonlinear programming was used based on the flow stress of the material measured experimentally. A comparison with some models and experimental data in the literature shows that the new model is simple to apply and is much better in terms of its prediction accuracy. It was shown that compared with the MTS model the new constitutive equation is explicit and can be easily embedded into a computational code of material dynamics; while compared with the Zerilli–Armstrong and Johnson–Cook models the new one reflects more precisely experimental observations. It was concluded that the new model is applicable to a wide range of problems with temperature variation from 77 K to 1096 K, strain rates ranging from 10 −3 s −1 to 10 4 s −1 , and strain as high as 1.

Polyelectrolyte multilayers (PEMs) composed of two natural polysaccharides-chitosan (Chi) and alginate (Alg) were deposited by Layer by layer (LbL) assembly on top of biocompatible poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs). Folic acid (FA) or FA grafted poly(ethylene glycol) (PEG–FA) were covalently bounded to the PEMs via carbodiimide chemistry. The assembly of biocompatible PEMs was monitored on planar surfaces by means of the quartz crystal microbalance with dissipation (QCM-D) technique and on top of PLGA NPs by means of ζ-potential measurements. BSA was used as model protein to characterize protein adsorption on PEMs. QCM-D showed protein deposition could not be observed on the Chi/Alg multilayer, for both Chitosan and Alginate as top layers. Finally, cellular uptake experiments were carried out by co-culture of HepG2 cells in presence of NPs. Flow Cytometry and confocal laser scanning microscopy (CLSM) were used to investigate the influence of the surface chemistry of the NPs on uptake. For the HepG2 cell line significantly less uptake of PLGA NPs coated with Chi/Alg than the bare NPs was observed but the uptake increased after attachment of FA molecules.

A thorough understanding of the growth and surface properties of calcium−phosphate nanocrystals is essential for uncovering the mechanism by which their nanostructure interacts with other molecules. Herein, we reported a facile wet-chemical approach using cetyltrimethylammonium bromide (CTAB) for the oriented growth of octacalcium phosphate (OCP) nanobelts with a clean surface. The effect of various synthesis conditions, such as aging time, calcium salt species, CTAB, and/or other additive concentrations, on the growth of OCP nanobelts was examined. The results showed that the morphology of OCP nanobelts from a simple core to complex clusters was easily controlled by increasing aging time and CTAB concentration, whereas the nanobelt growth was heavily inhibited by a minor amount of polyaspartate (i.e., 0.03−0.12 μM). The postadsorption tests indicated the nanobelt surface was highly inert to CTAB, but had affinity to polyaspartate. Furthermore, the adsorption capability of therapeutic biphosphonate on OCP...

PLLA microspheres were aminolyzed in hexanediamine/propanol solution to introduce free amino groups on their surface, which were further transferred into aldehyde groups by a treatment of glutaraldehyde. Chitosan-graft-lactose was then covalently coupled via Schiff base formation. Morphological variation and chitosan-graft-lactose immobilization were characterized. In vitro culture of rabbit auricular chondrocytes demonstrated that the PLLA microcarriers could effectively support the cell attachment and particularly induce cell aggregation on their surface. The formed cell aggregates/microcarriers composite showed higher viability and extracellular matrix production. Thus, the PLLA microcarriers can be potentially used as an injectable delivery system for cartilage repair.

Internalization of nano- and microparticles into live cells correlates closely with their potential applications, functions, cytotoxicity and intracellular drug delivery. Particularly, delivery of a large variety of cargoes such as proteins, peptides, nucleic acids and small particles into cells could be enhanced by some ligands such as Tat peptide. In this work, the ability of Tat mediated cellular uptake was assessed. The Tat peptide was covalently immobilized to fluorescein tagged SiO 2 particles (FITC–SiO 2 –NH 2 particles) with a diameter of 200 nm. BCA protein assay determined that the grafting amount of the Tat peptide could be controlled within a range of 0–3.5 μg/mg SiO 2 particles by the Tat feeding amount. Surface immobilization of the Tat peptide did not bring apparent changes on the surface morphology and charge property of the SiO 2 –NH 2 particles. By contrast, the surface charge of both the FITC–SiO 2 –NH 2 particles and the FITC–SiO 2 –Tat particles was reversed from slight positive in Dulbecco's Modified Eagles Medium (DMEM) to slight negative in DMEM/fetal bovine serum, conveying adsorption of plasma proteins on the particles. Flow cytometry measurement showed that the FITC–SiO 2 –Tat particles were internalized by HepG2 cells with a significant faster rate and a higher number of particles than that of the FITC–SiO 2 –NH 2 particles. Moreover, internalization of the Tat peptide decorated particles was less influenced by the low temperature at 4 °C. The Tat decoration affected the subcellular distribution of the particles as well, resulting in localization of the particles in the cell nucleus. No obvious cytotoxicity was detected for both the FITC–SiO 2 –NH 2 particles and the FITC–SiO 2 –Tat particles.

Carboxymethyl cellulose (CMC)-doped CaCO 3 microparticles with an average diameter of 5 μm were prepared and coated by chitosan and alginate multilayers. The prepared CaCO 3 microparticles had a dominant phase of vaterite and a spherical morphology with nanopores on their surface. After LbL assembly of chitosan and alginate, the CaCO 3 microparticles were significantly smoothened. Treatment of the multilayers-coated particles yielded hollow microcapsules. These particles could spontaneously load positively charged doxorubicin (DOX) molecules, whose amount was 475 and 482 mg DOX/g CaCO 3 for the CaCO 3 (CMC) microparticles and the (chitosan/alginate) 5 coated CaCO 3 (CMC) microparticles, respectively. Brunauer–Emmett–Teller (BET) method was used to analyze the specific surface area and the pore size distribution of the CaCO 3 (CMC) microparticles before and after DOX loading. After DOX loading, S BET and pore volume were reduced obviously, and the volume of smaller pores decreased significantly, whereas that of larger pores were increased. The increase of the volume of larger pores was explained by an electric charge screening effect. DOX release from the CaCO 3 microparticles in pH 5 was relatively slow within the first 15 h, and could be sustained to more than 150 h. The release amount at lower pH was larger at the same time. Coating of the CaCO 3 (CMC) microparticles with the chitosan/alginate multilayers could obviously assuage the initial burst release and reduce the release rate.

