Asymptotically correct shell model for nuclear fission

A two-center shell model with oscillator potentials, l→·s→ forces, and l→2 terms is developed. The shell structures of the original spherical nucleus and those of the final fragments are reproduced. For small separation of the two centers the level structure resembles the Nilsson scheme. This two-center shell model might be of importance in problems of nuclear fission

Investigation of the mechanical and chemical characteristics of nanotubular and nano-pitted anodic films on grade 2 titanium dental implant materials

Abstract Objective The objective of this study was to investigate the reproducibility, mechanical integrity, surface characteristics and corrosion behavior of nanotubular (NT) titanium oxide arrays in comparison with a novel nano-pitted (NP) anodic film. Methods Surface treatment processes were developed to grow homogenous NT and NP anodic films on the surface of grade 2 titanium discs and dental implants. The effect of process parameters on the surface characteristics and reproducibility of the anodic films was investigated and optimized. The mechanical integrity of the NT and NP anodic films were investigated by scanning electron microscopy, surface roughness measurement, scratch resistance and screwing tests, while the chemical and physicochemical properties were investigated in corrosion tests, contact angle measurement and X-ray photoelectron spectroscopy (XPS). Results and discussion The growth of NT anodic films was highly affected by process parameters, especially by temperature, and they were apt to corrosion and exfoliation. In contrast, the anodic growth of NP film showed high reproducibility even on the surface of 3-dimensional screw dental implants and they did not show signs of corrosion and exfoliation. The underlying reason of the difference in the tendency for exfoliation of the NT and NP anodic films is unclear; however the XPS analysis revealed fluorine dopants in a magnitude larger concentration on NT anodic film than on NP surface, which was identified as a possible causative. Concerning other surface characteristics that are supposed to affect the biological behavior of titanium implants, surface roughness values were found to be similar, whereas considerable differences were revealed in the wettability of the NT and NP anodic films. Conclusion Our findings suggest that the applicability of NT anodic films on the surface of titanium bone implants may be limited because of mechanical considerations. In contrast, it is worth to consider the applicability of nano-pitted anodic films over nanotubular arrays for the enhancement of the biological properties of titanium implants

Increased pore size of scaffolds improves coating efficiency with sulfated hyaluronan and mineralization capacity of osteoblasts

Background: Delayed bone regeneration of fractures in osteoporosis patients or of critical-size bone defects after tumor resection are a major medical and socio-economic challenge. Therefore, the development of more effective and osteoinductive biomaterials is crucial. Methods: We examined the osteogenic potential of macroporous scaffolds with varying pore sizes after biofunctionalization with a collagen/high-sulfated hyaluronan (sHA3) coating in vitro. The three-dimensional scaffolds were made up from a biodegradable three-armed lactic acid-based macromer (TriLA) by cross-polymerization. Templating with solid lipid particles that melt during fabrication generates a continuous pore network. Human mesenchymal stem cells (hMSC) cultivated on the functionalized scaffolds in vitro were investigated for cell viability, production of alkaline phosphatase (ALP) and bone matrix formation. Statistical analysis was performed using student's t-test or two-way ANOVA. Results: We succeeded in generating scaffolds that feature a significantly higher average pore size and a broader distribution of individual pore sizes (HiPo) by modifying composition and relative amount of lipid particles, macromer concentration and temperature for cross-polymerization during scaffold fabrication. Overall porosity was retained, while the scaffolds showed a 25% decrease in compressive modulus compared to the initial TriLA scaffolds with a lower pore size (LoPo). These HiPo scaffolds were more readily coated as shown by higher amounts of immobilized collagen (+ 44%) and sHA3 (+ 25%) compared to LoPo scaffolds. In vitro, culture of hMSCs on collagen and/or sHA3-coated HiPo scaffolds demonstrated unaltered cell viability. Furthermore, the production of ALP, an early marker of osteogenesis (+ 3-fold), and formation of new bone matrix (+ 2.5-fold) was enhanced by the functionalization with sHA3 of both scaffold types. Nevertheless, effects were more pronounced on HiPo scaffolds about 112%. Conclusion: In summary, we showed that the improvement of scaffold pore sizes enhanced the coating efficiency with collagen and sHA3, which had a significant positive effect on bone formation markers, underlining the promise of using this material approach for in vivo studies. © 2019 The Author(s)

Comparison of microfocus- and synchrotron x-ray tomography for the analysis of osteointgration around Ti6Al4V implants

Micro-computed tomography (µCT) provides quantitative three-dimensional information of bone around titanium implants similar to classical histology. The study, based on an animal model, using cuboid-shaped biofunctionalised Ti6Al4V implants with surrounding bone after 4 weeks, is performed using 3 µCT-systems with X-ray tubes, one synchrotron-radiation-based µCT-system (SRµCT), and classical histology. Although the spatial resolution of the µCTsystems is comparable, only the results of SRµCT agree with results of classical histology. The X-ray tube sources give rise to huge artefacts in the tomograms (interface scattering, beam hardening), which impaired the quantitative analysis of bone up to about 200 µm from the implant surface. Due to the non-destructive character of µCT the specimens can be subsequently examined by classical histology without restriction. The quantitative comparison of bone formation uncovers the strong dependence of the detected amount of newly formed bone from the selected slice. This implies the necessity of 3D analysis. SRµCT and classical histology prove that surface modifications of the titanium implant significantly influence the bone formation

