A short overview of powder-mixed electrical discharge machining in biomedical materials

Physical properties

Titanium experiences a phase shift from a hexagonal close-packed (HCP) crystal structure to a body-centered cubic (BCC) structure due to variations in temperature. At ambient temperature, economically pure titanium mostly resides in the α-phase, distinguished by its hexagonal close-packed structure. When the temperature surpasses roughly 883°C (1621°F), titanium transitions into the β-phase, characterized by a BCC structure. ⁴⁶ This transition dramatically affects several material qualities, including ductility and strength.

Titanium has a comparatively low density of around 4.5 g/cm³, about fifty percent that of steel or cobalt alloys. The low density enhances its lightweight characteristics, rendering it highly sought after for applications necessitating weight reduction, especially in aircraft and medical implants. In the realm of medical implants, diminished density is important in alleviating the total load and movement inertia on the human body.

Titanium has favorable thermal characteristics, with a melting point of about 1668°C (3034°F). The high melting point allows the material to endure increased temperatures during manufacture without compromising its structural integrity. Furthermore, titanium has a low coefficient of thermal expansion, indicating it undergoes little expansion or contraction when exposed to temperature fluctuations. This characteristic is especially significant in contexts where dimensional stability is essential, such as in precision medical equipment. ⁴⁷

Titanium is a relatively poor conductor of electricity compared to materials like copper or aluminum, making it beneficial for applications that need electrical insulation. In some medical applications, such as implanted devices, titanium's low electrical conductivity may be advantageous in mitigating unwanted electrical interactions with physiological tissues. ⁴⁷

Chemical properties

Titanium has a pronounced affinity for oxygen, resulting in the automatic development of a protective oxide coating on its surface upon exposure to oxidizing conditions. The oxide layer is essential for titanium's corrosion resistance and contributes to its biocompatibility, rendering it suitable for several applications, particularly at elevated temperatures. Titanium oxide manifests in two main crystalline forms, anatase and rutile, determined by environmental circumstances. The thickness of the natural oxide layer on titanium may fluctuate, affected by exposure circumstances and alloy composition, generally ranging from a few nanometers to around 10–30 nanometers. Alloys subjected to humid air at ambient temperature primarily form composite oxide layers including titanium (IV), titanium (III), and titanium (II) oxides.

In applications in medicine, the native oxide layer is essential for guaranteeing biocompatibility, serving as a protective barrier between the reactive metal and the biological environment. This layer mitigates corrosion, since the biological environment is intrinsically corrosive to metals, and also protects against detrimental consequences such as acute inflammation. ⁴⁸

Mechanical properties

Titanium alloys provide exceptional mechanical strength and rigidity, ensuring adequate load-bearing capability for applications such as orthopedic implants and dental prostheses. The precise mechanical characteristics may be customized by alloying with additional elements, with some alloys attaining ultimate loads similar to those of engineering steels. ⁴⁹ Like steels, titanium alloys possess a fatigue limit and remarkable fatigue resistance, making them appropriate for prolonged use in dynamic settings, such as orthopedic implants exposed to cyclic stress. Titanium alloys possess a comparatively low modulus of elasticity relative to other metals used in the biomedical sector. This attribute mitigates the stress-shielding phenomenon, thereby diminishing bone density reduction around the implants. ⁵⁰

Biological properties

The natural oxide layer on titanium and its alloys serves as a physical barrier between the metal and the biological environment; however, it is not completely inert. Dr Brånemark noted that bone tissue may adhere to and proliferate on titanium alloys, allowing titanium-based implants to attain full osseointegration over time.^51,52 Titanium's capacity to integrate with bone, recognized as a fundamental biomedical characteristic, is used in numerous biomedical devices, including scaffolds, to expedite bone tissue regeneration and enhance adhesion and stability. Another significant characteristic associated with native oxides is titanium's hypoallergenic quality, since it seldom induces allergic responses in humans. This feature is particularly essential for medical devices that maintain extended contact with the body. Titanium and its alloys are often regarded as non-toxic and are not thought to emit deleterious substances into the body, hence assuring patient safety over prolonged durations. Concerns have been expressed about the possible toxicity of some alloys, including titanium grade 5 and Nitinol, owing to the presence of aluminum/vanadium and nickel, respectively.

