From near hard spheres to colloidal surfboards.

This work revisits the synthesis of the colloidal particles most commonly used for making model near hard suspensions or as building blocks of model colloidal gels, i.e. sterically stabilised poly(methyl methacrylate) (PMMA) particles. The synthesis of these particles is notoriously hard to control and generally the problems are ascribed to the difficulty in synthesising the graft stabiliser (PMMA-g-PHSA). In the present work, it is shown that for improving the reliability of the synthesis as a whole, control over the polycondensation of the 12-polyhydroxystearic acid is the key. By changing the catalyst and performing the polycondensation in the melt, the chain length of the 12-polyhydroxystearic acid is better controlled, as confirmed by 1H-NMR spectroscopy. Control over the graft copolymer now enables us to make small variations of near hard sphere colloids, for example spherical PMMA particles with essentially the same core size and different stabilising layer thicknesses can now be readily produced, imparting controlled particle softness. The PMMA spheres can be further employed to create, in gram scale quantities, colloidal building blocks having geometrical and/or chemical anisotropy by using a range of mechanical deformation methods. The versatility of the latter methods is demonstrated for polystyrene latex particles as well.

Nanocomposites of high-density polyethylene with amorphous calcium phosphate: in vitro biomineralization and cytocompatibility of human mesenchymal stem cells.

Polyethylene is widely used as a component of implants in medicine. Composites made of high-density polyethylene (HDPE) containing different amounts of amorphous calcium phosphate nanoparticles were investigated concerning their in vitro biomedical performance. The nanoparticles were produced by flame spray synthesis and extruded with HDPE, the latter complying with Food and Drug Administration regulations. Mechanical properties such as Young's modulus and contact angle as well as in vitro biomineralization of the nanocomposites hot-pressed into thin films were evaluated. The deposition of a hydroxyapatite layer occurred upon immersion in simulated body fluid. Additionally, a cell culture study with human mesenchymal stem cells for six weeks allowed a primary assessment of the cytocompatibility. Viability assays (alamarBlue and lactate dehydrogenase detection) proved the absence of cytotoxic effects of the scaffolds. Microscopic images after hematoxylin and eosin staining confirmed typical growth and morphology. A preliminary experiment analyzed the alkaline phosphatase activity after two weeks. These findings motivate further investigations on bioactive HDPE in bone tissue engineering.

Small hook thread (Quill) and soft felt internal splint to increase the primary repair strength of lacerated rabbit Achilles tendons: biomechanical analysis and considerations for hand surgery.

BACKGROUND: For the prevention of re-rupture during early healing phase, the primary repair strength of repaired lacerated tendons in hand surgery should be maximal and the reconstructed diameter minimal. Two new repair methods (small hook thread and internal splint) were assessed for strength and reconstructed diameter characteristics. METHODS: Achilles tendons of 43 female New Zealand White rabbits were sectioned 2 cm above the calcaneus. Specimens were divided into 7 groups and repaired as follows: Kirchmayr method 2-strand with 4.0 polypropylene thread; Becker method 4-strand; 6-strand; internal splint; Kirchmayr method small hook 2-strand; Becker method small hook 4-strand, non-modified tendon. Load until failure, load until gap formation, gap length, cross-sectional area and failure stress were determined. FINDINGS: The small hook 2-strand suture had 1.3 fold higher loads until failure compared to a conventional 2-strand suture, P<0.05. The internal splint had a similar load until failure (22 N (SD 6)) as the conventional 2-strand suture (23 N (SD 4)); around half the load until failure of the conventional 4-strand suture (38 N (SD 9)). Load until gap formation correlated positively with load until failure (y=0.65+3.6; r(2)=0.72). The running suture increased the cross-sectional area at the repair site by a factor of 1.3. INTERPRETATION: Using a small hook thread instead of a 4.0 polypropylene thread significantly increases the primary repair strength with the same number of strands. Internal splints may be an alternative to conventional 2-strand sutures for bridging large gaps.

Light-curable polymer/calcium phosphate nanocomposite glue for bone defect treatment.

