Methacrylate-functionalized oligomers based on lactide, E-caprolactone and trimethylene carbonate for application in stereo-lithography

Photo-curable biodegradable macromers were prepared by ring opening polymerization of D,L-lactide (DLLA), (similar to)-caprolactone (CL) and 1,3-trimethylene carbonate (TMC) in the presence of glycerol or sorbitol as initiator and stannous octoate as catalyst, and subsequent methacrylation of the terminal hydroxyl groups. These methacrylated macromers, ranging in molecular weight from approximately 700 to 6000 g/mol, were cross-linked using ultraviolet (UV) light to form biodegradable networks. Homogeneous networks with high gel contents were prepared. One of the resins based on PTMC was used to prepare three-dimensional structures by stereo-lithography using a commercially available apparatus.

Methacrylate-functionalized oligomers based on lactide, ε- caprolactone and trimethylene carbonate for application in stereo-lithography

Photo-curable biodegradable macromers were prepared by ring opening polymerization of D,L-lactide (DLLA), ε-caprolactone (CL) and 1,3-trimethylene carbonate (TMC) in the presence of glycerol or sorbitol as initiator and stannous octoate as catalyst, and subsequent methacrylation of the terminal hydroxyl groups. These methacrylated macromers, ranging in molecular weight from approximately 700 to 6000 g/mol, were cross-linked using ultraviolet (UV) light to form biodegradable networks. Homogeneous networks with high gel contents were prepared. One of the resins based on PTMC was used to prepare three-dimensional structures by stereo-lithography using a commercially available apparatus.

A review of rapid prototyping techniques for tissue engineering purposes

Rapid prototyping (RP) is a common name for several techniques, which read in data from computer-aided design (CAD) drawings and manufacture automatically threedimensional objects layer-by-layer according to the virtual design. The utilization of RP in tissue engineering enables the production of three-dimensional scaffolds with complex geometries and very fine structures. Adding micro- and nanometer details into the scaffolds improves the mechanical properties of the scaffold and ensures better cell adhesion to the scaffold surface. Thus, tissue engineering constructs can be customized according to the data acquired from the medical scans to match the each patient’s individual needs. In addition RP enables the control of the scaffold porosity making it possible to fabricate applications with desired structural integrity. Unfortunately, every RP process has its own unique disadvantages in building tissue engineering scaffolds. Hence, the future research should be focused into the development of RP machines designed specifically for fabrication of tissue engineering scaffolds, although RP methods already can serve as a link between tissue and engineering.

The conversion of lignocellulosics to levulinic acid

Biomass represents an abundant and relatively low cost carbon resource that can be utilized to produce platform chemicals such as levulinic acid. Current processing technology limits the cost-effective production of levulinic acid in commercial quantities from biomass. The key to improving the yield and effi ciency of levulinic acid production from biomass lies in the ability to optimize and isolate the intermediate products at each step of the reaction pathway and reduce re-polymerization and side reactions. New technologies (including the use of microwave irradiation and ionic liquids) and the development of highly selective catalysts would provide the necessary step change for the optimization of key reactions. A processing environment that allows the use of biphasic systems and/or continuous extraction of products would increase reaction rates, yields and product quality. This review outlines the chemistry of levulinic acid synthesis and discusses current and potential technologies for producing levulinic acid from lignocellulosics.

Investigation of electrophoretic loading and enhanced mechanical properties of hydrogels for delivery of therapeutic proteins

