This is to certify that the thesis entitled "Synthesis and characterization of ultrafine hydroxyapatite (HAp) powder coating on stainless steel substrate by electrophoretic deposition" submitted by Deep K. In recent years, synthesis and characterization of ultrafine hydroxyapatite (HAp) powder coating on stainless steel substrate by electrophoretic deposition gives an active research area due to their improved applicability in the medical field. The HAp powder was deposited by electrophoretic deposition (EPD) using lead as anode and stainless steel substrate as cathode.
The powder was coated on the stainless steel substrate at 60 volts and the time varied from 15 minutes to 1.5 hours. From the XRD spectra, it was found that the XRD patterns of the HAp powder prepared by planetary milling, the HAp powder was deposited on a stainless steel substrate by EPD at 60 volts for 15 minutes. Here some of the HAp peaks in the coated substrate are visible along with the stainless steel peaks.
This is due to the presence of a large stainless steel top along with HAp. It was observed from SEM analysis that HAp deposited on stainless steel substrate after 1 hour shows smooth and good adhesion, whereas deposition at 1.5 hours shows discontinuous and non-adherent deposition. The coating thickness varies with applied condition such as time, voltage, time intervals, organic medium used, surfactants, coating area and sintering. In this project, these parameters have been varied to study the coating thickness and adhesion on 316 grade stainless steel.
It also presents a brief literature review of HAp coating on stainless steel substrate by EPD technique.
THEORY
- HYDROXYAPATITE (HAp)
- Medical uses
- Electrophoretic Deposition (EPD)
- Selection of 316L Stainless Steel Chemical Formula(316 SS)
Hydroxyapatite crystals are also found in the small calcifications (in the pineal gland and other structures) known as corpora arencea or 'brain sand'. HAp can be used to replace amputated bones and to promote bone growth in prosthetic implants. However, due to the degradation of most metals implanted in the human body, the clinically useful metals and alloys are very limited. However, clinical experience has shown that they are susceptible to localized corrosion in the human body, causing the release of metal ions into the tissues surrounding the implants.
The excellent biocompatibility and biostability of HAp coatings has become well established and the use of this material for prosthetic applications is rapidly gaining popularity in recent years (7). Another essential criterion is their deposition as coatings without the presence of non-stoichiometric phases of the powder. The aim of this work is to investigate the applicability of the electro-codeposition technique in the production of HAp/metal biomedical coatings.
In particular, this paper investigates the composition and microstructure of HAp/Ni composite coatings, discusses the growth process of the composite coating, and studies the influence of process conditions on the fraction of HAp in the fabricated composite coatings. In the first step, an electric field is applied between two electrodes and charged particles suspended in a suitable liquid move towards the oppositely charged electrode (electrophoresis). In the second step, the particles accumulate on the deposition electrode and create a relatively compact and homogeneous film (deposition).
The materials that are deposited are the major determinant of the actual processing conditions and equipment that can be used (9). Medical implants, including pins, screws and orthopedic implants such as total hip and knee replacement (10). 11) suggested that type 316L SS plays a key role in bone replacement surgery due to its excellent mechanical properties, availability at low cost, and ease of fabrication. Therefore, alternative methods for developing hydroxyapatite (HAp) coatings have been highlighted to impart corrosion resistance to the base metal and ensure biocompatibility of the ceramic on the metal surface.
This also could not match the implant at the host site due to the continuous interaction of the hostile environment with the implant and results in dissolution of both ceramic and metal. In this study, the effect of HNO3 treatments on 316L SS and the coatings on passivated 316L SS is investigated. Electrochemical studies involving cyclic anodic polarization experiments and impedance analysis in Ringer's solution were performed to determine the corrosion resistance of the coatings.
CHAPTER 2
LITERATURE REVIEW
The results also show that the operating conditions, such as temperature (T), pH, current density (D), have a remarkable effect on the composition of the fabricated HAp/Ni composite coatings. It is worth mentioning the somewhat toxic effect of nickel in the human body. Further work is to prepare HAp/Ti or HAp/Ti alloy composite coatings to investigate the reliability of the electro-co-deposition technique in the production of biomaterials for hard tissue replacement (8). 7) studied the preparation and characterization of electrophoretically deposited hydroxyapatite coatings on type 316L stainless steel and concluded that the optimal coating parameters for the electrophoretic deposition of HAp on type 316L SS were established at 60 V and 3 min.
XRD and SIMS studies confirm the presence of a stoichiomeric structure and the presence of Ca and P upon depth profiling of the HAp coatings. The OCP and degradation potentials of HAp-coated samples shifted to the nobler direction compared to the uncoated 316L SS. Marginal changes observed in the impedance parameters (|Z|, Rp and C) for the coated samples before and after polarization, indicating the stable nature of the coatings.
The different amount of colloidal silica slightly affects the quality of the mineral crystals formed in the new bone in vivo conditions. The stiffness of the newly formed bone in the implant with a lower amount of silica nanoparticles appears to be similar to the values of old cortex bone, showing short periods of maturation and mineralization of newly formed bone tissue around the implant. In both cases of the formation of HAp and brushite, 20–30 nm calcium phosphate aggregates in an amorphous state were formed at the early stage of the H2O2 electrolysis treatment and then rearranged.
The assemblies were transformed into ribbon-like flakes of HAp or brushite plaques, depending on the pH used. Unlike the SBF route where one uses only the inorganic components of body fluids, the current process mimics the philosophy of biomineralization, responsible for the highly sophisticated morphological features of bio-inorganic particles. -IR, EDXA and SEM analysis revealed the stoichiometric and microporous nature of the hydroxyapatite coatings.
The potentiodynamic polarization measurement and ICP-AES analysis show the protective nature of the HAp coatings on low carbon 316L SS and it also acts as a barrier to corrosion attack in simulated body fluid environment. The presence of HAp coatings over the passive layer plays a dual role of preventing the release of metal ions (making it more corrosion resistant) and making the metal surface more bioactive. Future work will be focused on characterizing the treated metal surface to find out surface changes that have occurred and to analyze the leaching of metal ions during polarization studies.
EXPERIMENTAL PROCEDURE
- Materials
- Electrophoretic deposition
The electrophoretic deposition process was performed at room temperature from a 1% suspension of HAp in isopropyl alcohol in a 100 mL glass beaker. A lead plate was used as the anode and the working electrode was used as the cathode. For better adhesion of HAp powders to the substrate, sintering of coated samples was performed at 8000C for 2 hours in open atmosphere.
RESULTS AND DISCUSSION
- X-ray diffraction (XRD) study
- Scanning electron microscopy (SEM) study
After the EPD process was completed, the samples were sintered at 800°C for 2 hours in an open atmosphere to ensure better adhesion of the particles to the substrate. It can be seen from the graph that HAp peaks are present after sintering, indicating that there is no degradation of HAp during sintering. When the application time is extended, a thick layer can form, which can cause cracks.
After sintering, there is a coarsening of the particles, but the adhesion of the coated layer is better. Due to the addition of a binder, adhesion is slightly increased than without a binder. In Fig. 12 we can see small HAp particles and a smooth coating layer, while in Fig. 13 the particles are buried after sintering and the smoothness disappears.
Even with the addition of a binder, the resulting coating did not achieve adequate bonding properties with the substrate. To measure the thickness of the HAp coating, cross-sections of the samples were studied by SEM.
Conclusions
Future work
