Capabilities of Powder-Mixed EDM using Carbon Nanotubes for Biomedical Application

5. Devgan

Khalsa College of Engineering & Technology

5.5. Sidhu

Beant College of Engineering &Technology

A. Mahajan

Khalsa College of Engineering & Technology


The demand for precise fabrication processes in the biomedical domain is increasing due to the exponential rise in total joint replacements or surgeries related to human anatomy (Sheikh et al. 2017). The high precision and geometric accuracy are the primary necessities for the effective functionality of implantations. However, stress shielding, poor adhesion, metallic ion toxicity, high corrosion, and excessive wear are some possible causes of failure in metallic implants (Maleki-Ghaleh et al. 2015). An unavoidable difference in implant and bone modulus leads to a stress shielding effect. Thus, wear debris is created at the implant-bone interface, resulting in implant loosening (Mahajan et al. 2019a, b). So, the low coefficient of friction along with hard and good wear-resistant surface resists the malfunctioning of the healthy bones (Nasab et al. 2010).

Similarly, the implant materials should have anticorrosion properties to reduce the undesirable release of metallic ions in the body (Devgan and Sidhu 2020a). The excessive corrosion on the implant surface generates the regular demolition of a material due to a lack of chemical inertness. However, material degradation leads to the undesirable release of metallic ions in blood, biofluids, and variant systems of the body (Devgan and Sidhu 2019b). So the implants’ surface should be designed with suitable biological, physicochemical, and tribological properties.

The long-term sustainability of implants is equally linked to the surface morphological properties such as roughness, surface energy, and porosity (Burstein and Pistorius 1995). However, more roughness and higher porosity lead to an increase in surface free energy, which promotes the cell growth and proliferation (Rupp et al. 2006). Nano-shaped morphology imitates the structures of extracellular matrix (ECM) proteins and osteoblastic cells, resulting in better cellular attachment and its proliferation (Das et al. 2008). Although the nano-roughness influences the cellular activities of matching parts since the ECM proteins or collagen fibrils of human bones are composed of nano-sized organics (Fratzl et al. 2004). Figure 6.1 represents the macro-, micro-, and nano-level topology of the implant-bone interface.

Recently, carbon nanotubes (CNTs) are potentially utilized for biomedical applications due to their unique properties (Dresselhaus et al. 1996). CNTs consist of cylinders of graphite along with carbon atoms in the hexagonal arrangement (Ichkitidze et al. 2016). CNTs exhibit unique properties such as favorable weight-to-strength ratio and high Young’s modulus (1 TPa). Thus, CNTs are utilized for enhancing the mechanical properties of the substrate (Wang et al. 2008). CNT also has excellent physical features such as unique wetting behavior, high surface energy, and the ability to imitate dimensional similarities of body proteins that promote the bone growth properties (Hussain et al. 2014). These nanomaterials also have anticorrosion properties for sustaining the chemical inertness of coatings (Al-Jumaili et al. 2017).

The powder mixed-electrical discharge machining (PM-EDM) has capabilities to form a recast layer of desired properties and emerged as a novel technique in the field of surface modification (Sidhu et al. 2014). PM-EDM generates the integral nano-textured, hard wear-resistant layer, which resists the implant from corrosion and promotes bioactivity (Devgan and Sidhu 2020b). However, the layer produced by PM-EDM is of superior surface integrity, which escalates the bone in growth (Mahajan and Sidhu 2019a, b).

Figure 6.2 illustrates the working mechanism of the PM-EDM process. During machining, a series of electrical sparks is produced between the workpiece and the tool electrode, which provides a high-temperature heating zone (Sidhu and Bains 2017). The targeted workpiece, along with a small fraction of electrode, was melted in the presence of dielectric medium (Devgan and Sidhu 2019b). The heat-affected area forms the plasma channel by uniting the partial content of the workpiece with the constituents of dielectric medium (Bhui et al. 2018). This phenomenon leads to material and phase transformation of the recast layer. Thus, it results in a change in surface integrity and chemical composition of the substrate surface (Bains et al. 2016).

The macro-, micro-, and nano-level topology of implant-bone interface representing the osteogenic cell growth at nano-textured surface

FIGURE 6.1 The macro-, micro-, and nano-level topology of implant-bone interface representing the osteogenic cell growth at nano-textured surface.

