Karolina Schickle

The effect of crystallization of bioactive bioglass 45S5 on apatite formation and degradation.

OBJECTIVE Amorphous bioglass 45S5 has been used for many years as bone substitute material. Bioactive glasses are also suitable as coating materials for implants in order to improve the bone ongrowth behavior. We hypothesize that both the apatite formation on the surface and the chemical stability can be improved by crystallization of the bioglass. METHODS Synthesized amorphous bioglass 45S5 specimens as well as samples which were crystallized at 1000 °C were stored in simulated body fluid for 1, 7, and 14 days. The respective apatite formation was gravimetrically determined and characterized by SEM and XRD analysis. Moreover, the degradation behavior was studied after storage in distilled water. RESULTS The weight of the crystallized samples decreased 6.3% less than that of the amorphous samples. Calcium silica and calcium carbonate layers were found on amorphous bioglass after 7 and 14 days. However, apatite formation was observed only on the crystallized 45S5 samples after storage. SIGNIFICANCE We conclude that the chemical resistance can be improved and, in parallel, a pronounced apatite formation on the surface of 45S5 can be obtained by controlled crystallization of the material for the particular test setup. Therefore, crystallized bioactive glasses should be considered to be promising coating material for dental implants.

Low-aspect ratio nanopatterns on bioinert alumina influence the response and morphology of osteoblast-like cells

Topographical features on the nanometer scale are known to influence cellular behavior. The response of specific cell types to various types of surface structures is currently still being investigated. Alumina ceramics play an important role as biomaterials, e.g., in medical and dental applications. In this study, we investigated the influence of nanoscale surface features with low aspect ratio (< 0.1) on the response of osteoblast-like MG-63 cells. To this end, low-energy ion irradiation was employed to produce shallow nanoscale ripple patterns on Al2O3(0001) surfaces with lateral periodicities of 24 nm and 179 nm and heights of only 0.7 and 11.5 nm, respectively. The nanopatterning was found to increase the proliferation of MG-63 cells and may lead to pseudopodia alignment along the ripples. Furthermore, focal adhesion behavior and cell morphology were analyzed. We found that MG-63 cells are able to recognize surface nanopatterns with extremely low vertical variations of less than 1 nm. In conclusion, it is shown that surface topography in the sub-nm range significantly influences the response of osteoblast-like cells.

Biological Activation of Inert Ceramics: Recent Advances Using Tailored Self-Assembled Monolayers on Implant Ceramic Surfaces

High-strength ceramics as materials for medical implants have a long, research-intensive history. Yet, especially on applications where the ceramic components are in direct contact with the surrounding tissue, an unresolved issue is its inherent property of biological inertness. To combat this, several strategies have been investigated over the last couple of years. One promising approach investigates the technique of Self-Assembled Monolayers (SAM) and subsequent chemical functionalization to create a biologically active tissue-facing surface layer. Implementation of this would have a beneficial impact on several fields in modern implant medicine such as hip and knee arthroplasty, dental applications and related fields. This review aims to give a summarizing overview of the latest advances in this recently emerging field, along with thorough introductions of the underlying mechanism of SAMs and surface cell attachment mechanics on the cell side.

Immobilization of specific proteins to titanium surface using self-assembled monolayer technique

OBJECTIVES The bone bonding to a titanium dental implant surface strongly depends on their individual chemical surface properties. Here we hypothesize that a tailored surface chemistry obtained through a self-assembled monolayer technique on the titanium surface and subsequent immobilization of biological agents can be arbitrarily adjusted to meet any desired requirements for future dental applications. METHODS Self-assembled monolayers were applied to titanium surfaces inducing -(CH2)nCH2, -(CH2)n-NH2, -(CH2)n-OH, and -(CH2)n-COOH functional groups. To investigate the cytocompatibility of these modifications, human mesenchymal stem cells (MSCs) were seeded on the functionalized surfaces and characterized by live/dead staining and cell proliferation. Additionally, bovine serum albumin (BSA) as a model protein was immobilized on the functionalized surfaces. RESULTS Water contact angle measurements and X-ray photoelectron spectroscopy (XPS) proved a successful functional group coupling on the surface. Cell proliferation and viability was supported on the functionalized surfaces. The immobilized proteins were detected on each functionalized surface with an increase in quantity in the following order: -(CH2)n-COOH< -(CH2)n-NH2, -(CH2)n-OH< -(CH2)nCH2. The successful immobilization of BSA by carboxyl-to-amine cross-linking was spectrophotometrically confirmed. SIGNIFICANCE It was proved that self-assembled monolayer (SAM)-technique can be utilized to couple diverse functional groups and biological agents on titanium surfaces allowing controlled design of their surface chemistry. The novel functionalization technique and the new knowledge on MSCs response holds great potential for the development of novel functionalized and biologically activated titanium-based dental implants.

Preparation of spherical calcium phosphate granulates suitable for the biofunctionalization of active brazed titanium alloy coatings

Abstract Titanium-based alloys can be actively brazed onto bio-inert ceramics and potentially be used as biocompatible coatings. To further improve their bioactivity in vivo, introduction of calcium phosphate (CaP)-based granulates onto their surface layer is possible. For this, mechanically stable CaP-based granulates need to be able to withstand the demand of the brazing process. In this study, spherical granulates, made of a calcium phosphate composite composed primarily of β-tricalcium phosphate and hydroxyapatite, a bioactive glass, and a mixture of the previous two, were manufactured by spray drying. The influence of organic additives (Dolapix CE64, trisodium citrate) and solids content (30–80 wt%) in the slurry on the physical characteristics of granulates was investigated. X-ray diffraction, Brunauer, Emmett, Teller specific surface area standard method, scanning electron microscopy, granulate size analysis, and single granule strength were performed. Our results showed that trisodium citrate permitted the production of granulates with regular morphology, high density, and increased failure stress values. The strong granules also withstood the brazing process. These results show that CaP bioactive agents can be generated and be integrated during the demanding metallurgical processes, allowing for one-step bioactivation of metal brazes.

Ensuring defined porosity and pore size using ammonium hydrogen carbonate as porosification agent for calcium phosphate scaffolds

Abstract Up to now, it has been very challenging to manufacture a degradable bone replacement material having a specific pore size as well as a specific percentage of porosity which can be set independently of one another. We hypothesize that this is possible by using ammonium hydrogen carbonate (NH4HCO3) as porosification agent in varying particle size fractions and varying percentages in combination with β-tricalcium phosphate (β-TCP) material to manufacture tailored porous β-TCP scaffolds. In our study the pore sizes of the sintered material were comparable to the selected particle size fraction of the porosification agent. Porosities ranging between 71 and 78 vol.% were achieved. It was possible to control the volume percentage of porosity by using different weight ratios of NH4HCO3 and β-TCP. It can be concluded that ammonium hydrogen carbonate is an excellent porosification agent to design β-tricalcium phosphate scaffolds. This agent allows the independent setting of a specific pore size range as well as a specific volume percentage of porosity.