Poly(allylamine)-graft-poly(N-isopropylacrylamide) (PAH-g-PNIPAAm)/poly(styrene sulfonate) sodium salt (PSS) multilayer films are prepared using electrostatic layer-by-layer assembly. Buildup of the PAH/PSS and PAH-g-PNIPAAm/PSS multilayers under different salt concen- trations and different temperatures is compared by using ellipsometry and scanning force microscopy. All the film thicknesses increase linearly with the increase of layer number regardless of their assembly conditions. However, the average layer thickness of the PAH-g- PNIPAAm/PSS multilayers is larger than that of the PAH/PSS multilayers under the same assembling conditions. Their surfaces also become rougher and show higher water contact angles. In contrast to the apparent loss transition in the friction force curve of the PAH/PSS multilayers, the PAH-g-PNI- PAAm/PSS multilayers with PAH-g-PNIPAAm as the outmost layer do not undergo a pressure-induced glass transition in water. Nanoindentation tests show that the elastic modulus of the PAH-g-PNI- PAAm/PSS multilayers is only 75% of that of the PAH/PSS multilayers.

Complex microcapsules containing thermo-responsive poly(allylamine)-g-poly(N-isopropylacrylamide) (PAH-g-PNIPAAm) were fabricated by adsorbing one layer of PAH-g-PNIPAAm onto CaCO 3 microparticles doped with poly(styrene sulfonate) sodium salt (PSS), followed by dissolution of the CaCO 3 particles. The complex capsules were characterized by confocal microscopy, scanning electron microscopy, transmission electron microscopy and atomic force microscopy. The existence of PAH-g-PNIPAAm in the complex microcapsules was confirmed by FTIR spectroscopy, and its thermo-responsive property was studied by 1 H NMR. The capsules showed different morphologies when dried at 25 and 50 °C, as well as enhanced stability at 40 °C in alkaline solution due to the additional hydrophobic interaction.

A stable gelatin gradient providing continuous increment of signaling for cell adhesion and proliferation was fabricated within 3D poly(L-lactic acid) (PLLA) scaffolds. The porous PLLA scaffold fabricated by NaCl particle leaching was vertically fixed on a glass vial. 1,6-Hexanediamine/propanol solution was continuously injected into the vial by a micropump to aminolyze the PLLA scaffold. As a result of reaction time difference, the introduced —NH2 groups increased continuously along with the longitude of the PLLA scaffold in the z-direction. After covalent immobilization of gelatin by glutaraldehyde coupling, the gelatin gradient scaffold was thus obtained. In vitro chondrocyte culture showed that the cells had higher viability and more extending morphology in the gelatin gradient scaffold than that in the uniform gelatin control.

Spontaneous deposition of fluorescein isothiocyanate labeled dextran (FITC-dextran) in covalently assembled poly(glycidyl methylacrylate) (PGMA)/poly(allylamine hydrochloride) (PAH) microcapsules was studied and its mechanism was proposed. Incubation of the microcapsules in the FITC-dextran solution resulted in strong fluorescence emission from the capsule interiors. The deposition was found to be molecular weight (M w ) dependent and the number of capsules filled with FITC-dextran was increased along with the M W of FITC-dextran. Furthermore, the correlation between the deposited substances and the charged species in the capsules was explored quantitatively through UV-Vis and fluorescence spectroscopy.

The micro-molding technology has played an important role in fabrication of polymer micro-patterns and development of functional devices. In such a process, suitable solvent can swell or dissolve the polymer films to decrease their glass transition temperature (Tg) and viscosity and thereby improve flowing ability. Consequently, it is easy to obtain the 2D and 3D patterns with high fidelity by the solvent-assisted micro-molding. Compared with the high temperature molding, this technology overcomes some shortcomings such as shrinking after cooling, degradation at high temperature, difficulty in processing some functional materials having high Tg, etc. It can be applied to making patterns not only on polymer monolayers but also on polyelectrolyte multilayers. Moreover, the compression-induced patterns on the multilayers are chemically homogenous but physically heterogeneous. In this review, the controlling factors on the pattern quality are also discussed, including materials of the mold, solvent, pressure, temperature and pattern density.

β-Tricalcium phosphate (β-TCP) particles with a size of ~ 200 nm were blended with fibrinogen and thrombin to obtain an injectable composite scaffold. Clotting time of the composite systems was compared with the fibrin gel control. Results show that incorporation of the β-TCP particles could pronouncedly prolong the clotting time, and endow the resulted scaffold with a denser microstructure. The β-TCP particles were evenly distributed in the fibrin gel, with an increased particle size in a scaffold of a larger amount of the particles. Elastic modulus of the scaffold was increased with the increase of β-TCP particles' content too. In vitro human mesenchymal stem cell culture showed that both cytoviability and cell number were increased along with increase of the β-TCP particle amount. At a 1.5% β-TCP particle, the highest activity of alkaline phosphatase was measured. Since the fibrin gel itself is already very biocompatible, compounding with the β-TCP particles may enable the resulted scaffold more suitable for bone regeneration, with the preserved merit of potential injection in situ.

