Ti-30Nb-3Ag alloy with improved corrosion resistance and antibacterial properties for orthopedic and dental applications produced by mechanical alloying.

Titanium alloys have gained popularity as a bioimplant material due to their biocompatibility, low modulus of elasticity, and increased strength. However, other issues, such as corrosion resistance, and infections can reduce the implant's lifespan. This paper aims to fabricate a new Ti-30Nb-3Ag at% alloy with enhanced in vitro corrosion and antibacterial properties by mechanical alloying (MA) followed by powder consolidation. XRD, SEM/EDX, and Vickers microhardness analyses were used to examine the phases compositions, microstructure, and microhardness, respectively. The in vitro corrosion performance of Ti-30Nb-3Ag alloy was inspected in a simulated body medium and artificial saliva. The alloy's antibacterial properties were evaluated in the gram-positive and negative bacterial medium. The results showed that after MA for 60 h, nanocrystalline ß-Ti (BCC) and α-Ti (HCP) solid solutions were formed with crystallite sizes of 7.44 and 3.47 nm, respectively. The sintered sample exhibited densifications of 97%, with a microstructure composed of ß-Ti, α-Ti, and a minor quantity of ultrafine Ti2Ag phase. The microhardness result showed that Ti-30Nb-3Ag alloy possesses HV 491.5. Ti-30Nb-3Ag alloy has a potent antibacterial capability of 85.75% and 88.81% relative to Ti-6Al-4V alloy and CP-Ti, respectively. In vitro corrosion results revealed that the Ti-30Nb-3Ag alloy exhibited the widespread passive area in the investigated anodic regions and presented the highest impedance values in comparison with the commercial alloys, confirming its improved corrosion resistance performance in both studied mediums. Ti-30Nb-3Ag alloy possibly be a competitive bioimplant material for orthopedic and dental uses owing to its enhanced biocorrosion and antibacterial properties compared to commercial Ti-6Al-4V alloy and CP-Ti.

Transgranular liquation cracking of grains in the semi-solid state.

Grain refinement via semi-solid deformation is desired to obtain superior mechanical properties of cast components. Using quantitative in situ synchrotron X-ray tomographic microscopy, we show an additional mechanism for the reduction of grain size, via liquation assisted transgranular cracking of semi-solid globular microstructures. Here we perform localized indentation of Al-15wt.%Cu globular microstructures, with an average grain size of ∼480 µm, at 555 °C (74% solid fraction). Although transgranular fracture has been observed in brittle materials, our results show transgranular fracture can also occur in metallic alloys in semi-solid state. This transgranular liquation cracking (TLC) occurs at very low contact stresses (between 1.1 and 38 MPa). With increasing strain, TLC continues to refine the size of the microstructure until the grain distribution reaches log-normal packing. The results demonstrate that this refinement, previously attributed to fragmentation of secondary arms by melt-shearing, is also controlled by an additional TLC mechanism.

Cardiac and intestinal contractions under the influence of triturated drug dilutions.

Triturated dilutions of acetylcholine and adrenaline are found to produce reverse effects than their parent one on the mechanical performance of mammalian heart and intestine in vitro. However, there is a variation in the magnitude of reverse response observed for both the tissues. It is concluded that variation in the effect of triturated dilutions is probably due to handling and shaking of the diluted drug before use in experiments. In addition, no relation exists between degree of dilution and the magnitude of response for both the tissues.

Effect of short term immobilization on mechanical characteristics of skeletal muscle in uromastix.

Gastrocnemius muscles of Uromastix were used to observe the effects of short term (7 days) immobilization in flexed position. Results demonstrated significantly (P < 0.01) lesser magnitude as well as rate of rise in isometric twitch and tetanic tensions with insignificantly different twitch/tetanus ratio in the immobilized muscles. Both the twitch and tetanus also demonstrated significantly (P<0.01) higher twitch half relaxation and twitch/tetanus half relaxation time ratio. While, immobilized muscles showed insignificantly higher twitch contraction, tetanus half relaxation and duration of active state as well as peak twitch duration, than control ones. These changes in the mechanical contraction parameters were not found to be associated with changes in weight, resting, stretched and shortened length of the immobilized muscles. A comparison of present results with previous work performed on skeletal muscles of Uromastix at longer period (20 days) of immobilization has suggested that Uromastix muscles are no prone to a significant immobilization atrophy. However, decreased mechanical response after immobilization irrespective of the period of immobilization in Uromastix muscles is probably due to a depletion in various substrates involved in muscle mechanics.

Seasonal variations in the contractile behaviour of gastrocnemius muscles of Uromastix hardwickii.

Seasonal variations in the isometric activity of the isolated gastrocnemius muscle of Uromastix hardwickii was studied from winter to summer in Karachi, Pakistan. A constant 20 degrees C temperature was maintained during experimentation to avoid influence of this factor on seasonal changes. The twitch and tetanic tensions recorded at resting lengths showed a significant rise from winter to summer (p less than 0.0005) with a greater effect on tetanic tensions. The rate of rise of tensions also showed a significant elevation (p less than 0.0005) from winter to summer, while the duration of active state decreased by 66% during spring and summer. The results are discussed in terms of speed of summation of active state, cross bridge interaction, and characteristic expression of gastrocnemius muscle morphology on its mechanical behaviour from winter to summer.

Effect of temperature on the maximum rate of rise of tension in denervated rat diaphragm muscle.

Effects of chronic denervation and temperature were studied on the maximum rate of rise of tension in isometric twitch and tetanus of rat diaphragm muscles. The muscles were denervated for 15-20 days and the maximum rate of rise of tension was measured according to Hill (1951). The results showed that the maximum rate of rise of tension in twitch and tetanus was temperature dependent, exponentially increasing with increasing temperatures in both the normal and denervated muscles. A further observation was that the maximum rate of rise of tension in denervated muscle was always smaller than normal controls. It is suggested that probable changes in the series elasticity and duration of active state in the denervated muscle are responsible for the observed changes.

Effect of hypothermia on the twitch and tetanic contractions of denervated rat diaphragm muscle under isotonic conditions.

Effect of hypothermia was studied on the twitch and tetanic contractions of the chronically denervated rat diaphragm muscles under isotonic conditions. The muscles were denervated for 15-20 days and the temperature was lowered from 35 degrees C to 15 degrees C. The results showed that hypothermia and chronic denervation had very little effect on the isotonic contraction parameters since these were found to be unaltered at all temperatures except at 15 degrees C. It is suggested that denervation has no significant effect on the contractile component of our experimental muscles.