Densification of cancellous bone with autologous particles can enhance the primary stability of uncemented implants by increasing the interface friction coefficient.

Sufficient primary stability is one of the most important prerequisites for successful osseointegration of cementless implants. Bone grafts, densification and compaction methods have proven clinically successful, but the related effects and causes have not been systematically investigated. Postoperatively, the frictional properties of the bone-implant interface determine the amount of tolerable shear stress. Frictional properties of different implant surfaces have been widely studied. Less attention has been paid to the influence of host bone modifications. The purpose of this study was to investigate the influence of densification of cancellous bone with bone particles on the interface friction coefficient. Cancellous bone samples from femoral heads were densified with bone particles obtained during sample preparation. The densification was quantified using micro-Ct. Friction coefficients of the densified and paired native samples were determined. Densification increased the BV/TV in the first two millimeters of the bone samples by 10.5 ± 2.7% to 30.5 ± 2.7% (p < 0.001). The static friction coefficient was increased by 10.5 ± 6.1% to 0.43 ± 0.03. The static friction coefficient increased with higher BV/TV of the bone interface, which is represented by the top 2 mm of the bone. The increase in contact area, intertrabecular anchorage and particle bracing could be responsible for the increase in friction. Optimization of particle shape and size based on the patient's individual bone microstructure could further increase frictional resistance. Bone densification has the potential to improve the primary stability of uncemented implants.

Fatigue strength reduction of Ti-6Al-4V titanium alloy after contact with high-frequency cauterising instruments.

Contact of implants with high-frequency cauterising instruments has serious implications for patient safety. Studies have reported a possible direct connection of fatigue failure of Ti-6Al-4V implants with electrocautery contact. Such contacts were observed at the polished neck of titanium hip stems, which are subjected to high-tension loads. Evidence of electrocautery contact has also been found on a retrieved spinal fixator with a rough surface; however, no fatigue failure related to electrocautery contact has been reported thus far. The influence of the heat-affected zone caused by flashover on the mechanical behaviour of the Ti-6Al-4V titanium alloy is not yet fully understood. Then, the aim of this study was to investigate whether the polished areas of Ti-6Al-4V implants are especially susceptible to fatigue failure after electrocautery contact. Flashovers caused by electrocautery contact were induced on titanium specimens with different surface roughnesses. These specimens were subjected to cyclic loading in a four-point-bending test setup, which represented the stress resulting from physiological loading activities (~861 MPa). In this test setup, electrocautery contact was found to reduce the fatigue strength of the titanium alloy significantly-by up to 96%-as revealed from the median value of the cycles to failure. Cycles to failure showed a dependence on the flashover duration, with a flashover for 40 ms leading to fatigue fracture. Despite the lower fatigue strength of a rough polished surface in the undamaged state, it is less prone to the damaging effect of flashover than a smooth polished surface.

Redo procedures for degenerated stentless aortic xenografts and the role of valve-in-valve transcatheter techniques.

Objectives: This study evaluates reinterventions for degenerated stentless aortic xenografts. Methods: Between 2010 and 2015, 52 consecutive patients (age 72.3 ± 9.7 years, EuroSCORE II 11.1 ± 8.9%) underwent reintervention for failed stentless aortic valves (60% porcine, 40% pericardial, 87% sub-coronary, 81% isolated/combined regurgitation). Results: Based on age, EuroSCORE II, the presence of pulmonary hypertension, renal failure, a patent internal mammary artery graft and required concomitant procedures, the heart team assigned 25 patients to reoperation and 27 to valve-in-valve transcatheter aortic valve implantation (ViV-TAVI). Valve implantation was successful in all surgical (24% root replacement) and in 24 transcatheter cases (93% trans-femoral, 56% balloon-expandable). Procedural complications were aortic dissection ( n = 1) during reoperation and coronary obstruction ( n = 4), device malpositioning ( n = 3), deployment of >1 valve ( n = 2) and vascular access site complications ( n = 2) during ViV-TAVI. Thirty-day mortality (10%, three ViV-TAVI patients, two surgical patients, P = 1.0) was associated with preoperative renal failure, >1 concomitant procedure, life-threatening bleeding, coronary obstruction and necessity for prolonged circulatory support. ViV-TAVI was beneficial regarding ventilation time, transfusion requirements and the incidence of sepsis. Overall, functional (94% New York Heart Association Class I/II) and echocardiographic results (indexed effective orifice area 0.95 ± 0.27 cm 2 /m 2 , mean transvalvular gradient 14 ± 6.8 mmHg) were favourable. After ViV-TAVI, aortic regurgitation was mild and moderate in two and three patients. One-year survival was 82.3 ± 5.4% and similar after surgery (83.1 ± 7.7%) and ViV-TAVI (81.5 ± 7.5%, P = 0.76). Conclusions: Reinterventions for degenerated stentless aortic valves are challenging. Although ViV-TAVI is appropriate in high-risk patients, limitations and potential complications must be considered. Redo surgery has its place in low-risk patients and if concomitant procedures are required.

Metabolic response of Pseudomonas putida to increased NADH regeneration rates.

Pseudomonas putida efficiently utilizes many different carbon sources without the formation of byproducts even under conditions of stress. This implies a high degree of flexibility to cope with conditions that require a significantly altered distribution of carbon to either biomass or energy in the form of NADH. In the literature, co-feeding of the reduced C1 compound formate to Escherichia coli heterologously expressing the NAD+-dependent formate dehydrogenase of the yeast Candida boidinii was demonstrated to boost various NADH-demanding applications. Pseudomonas putida as emerging biotechnological workhorse is inherently equipped with an NAD+-dependent formate dehydrogenase encouraging us to investigate the use of formate and its effect on P. putida's metabolism. Hence, this study provides a detailed insight into the co-utilization of formate and glucose by P. putida. Our results show that the addition of formate leads to a high increase in the NADH regeneration rate resulting in a very high biomass yield on glucose. Metabolic flux analysis revealed a significant flux rerouting from catabolism to anabolism. These metabolic insights argue further for P. putida as a host for redox cofactor demanding bioprocesses.

A rapid method to estimate NADH regeneration rates in living cells.

We introduce a rapid whole cell assay for the estimation of NADH regeneration rates based on the fluorescent dye resazurin. A co-feed of formate and glucose, known to increase the intrinsic NADH regeneration rate of P. putida KT2440, was chosen as model system for the validation of this assay.

Tn7-Based Device for Calibrated Heterologous Gene Expression in Pseudomonas putida.

The soil bacterium Pseudomonas putida is increasingly attracting considerable interest as a platform for advanced metabolic engineering through synthetic biology approaches. However, genomic context, gene copy number, and transcription/translation interplay often introduce considerable uncertainty to the design of reliable genetic constructs. In this work, we have established a standardized heterologous expression device in which the promoter strength is the only variable; the remaining parameters of the flow have stable default values. To this end, we tailored a mini-Tn7 delivery transposon vector that inserts the constructs in a single genomic locus of P. putida's chromosome. This was then merged with a promoter insertion site, an unvarying translational coupler, and a downstream location for placing the gene(s) of interest under fixed assembly rules. This arrangement was exploited to benchmark a collection of synthetic promoters with low transcriptional noise in this bacterial host. Growth experiments and flow cytometry with single-copy promoter-GFP constructs revealed a robust, constitutive behavior of these promoters, whose strengths and properties could be faithfully compared. This standardized expression device significantly extends the repertoire of tools available for reliable metabolic engineering and other genetic enhancements of P. putida.