Synthesis and characterization of a POSS-PEG macromonomer and POSS-PEG-PLA hydrogels for periodontal applications

A novel water-soluble macromonomer based on octavinyl silsesquioxane has been synthesized and contains vinyl-terminated PEG 400 in each of the eight arms to promote water solubility. The macromonomer was characterized by NMR and FTIR and its aqueous solution properties examined. In water it exhibits an LCST with a cloud point at 23 °C for a 10 wt % aqueous solution. It is surface active with a CMC of 1.5 × 10(-5) M in water and in 20:80 v/v acetone/water the CMC is 7.1 × 10(-5) M, and TEM images showed spherical 22 nm aggregates in aqueous solution above the CMC. The macromonomer was copolymerized in a 20:80 v/v acetone/water mixture with a vinyl-terminated, triblock copolymer of lactide-PEG-lactide to form a library of cross-linked hydrogels that were designed for use as scaffolds for alveolar bone repair. The cross-linked copolymer networks were shown to contain a range of nm-μm sized pores and their swelling properties in water and PBS at pH 7.4 were examined. At pH 7.4 the hydrogel networks undergo a slow hydrolysis with the release of principally PEG and lactic acid fragments. The hydrogels were shown to be noncytotoxic toward fibroblast cultures at pH 7.4, both initially (days 1-5) and after significant hydrolysis had taken place (days 23-28).

Understanding the Diffusion of Dextrans in ‘Click' PNIPAAm Hydrogels

Arguably the most important property of a hydrogel is the ability to allow the diffusion of solutes through the crosslinked network. Studies of the diffusion in hydrogels are important for providing information on the rate and extent of the passage of the solute and on the details of the microstructure of the hydrogel. Such knowledge is directly relevant for applications such as controlled drug delivery systems. The structure of novel poly(N-isopropylacrylamide) (PNIPAAm) hydrogels can be revealed by the restricted diffusion of appropriate probe molecules. Dextran molecules, labelled with fluorescent moieties, were incorporated into well-defined PNIPAAm hydrogels to investigate the effects of hydrogel mesh size and dextran molecular size on the diffusivities of solute molecules.

Self-assembled magnetic luminescent hybrid micelles containing rare earth Eu for dual-modality MR and optical imaging

In this study, we report new water-soluble multifunctional nanomaterials based on amphiphilic poly(HFMA-co-Eu(AA)₃Phen)-g-PEG copolymers and oleic acid modified Fe₃O₄ nanoparticles. The nanoparticles can self-assemble to form magnetic and luminescent hybrid micelles and show a spherical morphology, paramagnetic properties with a maximum saturation magnetization of 7.05 emu g^-1, and a high transverse relaxivity of 340 mM^-1 s^-1. According to in vivo magnetic resonance imaging (MRI) experiments, excellent contrast of the liver and spleen was achieved after injection of the hybrid micelles. Fluorescence spectra show characteristic emission peaks from the rare earth Eu at 616 nm and vivid red fluorescence can be observed by 2-photon confocal laser scanning microscopy (CLSM). In vivo optical imaging demonstrates the unique fluorescent characteristics of the magnetic and luminescent hybrid micelles in the liver and spleen and the excellent multifunctional properties suggest the possibility of clinical use as nanocarriers in magnetic resonance imaging and optical imaging.

Electrospinning and crosslinking of low-molecular-weight poly(trimethylene carbonate-co-(L)-lactide) as an elastomeric scaffold for vascular engineering

The growth of suitable tissue to replace natural blood vessels requires a degradable scaffold material that is processable into porous structures with appropriate mechanical and cell growth properties. This study investigates the fabrication of degradable, crosslinkable prepolymers of l-lactide-co-trimethylene carbonate into porous scaffolds by electrospinning. After crosslinking by γ-radiation, dimensionally stable scaffolds were obtained with up to 56% trimethylene carbonate incorporation. The fibrous mats showed Young's moduli closely matching human arteries (0.4-0.8MPa). Repeated cyclic extension yielded negligible change in mechanical properties, demonstrating the potential for use under dynamic physiological conditions. The scaffolds remained elastic and resilient at 30% strain after 84days of degradation in phosphate buffer, while the modulus and ultimate stress and strain progressively decreased. The electrospun mats are mechanically superior to solid films of the same materials. In vitro, human mesenchymal stem cells adhered to and readily proliferated on the three-dimensional fiber network, demonstrating that these polymers may find use in growing artificial blood vessels in vivo.

Control of the orientation of symmetric poly(styrene)-block-poly(D,L-lactide) block copolymers using statistical copolymers of dissimilar composition

