Browsing by Author "Deep, Shankar"

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    Improvement in the Properties of Thermally Sprayed Hydroxyapatite Coating Reinforced with Carbon Nanotube for Orthopaedic Applications
    (National Institute Of Technology Karnataka, Surathkal., 2024) Deep, Shankar; Jambagi, Sudhakar C
    Aseptic loosening is responsible for ~21.9% of Total Knee Arthroplasty (TKA) failures in Germany, while non-hemocompatibility accounts for ~ 31% of medical device failures in the US, often resulting in expensive and painful revision surgery. Although hydroxyapatite (HA) has been used to provide a bioactive coating to titanium implants, its mechanical strength is limited and tends to phase changes at high temperatures, contributing to implant failure. This study firstly examines the physiochemical properties and blood compatibility of bioactive powders ((0.5−2 wt % carbon nanotube (CNT)/alumina)-20 wt %)) produced through a heterocoagulation colloidal technique followed by ball milling HA. Heterocoagulated powder with 2wt% CNT (HAC2) showed a dispersion index of 1.20, indicating the uniform and homogenous dispersion of CNT in the matrix. The 1wt.% CNT (HAC1) composite demonstrated a surface charge ~5 times higher than HA at pH 7.4, with a value of -11 mV compared to -2 mV. This increase in electrostatic charge is desirable for achieving hemocompatibility, as evidenced by a range of blood compatibility assessments. The HAC1 powder exhibited hemolysis ranging from 2-7%, and the blood clot investigation indicated its nonthrombogenecity with no platelet activation, suggesting the excellent hemocompatibility for HAC1 powder than others, thereby attesting to the non-toxicity of CNTs when introduced to human blood. The next step is identifying the most suitable thermal spray process for spraying the powders. For this purpose, we aimed to investigate the relative efficacy of three thermal spray processes of different temperature ranges: Atmospheric plasma spray (APS) (high temperature), Flame spray (FS) (moderate temperature), and High-Velocity Oxy-Fuel spray (HVOF) (low temperature), and study their impact on HA coating's surface properties, affecting blood components and implant's strength. The crystallinity of the HA coating increased by 32 % with a decrease in the operating temperature (APS < FS < HVOF). HVOF coating exhibited a ~ 34 % and ~ 120 % improvement in adhesion strength and ~ 31 % and 59 % increment in hardness compared to APS and FS coating, respectively, attributed to its low porosity, low coating thickness (~55 μm), and high degree of crystallinity. The HVOF coating displayed good apatite growth, non-hemolytic, and nonthrombogenicity with no platelet activation owing to its low processing temperature, high degree of crystallinity (89.7%), hydrophilicity, smooth (~4 μm) and dense (~97%) microstructural properties. Finally, the powder with excellent hemocompatibility, i.e., HAC1 powder, was sprayed onto titanium implants with the HVOF spray (best thermal spray) and assessed for the implant’s durability, longevity, and biocompatibility. HAC1 coating improved adhesion strength by ~120%, hardness by ~45%, wear resistance by ~32%, and ~17% under simulated body fluid (SBF) and dry environments, respectively than HA coating, attributed to the retention and uniform distribution of CNT obtained by heterocoagulation and the use of low temperature. HAC1 coating showed 52% more apatite growth than HA after 30 days and displayed exceptional non-hemolytic behavior (~0.2%). Furthermore, the platelet adhered to the HAC1 coating was ~2.8 times lower than the negative control, attributed to its hydrophilicity (~88º), dense microstructure (97.2%), and surface charge (-11 mV), indicating its excellent hemocompatibility. Ultimately, an in-vivo study revealed encouraging results for HAC1 implants implanted in rabbits. The HAC1 implants showed an improvement of ~11.4% in the histological values, as seen from the microscopic images of the implantation sites. Thus, HVOF HAC1 coating could be a promising material for orthopedic applications intended for human use due to its enhanced mechanical integrity, tribological resistance, and biocompatibility.