Lamellar-twisting-induced circular dichroism of chromophore moieties in banded spherulites with evolution of homochirality.

Banded spherulites are formed by crystallization of a chiral polymer that is end-capped with chromophore. Induced circular dichroism (ICD) of the chromophore can be found in the crystallized chiral polymers, giving exclusive optical response of the ICD. The ICD signals are presumed to be driven by the lamellar twisting in the crystalline spherulites, and the exclusive optical activity is attributed to the chirality transfer from molecular level to macroscopic level. To verify the suggested mechanism, the sense of the lamellar twisting in the crystalline spherulite is determined using PLM for the comparison with the ICD signals of the chromophore in the electron circular dichroism spectrum. The conformational chirality of the chiral polymer is determined by the vibrational circular dichroism spectrum. On the basis of the chiroptical results, evolution of homochirality from helical polymer chains (conformational chirality) to lamellar twisting in the banded spherulite (hierachical chirality) is suggested.

Transfer of chirality from molecule to phase in self-assembled chiral block copolymers.

Here, we report the mechanisms of chiral transfer at various length scales in the self-assembly of enantiomeric chiral block copolymers (BCPs*). We show the evolution of homochirality from molecular chirality into phase chirality in the self-assembly of the BCPs*. The chirality of the molecule in the BCP* is identified from circular dichroism (CD) spectra, while the handedness of the helical conformation in the BCP* is determined from a split-type Cotton effect in vibrational circular dichroism spectra. Microphase separation of the BCP* is exploited to form a helical (H*) phase, and the handedness of helical nanostructure in the BCP* is directly visualized from transmission electron microscopy tomography. As examined by CD and fluorescence experiments, significant induced CD signals and a bathochromic shift of fluorescence emission for the achiral perylene moiety as a chemical junction of the BCPs* can be found while the concentration of the BCPs* in toluene solution is higher than the critical micelle concentration, suggesting a twisting and shifting mechanism initiating from the microphase-separated interface of the BCPs* leading to formation of the H* phase from self-assembly.

Epitope-cavities generated by molecularly imprinted films measure the coincident response to anthrax protective antigen and its segments.

A molecularly imprinted film was fabricated, in the presence of epitope-peptides, onto a quartz crystal microbalance (QCM) chip. These five peptides are known linear or conformational epitopes of the anthrax protective antigen PA(83). Imprinting resulted in an epitope-cavity with affinity for the corresponding template. With the use of a basic monomer, the binding-effect was further enhanced increasing the affinity to nanomolar levels. The affinities of the peptide to their corresponding molecularly induced polymers (MIPs) were more closely related to the molecular weight of the analyte than to the number of residues. All epitope-cavities differentiated their epitope region on the protective antigen PA(83) as well as the corresponding furin cleavage fragments PA(63) and PA(20). The QCM chip differential response to the protective antigen fragment was observed in the picomolar range, thus demonstrating a method to manipulate protein on the surface with defined orientation.

The application of type II collagen and chondroitin sulfate grafted PCL porous scaffold in cartilage tissue engineering.

This study investigates a poly(epsilon-caprolactone)-graft-type II collagen-graft-chondroitin sulfate (PCL-g-COL-g-CS) biomaterial as a scaffold for cartilage tissue engineering. Biodegradable polyester, PCL, was utilized to fabricate three-dimensional (3D) porous scaffolds by particulate leaching. The PCL scaffold was then surface modified by chemical bonding of 1,6-hexanediamine and the grafting of a bioactive polymer layer of COL and CS with the help of 1-ethyl-3-(3-dimethyl- aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) on the modified PCL surface to produce PCL-g-COL and PCL-g-COL-g-CS, respectively. The characteristics of these modified and grafted matrices were examined by ESCA, aminolysis, collagen and CS assay, porosity and water-binding capacity. Grafted COL and CS markedly increased water-binding capacity, and promoted the spreading and growth of chondrocytes. During a 4-week culture period, PCL-g-COL and PCL-g-COL-g-CS matrices both provided more cell proliferation, as determined by measuring the DNA assay. Additionally, a larger amount of secreted collagen and glycosaminoglycans (GAGs) appeared in the PCL-g-COL-g-CS matrices than in the control (PCL) as indicated by the histochemical sections via Hematoxylin and eosin (H&E) stain, Masson trichrome stain and Safranin-O stain. The chondrocytes were induced to function normally; the cell phenotype was maintained, and the GAGs and collagen in the PCL-g-COL-g-CS scaffold were secreted in vitro. These results serve as a basis for future studies of the fabrication process and reveal the potential biocompatibility of the biomimetic matrix for regenerating articular cartilage or other organs.