Investigation of the Peptide Adsorption on ZrO₂, TiZr, and TiO₂ Surfaces as a Method for Surface Modification

Specific surface binding peptides offer a versatile and interesting possibility for the development of biocompatible implant materials. Therefore, eight peptide sequences were examined in regard to their adsorption on zirconium oxide (ZrO₂), titanium zircon (TiZr), and titanium (c.p. Ti). Surface plasmon resonance (SPR) measurements were performed on Ti coated sensor chips to determine the kinetics of the interactions and kinetic rate constants (<i>k</i>_on, <i>k</i>_off, <i>K</i>_D, and <i>R</i>_max). We also investigated the interactions which are present in our system. Electrostatic and coordinative interactions were found to play a major role in the adsorption process. Four of the eight examined peptide sequences showed a significant adsorption on all investigated materials. Moreover, the two peptides with the highest adsorption could be quantified (up to 370 pmol/cm²). For potential biomaterials applications, we proved the stability of the adsorption of selected peptides in cell culture media, under competition with proteins and at body temperature (37 °C), and their biocompatibility via their effects on the adhesion and proliferation of human mesenchymal stem cells (hMSCs). The results qualify the peptides as anchor peptides for the biofunctionalization of implants

Biological nano-functionalization of titanium-based biomaterial surfaces: a flexible toolbox

Surface functionalization with bioactive molecules (BAMs) on a nanometre scale is a main field in current biomaterial research. The immobilization of a vast number of substances and molecules, ranging from inorganic calcium phosphate phases up to peptides and proteins, has been investigated throughout recent decades. However, in vitro and in vivo results are heterogeneous. This may be at least partially attributed to the limits of the applied immobilization methods. Therefore, this paper highlights, in the first part, advantages and limits of the currently applied methods for the biological nano-functionalization of titanium-based biomaterial surfaces. The second part describes a new immobilization system recently developed in our groups. It uses the nanomechanical fixation of at least partially single-stranded nucleic acids (NAs) into an anodic titanium oxide layer as an immobilization principle and their hybridization ability for the functionalization of the surface with BAMs conjugated to the respective complementary NA strands

Sulfation degree not origin of chondroitin sulfate derivatives modulates keratinocyte response

Chondroitin sulfate (CS) sulfation-dependently binds transforming growth factor-β1 (TGF-β1) and chronic wounds often accompany with epidermal hyperproliferation due to downregulated TGF‐β signaling. However, the impact of CS on keratinocytes is unknown. Especially biotechnological-chemical strategies are promising to replace animal-derived CS. Thus, this study aims to evaluate the effects of CS derivatives on the interaction with vascular endothelial growth factor-A (VEGF-A) and on keratinocyte response. Over-sulfated CS (sCS3) interacts stronger with VEGF-A than CS. Furthermore, collagen coatings with CS variants are prepared by in vitro fibrillogenesis. Stability analyses demonstrate that collagen is firmly integrated, while the fibril diameters decrease with increasing sulfation degree. CS variants sulfation-dependently decelerate keratinocyte (HaCaT) migration and proliferation in a scratch assay. HaCaT cultured on sCS3-containing coatings produced increased amounts of solute active TGF-β1 which could be translated into biomaterials able to decrease epidermal hyperproliferation in chronic wounds. Overall, semi-synthetic and natural CS yield to comparable response

Sodium alendronate loaded poly(L-lactide-co-glycolide) microparticles immobilized on ceramic scaffolds for local treatment of bone defects

Bone tissue regeneration in critical-size defects is possible after implantation of a three-dimensional scaffold and can be additionally enhanced once the scaffold is enriched with drugs or other factors supporting bone remodelling and healing. Sodium alendronate (Aln), a widely used anti-osteoporosis drug, exhibits strong inhibitory effect on bone resorption performed by osteoclasts. Thus we propose a new approach for the treatment of bone defects in craniofacial region combining biocompatible titanium dioxide (TiO2) scaffolds and poly(L-lactide-co-glycolide) (PLGA) microparticles (MPs) loaded with Aln. The MPs were effectively immobilized on the surface of the scaffolds’ pore walls by human recombinant collagen. Drug release from the scaffolds was characterised by initial burst (24 ± 6% of the drug released within first 24 h) followed by a sustained release phase (on average 5 µg of Aln released per day from day 3 to day 18). In vitro tests showed that Aln in concentrations of 5 µg/mL and 2.5 µg/mL was not cytotoxic for MG-63 osteoblast-like cells (viability between 81 ± 6% to 98 ± 3% of control) but it prevented RANKL-induced formation of osteoclast-like cells from macrophages derived from peripheral blood mononuclear cells (PBMCs), as shown by reduced fusion capability and decreased TRAP 5b activity (56 ± 5% reduction in comparison control after 8 days of culture). Results show that it is feasible to design the scaffolds providing required doses of Aln inhibiting osteoclastogenesis, reducing osteoclast activity, but not affecting osteoblast functions, which may be beneficial in the treatment of critical-size bone tissue defects