Therefore, PM-EDM is employed in this study by utilizing multiwalled carbon nanotubes (MWCNTs) in the dielectric medium. The MWCNTs have extraordinary properties for tailoring the surface integrity of the implant surface. MWCNTs also act as a prominent candidate for increasing the biocompatibility of treated surfaces. In this class, PM-EDM was performed by employing MWCNTs on the P-titanium alloy. This study aimed to scrutinize the PM-EDM processing abilities for attaining the desired surface integrity. The comparison between untreated, deionized water- treated, and MWCNT-treated substrates is scrutinized in terms of bioactivity and surface integrity.

Schematic arrangement of PM-EDM

FIGURE 6.2 Schematic arrangement of PM-EDM.

Material and Method Used

The (3-type titanium alloy (composition (wt.%); Ti: 53%, Nb: 35%, Та: 7%, Zr: 5%, O: 0.08%) is used for investigation. To investigate the effectiveness of the powder-mixed treatment, experiments were conducted by incorporating two different dielectric mediums, i.e., deionized water and deionized water + MWCNTs. The MWCNTs with a diameter of 10-20 nm and a length of 3-8 pm were procured with 99.9% purity. The dielectric medium has a powder concentration of 5g/L of deionized water. The graphite (grained ~ 5 pm) was used as a tool electrode material. The experiments were executed on EDM (Model: SZNC-35-5030) at different values of current and pulse on-time and pulse off-time at a predetermined gap of 140 V.

Biocompatibility Testing (In Vitro Hemolysis Test)

The in vitro hemolysis test was carried out to scrutinize the biological performance of the treated and untreated samples. Experimentation was executed in triplicate. Autoclaving was carried out at 121°C for 20min by moist heat sterilization method for the extinction of unwanted entities from the specimens. First, the healthy human blood was extracted in microtubes, and RBCs were separated by centrifuging the blood for 5 min at 2500rpm at 4°C. The supernatant plasma content and the buffy layer of leukocytes were removed. The dense RBC pellet was obtained by rinsing the supernatant thrice with phosphate-buffered saline (PBS). For the hemolysis, the 1%

RBC suspension was poured on the surface of samples. For the two reference values, Triton XTM-100 was considered a positive control because it can create complete hemolysis. The PBS was utilized as negative control because it has negligible hemolytic properties. Further, the well plate (dish) containing samples were incubated for 1 hour at 37°C. The RBC lysis was carried out in 12-well plates (dishes) in incubator. Hemolytic RBC suspensions from each sample were collected in microcentrifuge tubes. Further, the tubes were centrifuged at 4°C with 2500 rpm for 5 minutes. The absorbance of the supernatant portion was calculated by the spectrophotometric technique at 540 nm. The % hemolysis of each sample was calculated, which is shown in the following equation:

where Abp is the absorbance value of the positive control sample and Abs is the absorbance value of the tested surface.

Surface Morphological Analysis

The surface morphology is one of the crucial aspects to investigate the processing capabilities of PM-EDM. The surface morphology of the substrates was examined under field emission scanning electron microscopy (FE-SEM) (ZEISS SIGMA VP). The elemental composition of treated substrates was examined using energy- dispersive X-ray spectroscopy (EDX) analysis. The phase compositions were investigated through XRD (XRD-7000 Series, Shimadzu Corporation, Japan) using Cu-Ka X-ray radiation.

Results and Discussion

In Vitro Hemolysis Test Results

The biological outcomes of each sample were scrutinized by calculating the absorbance of each sample. The absorbance values were measured thrice for each sample, as listed in Table 6.1. Figure 6.3 presents the percentage of hemolysis of all treated and untreated samples. Triton XTM-100 exhibited the 100% hemolysis, and isotonic PBS was observed with 3.39% ± 0.42% hemolysis. The untreated surface affirmed the % hemolysis of 39.84 ± 1.50. However, MWCNT-treated surface was considered as least hemolytic among all samples. The % hemolysis of the MWCNT-treated sample was calculated as 9.05 ± 3.56, whereas the water-treated surface exhibited a considerable difference to the best value of outcomes. However, % hemolysis of the water-treated sample (i.e., 27.19% + 2.72%) was twofold higher in comparison with MWCNT-treated substrate (i.e., 9.02%). Similar results were also seen in RBCs’ images of all surfaces, as shown in Figure 6.4. MWCNT- treated surface showed the retention of the circular-shaped RBCs, which affirmed that no hemolysis occurs at the surface. The untreated surface had hemolyzed cells and the cells with busted boundaries; however, some clumped cells were seen on the water-treated surface.