Fabrication and characterization of poly(gamma-glutamic acid)-graft-chondroitin sulfate/polycaprolactone porous scaffolds for cartilage tissue engineering.

The development of blended biomacromolecule and polyester scaffolds can potentially be used in many tissue engineering applications. This study was to develop a poly(gamma-glutamic acid)-graft-chondroitin sulfate-blend-poly(epsilon-caprolactone) (gamma-PGA-g-CS/PCL) composite biomaterial as a scaffold for cartilage tissue engineering. Chondroitin sulfate (CS) was grafted to gamma-PGA, forming a gamma-PGA-g-CS copolymer with 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide (EDC) system. The gamma-PGA-g-CS copolymers were then blended with PCL to yield a porous gamma-PGA-g-CS/PCL scaffold by salt leaching. These blended scaffolds were characterized by (1)H NMR, ESCA, water-binding capacity, mechanical test, degradation rate and CS assay. The results showed that with gamma-PGA-g-CS as a component, the water-binding capacity and the degradation rate of the scaffolds would substantially increase. During a 4 week period of culture, the mechanical stability of gamma-PGA-g-CS/PCL scaffolds was raised gradually and chondrocytes were induced to function normally in vitro. Furthermore, a larger amount of secreted GAGs was present in the gamma-PGA-g-CS/PCL matrices than in the control (PCL), as revealed by Alcian blue staining of the histochemical sections. Thus, gamma-PGA-g-CS/PCL matrices exhibit excellent biodegradation and biocompatibility for chondrocytes and have potential in tissue engineering as temporary substitutes for articular cartilage regeneration.

Ring-opening polymerization of epsilon-caprolactone initiated by the antitumor agent doxifluridine.

A novel 5'-deoxy-5-fluorouridine-poly(epsilon-caprolactone) (5'-DFUR-PCL) polymer was synthesized from the antitumor agent doxifluridine (5'-DFUR) by the ring-opening polymerization of epsilon-caprolactone (epsilon-CL) using Sn(II) 2-ethylhexanoate (Sn(Oct)2) as the catalyst. The structure and molecular weight of these polymers were further elucidated by proton nuclear magnetic resonance and gel-permeation chromatography. The results revealed that the molecular weights of the 5'-DFUR-PCL polymers were close to the theoretical values calculated from the epsilon-CL to 5'-DFUR molar ratios and their recovery yields were as high as 90%. Two mechanisms of epsilon-CL polymerization initiated by Sn(Oct)2 were proposed involving either a single or two 5'-DFUR molecules. This study has provided an efficient method for the preparation of 5'-DFUR-PCL polymers. These novel 5'-DFUR-PCL polymers can be applied as drugs on carriers without the need for the coating or grafting processes associated with drugs in drug delivery and have great potential for cancer therapy.

A multi-array sensor via the integration of acrylic molecularly imprinted photoresists and ultramicroelectrodes on a glass chip.

A novel multi-array sensor using molecularly imprinted photoresists (MIPhs) as the recognition element has been fabricated with good resolution, stability and selectivity. The versatility of MIPhs in patterning electrodes with desirable configurations has been demonstrated in our lab previously. Herein, the conventional three-electrode cell was miniaturized within a confined space by taking advantage of photolithography. A novel series of acrylic MIPhs with a resolution of 20 microm were utilized to construct MIPh-based chips (MIPCs), which can discriminate albuterol from the interfering analogies, such as clenbuterol and terbutaline. Excellent selectivity toward these analytes (beta(Analytes)) was obtained for the MIPCs as compared to the non-template MIPh-based and bare Pt chips. Furthermore, the peak currents of albuterol measured on MIPC have good linear relations with its concentrations in the two ranges of 1-50 microM with the correlation coefficient (R) of 0.9995, and 100-200 microM with R of 0.9999 by differential pulse voltammetry (DPV). As the electrochemical cell on MIPC was reused 20 times, the peak current of albuterol changed from 2.453 pA (pico-ampere) to 1.802 pA with a relative standard deviation (R.S.D.) of 7.88%. The surface morphologies of molecularly imprinted and non-imprinted layers (observed by SEM and AFM) also displayed significantly different features. Because of small size, light weight and high specificity towards the template molecule, the multi-array sensor developed in this work is potentially useful for determining trace electroactive species either in vitro or in vivo.

Synthesis of high loading and encapsulation efficient paclitaxel-loaded poly(n-butyl cyanoacrylate) nanoparticles via miniemulsion.