Mechanism of material removal of PMEDM

In PMEDM, applying a voltage between 80 and 320 V between the electrodes generates an electric field with an intensity of 10⁵ to 10⁷ V/m, resulting in the buildup of positive and negative charges on the top and bottom surfaces of the powder particles, respectively. ⁷² The principal discharge breakdown transpires at the locus of highest electric field intensity, situated between points a and b in Figure 10. This disintegration may occur among powder particles or between the powder particles and the tool or workpiece electrode. After the initial discharge, electric charges redistribute, ultimately accumulating at positions c and d. A sequence of sparks persists due to the electric field density. ⁷³ The interconnection of several powder particles forms a chain that promotes short-circuiting, resulting in a premature explosion in the gap. ⁷⁴ The combined influence of particle bridging and suspended additive particles modifies the plasma channel, diminishes discharge power density, and adjusts explosive gas pressure pulses.

PMEDM process parameters

PMEDM parameters significantly affect the processing efficiency and surface properties of biomedical materials. Key parameters include:

- Characteristics of powders: The selection and characteristics of powders significantly affect machining performance.

One of the most important parameters of the PMEDM process is the choice of the right powder. Powders can enhance factors such as material removal rate (MRR), surface quality, and cooling efficiency during the machining process. Common powders include aluminum (Al), silicon carbide (SiC), graphite, copper (Cu), chromium (Cr), and nickel (Ni), each with unique properties that optimize machining outcomes. Choosing the appropriate powder type is essential for achieving high machining efficiency and minimizing tool wear. The concentration of powder in the dielectric fluid plays a crucial role in PMEDM performance. At low concentrations, the effect on machining performance may not be significant, while optimizing the powder concentration can improve MRR and surface finish. However, an excessively high concentration of powder may lead to issues such as short-circuiting and arcing. Additionally, the particle size of the powder influences machining efficiency: smaller particles create a smaller machining gap, improving MRR and surface quality, while larger particles may result in reduced machining performance. ⁷⁵

The properties of powders, such as electrical conductivity, thermal conductivity, melting point, and specific heat, are essential in the PMEDM process. High electrical and thermal conductivity helps improve material removal and cooling during machining. The melting point and specific heat of the powder determine how it behaves under the intense heat generated during discharge. Selecting powders with suitable properties in alignment with machining parameters ensures optimal performance and enhances the quality of the final product. ⁷⁵

In the PMEDM process, various powders are commonly used to enhance the machining of biomaterials, improving material removal rate (MRR), surface quality, and machining efficiency. Graphite is used for its lubricating properties, reducing tool wear, and improving surface finish. Aluminum enhances thermal conductivity, aiding in heat dissipation during machining. ¹⁴ Copper improves electrical and thermal conductivity, increasing MRR. Silicon carbide contributes to reduced tool wear and better surface integrity due to its hardness. Nickel enhances corrosion resistance and surface integrity, while cobalt provides high hardness and wear resistance. Titanium powder itself is used to improve the machining of titanium-based biomaterials. Tungsten offers high stability and strength, ideal for machining hard biomaterials. Boron carbide is utilized for its extreme hardness, suitable for machining tough materials, and zirconia is commonly used for dental implants due to its strength and biocompatibility. These powders significantly improve the machining performance and quality of biomedical materials like titanium alloys, stainless steel, and ceramics. ⁷²

Many individuals have written on how powder concentration, pulse-on-time, and dielectric flow rate affect each other, but not many people have written about how they work together to create a heat-affected zone (HAZ). ⁷⁶ The thickness of the HAZ in PMEDM is determined by the dynamic balance between how much heat is added, how well the plasma spreads, and how well it cools. Increasing the pulse-on-time directly increases the discharge energy per spark, which makes the molten pool last longer and lets heat penetrate deeper into the substrate. When the powder concentration is low, the discharge energy stays mostly in one place. This could lead to deeper thermal penetration and a thicker HAZ. But when the powder concentration is moderate, the plasma channel gets wider because of inter-particle bridging effects. This spreads out the energy release and lowers the peak temperature intensity. The impact of spreading out can help make up for the heat buildup that happens when the pulse-on time is prolonged. The dielectric flow rate is a very important part of this interaction. Better flow helps get rid of waste more quickly and boosts convective heat dissipation, which speeds up solidification and stops HAZ growth. On the other hand, not enough dielectric circulation can cause heat to build up, especially when the pulse-on-time is high and the powder concentration is high. This can lead to unstable plasma behavior and uneven HAZ thickness. So, the production of HAZ in PMEDM should be seen as the result of a three-way coupling mechanism: energy input (pulse-on-time), energy dispersion (powder concentration), and heat extraction (dielectric flow rate). To get the best biomedical surface modification, these factors need to be balanced so that there isn't too much heat damage while yet being able to functionalize the surface.^77,78

