3D osteotomies-improved accuracy with patient-specific instruments (PSI).

PURPOSE: Three-dimensional (3D) printed patient-specific instruments (PSI) have been introduced to increase precision and simplify surgical procedures. Initial results in femoral and tibial osteotomies are promising, but validation studies on 3D planning, manufacturing of patient-specific cutting blocks and 3D evaluation of the attained results are lacking. METHODS: In this study, patient-specific cutting blocks and spacers were designed, fabricated, and used to perform a high tibial osteotomy (HTO). After segmentation of CT data sets from 13 human tibiae, 3D digital planning of the HTO was performed with a medial opening of 8 mm. These 3D models were used to fabricate patient-specific cutting blocks and spacers. After the surgical procedure, accuracy was evaluated measuring 3D joint angles and surface deviations. RESULTS: The lowest mean deviation was found to be 0.57° (SD ± 0.27) for the MPTA. Medial and lateral tibial slope deviated from the 3D planning by an average of 0.98° (SD ± 0.53) and 1.26° (SD ± 0.79), respectively, while tibial torsion deviated by an average of 5.74° (SD ± 3.24). Color analysis of surface deviations showed excellent and good agreement in 7 tibiae. CONCLUSION: With 3D cutting blocks and spacers, the 3D planning of the HTO can be translated into reality with small deviations of the resulting joint angles. Within this study, the results of the individual steps are examined for errors and thus a critical evaluation of this new and promising method for performing patient-specific HTOs is presented.

Reliability of 3D planning and simulations of medial open wedge high tibial osteotomies.

Purpose: In medial open-wedge high tibial osteotomy (HTO) hinge axis and osteotomy plane influence the resulting anatomy, but accurate angular quantifications using 3D-planning-simulations are lacking. The objectives of this study were developing a standardized and validated 3D-planning method of an HTO and to perform several simulated realignments to explain unintended anatomy changes. Methods: The cutting direction of the main osteotomy was defined parallel to the medial tibial slope and the hinge axis 1.5 cm distal to the lateral plateau. For interobserver testing, this 3D planning was performed on 13 digital models of human tibiae by two observers. In addition, four different hinge axis positions and five differently inclined osteotomy planes each were simulated. The osteotomy direction ranged from medial 0°-30° anteromedial, while the tilt of the osteotomy plane compared to the tibial plateau was -10° to +10°. All anatomic angular changes were calculated using 3D analysis. Results: Multiple HTO plannings by two medical investigators using standardized procedures showed only minimal differences. In the 3D-simulation, each 10° rotation of the hinge axis resulted in a 1.7° significant increase in slope. Tilting the osteotomy plane by 10° resulted in significant torsional changes of 2°, in addition to minor but significant changes in the medial proximal tibial angle (MPTA). Conclusion: Standardized 3D-planning of the HTO can be performed with high reliability using two-observer planning. 3D-simulations suggest that control of the osteotomy plane is highly relevant to avoid unintended changes in the resulting anatomy, but this can be a helpful tool to modify specific angles in different pathologies in the HTO.

How Formaldehyde Inhibits Hydrogen Evolution by [FeFe]-Hydrogenases: Determination by ¹³C ENDOR of Direct Fe-C Coordination and Order of Electron and Proton Transfers.

Formaldehyde (HCHO), a strong electrophile and a rapid and reversible inhibitor of hydrogen production by [FeFe]-hydrogenases, is used to identify the point in the catalytic cycle at which a highly reactive metal-hydrido species is formed. Investigations of the reaction of Chlamydomonas reinhardtii [FeFe]-hydrogenase with formaldehyde using pulsed-EPR techniques including electron-nuclear double resonance spectroscopy establish that formaldehyde binds close to the active site. Density functional theory calculations support an inhibited super-reduced state having a short Fe-(13)C bond in the 2Fe subsite. The adduct forms when HCHO is available to compete with H(+) transfer to a vacant, nucleophilic Fe site: had H(+) transfer already occurred, the reaction of HCHO with the Fe-hydrido species would lead to methanol, release of which is not detected. Instead, Fe-bound formaldehyde is a metal-hydrido mimic, a locked, inhibited form analogous to that in which two electrons and only one proton have transferred to the H-cluster. The results provide strong support for a mechanism in which the fastest pathway for H2 evolution involves two consecutive proton transfer steps to the H-cluster following transfer of a second electron to the active site.

Solar-driven proton and carbon dioxide reduction to fuels­lessons from metalloenzymes.

