Enhanced bioactivity and interfacial bonding strength of Ti3Zr2Sn3Mo25Nb alloy through graded porosity and surface bioactivation

The gradient porous Ti3Zr2Sn3Mo25Nb(TLM)alloy rods were fabricated through sintering the alloyed powder to a solid core.The porous sample was then modified by a Micro Arc Oxidation(MAO)treatment in an electrolyte containing calcium and phosphate,a hydrothermal treatment enabled secondary microporous hydroxyapatite(HA)coating,and a further bone morphogenetic protein-2(BMP-2)loading treatment through immersion and freeze-drying.The treatment led to an orderly secondary microporous coating containing HA nano-particles and evenly distributed BMP-2 in the porous coatings.As a result,osteoblasts could adhere and grow well on the coatings with a high cell adhesion rate and cell functional activity.The in-situ shear testing indicated that the interfacial strength had been enhanced significantly.Improvement of the bond formation and osseointegration with the titanium implant is attributed to increased surface area for the cell to attach,creating voids for the cell to grow in,and activating titanium surface by introducing bioactive ingredients such as HA and BMP-2.

Cascade biocatalysis for production of enantiopure(S)-2-hydroxybutyric acid using recombinant Escherichia coli with a tunable multi-enzyme-coordinate expression system

Racemize 2-hydroxybutyric acid is usually synthesized by organic methods and needs additional deracemization to obtain optically pure enantiomers for industrial application.Here we present a cascade biocatalysis system in Escherichia coli BL21 which employed L-threonine deaminase(TD),NAD-dependent L-lactate dehydrogenase(LDH)and alcohol dehydrogenase(ADH)for producing optically pure(S)-2-hydroxybutyric acid((S)-2-HBA)from bulk chemical L-threonine.To solve the mismatch in the conversion rate and the consumption rate of intermediate 2-oxobutyric acid(2-OBA)formed in the multi-enzyme catalysis reaction,ribosome binding site regulation strategy was explored to control TD expression levels,achieving an eightfold alteration in the conversion rate of 2-OBA.With the optimized activity ratio of the three enzymes and using ADH for NADH regeneration,the recombinant strain ADH-r53 showed increased production of(S)-2-HBA with the highest titer of 129 g/L and molar yield of 93%within 24 h,which is approximately 1.65 times that of the highest yield reported so far.Moreover,(S)-2-HBA could easily be purified by distillation,making it have great potential for industrial application.Additionally,our results indicated that constructing a tunable multi-enzyme-coordinate expression system in single cell had great significance in biocatalysis of hydroxyl acids.