Absorbance Values and Percentage Hemolysis of Different Samples


Attempt (N) = 1

Attempt (N) = 2

Attempt (N) = 3

% Hemolysis Avg + S.D.


% Hemolysis


% Hemolysis


% Hemolysis

PBS (negative control)







3.39 ±0.42

Triton (positive control)








Untreated surface







39.846 ± 1.50

Water treated







27.19 + 2.72

MWCNTs’ surface







9.054 ± 3.56

Hemolysis percentage of different samples

FIGURE 6.3 Hemolysis percentage of different samples.

RBCs’ morphology of (a) MWCNT-treated, (b) water-treated, and (c) untreated

FIGURE 6.4 RBCs’ morphology of (a) MWCNT-treated, (b) water-treated, and (c) untreated


Surface morphology of (a) MWCNT-treated, (b) water-treated, and (c) untreated substrates

FIGURE 6.5 Surface morphology of (a) MWCNT-treated, (b) water-treated, and (c) untreated substrates.

Surface Morphological Analysis

The surface morphological analysis of the substrates was carried out using FE-SEM. Figure 6.5a-c illustrates the surface morphology of MWCNT-coated, water- treated, and untreated surfaces, respectively. Figure 6.5a shows the microstructure of MWCNT-treated surface, which demonstrates the best surface integrity for bioimplants. The MWCNT surface exhibited a well-patterned structure with

XRD of (a) untreated and (b) water-treated surfaces

FIGURE 6.6 XRD of (a) untreated and (b) water-treated surfaces.

pores’ surface. This was due to the conductive properties of MWCNTs present in the dielectric medium. The MWCNT powder generates a homogeneous heat flux zone that enlarges the surface area of the plasma. The swelling of the plasma channel leads to the proper circulation of spark heat. This phenomenon diminishes the thermal shocks and facilitates the adequate liberation of heat. Thus, it develops the uniform recast layer without any blowholes and microcracks. The surface morphological analysis of water-treated substrate shows some surface irregularities such as voids, pockmarks, and ridges of redeposited material (Figure 6.5b). Also, the water- treated substrate affirms some extent of microcracks and uneven residues of molten metal (Figure 6.5c). Therefore, the PM-EDM generates an efficient surface integrity, which stimulates the cellular activities and demonstrates an excellent tissue- material interaction.

The XRD results of untreated alloy and MWCNT-treated surface are presented in Figure 6.6a-b. The results of the untreated surface affirmed the base metal constituents of alloy, which include P-phases of Ti, Nb. Zr, and Та. The MWCNT-treated surface (Figure 6.6b) exhibits the compounds of oxides with base constituents such as Ti02, Ti20„ TaO, Zr02, and Nb2Os. These nonreactive compounds shaped inert layers on the surface that also endorsed the corrosion resistance of the alloy (Gai et al. 2018). The configuration of oxide phases on the treated substrate is considered as the sympathetic surface topology for increasing the biological performance of the implant material (Jenko et al. 2018). Also, the MWCNT-treated surface exhibited entities of carbon that resulted in the formation of carbides of the base material, i.e., TiC2, Nb2C, and ZrC. The compounds of the carbon contributed to the microhardness and wear resistance of the recast layer (Chen et al. 2007). Thus, the carbon compounds, along with oxides, are likely responsible for the formation of the layer having superior tribological properties.


This study presents the PM-EDM of P-titanium alloy to achieve the biomimetic surface by incorporating MWCNTs. It explores the capabilities of MWCNTs during machining to produce a biocompatible coating along with desired surface integrity. It concludes that the efficient surface integrity was successfully achieved on the p-titanium alloy as MWCNTs had superior mechanical properties, chemical inertness, and exceptional thermal conductivity. The MWCNTs’ substrate exhibited a well-patterned surface with porosity at the nano-scale level, which promotes cellular activities within the body. The biological test concluded that MWCNT-treated surface exhibited superior outcomes of hemolysis (i.e., 9.02%), whereas the untreated sample was considered as most hemolytic. XRD results found that the breakdown of powder entities from dielectric medium and some oxide phases was significantly involved in the formation of the highly inert and biocompatible surface. Also, the MWCNTs’ deposition favors the creation of a high-quality wear-resistant surface.

In conclusion, PM-EDM with MWCNTs is a prominent technique to achieve the preferred surface properties that increase the overall performance of the implant.


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