Papers by Author: Helga Füredi-Milhofer

Abstract: Damages to articular cartilage that are caused by trauma, age-related diseases (arthritis, arthrosis) and/or physical stress pose major medical problems. A possible solution is to introduce a biodegradable sponge-like scaffold containing cartilage-forming cells. In the current work we developed a model for a partially calcified functional biomedical membrane with a gradient of calcium phosphate crystal density to form the interface between bone and a sponge-like cell containing scaffold for cartilage regeneration. The membrane consists of a biocompatible, biodegradable, partially calcified hydrogel, in our case gelatin was used. One part is an organic-inorganic nanocomposite consisting of nanocrystalline calcium phosphate particles, formed in situ within the hydrogel, while the other part is the hydrogel without inorganic crystals. The experimental method used was one-dimensional single diffusion. Gelatin gels containing calcium or phosphate ions, respectively, were exposed from the upper side to a solution of the other constituent ion (i.e. a sodium phosphate solution was allowed to diffuse into a calcium containing gel and vice versa). Scanning electron microscopy (E-SEM), EDX, XRD and ATR-FTIR spectroscopy confirmed the existence within the gel of a density gradient of carbonate apatite crystals, with a dense top layer extending several microns into the gel. Ca/P atomic ratios were in the range characteristic of calcium deficient apatites. The effect of different experimental parameters on the calcification process within the gelatin membranes is discussed.

Abstract: Extracellular matrix (ECM) proteins play an essential role during biomineralization in bone and engineered tissues. In a previous study [1], we showed that calcite preferentially nucleated on pure elastin fibers. However, the actual cellular ECM fibers are composed of a combination of proteins, primarily collagen, fibronectin and some elastin. Here we follow the calcium carbonate- and calcium phosphate- mineralization process in vitro when these ECM proteins are combined and determine the differences between these proteins in the biomineralization process. The surface morphology and mechanical properties of the protein fibers during the early stages were probed by atomic force microscopy (AFM) and shear modulation force microscopy (SMFM). The nucleation of the mineral crystals on the protein matrices was investigated by scanning electron microscopy (SEM). Preliminary data showed that the moduli of all protein fibers increased at the early stages, with collagen having the largest increase in supersaturated calcium bicarbonate solution. In metastable calcium phosphate solutions the modulus of the mixed elastin-fibronectin fibres increased to a greater extent than the moduli of the fibers composed of the single proteins. Longer exposure in the mineral solutions led to the formation of crystals templated along the self-assembled fiber structures.

Abstract: Biological mineralization proceeds within an organic matrix and is induced and controlled by extracellular, highly acidic matrix macromolecules. Our group has recently prepared organic-inorganic nanocomposite coatings by a strategy that closely mimics these processes. The strategy involves depositing a matrix of polyelectrolyte multilayers (PE MLs), alternating with layers of amorphous calcium phosphate (ACP) particles, then "in situ" growing nanosized apatite crystals within that matrix [1, 2]. Here we describe the results of biological "in vitro" and "in vivo" testing of these materials.

Abstract: In the production of artificial bone and tooth implants, coating of the surfaces of hard, but bioinert materials (metals, polymers) with calcium phosphate crystals has been used to improve bioactivity and facilitate osteointegration. Recently low temperature methods, involving precipitation from aqueous solutions (biomimetic precipitation) including coprecipitation of specific organic macromolecules (growth hormones, enzymes, proteins) have been developed. In this paper an alternative approach is presented, which consists in first laying down a matrix consisting of polyelectrolyte multilayers (PE MLs) alternating with layers of amorphous calcium phosphate (ACP) particles and subsequently growing calcium phosphate crystals upon/within the multilayers. This attractive approach leads to the formation of a new class of true organic-inorganic nanocomposite coatings. In a previous communication we have shown preliminary results, which point to the feasibility of this approach [1]. Here we describe in detail the design, synthesis and characteristics of the thus obtained nanocomposite coatings.