Additionally, in PMEDM, the size of the particles in the suspended powders is important for keeping the plasma channel stable, which helps ensure that the surface modification is even. Fine powder particles create a larger surface area and less space between them in the discharge gap, which helps form many tiny connections between the tool electrode and the workpiece. This situation creates a more stable and evenly spread plasma channel, which leads to fewer changes in discharge energy and better consistency in how material is removed and the texture of the surface. ⁷⁹ On the other hand, larger powder particles or a wide range of particle sizes can cause uneven discharge and unstable plasma. Large particles can disrupt the evenness of the electric field, causing sparks to start unevenly and leading to hot spots. From a critical perspective, while numerous PMEDM research studies report average surface roughness values, a limited number of analyses systematically assess surface uniformity across extensive areas or consider the statistical variability of surface characteristics. This constraint underscores the necessity of managing the distribution of powder particle sizes, rather than depending exclusively on mean particle size, to attain consistent and dependable surface modification results.^76,80

The creation and features of the white layer and recast layer in PMEDM are mainly affected by the thermal and physical properties of the suspended particles, not just by the discharge settings. Powder materials with high thermal conductivity, such as copper or aluminum, facilitate quicker cooling rates and improve heat dissipation from the molten pool. This behavior typically leads to a decrease in microcrack density and thinner recast layers. However, the solidified layer might have oxide phases because metal particles can oxidize, which can impact how compatible they are with biological systems and how they resist. On the other hand, ceramic or semi-conductive powders like hydroxyapatite or silicon carbide have higher melting points and lower heat.^77,81 These properties can make the molten pool take longer to solidify, leading to thicker recast layers that have ceramic materials mixed in. In biomedical alloys, these embedded phases can change the structure and hardness of the material, and for bioactive granules, they might also enhance how well the surface works with biological systems. Nevertheless, residual stresses may be exacerbated, and microcrack formation within the white layer may be facilitated by an excessive thermal mismatch between the powder and substrate. Carbon-based particles, such as graphite and carbon nanotubes, exhibit unique behavior as a result of their exceptional thermal stability and electrical conductivity. These powders are reported to generate relatively uniform white layers with refined microstructures while concurrently facilitating localized heat spreading, which contributes to plasma channel stabilization. Therefore, the microstructure of the white and recast layers in PMEDM should be understood as a result of both the energy from the discharge and the specific thermal and physical properties of the powders, like how well they conduct heat, their melting point, and how they. This mechanistic linkage underscores the fact that the generalization of the white layer and recast formation across PMEDM studies is impossible without explicit consideration of particle properties. As a result, it is imperative to make a rational choice of particle materials to customize surface microstructures and guarantee the desired level of surface integrity in biomedical implant applications.^82,83

The way metallic powders like aluminum and copper oxidize in dielectric fluids greatly influences how compatible PMEDM-modified surfaces are with living tissues. The hot plasma created during the electrical discharge speeds up the oxidation of metallic powders, leading to the formation of oxide materials like Al₂O₃ and CuO/Cu₂O. These oxides may be included in the recast layer using resolidification and material transfer processes. From a biomedical standpoint, the existence of oxide phases does not automatically ensure enhanced biocompatibility. Although specific oxides might improve corrosion resistance, excessive or uncontrolled incorporation of oxides can modify surface chemistry and potentially trigger cytotoxic responses, especially in copper-containing systems where ionic release may take place. Many studies show that surfaces with greater copper oxide content can increase ion release in the body, which could harm long-term biocompatibility if not properly controlled.^77,83,84 As a result, while metallic powders are good at keeping plasma channels and improving machining efficiency, their tendency to oxidize requires careful consideration in biological PMEDM applications. To avoid biocompatibility problems, it's important to use strategies such as limiting the amount of powder, using safe or beneficial powders, adjusting pulse settings to reduce oxidation, and applying surface treatments after processing. This viewpoint emphasizes that powder selection in PMEDM must reconcile machining performance with the surface-chemistry requirements of biomedical implants.