Light-curable, methacrylate-based resins are clinically used for complex defect repair in dentistry (Heliobond). The present study investigates how such easy-to-apply polymers may be used on a much broader range of applications, particularly for gluing wet bone. We investigate the significantly improved adhesion of the polymer to wet bone surfaces in a close to in vivo setup using freshly cut cow hip bone as a model. The use of a reactive filler (20 wt.% amorphous, glassy calcium phosphate nanoparticles, a-CaP) allows for combination of the properties of the polymer (strength; light-curing) and the reactive filler (recrystallization of amorphous CaP to hydroxyapatite within minutes). This filler alone has been earlier suggested for use as an injectable bone cement since it reacts under in vivo conditions within 10-15 min. Our study transfers this reactivity into a composite, thus using the reactive CaP phase to establish an improved adhesion of the composite to wet bone surfaces. Additional in vitro bioactivity tests, compressive and tensile strength suggest use of such light-curable nanocomposites for complex-shaped load-bearing implant materials and fracture repair.

Collagen nerve conduits releasing the neurotrophic factors GDNF and NGF.

Artificial nerve conduits (NC) can clinically be instrumental for facilitating the surgery of damaged peripheral nerves. To improve axonal regeneration of injured peripheral nerves, we have developed collagen nerve conduits (NC) releasing glial cell line-derived neurotrophic factor (GDNF) alone or in combination with nerve growth factor (NGF), which exert synergistic action on axonal growth. Degradation of the NC and their mechanical and drug release properties were controlled by two means: (i) cross-linking the collagen tubes by physical means, through a dehydro-thermal treatment (DHT), before loading with the neurotrophic factors (NTFs) GDNF or GDNF/NGF; and (ii) coating the drug-loaded collagen tubes with layers of poly(lactide-co-glycolide) (PLGA). Non-cross-linked collagen NC (C-NC) released high amounts of NTFs during the initial 2-3 days of incubation, whereas the DHT-treated collagen NC (C(dht)-NC) did not show a prominent burst effect. The release kinetics was similar for GDNF alone and GDNF co-delivered with NGF. Within 30 days, the C-NC released 78% and 83% of the total doses of GDNF and NGF, respectively, whereas the C(dht)-NC released only 68% of GDNF and 56% of NGF. The bioactivity of the NTFs released up to 30 days was confirmed by an in vitro bioassay using chicken embryonic dorsal root ganglion (DRG) explants. The C(dht)-NC also possessed adequate mechanical resistance against radial compression, the pull-out of a suture thread, and loss of patency upon bending. Modulus and pull-out strength increased in the order of C-NC, C(dht)-NC approximately Neuragen, and Neurolac, with the latter two products being commercially available collagen and polyester NC, respectively. In vitro degradation time upon incubation with collagenase increased in the same order for the collagen-based NC. In conclusion, co-delivery of synergistically acting GDNF and NGF from structurally improved NC may be a promising tool for the successful repair of peripheral nerve defects.

Low toxic, thermoresponsive dendrimers based on oligoethylene glycols with sharp and fully reversible phase transitions.

Novel first (G1) and second (G2) generation dendrimers based on three-fold branched oligoethylene glycol dendrons are efficiently synthesized which show characteristic thermoresponsive behavior and negligible cytotoxicity (for G2).

Synthesis of compounds presenting three and four anthracene units as potential connectors to mediate infinite lateral growth at the air/water interface.

We report the synthesis of molecular sheets based on the photochemically initiated dimerization of monomers with lateral anthracene units. The film thickness and composition were investigated by ellipsometry and X-ray photoelectron spectroscopy (XPS). The mechanical stability of the film was sufficient to span it over 45x45 microm-sized holes. Several model reactions were performed to illustrate the underlying chemistry and to assist in analysis. The reported experiments are considered first steps towards the ultimate goal of the rational synthesis of laterally "infinite", one-monomer-unit-thick molecular sheets with a long-range positional order and a periodic covalent-bonding pattern. Such sheets are referred to as 2D polymers and are considered a prime goal of chemical synthesis with intriguing applications.