3-Mercaptopropyl acid (MPA) capped CdTe quantum dots (QDs) were embedded into CaCO 3 microparticles with a size of 1.4–4.4 μm by addition of the QDs into Ca(NO 3 ) 2 solution during a mineralization process. Compared to the parent QDs, about 1/7–1/3 photoluminescence efficiency of the embedded QDs was preserved, enabling the CaCO 3 (CdTe) particles visible under UV irradiation. The structure and morphology of the CaCO 3 (CdTe) particles were characterized by X-ray diffraction (XRD), UV–vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). Protected by the CaCO 3 particles, the QDs in the composites were more stable against long term storage, UV irradiation and cell culture medium containing serum. The CaCO 3 (CdTe) particles could be internalized into live cells, human liver cancer cells (HepG2), for example, and most of which distributed in the lysosomes as revealed by confocal microscopy. Also the CaCO 3 (CdTe) particles had low cytotoxicity in comparison with the parent CdTe QDs.

The industrial use of polypropylene (PP) films is limited because of undesirable properties such as poor adhesion and printability. In the present study, a DC glow discharge plasma has been used to improve the surface properties of PP films and make it useful for technical applications. The change in hydrophilicity of modified PP film surface was investigated by contact angle (CA) and surface energy measurements as a function of exposure time. In addition, plasma-treated PP films have been subjected to an ageing process to determine the durability of the plasma treatment. Changes in morphological and chemical composition of PP films were analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The improvement in adhesion was studied by measuring T-peel and lap shear strength. The results show that the surface hydrophilicity has been improved due to the increase in the roughness and the introduction of oxygen-containing polar groups. The AFM observation on PP film shows that the roughness of the surface increased due to plasma treatment. Analysis of chemical binding states and surface chemical composition by XPS showed an increase in the formation of polar functional groups and the concentration of oxygen content on the plasma-processed PP film surfaces. T-peel and lap shear test for adhesion strength measurement showed that the adhesion strength of the plasma-modified PP films increased compared with untreated films surface.

A composite scaffold of poly(L-lactic-co-glycolic acid) (PLGA) microspheres and fibrin gel was fabricated by blending fibrinogen-immobilized PLGA microspheres with fibrinogen and thrombin solution. The PLGA microspheres with a size of 70 approximately 100 microm were aminolyzed in a hexanediamine/n-propanol solution to introduce free amino groups on their surface. The fibrinogen immobilization was achieved by glutaraldehyde coupling. When the --NH(2) content on the microsphere surface was increased from approximately 2 x 10(-8) mol/mg to approximately 4 x 10(-8) mol/mg, the fibrinogen amount was correspondingly increased from approximately 35 microg/mg to approximately 70 microg/mg. Measured by UV-VIS spectroscopy, the clotting time of the composite was less influenced by the microsphere amount, but mainly controlled by the thrombin concentration. When the thrombin concentration was higher than 15 U/mL, the gelation could be finished within 1 min and yielded a composite with evenly suspended and distributed PLGA microspheres. Blending with the microspheres could significantly improve the elastic modulus of the hydrogel as well, whereas less influence on the chondrocyte proliferation and extracellular matrix production.

A collagen gradient was constructed to interrogate cell adhesion on a poly( l -lactide) (PLLA) membrane surface. Utilizing a microinfusion pump, gradients of amino groups were generated on the PLLA surface by an aminolysis method. Immobilization of collagen onto the gradient surfaces was performed by glutaraldehyde (GA) coupling to form the collagen gradients. The –NH 2 and immobilized collagen density profiles on the PLLA membranes were quantitatively determined by ninhydrin and hydroproline (Hyp) analysis, respectively. By using fluorescein isothiocyanate (FITC) labeled collagen (FITC-Col), the profile of the as-prepared collagen gradient was directly monitored by a fluorescence microscope. The scanning force microscopy and water contact angle studies revealed that the morphology and wettability of the modified membranes changed progressively as a function of position along the gradient surface. Rabbit auricular chondrocytes were cultured on the collagen gradient membranes to test their cellular response. The attachment and spreading behaviors of the chondrocytes were dependent on the surface collagen density. These results indicate a surface on which the variation of collagen gradient strongly modifies the biological response of chondrocytes.

Chitosan nanoparticles were fabricated by a method of tripolyphosphate (TPP) cross-linking. The influence of fabrication conditions on the physical properties and drug loading and release properties was investigated by transmission electron microscopy (TEM), dynamic light scattering (DLS), and UV–vis spectroscopy. The nanoparticles could be prepared only within a zone of appropriate chitosan and TPP concentrations. The particle size and surface zeta potential can be manipulated by variation of the fabrication conditions such as chitosan/TPP ratio and concentration, solution pH and salt addition. TEM observation revealed a core–shell structure for the as-prepared nanoparticles, but a filled structure for the ciprofloxacin (CH) loaded particles. Results show that the chitosan nanoparticles were rather stable and no cytotoxicity of the chitosan nanoparticles was found in an in vitro cell culture experiment. Loading and release of CH can be modulated by the environmental factors such as solution pH and medium quality. Copyright © 2008 John Wiley & Sons, Ltd.

Artificial dermis lacks a vascular network, and angiogenesis is slow in vivo. Controlled delivery of angiogenin (ANG), a potent inducer of angiogenesis, should promote angiogenesis in artificial dermis. In this study, a porous collagen-chitosan scaffold was fabricated and heparinized using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) with a freeze-drying method. Using radioiodine labeling, the effect of heparin on the binding of ANG to the scaffold was studied. The release of ANG from the heparinized scaffold was investigated using a radioiodine labeling method or an enzyme-linked immunosorbent assay method. In vivo angiogenesis of the scaffold was studied for 28 days. All scaffolds possess three-dimensional porous structures, and their mean pore sizes increase upon EDC-NHS cross-linking. The binding of ANG to the scaffold showed a linear correlation with ANG concentration. With ANG concentrations of 160 ng/mL, the binding of ANG to the heparinized scaffold was 36.5%. In vitro, ANG was released from the heparinized scaffold in a controlled manner. The presence of ANG enhanced the angiogenesis of the heparinized scaffold after subcutaneous implantation into rabbits. The results of this study indicate that a porous collagen-chitosan scaffold loaded with ANG may be valuable in the development of artificial dermis requiring enhanced angiogenesis.