To compare the pros and cons of PMEDM for biomedical surfaces, we compare it to two other common non-conventional processes: laser beam machining (LBM) and abrasive waterjet machining (AWJM). LBM is a thermal process that usually creates a heat-affected zone (HAZ) and features that have solidified. For titanium alloys, surface roughness values can reach sub-micron levels (e.g., Ra ≈ 0.965 μm) under the right conditions. The thickness of the HAZ depends a lot on the pulse energy and assist gas used, with ∼10 μm HAZ reported at certain pulse-energy windows. ⁸⁵ AWJM, on the other hand, is mostly a cold erosion process. Plastic deformation, striations, and possible abrasive embedment are what keep the surface intact. Roughness, hardness, and leftover stress are often used to describe the surface, along with chemical analysis methods (like XPS/XRD) for Ti-6Al-4V. ⁸⁶ To check how safe it is for living cells, EDM-type methods have been directly tested using standard cytotoxicity tests (like LDH assays following ISO 10993-5) on Ti-6Al-4V after EDM surface changes, creating a way to link the processing, surface features, and how. There has been a lot of research on laser-based surface structuring to change the wettability and cell adhesion of Ti-6Al-4 V. ⁸⁷ This includes continuous-wave fiber laser texturing to make it more biocompatible and femtosecond-laser texturing to change the surface topography and cell response. ⁸⁸ AWJ/hydrojet surface treatment for titanium can make it easier to remove defects and improve the surface quality. However, when working with biomedical surfaces, it's important to consider the known problem of abrasive entrapment. In biomedical uses, PMEDM should be assessed not just by its average roughness but also by looking at recast/HAZ features, changes in chemical state, and standardized biological tests, which help make fair comparisons with laser and waterjet methods. ⁸⁹

Optimizing these parameters is key to achieving high processing efficiency while maintaining smooth, high-quality surfaces suitable for biomedical applications.

Powder dispersion and stability

One of the primary challenges in PMEDM is ensuring a uniform dispersion of powder particles in the dielectric fluid. Poor dispersion can lead to inconsistent machining performance, affecting material removal rates, surface finish, and overall product quality. Factors influencing powder stability include:

- Particle size and concentration

To mitigate these issues, researchers are exploring optimized fluid flow techniques, improved powder suspension methods, and alternative dielectric compositions.

Potential cytotoxicity of residual embedded powder particles

A major but often overlooked issue in PMEDM surface changes is the potential harm from leftover powder particles stuck in the new layer.^90,91 During discharge, explosive powder particles may partially melt, oxidize, or become mechanically stuck in the resolidified surface. The added particles might improve how the surface works, but they could also create problems for compatibility with living tissues, especially if incompatible particles like silicon carbide (SiC) are used. In biomedical settings, implanted particles may experience progressive chemical deterioration or mechanical separation due to cyclic loading. These conditions may result in the discharge of debris or ionic species into adjacent tissues. For example, silicon-based particles and carbonaceous residues have been reported to influence cellular response depending on particle size, concentration, and surface chemistry. The chemical stability of particles, their state of oxidation, or their discharge as wear debris significantly influences the biological effect. ⁸⁷ While most PMEDM studies highlight improvements in surface roughness and corrosion resistance, fewer investigations focus on residual particle content or assess cytotoxicity according to standardized biomedical standards.^92,93 Therefore, choosing the right powder, thoroughly cleaning after processing, and following standard toxicity tests (like ISO 10993-5) are crucial when using PMEDM to make. This perspective emphasizes that the effectiveness of surface modification should be assessed not only on mechanical or morphological enhancements but also on long-term biological safety.

Environmental and health concerns

The use of powder in EDM presents environmental and health issues, especially in biomedical applications where contamination management is essential. The concerns encompass:

- Powder Waste Management: Surplus powder may result in disposal difficulties, necessitating effective filtering and recycling methods.

