Kåre Larsson

The interface zone of inorganic implantsIn vivo: Titanium implants in bone

The interface zone between titanium implants and bone is considered at the macroscopic, microscopic, and molecular levels. A high rate of successful dental implants of pure titanium is associated with a very close apposition of the bone to the titanium surface, called osseointegration. At the macroscopic level, osseointegration allows efficient stress transfer from the implant to the bone without abrasion or progressive movement that can take place if a fibrous layer intervenes. At the microscopic level, surface roughness and porosity provide interlocking of the implant and bone tissue which grows into direct contact with titanium. Sections studied in the electron microscope show that calcified tissue can be identified within 50 Å of the implant surface. The interface zone includes a tightly adherent titanium oxide layer on the surface of the implant which may be similar to a ceramic material in relation to tissue response. The five year success rate of 90% in 2895 implants in clinical trials since 1965 is associated with the favorable behavior of bone tissue at the interface zone with pure titanium.

Structural relationships between lamellar, cubic and hexagonal phases in monoglyceride-water systems. possibility of cubic structures in biological systems

Abstract The transitions lamellar → cubic → hexagonal in the aqueous system of sunflower oil monoglycerides are analysed. X-Ray diffraction data show linear relationships between the lattices of the three phases, which are discussed on the basis of structures formed by lipid bilayer units. The cubic structure is related to ‘Schwarzs primitive cubic minimal surface’ and consists of a three-dimensional continuous bilayer system separating two separate water channel systems. It is also pointed out that the three-dimensional membrane system in plant plastids, the prolamellar body, which is involved in the formation of thylakoid membranes of chloroplasts, has a structure which is closely related to or identical with that of the cubic phase of monoglyceride-water systems.

Aqueous dispersions of cubic lipid–water phases

Abstract Inverse lipid–water phases such as cubic phases can form kinetically stable dispersions by fragmentation in water. Cubic lipid phases can be dispersed by polar lipids favoring lamellar phases or by block copolymers, which can close the bilayer at the surface so that the hydrocarbon chain core is not exposed to water. Monodisperse particles based on glycerol monooleate, with their bilayer curved as the P-, D- or G-minimal surface, have been prepared in this way. Their inner bilayer conformation and outer shape have been examined, mainly by X-ray diffraction and cryo transmission electron microscopy. There is also a different type of cubic lipid bilayer particles with a periodicity in the micrometer range, which have been identified in phospholipid–water dispersions and in cell membrane assemblies. The mechanism behind formation in vivo of such cubic membranes, which also follow the P-, D- and G-surfaces, is discussed. Other lipid–water dispersions with lower symmetry are finally considered; dispersions formed by the inverse hexagonal phase and the dispersed state of a tetragonal bilayer structure formed by lung surfactants.

Cereals in breadmaking: a molecular colloidal approach

Basic concepts of surface and colloid chemistry physicochemical behaviour of the components of wheat flour interactions between components components in other cereals flour dough bread.

Addition of hydrophilic and lipophilic compounds of biological relevance to the monoolein/water system. I. Phase behavior.

The solubilization of hydrophilic and lipophilic molecules, with biological relevance, in the monoolein/water (MO/W) system has been investigated for phase behavior. Small angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR) and optical microscopy (OM) have been used to characterize the microstructure of the liquid crystalline phases. Partial phase diagrams of the MO/W system in the presence of sodium decanoate, 1-adamantanamine hydrochloride, decanoic and dodecanoic acids, acetyl salicilic acid and retinol have been determined. The stability of the various phases has been followed for at least eight months. The polarity and the molecular structure of the additive determine whether it is located at the polar interface or in the apolar region of the lipid layer. Therefore, the additive affects the interfacial curvature of the lipid layer differently, which in turn will trigger transition to disparate phases. A cubic-to-reverse hexagonal phase transition has been observed with time for most of the ternary systems, with the exception of 1-adamantanamine hydrochloride and retinol. The release of free glycerol and oleic acid due to MO hydrolysis has been clearly demonstrated by 13C NMR. This would account for the changes in phase behavior observed with time. The released oleic acid, located in the MO acyl chain region, favors the inverse interfacial curvature. The average lipid dimensions in the cubic and in the reverse hexagonal phases have been calculated from SAXS data.

Aqueous lipid phases of relevance to intestinal fat digestion and absorption.

The phase behavior of monoglyceride/water systems, with oleic and linoleic acid as the dominating fatty acid residues, was investigated. Increased solubilization of triglycerides (oil) or oleic acid in the cubic liquid-crystalline phase formed by monoglyceride and water resulted in the formation of a reversed hexagonal liquid-crystalline phase followed by an L2-phase. The liquid-crystalline phases have different dispersion properties compared to each other in dilute micellar bile salt solutions. The cubic phase is found to be easily dispersed. The relevance of aqueous lipid phases other thah micellar is discussed in relation to intestinal lipid digestion and absorption.

On lipid surface films on the sea. I. A simple method for sampling and studies of composition

Abstract A method for collection of surface films on the sea has been developed and tested at various places along the Swedish West Coast. Considerable amounts of lipids on the sea surface were found even when no seaslicks were observed. Triglycerides, free fatty acids, and wax esters are the dominating constituents, and there are characteristic deviations in the fatty-acid patterns compared to the corresponding lipids dissolved in the sub-surface water. Organochlorine residues, phthalic acid esters and heavy metals also occur in considerable amounts.

A cubic protein-monoolein-water phase.

A cubic monoacylglycerol-protein-water phase has been identified by low-angle X-ray diffraction, and the main features of the ternary phase diagram monoolein/lysozyme/water are presented. The thermal stability of the protein in the lipid-protein cubic phase has been examined by differential scanning calorimetry. According to the physical properties of the phase it is proposed that the protein molecules are located in the water medium, i.e. in the water channel systems of the cubic structure earlier suggested. The ability of various proteins to form this cubic phase has been studied, and it was found that the formation of this phase is favoured by an isoelectric point (pI) far from pH 7 in a salt-free solution, thus by high electrostatic repulsive forces.

Molecular arrangements in glycosphingolipids.

Abstract A number of homogeneous glycosphingolipids have been prepared and their structural behaviour studied in the solid state as well as in lipid-water systems and in surface films. Mainly X-ray diffraction techniques have been used in the phase analyses. A very complex phase pattern is usually found — e.g. cerebroside containing 2-hydroxy fatty acids has 5 crystalline phases and 2 thermotropic mesophases. This is also the case in the water systems, where hexagonal, lamellar and cubic mesophases are observed. Whereas in earlier surface film studies of complex lipids, such as phospholipids, only one liquid expanded phase usually has been found, cerebrosides also exhibit numerous condensed phases. Comparisons with corresponding natural lipids have shown a close relationship both in the phase behaviour and structure of the different polymorphs.

Phase behaviour and rheological properties of aqueous systems of industrial distilled monoglycerides

Abstract On the basis of earlier studies on a series of pure monoglyceride—water systems, the phase behaviour of industrial samples of distilled monoglycerides in aqueous systems is presented. The rheological properties have been examined and related to our knowledge of molecular arrangements in the phases. The effect of ionic strength and pH on the existence range of different phases was also studied, and it was found that drastic changes in phase equilibria could be obtained.