The manufacture of stable paclitaxel-loaded poly(n-butyl cyanoacrylate) (PBCA) nanoparticles containing high loading and encapsulation efficiency simultaneously were achieved in the presence of pluronic F127 via miniemulsion. It was found that both drug loading and encapsulation efficiencies of PBCA nanoparticles prepared by miniemulsion were higher (approximately three times) than those obtained by emulsion with similar paclitaxel content in the feed monomer (1%, w/w). Furthermore, the loading and encapsulation efficiencies increased concurrently (to a maximum of 4 and 80%, respectively) with increasing paclitaxel content and these nanoparticles were spherical in shape and with size near 100 nm. XRD patterns revealed that paclitaxel in particles was distributed in the molecular or amorphous state or in the form of small crystals. The in vitro drug release profile of drug-loaded PBCA nanoparticles prepared from miniemulsion exhibited a gradual release; more than 80% (w/w) of the paclitaxel was released after 96 h.

Synthesis and characterizations of amphiphilic poly(L-lactide)-grafted chondroitin sulfate copolymer and its application as drug carrier.

In this investigation, new biodegradable brush-like amphiphilic copolymers were synthesized by ring opening polymerization. Poly(L-lactide) (PLLA) was grafted onto chondroitin sulfate (CS), which is one of the physiologically significant specific glycosaminoglycans (GAGs), using a tin octanoate [Sn(Oct)2] catalyst in DMSO. The hydroxyl groups of the chondroitin sulfate were used as initiating groups. These functional groups enable specific mucoadhesion or receptor recognition. The degree of substitution (DS), the degree of polymerization (DP) and the chondroitin sulfate content (from 1.1 to 15.4%) were analyzed by 1H NMR. The characteristics of these grafted copolymers, including the structure, the thermal properties and biodegradability, etc., were examined with respect to CS content. Meanwhile, the amphiphilic core (PLLA)-corona (CS) nanoparticles, with size smaller than 200 nm, was examined by dynamic light scattering (DLS). Zeta potential analysis exhibited the value in the range -18.3 to -49.4 mV. The morphologies of the nanoparticles were observed by field-emission scanning electron microscopy (FE-SEM). The nanoparticles with lower cytotoxicity were examined by MTT assay. Furthermore, the in vitro BSA release kinetics of those CSn-PLLA nanoparticles was also determined in this study.

Preparation of porous biodegradable poly(lactide-co-glycolide)/ hyaluronic acid blend scaffolds: characterization, in vitro cells culture and degradation behaviors.

A series of poly(lactide-co-glycolide) (PLGA)/ hyaluronic acid (HA) blend with different HA composition were used to fabricate scaffolds successfully. The pores of the three dimensional scaffold were prepared by particle leaching and freeze drying. The pore size was about 50-200 microm and the porosity was about 85%. The characterizations of the scaffold, such as mechanical properties, hydrophilicity and surface morphologies were determined. Mouse 3T3 fibroblast was directly seeded on the scaffolds. The cell adhesion efficiency, cell morphology observed by scanning electron microscopy (SEM) and the degradation behavior of the blend scaffold were evaluated. In summary, the results show that the adhesion efficiency of cells on the PLGA/HA blend scaffold is higher than that on the PLGA scaffold. Moreover, the incorporation of HA in PLGA not only helps to increase the cell affinity but also tends to lead the water and nutrient into the scaffold easily.

Core-shell type of nanoparticles composed of poly[(n-butyl cyanoacrylate)-co-(2-octyl cyanoacrylate)] copolymers for drug delivery application: synthesis, characterization and in vitro degradation.

Core-shell type of nanoparticles (NPs) with manipulated degradation rate and balanced hydrophilic/hydrophobic properties were designed and characterized. The NPs based on the copolymers of n-butyl cyanoacrylate (BCA) and 2-octyl cyanoacrylate (OCA) were prepared by anion emulsion polymerization in 0.01N HCl solution with pluronic F127 as the stabilizer. These NPs were spherical in shape and with size smaller than 100 nm in a narrow distribution. The particle size, zeta potential, molecular weight, hydrophobicity and degradation rate of the copolymer depended on its composition significantly. In vitro chemical hydrolytic studies indicated that the degradation rate of the NPs could be controlled over 200-fold by adjusting the BCA/OCA ratio. Differential scanning calorimetry (DSC) measurements verified the existence of copolymer with tapered structure which was induced by the reactivity difference of the monomers. A BCA/OCA core-shell structure is postulated that the OCA rich segments were mainly located in the core of the NPs. The cytotoxicity of poly(2-octyl cyanoactylate) (POCA) is quite lower than that of poly(n-butyl cyanoacrylate) (PBCA) and the toxicity of poly(BCA-co-OCA) NPs is similar to that of PBCA NPs.