Future research aims to produce environmentally sustainable powders, biodegradable dielectric fluids, and enhanced filtering systems to reduce environmental and health hazards.

Process control and optimization

Attaining the optimal equilibrium of machining parameters in PMEDM is intricate owing to the interaction of several elements, including:

- Powder concentration and type;

Minor fluctuations in these parameters may lead to significant alterations in machining efficiency, surface roughness, and material integrity. Advanced optimization methodologies, including artificial intelligence (AI)-driven process modeling, machine learning, and real-time monitoring, are being investigated to enhance control and repeatability.

Surface integrity and mechanical properties

While PMEDM generally improves surface finish and biocompatibility, achieving uniform surface characteristics remains a challenge. Issues include:

- Microcrack formation due to high thermal stresses;

In addition, there are two major challenges with the PMEDM process to enhance chemical corrosion resistance and reduce surface stress. For chemical corrosion resistance, the PMEDM process, while beneficial for machining biomedical materials, can pose challenges to chemical corrosion. The high temperatures generated during PMEDM may cause localized melting or re-solidification, potentially degrading the surface integrity and compromising the material's corrosion resistance, which is critical in biomedical applications. Additionally, powders mixed with the dielectric fluid can contaminate the material surface, disrupting protective oxide layers and further reducing corrosion resistance. ¹³ The process can also produce rough surfaces, which increase the surface area exposed to chemical attack, making the material more susceptible to corrosion, especially in biological environments. Furthermore, PMEDM can alter the material's microstructure due to thermal cycles, potentially weakening its overall corrosion resistance. Lastly, the heat-affected zone (HAZ) created during PMEDM can result in microstructural changes that make the material more prone to corrosion, especially in aggressive environments. These factors require careful process optimization to maintain the corrosion resistance of biomedical materials.

Surface stress during the PMEDM process is primarily induced by the high-temperature sparks generated between the electrode and the workpiece, leading to thermal gradients and rapid cooling. This thermal cycling creates thermal stresses on the material surface as it heats and cools rapidly, resulting in residual stresses that can be either tensile or compressive, depending on the cooling rate. ⁹⁴ Additionally, the presence of powder particles in the dielectric fluid can influence the surface stress by affecting material removal, introducing small impacts, or altering the cooling rate, further contributing to stress concentrations. The surface roughness produced by PMEDM also plays a role, as microscopic peaks and valleys can act as initiation points for cracks or corrosion. Overall, the surface stress in PMEDM affects the material's mechanical properties and requires careful process optimization to minimize negative impacts such as surface degradation and reduced material performance.

Titanium alloys like Ti-6Al-4V exhibit different properties depending on the direction of stretching or compression, and regions with a specific α-grain arrangement can influence how cracks initiate and how the material holds up over time. Recent machining studies indicate that near-surface residual stresses are not merely “macroscale averages” but exhibit considerable microscale variability that correlates with local crystallographic texture/microtexture, suggesting that surface-processing methods may preferentially induce tensile or compressive stress states in specific orientations. ⁹⁵ In the realm of EDM/PMEDM, the thermal cycle (rapid melting and quenching) and the development of a white or recast layer can induce residual stresses and microstructural characteristics that serve as loci for fatigue fracture initiation. The fatigue strength of Ti-6Al-4V is known to diminish during EDM, and residual-stress assessments indicate that post-processing techniques, such as bead blasting, can introduce significant compressive near-surface stresses that substantially affect fatigue performance. ⁹⁶ Collectively, these findings necessitate a more informed interpretation of PMEDM surface integrity through the lens of crystallography: (i) process parameters dictate the thermal gradient and resolidification microstructure that establish the foundational residual stress field; (ii) crystallographic anisotropy and microtexture can affect local elastic recovery and plastic accommodation, resulting in orientation-dependent variations in residual stress; and (iii) such variations can impact fatigue crack nucleation, especially under high-cycle loading conditions where microtexture-induced facets are frequently involved. ⁹⁷ Due to the predominance of PMEDM studies that solely present area-averaged residual stresses and mean roughness values, subsequent research should integrate residual stress depth profiling with EBSD-based texture mapping (and/or microscale residual-stress techniques) to quantify orientation-resolved stress states and establish a direct correlation with fatigue performance in biomedical titanium components.