Microarrays of spherical vessel-like colloids such as liposomes, polymerized vesicles and polyelectrolyte capsules may find diverse applications in bioanalysis, biosensing, and combinatorial chemistry, for their capabilities in encapsulating chemical species such as drugs, biomolecules, probes, polymers and nanoparticles. This review reports the advances on methods for fabricating microarrays of the various hollow colloids. Related strategies are described in detail, including patterning techniques, surface modification methods, and tethering approaches such as oligonucleotide hybridization, receptor-ligand binding, covalent coupling and electrostatic interaction. The preliminary developments of functionalities of these arrays serving as sensor chips, microcarriers and microreactors are summarized as well.

Chitosan hydrogels were prepared from water soluble chitosan derivatives (chitosan-MA-LA, CML) by photoinitiating polymerization under the existence of Irgacure2959 and the irradiation of UV light. The CML was obtained by amidation of the amine groups of chitosan with lactic acid and methacrylic acid. Gelation time of the hydrogel could be adjusted within a range of 5–50 min, and controlled by factors such as the degree of MA substitution, initiator concentration, existence of oxygen, and salt. The dry hydrogel adsorbed tens to hundred times of water, forming a highly hydrated gel. The swelling ratio was smaller at the higher degree of MA substitution, higher pH, and higher salt concentration. Rheological test showed that the hydrogel is elastomeric in the measuring frequency range, with a storage modulus and loss modulus of 0.8–7 kPa and 10–100 Pa, respectively. In vitro culture of chondrocytes demonstrated that the cells could normally proliferate in the extractant of the hydrogels, showing no cytotoxicity at lower initiator concentration. By contrast, the extractant of the hydrogel made by the redox initiating system, i.e., ammonium persulfate (APS) and N,N,N′,N′-tetramethylethylenediamine (TEMED), showed apparent cytotoxicity. Thus, the chitosan hydrogels initiated by the Irgacure2959 have better comprehensive properties, in particular better biocompatibility, and are more suitable for biomedical applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

In this study, the adhesive properties of the plasma modified polypropylene (PP) and polyethylene terephthalate (PET) film surfaces have been investigated. Hydrophilicity of these polymer film surfaces was studied by contact angle measurements. The surface energy of the polymer films was calculated from contact angle data using Fowkes method. The chemical composition of the polymer films was analyzed by X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) was used to study the changes in surface feature of the polymer surfaces due to plasma treatment. The adhesion strength of the plasma modified film was studied by T-peel strength test. The results showed a considerable improvement in surface wettability even for short exposure times. The AFM and XPS analyses showed changes in surface topography and formation of polar groups on the plasma modified PP and PET surfaces. These changes enhanced the adhesive properties of polymer film surfaces.

Poly(ethyleneimine) (PEI) microcapsules were prepared via the method of glutaraldehyde (GA)-mediated covalent layer-by-layer (LbL) assembly, which utilized GA to cross-link the adsorbed PEI layer and to introduce free aldehyde group on the surface for the next PEI adsorption on MnCO3 microparticles, followed by core removal. Evidenced by ellipsometry, the PEI multilayers grew nearly linearly along with the layer number and their thickness was controlled at the nanometer scale. The hollow structure, morphology, and wall thickness were characterized by scanning electron microscopy (SEM), scanning force microscopy (SFM), and confocal laser scanning microscopy (CLSM), revealing that the capsule structure as well as the cut-off molecular weight of the capsule wall could be tuned by the molecular weight of PEI. This offers a general and novel pathway to fabricate single component capsules with pre-designed structure (size, shape, and wall thickness) and properties. Copyright © 2007 John Wiley & Sons, Ltd.

Poly(allylamine hydrochloride) (PAH) derivatives, that is, PAH-g-β-cyclodextrin (PAH-g-β-CD) and PAH-g-ferrocene with the same positive charges on their chains, were synthesized and employed as building blocks to obtain multilayer microcapsules by using a host−guest interaction between the β-CD and ferrocene. Alternative assembly of PAH-g-β-CD and PAH-g-ferrocene was conducted on sacrificial carbonate microparticles in a layer-by-layer (LbL) manner, followed by core dissolution with disodium ethylene diamine tetraacetate dihydrate (EDTA) to obtain the microcapsules. Step-wise increase of the layer thickness on silicone water was evidenced by ellipsometry, confirming the LbL growth mechanism. The hollow structure and morphology of the host−guest multilayer microcapsules were characterized by electron and scanning force microscopy. Owing to the charge interaction and host−guest interaction, the as-prepared microcapsules showed multiresponsiveness to pH, ionic strength, and host/guest molecules. For example,...

A hydroxyapatite (HAp)/biopolymer composite scaffold was fabricated by mineralizing a crosslinked collagen/chitosan, which was pre-mineralized with Ca2+ and phosphate salts, in simulated body fluid (SBF) for only 24 hr. A self-organized structure similar to bone is expected. Microstructures of the crosslinked collagen/chitosan scaffold, the pre-mineralized collagen–chitosan scaffold (CCS), and the mineralized collagen-chitosan/HAp scaffolds (MCCHS) were characterized by scanning electron microscopy (SEM), revealing non-alteration of the porous structure and formation of the HAp particles. X-ray diffractometer (XRD) confirmed the crystalline structure of the HAp. Thermal gravimetric analysis found that more HAp particles were formed when the CCSs were pre-mineralized in a higher concentration of Ca2+. Water-uptake ratio of the crosslinked CCS was ∼160, decreased to ∼120 after incubating in Ca2+ solution, and further decreased to ∼20 after mineralization. Mechanical strength of the CCS was improved significantly after the in situ mineralization too. The method introduced here may be potentially applied to obtain other biopolymer/HAp composite in a short period. Copyright © 2008 John Wiley & Sons, Ltd.