Hydrogels, which are three-dimensional crosslinked hydrophilic polymers, have been used and studied widely as vehicles for drug delivery due to their good biocompatibility. Traditional methods to load therapeutic proteins into hydrogels have some disadvantages. Biological activity of drugs or proteins can be compromised during polymerization process or the process of loading protein can be really timeconsuming. Therefore, different loading methods have been investigated. Based on the theory of electrophoresis, an electrochemical gradient can be used to transport proteins into hydrogels. Therefore, an electrophoretic method was used to load protein in this study. Chemically and radiation crosslinked polyacrylamide was used to set up the model to load protein electrophoretically into hydrogels. Different methods to prepare the polymers have been studied and have shown the effect of the crosslinker (bisacrylamide) concentration on the protein loading and release behaviour. The mechanism of protein release from the hydrogels was anomalous diffusion (i.e. the process was non-Fickian). The UV-Vis spectra of proteins before and after reduction show that the bioactivities of proteins after release from hydrogel were maintained. Due to the concern of cytotoxicity of residual monomer in polyacrylamide, poly(2-hydroxyethyl- methacrylate) (pHEMA) was used as the second tested material. In order to control the pore size, a polyethylene glycol (PEG) porogen was introduced to the pHEMA. The hydrogel disintegrated after immersion in water indicating that the swelling forces exceeded the strength of the material. In order to understand the cause of the disintegration, several different conditions of crosslinker concentration and preparation method were studied. However, the disintegration of the hydrogel still occurred after immersion in water principally due to osmotic forces. A hydrogel suitable for drug delivery needs to be biocompatible and also robust. Therefore, an approach to improving the mechanical properties of the porogen-containing pHEMA hydrogel by introduction of an inter-penetrating network (IPN) into the hydrogel system has been researched. A double network was formed by the introduction of further HEMA solution into the system by both electrophoresis and slow diffusion. Raman spectroscopy was used to observe the diffusion of HEMA into the hydrogel prior to further crosslinking by ã-irradiation. The protein loading and release behaviour from the hydrogel showing enhanced mechanical property was also studied. Biocompatibility is a very important factor for the biomedical application of hydrogels. Different hydrogels have been studied on both a three-dimensional HSE model and a HSE wound model for their biocompatibilities. They did not show any detrimental effect to the keratinocyte cells. From the results reported above, these hydrogels show good biocompatibility in both models. Due to the advantage of the hydrogels such as the ability to absorb and deliver protein or drugs, they have potential to be used as topical materials for wound healing or other biomedical applications.

Synthesis and characterisation of hybrid gold/polymer nanoparticles for bioassay application

A bioassay technique, based on surface-enhanced Raman scattering (SERS) tagged gold nanoparticles encapsulated with a biotin functionalised polymer, has been demonstrated through the spectroscopic detection of a streptavidin binding event. A methodical series of steps preceded these results: synthesis of nanoparticles which were found to give a reproducible SERS signal; design and synthesis of polymers with RAFT-functional end groups able to encapsulate the gold nanoparticle. The polymer also enabled the attachment of a biotin molecule functionalised so that it could be attached to the hybrid nanoparticle through a modular process. Finally, the demonstrations of a positive bioassay for this model construct using streptavidin/biotin binding. The synthesis of silver and gold nanoparticles was performed by using tri-sodium citrate as the reducing agent. The shape of the silver nanoparticles was quite difficult to control. Gold nanoparticles were able to be prepared in more regular shapes (spherical) and therefore gave a more consistent and reproducible SERS signal. The synthesis of gold nanoparticles with a diameter of 30 nm was the most reproducible and these were also stable over the longest periods of time. From the SERS results the optimal size of gold nanoparticles was found to be approximately 30 nm. Obtaining a consistent SERS signal with nanoparticles smaller than this was particularly difficult. Nanoparticles more than 50 nm in diameter were too large to remain suspended for longer than a day or two and formed a precipitate, rendering the solutions useless for our desired application. Gold nanoparticles dispersed in water were able to be stabilised by the addition of as-synthesised polymers dissolved in a water miscible solvent. Polymer stabilised AuNPs could not be formed from polymers synthesised by conventional free radical polymerization, i.e. polymers that did not possess a sulphur containing end-group. This indicated that the sulphur-containing functionality present within the polymers was essential for the self assembly process to occur. Polymer stabilization of the gold colloid was evidenced by a range of techniques including, visible spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and Raman spectroscopy. After treatment of the hybrid nanoparticles with a series of SERS tags, focussing on 2-quinolinethiol the SERS signals were found to have comparable signal intensity to the citrate stabilised gold nanoparticles. This finding illustrates that the stabilization process does not interfere with the ability of gold nanoparticles to act as substrates for the SERS effect. Incorporation of a biotin moiety into the hybrid nanoparticles was achieved through a =click‘ reaction between an alkyne-functionalised polymer and an azido-functionalised biotin analogue. This functionalized biotin was prepared through a 4-step synthesis from biotin. Upon exposure of the surface-bound streptavidin to biotin-functionalised polymer hybrid gold nanoparticles, then washing, a SERS signal was obtained from the 2-quinolinethiol which was attached to the gold nanoparticles (positive assay). After exposure to functionalised polymer hybrid gold nanoparticles without biotin present then washing a SERS signal was not obtained as the nanoparticles did not bind to the streptavidin (negative assay). These results illustrate the applicability of the use of SERS active functional-polymer encapsulated gold nanoparticles for bioassay application.