Research is focusing on hybrid approaches, such as combining PMEDM with laser texturing or ultrasonic assistance-to further refine surface modifications while maintaining mechanical integrity.

Cost and scalability

Despite its benefits, PMEDM is not yet widely adopted in industrial-scale biomedical manufacturing due to:

- Higher operational costs: Powder materials and specialized dielectric fluid handling increase production costs.

Creating economical powders, optimizing process efficiency, and integrating PMEDM with Industry 4.0 technologies are viable strategies to augment its practicality in commercial biomedical applications.

In addition to surface appearance and chemical properties, the mechanical behavior of biomedical materials is essential for the long-term efficacy of implants. It is necessary to assess PMEDM-induced surface change not just regarding surface integrity and biocompatibility but also from a biomechanical standpoint. One essential thing to think about is how the residual stresses and microhardness change in the white and recast layers. Thermal cycling associated with EDM may cause tensile residual stresses, which might affect fatigue life when the body is under cyclic physiological loads. ⁸⁴ On the other hand, optimal PMEDM conditions with controlled heat penetration may create compressive residual stresses that help prevent cracks. Another important thing is how well the modulus works with other materials. In load-bearing implants, too much stiffness difference between the implant material and the bone around it might cause stress shielding. Controlled PMEDM can change the surface in a way that creates gradient microstructures or porous features. This can lower the effective stiffness at the interface, which can help with load transfer and osseointegration. PMEDM-induced surface roughness and micro-texturing also have an effect on how things move. In joint implants, the surface topography affects the friction coefficient, the amount of wear debris that is made, and the way the lubricant works. ⁹⁸ So, it is important to adjust the PMEDM settings to find a good balance between surface hardness and roughness in order to reduce wear-induced inflammatory responses. Finally, the thickness and microstructure of the recast layer may change where cracks start while the material is under mechanical load. Recast layers that are too thick or brittle may operate as stress concentrators, which lowers fatigue strength. So, when optimizing PMEDM for biomedical uses, mechanical reliability should be taken into account together with biological performance.^77,99

Integration with hybrid manufacturing

Integrating PMEDM with other advanced manufacturing processes, including additive manufacturing (AM), laser surface modification, and ultrasonic machining, may significantly improve the processing of biological materials. For instance:

- PMEDM with Additive Manufacturing: Employing PMEDM to enhance the surfaces of 3D-printed titanium implants for superior osseointegration.

AI and smart control systems

Artificial intelligence (AI) and machine learning (ML) methods have been used more and more to model, predict, and improve PMEDM performance parameters such as surface roughness, material removal rate (MRR), tool wear rate (TWR), and recast layer thickness. But their use in control systems is still at varied levels of development. During the modeling phase, supervised learning algorithms like artificial neural networks (ANN), support vector machines (SVM), and random forest regression have been used to find nonlinear links between input parameters (pulse-on-time, pulse-off-time, peak current, powder concentration, dielectric flow rate) and output responses (Ra, MRR, white layer thickness). Recent research has shown that machine learning may be used to optimize performance in multiple dimensions in nanopowder-mixed EDM.^100,101 This allows for more accurate predictions of surface roughness and process stability than standard regression models. AI approaches can be used in adaptive control frameworks in addition to offline optimization. In these kinds of systems, real-time monitoring signals like discharge voltage, current waveform characteristics, acoustic emission, or spark frequency are used as feedback inputs. A trained predictive algorithm can tell you in real time how stable the plasma is or how well the surface is holding up. After that, control algorithms change the pulse settings or powder concentration in real time to keep the process stable and stop too much heat from building up. Reinforcement learning and model predictive control (MPC) are two potential new ways to control PMEDM systems. These methods could make it possible for machining environments to optimize themselves. In these environments, the system would constantly change its set of parameters based on performance input to get the desired surface characteristics. For biomedical uses, these kinds of adaptive systems may make it possible to improve both machining efficiency and surface biocompatibility at the same time. The current focus of applications is mostly on predictive modeling and parameter optimization. However, the move toward intelligent closed-loop PMEDM systems is still a very important area of research. ¹⁰²

Development of biocompatible powders and dielectrics

Future research aims to develop specialized biocompatible powders and eco-friendly dielectric fluids tailored for biomedical applications. Some emerging areas include:

- Nanoparticle-enhanced PMEDM: Utilizing nanoscale powders (e.g., nanohydroxyapatite, nanodiamond) to improve surface bioactivity.