Microcapsules with charge-controlled permeation forelectrolytes were fabricated by anin situ coacervation method in the presence of polyelectrolyte during core removal. A layer of PAH was adsorbed onto PSS-doped CaCO3 microparticles, followed by crosslinking of the PAH layer with GA and core removal in a solution of EDTA with or without PAH. In the presence of PAH, microcapsules with a larger size, weight and PSS content than with PAH were obtained. Microcapsules produces without PAH showed a unique feature of charge-controlled permeation for electrolytes: negatively charged probes were completely rejected, but positively charged ones were attracted.

The properties of coacervated sodium poly(styrene sulfonate) (PSS)/poly(allylamine hydrochloride) (PAH) microcapsules were manipulated by glutaraldehyde crosslinking at mild conditions. Although the crosslinking took place only between the PAH component, only 10% of PSS was lost from the 2-h crosslinked microcapsules. Significant variation in terms of capsule morphology, diameter, and wall thickness was not found by scanning electron microscopy and scanning force microscopy. Although all the microcapsules were not affected by annealing at 70 °C and incubation in 0.1 M HCl for 2 h, the crosslinked microcapsules indeed showed strong ability to resist osmotic-induced capsule invagination. Also, the 20-min and 2-h crosslinked capsule walls have elasticity modulii of 166 and 200 MPa, respectively, which are both larger than that of the original one (140 MPa). The crosslinked microcapsules also showed good stability in 0.01 M NaOH solution and poorer permeability for a large fluorescent probe.

Lactose- and heparin-modified chitosan films were prepared and their physical and biological properties were compared with chitosan, chitosan-g-heparin, and chitosan-g-lactose films. Atomic force microscopy (AFM) measurement showed that all these films in the dry state were rather flat with a roughness smaller than 20 nm. While the chitosan-g-lactose/heparin and chitosan-g-lactose films have the highest swelling and weight loss ratios, the chitosan and chitosan-g-heparin films have the lowest. The chitosan-g-lactose/heparin film showed stronger ability to induce chondrocyte attachment, proliferation, viability, and glycosaminoglycan (GAG) secretion than that of the chitosan, chitosan-g-heparin, and chitosan-g-lactose films. Chondrocyte aggregates and nodules were observed on the chitosan-g-lactose/heparin and chitosan-g-lactose films, which still preserved viable metabolic ability. These results show that the lactose-modified and heparin-incorporated chitosan film can enhance the cell–biomaterial interaction synchronously. The resulting chitosan-g-lactose/heparin material is more bioactive that might be applicable as promising scaffold for chondrogenesis. Copyright © 2007 John Wiley & Sons, Ltd.

Anti-cancer drug daunorubicin (DNR) was encapsulated in preformed multilayer microcapsules and was applied in tumor treatment by in vitro cell culture and in vivo animal experiments. The microcapsules were fabricated by an alternate deposition of oppositely charged polysaccharides, i.e. chitosan and alginate onto carboxymethyl cellulose (CMC) doped CaCO3 colloidal particles in a sequential assembly procedure, followed by crosslinking of the capsule shells with glutaraldehyde (GA) and removal of the templates by disodium ethylenediaminetetraacetic acid (EDTA). The as-prepared microcapsules showed strong ability to induce the positively charged DNR to deposit into the microcapsule interiors. Confocal microscopy and transmission electron microscopy observed homogeneous distribution of the drug within microcapsules. The loaded DNR could be released again, following a diffusion-controlled model at the initial stage. In vitro experiments demonstrated that the encapsulated DNR can effectively induce the apoptosis of BEL-7402 tumor cells, as evidenced by various microscopy techniques after acridine orange (AO), Hoechst 33342, and osmium tetraoxide staining. By seeding the BEL-7402 hepatoma cells into BALB/c/nu mice, tumors were created for the animal experiments. The results showed that the encapsulated DNR had better efficacy than that of the free drug in terms of tumor inhibition in a 4 week in vivo culture period. Copyright © 2007 John Wiley & Sons, Ltd.

A novel structure of injectable scaffold is designed and fabricated by combining collagen-coated polylactide (PLA) microcarriers and crosslinkable chitosan hydrogel. The collagen-coated PLA microcarriers were firstly mixed with the hydrogel precursor, a thickening agent of konjac glucomannan (KGM), and redox initiators of ammonium persulfate and tetramethylethylenediamine (TMEDA). The mixture was then injected into a mold and incubated at 37°C to obtain the composite scaffold. The hydrogel can deliver the collagen-coated PLA microcarriers to the desired site and, after gelation, will prevent them from uncontrolled movement. On the other hand, the collagen-coated PLA microcarriers can substantially enhance the mechanical properties of the composite system. It was found that the microcarriers suspended stably in 0.6% KGM/1% chitosan derivative (CML) solution at 37°C at least for 15 min. The dynamic elastic modulus (G′) of the composite scaffold increased along with the increase of the microcarrier content. G′ of the composite scaffold with 10% microcarriers was measured as 0.87–2.15 MPa at a frequency range of 0.1–100 rad/s, which was 120–90 times higher than that of its hydrogel system alone (12.1–24.4 kPa). In vitro culture of chondrocytes/composite scaffold showed that the cell metabolic activity increased rapidly before day 9, then leveled off. Cells in the hydrogel could attach and grow on the surface of the collagen-coated PLA microcarriers to form confluent cell layers after days 9–12. These features make the composite scaffold to be injectable and applicable in either tissue engineering, or regenerative medicine, and in particular, in orthopaedics. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008