The interactions of block copolymers with surfaces can be controlled by coating those surfaces with appropriate statistical copolymers. Usually, a statistical copolymer comprised of monomer units identical to those of the block copolymer is used; that is, typically a poly(styrene)-stat-poly(methyl methacrylate) (PS-stat-PMMA) is used to direct the alignment of poly(styrene)-block-poly(methyl methacrylate) (PS-block-PMMA), and poly(styrene)-stat-poly(2-vinylpyridine) (PS-stat-P2VP) has been used for poly(styrene)-block-poly(2-vinylpyridine) (PS-block-P2VP). Reports of controlling the orientation of block copolymers with statistical copolymers with a dissimilar composition are limited. Here, we demonstrate that this method can be further extended to show that PS-stat-PMMA can be used to control the wetting properties of poly(styrene)-block-poly(D,L-lactide) (PS-block-PDLA). Surfaces were modified with a series of cross-linked PS-stat-PMMA-stat-glycidyl methacrylate terpolymers, and the surface chemistries and energies were assessed using angle-dependent X-ray photoelectron spectroscopy and the two-liquid harmonic method, respectively. From these experiments, an expected neutral compositional window was identified for symmetrical PS-block-PDLA. Moreover, high-resolution SEM, AD-XPS, and grazing-incidence SAXS measurements were used to evaluate the morphology of PS-block-PDLA as a function of the surface composition of the underlying cross-linked copolymer films, and the neutral composition was found to range from 32 to 38 mol % of PS, in the bulk polymer. Ultimately, we demonstrated the determination of nonpreferential surface compositions that allow the self-assembly of lamellae with sizes in the sub-10 nm regime that are oriented perpendicular to the substrate. These findings have important implications for the use of PS-block-PDLA block copolymers in directed self-assembly, most specifically in advanced lithographic processes.

Mass uptake study of the diffusion of water and SBF into poly(2-hydroxyethyl methacrylate-co-tetrahydrofurfuryl methacrylate) containing aspirin or vitamin B12

The ingress of water and Kokubo simulated body fluid (SBF) into poly(2-hydroxyethyl methacrylate) (PHEMA), and its co-polymers with tetrahydrofurduryl methacrylate (THFMA), loaded with either one of two model drugs, vitamin B12 or aspirin, was studied by mass uptake over the temperature range 298-318 K. The polymers were studied as cylinders and were loaded with either 5 wt% or 10 wt% of the drugs. From DSC studies it was observed that vitamin B12 behaved as a physical cross-linker restricting chain segmental mobility, and so had a small anti-plasticisation effect on PHEMA and the co-polymers rich in HEMA, but almost no effect on the Tg of co-polymers rich in THFMA. On the other hand, aspirin exhibited a plasticising effect on PHEMA and the co-polymers. All of the polymers were found to absorb water and SBF according to a Fickian diffusion mechanism. The polymers were all found to swell to a greater extent in SBF than in water, which was attributed to the presence of Tris buffer in the SBF. The sorptions of the two penetrants were found to follow Fickian kinetics in all cases and the diffusion coefficients at 310 K for SBF were found to be smaller than those for water, except for the polymers containing aspirin where the diffusion coefficients were higher than for the other systems. For example, for sorption into PHEMA the diffusion coefficient for water was 1.41 x 10(-11) m2/s and for SBF was 0.79 x 10(-11) m2/s, but in the presence of 5 wt% aspirin the corresponding values were 1.27 x 10(-11) m2/s and 1.25 x 10(-11) m2/s, respectively. The corresponding values for PHEMA loaded with 5 wt% B12 were 1.25 x 10(-11) m2/s and 0.74 x 10(-11) m2/s, respectively.

Ageing-induced solubility loss in milk protein concentrate powder: effect of protein conformational modifications and interactions with water

BACKGROUND

Protein conformational modifications and water-protein interactions are two major factors believed to induce instability of protein and eventually affect the solubility of milk protein concentrate (MPC) powder. To test these hypotheses, MPC was stored at different water activities (a(w) 0.0-0.85) and temperatures (25 and 45 °C) for up to 12 weeks. Samples were examined periodically to determine solubility, change in protein conformation by Fourier transform infrared (FTIR) spectroscopy and water status (interaction of water with the protein molecule/surface) by measuring the transverse relaxation time (T(2) ) with proton nuclear magnetic resonance ((1) H NMR).

RESULTS

The solubility of MPC decreased significantly with ageing and this process was enhanced by increasing water activity (a(w) ) and temperature. Minor changes in protein secondary structure were observed with FTIR which indicated some degree of unfolding of protein molecules. The NMR T(2) results indicated the presence of three distinct populations of water molecules and the proton signal intensity and T(2) values of proton fractions varied with storage condition (humidity) and ageing.

CONCLUSION

Results suggest that protein/protein interactions may be initiated by unfolding of protein molecules that eventually affects solubility.

Cross-linked poly(trimethylene carbonate-co-L-lactide) as a biodegradable, elastomeric scaffold for vascular engineering applications

A series of copolymers of trimethylene carbonate (TMC) and L-lactide (LLA) were synthesized and evaluated as scaffolds for the production of artificial blood vessels. The polymers were end-functionalized with acrylate, cast into films, and cross-linked using UV light. The mechanical, degradation, and biocompatibility properties were evaluated. High TMC polymers showed mechanical properties comparable to human arteries (Young's moduli of 1.2-1.8 MPa and high elasticity with repeated cycling at 10% strain). Over 84 days degradation in PBS, the modulus and material strength decreased gradually. The polymers were nontoxic and showed good cell adhesion and proliferation over 7 days using human mesenchymal stem cells. When implanted into the rat peritoneal cavity, the polymers elicited formation of tissue capsules composed of myofibroblasts, resembling immature vascular smooth muscle cells. Thus, these polymers showed properties which were tunable and favorable for vascular tissue engineering, specifically, the growth of artificial blood vessels in vivo.