Impact of sodium polyacrylate on the amorphous calcium carbonate formation from supersaturated solution.

A detailed in situ scattering study has been carried out on the formation of amorphous calcium carbonate (ACC) particles modulated by the presence of small amounts of sodium polyacrylate chains. The work is aiming at an insight into the modulation of ACC formation by means of two polyacrylate samples differing in their molecular weight by a factor of 50. The ACC formation process was initiated by an in situ generation of CO(3)(2-) ions via hydrolysis of 10 mM dimethylcarbonate in the presence of 10 mM CaCl(2). Analysis of the formation process by means of time-resolved small-angle X-ray and light scattering in the absence of any additives provided evidence for a monomer addition mechanism for the growth of ACC particles. ACC formation under these conditions sets in after a lag-period of some 350 s. In the presence of sodium polyacrylate chains, calcium polyacrylate aggregates are formed during the lag-period, succeeded by a modulated ACC growth in a second step. The presence of anionic polyacrylate chains changed the shape of the growing particles toward loose and less homogeneous entities. In the case of low amounts (1.5-7.5 mg/L) of the long chain additive with 97 kDa, the size of the aggregates is comparable to the size of the successively formed hybrid particles. No variation of the lag-period has been observed in this case. Use of the short chain additive with 2 kDa enabled increase of the additive concentration up to 100 mg/L and resulted in a significant increase of the lag-period. This fact, together with the finding that the resulting hybrid particles remained stable in the latter case, identified short chain sodium polyacrylates as more efficient modulators than long chain polyacrylates.

Characterization of the PEG layer of sterically stabilized liposomes: a SAXS study.

Synchrotron small-angle X-ray scattering analysis of the bilayer structure of a pharmacologically relevant sterically stabilized liposome system is presented. Describing the electron density profile of the bilayer with the superposition of Gaussian functions, the contribution of the poly(ethylene glycol) (PEG) layers to the total electron density was identified. The changes in the thickness of the PEG layer as well as the distribution of the PEG chains among the outer and inner leaflets of the bilayers were followed by changing the molar ratio of the PEG-lipid and the molar weight of the PEG molecule.

The model Lysozyme-PSSNa system for electrostatic complexation: Similarities and differences with complex coacervation.

We review, based on structural information, the mechanisms involved when putting in contact two nano-objects of opposite electrical charge, in the case of one negatively charged polyion, and a compact charged one. The central case is mixtures of PSS, a strong flexible polyanion (the salt of a strong acid, and with high linear charge density), and Lysozyme, a globular protein with a global positive charge. A wide accurate and consistent set of information in different situations is available on the structure at local scales (5-1000Å), due to the possibility of matching, the reproducibility of the system, its well-defined electrostatics features, and the well-defined structures obtained. We have related these structures to the observations at macroscopic scale of the phase behavior, and to the expected mechanisms of coacervation. On the one hand, PSS/Lysozyme mixtures show accurately many of what is expected in PEL/protein complexation, and phase separation, as reviewed by de Kruif: under certain conditions some well-defined complexes are formed before any phase separation, they are close to neutral; even in excess of one species, complexes are only modestly charged (surface charges in PEL excess). Neutral cores are attracting each other, to form larger objects responsible for large turbidity. They should lead the system to phase separation; this is observed in the more dilute samples, while in more concentrated ones the lack of separation in turbid samples is explained by locking effects between fractal aggregates. On the other hand, although some of the features just listed are the same required for coacervation, this phase transition is not really obtained. The phase separation has all the macroscopic aspects of a fluid (undifferentiated liquid/gas phase) - solid transition, not of a fluid-fluid (liquid-liquid) one, which would correspond to real coacervation). The origin of this can be found in the interaction potential between primary complexes formed (globules), which agrees qualitatively with a potential shape of the type repulsive long range attractive very short range. Finally we have considered two other systems with accurate structural information, to see whether other situations can be found. For Pectin, the same situation as PSS can be found, as well as other states, without solid precipitation, but possibly with incomplete coacervation, corresponding to differences in the globular structure. It is understandable that these systems show smoother interaction potential between the complexes (globules) likely to produce liquid-liquid transition. Finally, we briefly recall new results on Hyaluronan/Lysozyme, which present clear signs of coacervation in two liquid phases, and at the same time the existence of non-globular complexes, of specific geometry (thin rods) before any phase separation. These mixtures fulfill many of the requirements for complex coacervation, while other theories should also be checked like the one of Shklovskii et al.

[Therapy success in the treatment of severe renal osteopathy as the result of effective interdisciplinary team work. Case report]. / Therapieerfolg in der Behandlung einer schweren renalen Osteopathie im Ergebnis einer effektiven interdisziplinären Zusammenarbeit. Ein Fallbericht.

Report about therapy of a severe renal osteopathy, a case of tertiary hyperparathyroidism. It will be shown the good team work between paediatrics, surgery and orthopaedics. Only on this way the patient get the ability for a later dialysis or kidney transplantation.

[Surgical treatment possibilities in tumors of the spine. Indications, technics, experiences]. / Operative Behandlungsmöglichkeiten bei Tumoren der Wirbelsäule. Indikation, Techniken, Erfahrungen.

Widely normal stability of the vertebral column with adequate load-bearing capacity should be achieved, following osseous reconstruction of a defect area from which benign tumours or tumour-like lesions had been removed by radical surgery. In malignant processes, surgical tumour removal may add to the effectiveness of chemotherapy or radiotherapy. Postoperative restoration of the vertebral column will also improve the psychic, physical, and social quality of survival.

Interface reactions between machinable bioactive glass-ceramics and bone.

A new biomaterial for bone substitution, a "machinable bioactive glass-ceramic" has been developed. The material contains two main crystal phases, mica and apatite, and is therefore machinable and bioactive. It has the advantage to be workable by the surgeon, if necessary, during operation. The preparation method of this glass-ceramic is described. Different types of the material can be produced in dependence of the composition, nucleation, and crystallization of the basic glass. In vivo and in vitro investigations showed a characteristic solubility of the material. A Ca-phosphate-rich interface layer with apatite crystals (from the basic glass-ceramic) and a thickness of about 5-10 micrometers grows as solid-state reaction between glass-ceramic and bone. This interface reaction is interpreted as a chemical process which includes a slight solubility of the glass-ceramic and a solid state reaction between the stable apatite crystals in the glass-ceramic and the bone.

[Mechanically processable bioactive glass ceramics--a new biomaterial for bone replacement. 1]. / "Maschinell bearbeitbare bioaktive Glaskeramiken"--ein neues Biomaterial für den Knochenersatz 1. Mitteilung.

Anorganic materials as glass ceramics with their main crystal phase apatite can be used as biomaterial for the bone substitute. An interior compound between bioglass-ceramics implants and the bone was showed in animal experiments. The apatite crystals in the bioglass-ceramics produce obviously the start point for this fusion process. The shear strength of the compound is on average the eightfold of highly compact Al2O3 ceramics. The bioactive glass ceramics could solve possibly the problems of implant loosening and defect bridging-over. Mechanical processable bioactive ceramics was developed and tested with regard to these employment spheres.