Diels-Alder reactions as an efficient route to high purity cyclic polymers

A simple and efficient route for the synthesis of cyclic polymer systems is presented. Linear furan protected α-maleimide-ω-cyclopentadienyl functionalized precursors (poly(methyl methacrylate) and poly(tert-butyl acrylate)) were synthesized via atom transfer radical polymerization (ATRP) and subsequent substitution of the bromine end-group with cyclopentadiene. Upon heating at high dilution, deprotection of the dieneophile occurs followed by an intramolecular Diels–Alder reaction yielding a high purity cyclic product.

Formation of nanoporous materials via mild retro-Diels–Alder chemistry

Poly(styrene)-block-poly(ethylene oxide) copolymers synthesized via the combination of reversible addition fragmentation chain transfer (RAFT) polymerization and hetero Diels–Alder (HDA) cycloaddition can be cleaved in the solid state by a retro-HDA reaction occurring at 90 °C. Nanoporous films can be prepared from these polymers using a simple heating and washing procedure.

(Ultra)fast catalyst-free macromolecular conjugation in aqueous environment at ambient temperature

Tailor-made water-soluble macromolecules, including a glycopolymer, obtained by living/controlled RAFT-mediated polymerization are demonstrated to react in water with diene-functionalized poly(ethylene glycol)s without pre- or post-functionalization steps or the need for a catalyst at ambient temperature. As previously observed in organic solvents, hetero-Diels-Alder (HDA) conjugations reached quantitative conversion within minutes when cyclopentadienyl moieties were involved. However, while catalysts and elevated temperatures were previously necessary for open-chain diene conjugation, additive-free HDA cycloadditions occur in water within a few hours at ambient temperature. Experimental evidence for efficient conjugations is provided via unambiguous ESI-MS, UV/vis, NMR, and SEC data.

Amphiphilic silicone archtectures via anaerobic thiol - ene chemistry

Despite broad application, few silicone-based surfactants of known structure or, therefore, surfactancy have been prepared because of an absence of selective routes and instability of silicones to acid and base. Herein the synthesis of a library of explicit silicone-poly(ethylene glycol) (PEG) materials is reported. Pure silicone fragments were generated by the B(C(6)F(5))(3)-catalyzed condensation of alkoxysilanes and vinyl-functionalized hydrosilanes. The resulting pure products were coupled to thiol-terminated PEG materials using photogenerated radicals under anaerobic conditions.

Real-time measurement of F-Actin remodelling during exocytosis using lifeact-EGFP transgenic animals

F-actin remodelling is essential for a wide variety of cell processes. It is important in exocytosis, where F-actin coats fusing exocytic granules. The purpose of these F-actin coats is unknown. They may be important in stabilizing the fused granules, they may play a contractile role and promote expulsion of granule content and finally may be important in endocytosis. To elucidate these functions of F-actin remodelling requires a reliable method to visualize F-actin dynamics in living cells. The recent development of Lifeact-EGFP transgenic animals offers such an opportunity. Here, we studied the characteristics of exocytosis in pancreatic acinar cells obtained from the Lifeact-EGFP transgenic mice. We show that the time-course of agonist-evoked exocytic events and the kinetics of each single exocytic event are the same for wild type and Lifeact-EGFP transgenic animals. We conclude that Lifeact-EGFP animals are a good model to study of exocytosis and reveal that F-actin coating is dependent on the de novo synthesis of F-actin and that development of actin polymerization occurs simultaneously in all regions of the granule. Our insights using the Lifeact-EGFP mice demonstrate that F-actin coating occurs after granule fusion and is a granule-wide event.