Hartmut Worch

Collagen type I‐coating of Ti6Al4V promotes adhesion of osteoblasts

The initial contact of osteoblasts with implant surfaces is an important event for osseointegration of implants. Osseointegration of Ti6Al4V may be improved by precoating of its surface with collagen type I. In this study, the adhesion of rat calvarial osteoblasts to uncoated and collagen type I-coated titanium alloy was investigated over a period of 24 h. Collagen type I-coating accelerates initial adhesion of osteoblasts in the presence of fetal calf serum. One hour after plating, no differences in the percentage of adherent cells between the surfaces investigated were found. Adhesion of osteoblasts to uncoated surfaces was reduced by the GRGDSP peptide by about 70%, whereas adhesion to collagen type I-coated surfaces remained unaffected by treatment of the cells with the peptide. Cell adhesion to coated materials was reduced by about 80% by anti-integrin beta1 antibody. The integrin beta1 antibody did not influence the adhesion to uncoated titanium alloy. The results suggest that osteoblasts adhere to collagen type I-coated materials via integrin beta1 but not by interacting with RGD peptides, whereas adhesion to uncoated titanium alloy is mediated by RGD sequences but not via integrin beta1. Fibronectin does not seem to be involved in the adhesion of osteoblasts to either coated or uncoated titanium alloy.

Generation of Ultrahydrophobic Properties of Aluminium – A first Step to Self‐cleaning Transparently Coated Metal Surfaces

In the last few years, significant efforts have been made to provide surfaces with self-cleaning properties. This approach utilises principles wich have been discovered in nature, like the well known lotus-effect. The transformation of this strategy to metallic surfaces is a scientifically and technologically challenging target. This publication focuses on the investigation of different routes for the generation of the necessary micro-morphological propoerties of Al

Three-dimensional chitin-based scaffolds from Verongida sponges (Demospongiae: Porifera). Part I. Isolation and identification of chitin.

Marine invertebrate organisms including sponges (Porifera) not only provide an abundant source of biologically active secondary metabolites but also inspire investigations to develop biomimetic composites, scaffolds and templates for practical use in materials science, biomedicine and tissue engineering. Here, we presented a detailed study of the structural and physico-chemical properties of three-dimensional skeletal scaffolds of the marine sponges Aiolochroia crassa, Aplysina aerophoba, A. cauliformis, A. cavernicola, and A. fulva (Verongida: Demospongiae). We show that these fibrous scaffolds have a multilayered design and are made of chitin. (13)C solid-state NMR spectroscopy, NEXAFS, and IR spectroscopy as well as chitinase digestion and test were applied in order to unequivocally prove the existence of alpha-chitin in all investigated species.

Mineralization of the metre-long biosilica structures of glass sponges is templated on hydroxylated collagen

The minerals involved in the formation of metazoan skeletons principally comprise glassy silica, calcium phosphate or carbonate. Because of their ancient heritage, glass sponges (Hexactinellida) may shed light on fundamental questions such as molecular evolution, the unique chemistry and formation of the first skeletal silica-based structures, and the origin of multicellular animals. We have studied anchoring spicules from the metre-long stalk of the glass rope sponge (Hyalonema sieboldi; Porifera, Class Hexactinellida), which are remarkable for their size, durability, flexibility and optical properties. Using slow-alkali etching of biosilica, we isolated the organic fraction, which was revealed to be dominated by a hydroxylated fibrillar collagen that contains an unusual [Gly-3Hyp-4Hyp] motif. We speculate that this motif is predisposed for silica precipitation, and provides a novel template for biosilicification in nature.

Titanium powder sintering for preparation of a porous functionally graded material destined for orthopaedic implants.

This work focuses on basic research into a P/M processed, porous-surfaced and functionally graded material (FGM) destined for a permanent skeletal replacement implant with improved structural compatibility. Based on a perpendicular gradient in porosity the Youngs modulus of the material is adapted to the elastic properties of bone in order to prevent stress shielding effects and to provide better long-term performance of the implant-bone system. Using coarse Ti particle fractions the sintering process was accelerated by silicon-assisted liquid-phase sintering (LPS) resulting in a substantial improvement of the neck geometry. A novel evaluation for the strength of the sinter contacts was proposed. The Youngs modulus of uniform non-graded stacks ranged from 5 to 80 GPa as determined by ultrasound velocity measurements. Thus, the typical range for cortical bone (10–29 GPa) was covered. The magnitude of the Poissons ratio proved to be distinctly dependent on the porosity. Specimens with porosity gradients were successfully fabricated and characterized using quantitative description of the microstructural geometry and acoustic microscopy.

Biomimetic coatings functionalized with adhesion peptides for dental implants.

