Bone regeneration of minipig mandibular defect by adipose derived mesenchymal stem cells seeded tri-calcium phosphate- poly(D,L-lactide-co-glycolide) scaffolds

Reconstruction of bone defects represents a serious issue for orthopaedic and maxillofacial surgeons, especially in extensive bone loss. Adipose-derived mesenchymal stem cells (ADSCs) with tri-calcium phosphates (TCP) are widely used for bone regeneration facilitating the formation of bone extracellular matrix to promote reparative osteogenesis. The present study assessed the potential of cell-scaffold constructs for the regeneration of extensive mandibular bone defects in a minipig model. Sixteen skeletally mature miniature pigs were divided into two groups: Control group and scaffolds seeded with osteogenic differentiated pADSCs (n=8/group). TCP-PLGA scaffolds with or without cells were integrated in the mandibular critical size defects and fixed by titanium osteosynthesis plates. After 12 weeks, ADSCs seeded scaffolds (n=7) demonstrated significantly higher bone volume (34.8%+/- 4.80%) than scaffolds implanted without cells (n=6, 22.4%+/- 9.85%) in the micro-CT (p < 0.05). Moreover, an increased amount of osteocalcin deposition was found in the test group in comparison to the control group (27.98 +/- 2.81% vs 17.10 +/- 3.57%, p < 0.001). In conclusion, ADSCs seeding on ceramic/polymer scaffolds improves bone regeneration in large mandibular defects. However, further improvement with regard to the osteogenic capacity is necessary to transfer this concept into clinical use

Damage accumulation in thin ruthenium films induced by repetitive exposure to femtosecond XUV pulses below the single shot ablation threshold

The process of damage accumulation in thin ruthenium films exposed to multiple femtosecond XUV free electron laser FEL pulses below the critical angle of reflectance at the Free electron LASer facility in Hamburg FLASH was experimentally analyzed. The multi shot damage threshold is found to be lower than single shot damage threshold. Detailed analysis of the damage morphology and its dependence on irradiation conditions justifies the assumption that cavitation induced by the FEL pulse is the prime mechanism responsible for multi shot damage in optical coating

Characterization of megahertz X ray laser beams by multishot desorption imprints in PMMA

Proper diagnostics of intense free electron laser FEL X ray pulses is indisputably important for experimental data analysis as well as for the protection of beamline optical elements. New challenges for beam diagnostic methods are introduced by modern FEL facilities capable of delivering powerful pulses at megahertz MHz repetition rates. In this paper, we report the first characterization of a defocused MHz 13.5 nm beam generated by the free electron laser in Hamburg FLASH using the method of multi pulse desorption imprints in poly methyl methacrylate PMMA . The beam fluence profile is reconstructed in a novel and highly accurate way that takes into account the nonlinear response of material removal to total dose delivered by multiple pulses. The algorithm is applied to experimental data of single shot ablation imprints and multi shot desorption imprints at both low 10 Hz and high 1 MHz repetition rates. Reconstructed response functions show a great agreement with the theoretical desorption response function mode

Experimental study of EUV mirror radiation damage resistance under long term free electron laser exposures below the single shot damage threshold

The durability of grazing and normal incidence optical coatings has been experimentally assessed under free electron laser irradiation at various numbers of pulses up to 16 million shots and various fluence levels below 10 of the single shot damage threshold. The experiment was performed at FLASH, the Free electron LASer in Hamburg, using 13.5 nm extreme UV EUV radiation with 100 fs pulse duration. Polycrystalline ruthenium and amorphous carbon 50 nm thin films on silicon substrates were tested at total external reflection angles of 20 and 10 grazing incidence, respectively. Mo Si periodical multilayer structures were tested in the Bragg reflection condition at 16 off normal angle of incidence. The exposed areas were analysed post mortem using differential contrast visible light microscopy, EUV reflectivity mapping and scanning X ray photoelectron spectroscopy. The analysis revealed that Ru and Mo Si coatings exposed to the highest dose and fluence level show a few per cent drop in their EUV reflectivity, which is explained by EUV induced oxidation of the surfac

Mechanism of single shot damage of Ru thin films irradiated by femtosecond extreme UV free electron laser

Ruthenium is a perspective material to be used for XUV mirrors at free electron laser facilities. Yet, it is still poorly studied in the context of ultrafast laser matter interaction. In this work, we present single shot damage studies of thin Ru films irradiated by femtosecond XUV free electron laser pulses at FLASH. Ex situ analysis of the damaged spots, performed by different types of microscopy, shows that the weakest detected damage is surface roughening. For higher fluences we observe ablation of Ru. Combined simulations using Monte Carlo code XCASCADE 3D and the two temperature model reveal that the damage mechanism is photomechanical spallation, similar to the case of irradiating the target with optical lasers. The analogy with the optical damage studies enables us to explain the observed damage morphologie

Role of heat accumulation in the multi-shot damage of silicon irradiated with femtosecond XUV pulses at a 1 MHz repetition rate

The role played by heat accumulation in multi-shot damage of silicon was studied. Bulk silicon samples were exposed to intense XUV monochromatic radiation of a 13.5 nm wavelength in a series of 400 femtosecond pulses, repeated with a 1 MHz rate (pulse trains) at the FLASH facility in Hamburg. The observed surface morphological and structural modifications are formed as a result of sample surface melting. Modifications are threshold dependent on the mean fluence of the incident pulse train, with all threshold values in the range of approximately 36-40 mJ/cm². Experimental data is supported by a theoretical model described by the heat diffusion equation. The threshold for reaching the melting temperature (45 mJ/cm²) and liquid state (54 mJ/cm²), estimated from this model, is in accordance with experimental values within measurement error. The model indicates a significant role of heat accumulation in surface modification processes