Delivery and sustained release of toothpaste actives is an important but unexplored area. In this work, chitosan nanoparticles were prepared by a water-in-oil emulsion/glutaraldehyde crosslinking method. The typical number average diameter of chitosan and toothpaste active (cetylpyridiniumchloride and NaF) nanoparticles was within the range of 100–500 nm. The particles increased their size at higher pH value. The morphology, adherence, and stability of these nanoparticles were investigated by scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The size of the chitosan/NaF nanoparticles was doubled after they were stored at 4°C for 20 days, and then kept constant till 251 days, the examined time so far. These particles showed good stability in toothpaste lixivium after incubated at 60°C for 30 days too. By contrast, the chitosan/cetylpyridiniumchloride nanoparticles were easy to form floccules in the toothpaste lixivium. The loaded toothpaste actives showed a sustained released behavior for at least 10 h. All the particles could adhere onto the tooth analogs such as hydroxyapatite discs and glass slides in a simulated brushing and rinsing process. In vitro cell culture did not find any cytotoxicity of the as-prepared chitosan nanoparticles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Microcapsules with ultrathin wall and high stability are of both scientific and technological importance. They can provide ideal models for investigations of permeability, elasticity and responsivity on a nanometer scale, and be used as microcarriers and micro-reactors in a confined space. Among the established techniques such as nozzle reactor process, emulsion/phase separation, sol-gel processing and sacrificial templating, assembly of building blocks onto colloidal particles in a layer-by-layer (LBL) manner followed by core-removal is very promising to obtain hollow capsules with precise control over their wall thickness on a scale of ∼ 1 nm. The driving-forces for the LBL assembly applied so far are mostly electrostatic, H-bonding and coordinate interactions: all are of “weak” interactions. Therefore, the stabilities of the resulting microcapsules against high or low pH, high salt concentration and high temperature are not satisfactory. To enhance the binding strength between the building blocks, various post-treatments by glutaraldehyde (GA), oxidization, carbodiimide, UV irradiation and elevated temperature are applied to the pre-formed microcapsules or the core–shell particles, which either transform the ionic bonds into covalent bonds or create new covalent bonds in the multilayer walls. If direct covalent chemical reaction is adopted as a driving force instead of those “weak” interactions, a same stepwise assembly will yield simultaneously covalently crosslinked multilayer capsules, with no necessity of post-treatments. Covalently assembled multilayers on planer substrates have been fabricated by a reaction between two kinds of multifunctional molecules such as diamine and diisocyanate. However, direct covalent assembly of multilayers on colloidal particles remains still much intriguing to date, though in a broader scope fabrication of covalent microcapsules and nanotubes by a reaction between diazoresin and phenol-formaldehyde resin, and glutaraldehyde mediated assembly of poly(allylamine hydrochloride) (PAH), glucose oxidase and hemoglobin has been reported. However, except for the structure characterizations many other aspects, in particular physical and chemical properties of these covalent microcapsules are hardly explored due to their structure limitation. These properties are extremely important for demonstrating the merits of the covalent structures, and also for future applications. In this work, poly(glycidyl methylacrylate) (PGMA) is covalently immobilized onto aminosilanized SiO2 microparticles ( 3 lm) via a reaction between the epoxides and the amines to form the first layer. By the same reaction mechanism, a second PAH layer is formed and the surface amino groups are regained. Repeating n cycles will then produce n bilayers of continuous multilayers on the SiO2 microparticles, leaving behind the hollow capsules composed of (PGMA/ PAH)n upon core-removal by HF etching (Scheme 1). TEM observed that each SiO2 microparticle is continuously and homogeneously covered by a thin film, as is representatively shown in Figure 1a and undoubtedly ascertained by the magnified image in the inset of Figure 1a. The thickness of 8-layer PGMA/PAH film varies from ∼ 12 nm to ∼ 15 nm. Neither apparent adsorption of larger polymer grains on the particle surfaces nor particle coacervation is observed, as is evidenced by the derived capsules (Fig. 1b). More importantly, Figure 1b and Figure 1c demonstrate that the capsules possess hollow nature and continuous and intact shell structures after template removal. The polygonal shape, creases and folds are characteristics of microcapsules with ultrathin wall thickness, resulting from evaporation of the solvent. AFM images (Fig. 1d and e) reveal flat and smooth morphology, demonstrating again the completeness of the microcapsules. Using the same technique, multilayer microcapsules with varied layer numbers and SiO2 diameters were fabricated (Fig. S1–3 in Supporting Information). Moreover, copolymers of GMA and MMA could also be assembled with PAH, yielding intact hollow capsules after core removal (Fig. S4). The chemical compositions of the microcapsules were characterized by FTIR spectroscopy (Fig. 2). The absorbance of esters at 1725 cm confirms the presence of PGMA in the capsules, while the absence of epoxide groups (1482 cm and 1337 cm) reveals the complete reaction of PGMA. This reC O M M U N IC A IO N