A complete biological integration into the surrounding tissues (bone, gingiva) is a critical step for clinical success of a dental implant. In this work biomimetic coatings consisting either of collagen type I (for the gingiva region) and hydroxyapatite (HAP) or mineralized collagen (for the bone interface) have been developed as suitable surfaces regarding the interfaces. Additionally, using these biomimetic coatings as a matrix, adhesion peptides were bound to further increase the specificity of titanium implant surfaces. To enhance cell attachment in the gingiva region, a linear adhesion peptide developed from a laminin sequence (TWYKIAFQRNRK) was bound to collagen, whereas for the bone interface, a cyclic RGD peptide was bound to HAP and mineralized collagen using adequate anchor systems. The biological potential of these coatings deduced from cell attachment experiments with HaCaT human keratinocytes and MC3T3-E1 mouse osteoblasts showed the best results for collagen and laminin sequence coating for the gingiva region and mineralized collagen and RGD peptide coatings for regions with bone contact. Our concept opens promising approaches to improve the biological integration of dental implants.© 2001 Kluwer Academic Publishers

Modifications of hyaluronan influence the interaction with human bone morphogenetic protein-4 (hBMP-4).

In this study, we have demonstrated that the modification of hyaluronan (hyaluronic acid; Hya) with sulfate groups led to different binding affinities for recombinant human bone morphogenetic protein-4 (rhBMP-4). The high-sulfated sHya2.8 (average degree of sulfation (D.S.) 2.8) exhibited the tightest interaction with rhBMP-4, followed by the low-sulfated sHya1.0, as determined with surface plasmon resonance (SPR), ELISA, and competition ELISA. Unmodified Hya, chondroitin-sulfate (CS), and heparan sulfate (HS) showed significantly less binding affinity. SPR data could be fitted to an A + B = AB Langmuir model and binding constants were evaluated ranging from 13 pM to 5.45 microM. The interaction characteristics of the differentially sulfated Hyas are promising for the incorporation of these modified polysaccharides in bioengineered coatings of biomaterials for medical applications.

Bioactive silica-collagen composite xerogels modified by calcium phosphate phases with adjustable mechanical properties for bone replacement.

The development of composites has been recognized as a promising strategy to fulfil the complex requirements of biomaterials. The present study reports on the modification of a novel silica-collagen composite material by varying the inorganic/organic mass ratio and introducing calcium phosphate cement (CPC) as a third component. The sol-gel technique is used for processing, followed by xerogel formation under specific temperature and relative humidity conditions. Cylindrical monolithic samples up to 400mm(3) were obtained without any sintering processes. Various hierarchical phases of the organic component were applied, ranging from tropocollagen and collagen fibrils up to collagen fibers, each characterized by atomic force microscopy. Focusing on the application of fibrils, various inorganic/organic mass ratios were used: 100/0, 85/15 and 70/30; their influence on the structure of the composite material was demonstrated by scanning electron microscopy. The composition was extended by the addition of 25wt.% CPC which led to increased bioactivity by accelerating the formation of bone apatite layers in simulated body fluid. Synchrotron microcomputed tomography demonstrated the homogeneous distribution of the cement particles in the silica-collagen matrix. Compressive strength tests showed that the mechanical properties of the brittle pure silica gel are changed significantly due to collagen addition. The highest ultimate strength of about 115MPa at about 18% total strain was registered for the 70/30 silica-collagen composite xerogels. Incorporation of CPC lowered the gels strength. By demonstrating differentiation of human monocytes into osteoclast-like cells, an important feature of the composite material regarding successful bone remodeling is fulfilled.

Novel Textile Chitosan Scaffolds Promote Spreading, Proliferation, and Differentiation of Osteoblasts

Two novel scaffold models made of chitosan fibers were designed, fabricated, and investigated. Raw chitosan fibers were either tightened between plastic rings or were processed into stand-alone scaffolds. Chitosan fiber scaffolds were further modified by coating with a thin layer of fibrillar collagen type I to biologize the surface. Cell culture experiments were carried out using murine osteoblast-like cells (7F2). Confocal laser scanning microscopy (cLSM) as well as scanning electron microscopy (SEM) revealed fast attachment and morphological adaptation of the cells on both the raw chitosan fibers and the collagen-coated scaffolds. Cells were cultivated for up to 4 weeks on the materials and proliferation as well as osteogenic differentiation was quantitatively analyzed in terms of lactate dehydrogenase (LDH) and alkaline phosphatase (ALP) activity. We found a 14-16-fold increase of cell number and the typical pattern of ALP activity, whereas the collagen coating does not remarkably influence these parameters. The maintenance of osteogenic phenotype on the novel materials was furthermore confirmed by immunostaining of osteocalcin and study of matrix mineralization. The feature of the collagen-coated but also the raw chitosan fiber scaffolds to support the attachment, proliferation, and differentiation of osteoblast-like cells suggest a potential application of chitosan fibers and textile chitosan scaffolds for the tissue engineering of bone.

Three-dimensional chitin-based scaffolds from Verongida sponges (Demospongiae: Porifera). Part II: Biomimetic potential and applications

In order to evaluate the biomedical potential of three-dimensional chitinous scaffolds of poriferan origin, chondrocyte culturing experiments were performed. It was shown for the first time that freshly isolated chondrocytes attached well to the chitin scaffold and synthesized an extracellular matrix similar to that found in other cartilage tissue engineering constructs. Chitin scaffolds also supported deposition of a proteoglycan-rich extracellular matrix of chondrocytes seeded bioconstructs in an in vivo environment. We suggest that chitin sponge scaffolds, apart from the demonstrated biomedical applications, are highly optimized structures for use as filtering systems, templates for biomineralization as well as metallization in order to produce catalysts.