To find new ways for the synthesis of improved bone implant materials, we studied the mineralization of collagen in vitro. Collagen was mineralized by combining the collagen fibril assembly and the formation of calcium phosphate in one process step. Both reactions were initiated simultaneously by mixing an acid, calcium-containing collagen solution with a phosphate-containing neutralization buffer. Under suitable conditions first fibril assembly occurred along with the precipitation of an amorphous calcium phosphate phase. Subsequently, the amorphous calcium phosphate transformed into a crystalline, apatite-like phase, as revealed by IR spectroscopy and X-ray diffraction. In this way, a homogeneously mineralized collagen gel was obtained, consisting of a three-dimensional network of collagen fibrils covered with calcium phosphate. The attachment between the collagen fibrils and the calcium phosphate crystals could be further improved by the addition of polyaspartate to the reaction mixture. In the absence of polyaspartate the calcium phosphate crystals formed clusters loosely bound to the fibrils, while in its presence separate crystals were located on or inside the collagen fibrils. The applied method is useful for studying the mineralization of collagen and offers a promising approach for the development of new bone implant materials.

We have studied structure formation of thin monomeric collagen films prepared by spin coating on hydrophobic highly oriented pyrolytic graphite substrates. The biomolecular coatings have been investigated by scanning force microscopy. Pattern formation takes place as the result of dewetting of the liquid precursor initiated by pore nucleation in the drying film. The growth of pores leads to an accumulation of collagen monomers along the perimeter of the dry patches formed. Depending on the evaporation velocity of the solvent, different well-defined film morphologies have been observed. The pore radius distribution function exhibits two well-separated peaks, indicating the occurrence of two distinct dewetting mechanisms: heterogeneous pore nucleation and spinodal dewetting. The distribution function of the pores initiated by heterogeneous nucleation is analysed in detail. A model is introduced that captures the main distribution features depending on humidity.Investigations of the wetting properties of thin liquid films on solid substrates are of great importance for various areas of science and technology. Up to now, most of the research in this field has been concentrated on the development of methods that prevent a drying liquid film from dewetting the substrate [1]. On the other hand, by making use of dewetting processes, it should also be possible to pattern films in a controlled manner. The latter is especially interesting for the development of new biocompatible implant materials with patterned biomolecular coatings, which may induce bonding between the synthetic material and the tissue [2]. The rod-like collagen I molecule (l = 300 nm, d = 1.5 nm) provides cell adhesion sites for osteoblasts which are responsible for bone synthesis. Therefore, the study of the interaction between the mediating collagen film and implant surfaces is of great importance. Structure formation of monomeric collagen I films on substrates with different wetting properties has recently been investigated by Mertig et al. [3].Dewetting of thin nonvolatile liquid films has been extensively investigated during the last few years [4][5][6][7][8][9][10]. It has been found that dewetting takes place in three successive phases: rupture of the film, growth of pores resulting in a polygonal network of liquid rims, and evolution of the rims.Two different mechanisms are taken into consideration as the cause of film rupture: (1) nucleation of holes in the thin film and subsequent growth of dry patches [5,11] and (2) based on a hydrodynamic theory for viscous or viscoelastic thin liquid films, spontaneous growth of surface undulations under the influence of van der Waals long-range forces [12][13][14]. The latter theoretical models predict that spontaneous film rupture occurs with a characteristic wavelength that scales with the square of the film thickness: λ ∼ 1/h 2 . With these two mechanisms, the experimental observations have been discussed controversially. In investigations of dewetting of polystyrene films on silicon substrates a 1/h 4 de...

Monomeric collagen films were prepared by spin‐coating of acidic collagen solutions on different atomically flat surfaces. The thin biomolecular coatings have been investigated by scanning force microscopy. Depending on both the wetting behaviour and the microtopology of the substrates used, different film morphologies have been observed. Collagen monomers cover the surface of hydrophilic substrates homogeneously, whereas pore formation due to dewetting processes takes place at non‐structured hydrophobic surfaces. The size of pores depends on the evaporation velocity of the solvent during spin‐coating. Topological and metric properties of the resulting networks have been analysed and compared to soap foam network structures.© 1997 John Wiley & Sons, Ltd.

Tnw differeni kinds of collagen assembly have been sludied: The reconsifttlion of lype I collagen 2o fibrils and the formalion ofiwo dimensional neiworks on surfaces. The kinelics offibril assembly are influenced by polyaspar1ae, as measured turbidimeirically. Addition of polyaspaiiaie increases the fibril diameter. The reconsilned fi brils are imaged by atomic force microscopy and scanning elecfron microscopy. The preparalion of ihin collagen films on highly orienled pyrolylic graphite leads o neiworks or free like sfrnciures depending on the collagen conceniralion in the precursor. The resnils presenled are of inieres1 for the developmeni of new bone-like implant malerials and he covering of bone grafts with a biocompalible layer.