Biomimetic porous scaffolds made from poly(L-lactide)-g-chondroitin sulfate blend with poly(L-lactide) for cartilage tissue engineering.

A novel biodegradable graft copolymer chondroitin sulfate-grafted poly(L-lactide) (CS-PLLA) was synthesized. The graft copolymer was blended with PLLA to form biomimetic porous scaffolds. Natural CS was introduced into the polyester matrix to promote the proliferation of cells. Three-dimensional spongelike scaffolds were fabricated by a combination of salt leaching and solvent casting methods. The morphology of the scaffolds was observed with scanning electron microscopy with an average pore size between 50 and 250 microm, and its porosity was high (>85%). Compression analysis indicated that the mechanical properties of the scaffold were adequate to support the proliferation of cells. The hydrophilicity increased with an increase in the copolymer content in the blend, as determined by measuring the contact angle. Hematoxylin and eosin, Masson, and Safranin-O staining showed that cells formed a chondro tissue gradually. Histological results revealed that abundant cartilaginous matrixes surrounded spherical chondrocytes in the center of the explants. Chondrocytes cultured in this extracellular-matrix-like scaffold maintained a round morphology phenotype, characterized by a significant quantity of extracellular matrixes of sulfated glycosaminoglycans and collagens. Additionally, phenotypic gene expression (reverse transcriptase-polymerase chain reaction) indicated that chondrocytes expressed transcripts that encoded type II collagen and aggrecan and generated sulfated glycosaminoglycans.

Preparation of amphiphilic poly(L-lactide)-graft-chondroitin sulfate copolymer self-aggregates and its aggregation behavior.

Novel polymeric amphiphilic copolymers were synthesized using chondroitin sulfate (CS) as a hydrophilic segment and poly(L-lactide) (PLLA) as a hydrophobic segment. Micelles of those copolymers were formed in an aqueous phase and were characterized by 1H NMR spectra, fluorescence techniques, dynamic light scattering (DLS), atomic force microscopy (AFM), and confocal microscopy. Their critical aggregation concentrations (CAC) are in the range of 0.0043-0.0091 mg/mL at 25 degrees C. The partition equilibrium constants, Kv, of the pyrene probe in the aqueous solution were from 3.65 x 10(5) to 1.41 x 10(6) at 25 degrees C. The mean diameters of the micelles were below 200 nm, and their sizes were narrowly distributed. The AFM images revealed that the self-aggregates were spherical. Additionally, the CSn-PLLA micelles can efficiently transport within the cells via endocytosis as observed from confocal microscopy.

Synthesis and photoluminescence study of molecularly imprinted polymers appended onto CdSe/ZnS core-shells.

The Photoluminescence of quantum dots have been found to be a useful tool for the detection of small to medium sized analyte molecules in a host-guest environment. By the incorporation of quantum dots into molecularly imprinted polymers, which can offer shape and selectivity, the former can respond by quenching the photoluminescence emission upon template binding. In this work host polymers were synthesized and cased into thin films using functional monomers such as methacrylic acid (MAA), CdSe/ZnS core-shell derivatized with 4-vinyl pyridine and ethylene glycol dimethacrylic acid (EGDMA) as a cross-linker. The intensity of photoluminescence emission is detected upon analyte binding.

Molecularly imprinted polymeric film on semiconductor nanoparticles analyte detection by quantum dot photoluminescence.

Incorporation of semiconductor nanoparticles into molecularly imprinted polymer provides a sensor material which can be easily shaped and with better selectivity because the bound template would quench the photoluminescence (PL) emission of quantum dots significantly. In this work, artificial receptors of various templates were synthesized with functional monomers such as methacrylic acid (MAA), semiconductor like CdSe/ZnS core-shell derivatized with 4-vinylpyridine and ethylene glycol dimethacrylic acid as the cross-linker. The quenching of photoluminescence emissions is presumably due to the fluorescence resonance energy transfer between quantum dots and template molecules. The photoluminescence emission is unaffected upon incubation of analyte with the blank control polymer.

Photo-lithographically impregnated and molecularly imprinted polymer thin film for biosensor applications.

A voltammetric sensor for albuterol was investigated where we combined the techniques of microfabrication and molecular imprinting to construct on-chip devices using photoirradiation of cross-linkable polymers. Molecularly imprinted polymer was coated as a thin film onto the gold working electrode on chip and the analyte was directly quantified by differential pulse voltammetric measurements.