The response of host organism in macroscopic, cellular and protein levels to biomaterials is, in most cases, closely associated with the materials' surface properties. In tissue engineering, regenerative medicine and many other biomedical fields, surface engineering of the bio-inert synthetic polymers is often required to introduce bioactive species that can promote cell adhesion, proliferation, viability and enhanced ECM-secretion functions. Up to present, a large number of surface engineering techniques for improving biocompatibility have been well established, the work of which generally contains three main steps: (1) surface modification of the polymeric materials; (2) chemical and physical characterizations; and (3) biocompatibility assessment through cell culture. This review focuses on the principles and practices of surface engineering of biomedical polymers with regards to particular aspects depending on the authors' research background and opinions. The review starts with an introduction of principles in designing polymeric biomaterial surfaces, followed by introduction of surface modification techniques to improve hydrophilicity, to introduce reactive functional groups and to immobilize functional protein molecules. The chemical and physical characterizations of the modified biomaterials are then discussed with emphasis on several important issues such as surface functional group density, functional layer thickness, protein surface density and bioactivity. Three most commonly used surface composition characterization techniques, i.e. ATR-FTIR, XPS, SIMS, are compared in terms of their penetration depth. Ellipsometry, CD, EPR, SPR and QCM's principles and applications in analyzing surface proteins are introduced. Finally discussed are frequently applied methods and their principles to evaluate biocompatibility of biomaterials via cell culture. In this section, current techniques and their developments to measure cell adhesion, proliferation, morphology, viability, migration and gene expression are reviewed.

Hydrogen-bonded hollow microcapsules with a lightly cross-linked shell structure were fabricated by polymerization of acrylic acid in a solution containing surface-modified silica particles and pol...

Polymer porous scaffolds and hydrogels have been separately employed as analogues of the native extra-cellular matrix (ECM). However, both of these two kinds of materials have their own advantages and shortcomings. In this work, an attempt to combine the advantages of these two kinds of materials is carried out. Poly-L-lactide (PLLA) scaffolds with good mechanical properties were prepared by thermally induced phase separation, which were then filled with hydrogel aiming at entrapment of cells within a support of predefined shape. Agar, which has a function to promote chondrogenesis, was selected to entrap chondrocytes, acting as analogues of native ECM. A straight forward merit of this construct is that both mechanical strength and macroscopic shape, and analogous ECM can be simultaneously achieved. The morphology and distribution of the chondrocytes were studied by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The cell growth behaviors were determined by MTT assay and collagen and glycosaminoglycan (GAG) secretion. After culture for 7 and 14 days, the cells in the construct were round and surrounded by the hydrogel. The MTT viability and the cell secretion in the chondrocytes/agar/scaffold construct were also higher than that of the chondrocytes/scaffold construct (control). Gelatin was further introduced into the construct, yielding improved GAG secretion and cytoviability. After implantation in the subcutaneous dorsum of nude mice for 4 weeks, cartilage-like specimens maintaining their original rectangular shapes were harvested. Histological examination showed that new cartilage was regenerated and a large quantity of collagen and GAG were secreted, while the cells in the control PLLA scaffold turned to be fibroblast-like with less secretion of extracellular matrices. The method provides a useful pathway of scaffold preparation and cell transplantation, which can achieve suitable mechanical properties and good cell performance simultaneously.

N,N,N-Trimethylchitosan chloride with different degrees of quaternization has been synthesized and characterized by (1)H NMR spectroscopy. The particle size ranges from 150 to 600 nm, which is dependent on the N/P ratio and is less influenced by the degree of quaternization. The majority of the particles have a spherical morphology. The zeta potential of the particles increases with the N/P ratio and the quaternization degree of TMC. Short-term contact experiments show good biocompatibility of TMC, but long-term contact experiments reveal its high toxicity. This study suggests that TMC is a promising gene carrier, but further modification is still required to improve its cytocompatibility.

Gelatin, chitosan and hyaluronan with a weight ratio of 82.6%, 16.5% and 0.1% were chosen as a scaffold material to mimic the composition of natural cartilage matrix for cartilage tissue engineering. Water soluble carbodiimide was added into the biomacromolecule solution with a concentration of 5% to crosslink the complex. Following a freeze-drying procedure, a porous scaffold (control) was then prepared. To enhance chondrogenesis, heparin was covalently immobilized onto the scaffold by carbodiimide chemistry, through which basic fibroblast growth factor (bFGF) was further incorporated by a bioaffinity force. Incubation in phosphate buffered saline (PBS, pH 7.4) at 37 degrees C caused the weight loss of all kinds of the scaffolds, which could be brought by both the degradation and dissolution of the biomacromolecules. Compared with the control, however, the heparinized scaffold showed stronger ability to resist the weight loss, implying that a higher crosslinking degree was achieved by incorporation of the heparin. Rabbit auricular chondrocytes were seeded onto the ternary complex scaffold containing bFGF to assess cell response. Chondrocytes could adhere and proliferate in all kinds of the scaffold, regardless of the existence of bFGF. No significant difference on glycosaminoglycan (GAG) secretion was recorded between these scaffolds after cultured for 7 and 21 days too, although the absolute value from the Scaffold-heparin-bFGF was somewhat higher. However, chondrocytes seeded in the Scaffold-heparin-bFGF indeed showed significant higher viability than that on the control scaffold. These results reveal that the ternary complex scaffolds, in particular the one containing bFGF, are a potential candidate for cartilage tissue engineering.

Hollow microcapsules having shells of polyelectrolyte complexes were fabricated by polymerization of 4-vinylpyridine hydrochloride in a solution containing surface-modified silica particles and poly(sodium 4-styrenesulfonate), and followed by a core removal with HF. Here both the PSS molecules and the silica particles function as templates to guide the alignment of VPy monomers and support the deposition of the PSS/PVPy complexes, respectively. The continuous shells with a thickness of 5–15 nm on the silica particles are created by covalent linking of the PSS/PVPy complexes. The hollow and intact microcapsules in both wet and dry states were characterized and confirmed by transmission electron microscopy, scanning electron microscopy, and confocal laser scanning microscopy. The chemical compositions of the microcapsules were determined and confirmed by elemental analysis and FTIR spectroscopy.