Metalloenzymes such as hydrogenases and carbon monoxide dehydrogenase can be attached to light-harvesting agents to produce informative photocatalytic systems of varying intricacy. Systematic studies yield important insight into mechanistic and design principles of artificial photosynthesis­one route to future renewable energy conversion, and the unconventional experiments reveal interesting new criteria for the catalytic performance of metals in biology. Recent advances are interpreted in terms of the importance of enzyme active centres that have evolved to perform fast and efficient catalysis using abundant elements, along with the ability of enzymes to trap photo-generated electrons by virtue of having receding, buried relay centres with low reorganisation energies.

Selective visible-light-driven CO2 reduction on a p-type dye-sensitized NiO photocathode.

We present a photocathode assembly for the visible-light-driven selective reduction of CO2 to CO at potentials below the thermodynamic equilibrium in the dark. The photoelectrode comprises a porous p-type semiconducting NiO electrode modified with the visible-light-responsive organic dye P1 and the reversible CO2 cycling enzyme carbon monoxide dehydrogenase. The direct electrochemistry of the enzymatic electrocatalyst on NiO shows that in the dark the electrocatalytic behavior is rectified toward CO oxidation, with the reactivity being governed by the carrier availability at the semiconductor-catalyst interface.

A multi-heme flavoenzyme as a solar conversion catalyst.

The enzyme flavocytochrome c3 (fcc3), which catalyzes hydrogenation across a C═C double bond (fumarate to succinate), is used to carry out the fuel-forming reaction in an artificial photosynthesis system. When immobilized on dye-sensitized TiO2 nanoparticles, fcc3 catalyzes visible-light-driven succinate production in aqueous suspension. Solar-to-chemical conversion using neutral water as the oxidant is achieved with a photoelectrochemical cell comprising an fcc3-modified indium tin oxide cathode linked to a cobalt phosphate-modified BiVO4 photoanode. The results reinforce new directions in the area of artificial photosynthesis, in particular for solar-energy-driven synthesis of organic chemicals and commodities, moving away from simple fuels as target molecules.

How light-harvesting semiconductors can alter the bias of reversible electrocatalysts in favor of H2 production and CO2 reduction.

The most efficient catalysts for solar fuel production should operate close to reversible potentials, yet possess a bias for the fuel-forming direction. Protein film electrochemical studies of Ni-containing carbon monoxide dehydrogenase and [NiFeSe]-hydrogenase, each a reversible electrocatalyst, show that the electronic state of the electrode strongly biases the direction of electrocatalysis of CO2/CO and H(+)/H2 interconversions. Attached to graphite electrodes, these enzymes show high activities for both oxidation and reduction, but there is a marked shift in bias, in favor of CO2 or H(+) reduction, when the respective enzymes are attached instead to n-type semiconductor electrodes constructed from CdS and TiO2 nanoparticles. This catalytic rectification effect can arise for a reversible electrocatalyst attached to a semiconductor electrode if the electrode transforms between semiconductor- and metallic-like behavior across the same narrow potential range (<0.25 V) that the electrocatalytic current switches between oxidation and reduction.

Visible light-induced hole injection into rectifying molecular wires anchored on Co3O4 and SiO2 nanoparticles.

Tight control of charge transport from a visible light sensitizer to a metal oxide nanoparticle catalyst for water oxidation is a critical requirement for developing efficient artificial photosynthetic systems. By utilizing covalently anchored molecular wires for hole transport from sensitizer to the oxide surface, the challenge of high rate and unidirectionality of the charge flow can be addressed. Functionalized hole conducting molecular wires of type p-oligo(phenylenevinylene) (3 aryl units, abbreviated PV3) with various anchoring groups for the covalent attachment to Co(3)O(4) catalyst nanoparticles were synthesized and two alternative methods for attachment to the oxide nanoparticle surface introduced. Covalent anchoring of intact PV3 molecules on Co(3)O(4) nanoparticles (and on SiO(2) nanoparticles for control purposes) was established by FT-Raman, FT-IR, and optical spectroscopy including observation, in some cases, of the vibrational signature of the anchored functionality. Direct monitoring of the kinetics of hole transfer from a visible light sensitizer in aqueous solution ([Ru(bpy)(3)](2+) (and derivatives) light absorber, [Co(NH(3))(5)Cl](2+) acceptor) to wire molecules on inert SiO(2)(12 nm) particles by nanosecond laser absorption spectroscopy revealed efficient, encounter controlled rates. For wire molecules anchored on Co(3)O(4) nanoparticles, the recovery of the reduced sensitizer at 470 nm indicated similarly efficient hole transfer to the attached PV3, yet no transient hole signal was detected at 600 nm. This implies hole injection from the anchored wire molecule into the Co(3)O(4) particle within 1 µs or shorter, indicating efficient charge transport from the visible light sensitizer to the oxide catalyst particle.