We report here the finding of different dissolution rate between the core and shell of a manganese carbonate particle, which was prepared by mixing NH4HCO3 and MnSO4 at room temperature. Based on the results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), we believe that the denser crystallites in the shells have a stronger stability against acid decomposition compared with the randomly and loosely assembled crystallites in the particle cores. Hollow spheres were then fabricated by utilizing the difference of decomposition rate between the particle shells and the cores in acidic solution at room temperature. Furthermore, by incorporating polyelectrolyte multilayers onto the particles prior to core decomposition, hybrid organic/inorganic hollow spheres were successfully produced.

We report here the loading of the antitumor drug doxorubicin (DOX) in preformed multilayer microcapsules and its application in tumor treatment assayed by in vitro cell culture and in vivo animal experiments. The microcapsules, consisting completely of polysaccharides, were fabricated by deposition of oppositely charged chitosan and alginate onto carboxylmethyl cellulose (CMC)-doped CaCO(3) colloidal particles in a layer-by-layer fashion, followed by cross-linking with glutaraldehyde and decomposition of the cores by disodium ethylenediaminetetraacetic acid. The microcapsules as prepared contain negatively charged CMC-either in a free state or very possibly coupled with the excess chitosan of the first layer. They showed a strong ability to accumulate the positively charged DOX with a factor of tens to hundreds; that is, the drug concentration within the microcapsules was hundreds of times higher than the feeding concentration. Confocal microscopy and transmission electron microscopy revealed homogeneous distribution of the drug. The encapsulated DOX could be released again, following a diffusion-controlled model at the initial stage. In vitro experiments showed that the encapsulated drug can effectively induce the apoptosis of HepG2 tumor cells, as shown by various microscopy techniques after acridine orange, Hoechst 33342, and osmium tetraoxide staining. By seeding the HepG2 hepatoma cells into BALB/c/nu mice, tumors were created for the experimental studies. The results showed that the encapsulated DOX had better efficacy than that of the free drug in terms of tumor inhibition in a 4-week in vivo culture period.

Microgel rings have been fabricated on a glass surface by a micro-transfer technique. The polymer melt is transferred to the substrate surface in a confined space with a picoliter volume along the boundary of the polymeric stamp. The surface of the polymer features is smoothened by surface tension in an annealing cycle, which results in isotropic rings. After cross-linking, the microgels respond swiftly when immersed in water. Asymmetric rings are also obtained by tilting the substrate. The microgels can detach from the substrate to form a suspension of the rings. Conjugated rings have also been fabricated by supplementing functional molecules into the poly(ethylene glycol) network.

H acid is an important dye intermediate for the synthesis of direct, reactive and azo dyes. In this study, the method of complex extraction and stripping has been introduced for the treatment of high concentrated H acid wastewater. The extractant and diluent selected in the experiment are trialkylamine (N 7301 ) and kerosene, respectively. And the dependencies of the extraction efficiency on the extractant concentration, the initial pH value, the volume ratio of water to oil (W/O), and the temperature are investigated. Under the optimum condition that kerosene/N 7301 of 3:1, pH of 1.0, W/O of 2:1, and temperature of 45°C, through three-stage extraction, the COD cr value of H acid wastewater decreases from 13828.48 mg/l to 199.21 mg/l, and the overall COD cr removal rate can reach 98.56%. Finally, the extractant can be regenerated by stripping process with 10% NaOH, and the stripping rate can arrive at 100%. Compared with other methods, complex extraction and stripping is considered as a much more efficient and feasible one not only for that the extractant regenerated can reduce the operation cost but also for that the H acid extracted can be reused in the production process without degradation, which meets the requirement of zerodischarge and no sludge.

In vitro degradation and chondrocyte-encapsulation of chitosan hydrogel made of crosslinkable and water-soluble chitosan derivative (CML) at neutral pH and body temperature were studied with respect to weight loss, cytoviability, DNA content and cell morphology. In vitro degradation of the chitosan hydrogels was sensitive to their crosslinking degree and existence of lysozyme in the solution. Chitosan hydrogel (Gel-I5) fabricated from 1% CML and 5mM ammonium persulfate (APS)/N,N,N',N'-tetramethylethylenediamine (TMEDA) displayed no degradation in phosphate buffered saline (PBS) after 18d, but degraded completely at 8d in 1mg/ml lysozyme/PBS. The chitosan hydrogel fabricated from 10mM APS/TMEDA was non-degradable even in lysozyme/PBS solution after 18d. The hydrogel loaded with chondrocytes in cell culture medium, however, was susceptible to degradation during the in vitro culture. In vitro culture of the encapsulated chondrocytes in the chitosan hydrogel demonstrated that the cells retained round shaped morphology and could survive through a 12d-culture period, although the DNA assay detected an overall reduction of the cell number. These features provide a great opportunity to use the chitosan hydrogel as an injectable scaffold in tissue engineering and orthopaedics.

Wound dressing with high quality is a kind of highly demanded wound-repairing products. In this article, chitosan (CS) and hyaluronic acid (HA) were used to fabricate a novel wound dressing. CS/HA composite films with high transparency could be fabricated on glass or poly(methyl methacrylate) (PMMA) substrates, but not on poly(tetrafluoroethylene) (PTFE) plate. Along with the increase of HA amount, the resulting films became rougher as detected by atomic force microscopy (AFM). Increased also are water contact angle and water-uptake ratio. By contrast, increase of the HA amount weakened the water vapor permeability (WVP), bovine albumin adsorption, and fibroblast adhesion, which are desirable characteristics for wound dressing. In vivo animal test revealed that compared with the vaseline gauge the CS/HA film could more effectively accelerate the wound healing, and reduce the occurrence of re-injury when peeling off the dressing again. These results demonstrate that the CS mixed with a little amount of HA may produce inexpensive wound dressing with good properties for practical applications. Copyright © 2007 John Wiley & Sons, Ltd.