Expanding biomedical applications

The application of PMEDM in biomedical materials is expected to grow beyond implants and surgical tools into areas such as:

- Microfluidic Devices: Manufacturing precise channels and surfaces for lab-on-chip diagnostic systems.

Although PMEDM has shown considerable benefits in machining biomedical materials, issues such powder dispersion, environmental implications, and process regulation need to be resolved for broader industrial use. Future innovations in hybrid manufacturing, AI-driven optimization, and biocompatible materials will facilitate its wider use in the medical and healthcare industries. Ongoing research and development may enable PMEDM to transform the manufacturing of high-performance, patient-specific biomedical components.

PMEDM for titanium-based biomedical alloys

Titanium alloys, particularly Ti-6Al-4V ELI, are the most thoroughly researched materials owing to their prevalent use in orthopedic and dental implants. Farooq et al. ¹³⁵ examined the effects of silicon powder-mixed EDM on the surface integrity of Ti-6Al-4V ELI, revealing substantial alterations in surface topography, such as micro/nano-scale structures and reduced recast layer thickness, advantageous for biomedical applications. Mughal et al. ¹³⁶ subsequently proved that PMEDM serves as an effective surface modification strategy to enhance osseointegration, underscoring its potential beyond traditional material removal methods. Simultaneously, extensive evaluations have synthesized the impact of PMEDM process parameters on machining outcomes and surface characteristics of biomedical materials, integrating experimental data published to 2020 and establishing a basis for future study. ¹³⁷

Bioactive surface modification and hydroxyapatite-assisted PMEDM

A significant trend in contemporary PMEDM research is the integration of bioactive powders, especially hydroxyapatite (HAp), to facilitate surface biofunctionalization. Al-Amin et al. indicated that HAp-suspended EDM may proficiently alter the surface of 316L stainless steel, enhancing surface attributes pertinent to biological efficacy. ¹⁰³ Ekmekci and Efe elucidated the significance of powder properties by comparing nano- and micro-sized HAp powders in PMEDM of Ti-6Al-4V, revealing significant effects on surface integrity and coating behavior. ⁸²

Studies focused on optimization have arisen, seeking to regulate changing surface characteristics by systematic parameter selection. Danish et al. used statistical optimization methods to enhance the surface properties of 316L stainless steel treated by HAp-PMEDM, therefore substantiating the viability of PMEDM as a surface engineering approach for biomedical alloys. ¹³⁸ Adding powder to the dielectric solution enhanced surface quality and decreased the thickness of the recast layer, according to Le's study ¹³⁹ on AISI H13 steel under fine machining settings. Le ¹⁴⁰ compared two finishing and semi-finishing modes for AISI H13 steel and found that the finishing method produced improved surface quality with a thinner and more stable recast layer, whereas the semi-finishing mode obtained a higher material removal rate. Recently, Gul et al. examined carbon nanotube-assisted EDM on 316L steel and reported concurrent enhancements in surface integrity, corrosion resistance, and biological response, including improved cell viability, thus offering direct experimental evidence connecting PMEDM-induced surface modification to biocompatibility. ⁸³

Emerging trends: Data-driven optimization and critical evaluation of surface functionality

In conjunction with experimental progress, data-driven modeling and optimization methodologies have gained traction in PMEDM research. Sana et al. used machine learning approaches in nanopowder-mixed EDM, showcasing the potential of predictive models to enhance multi-dimensional performance attributes, such as surface roughness and material removal behavior. ¹⁰⁰ Such methodologies provide intriguing avenues for intelligent process regulation in biological PMEDM applications.

Recent review studies have highlighted emerging research trajectories. Gul presented an extensive analysis of the applicability of PMEDM processes, highlighting powder properties, surface functioning, and prospective problems in biomedical applications. Kumar et al. ¹⁴¹ provided a contemporary assessment in 2025, including advancements in dielectric improvement, machining efficiency, and novel applications of PMEDM, therefore highlighting the rapid progression of the area in recent years. Furthermore, the production of functional surfaces using EDM, including biomedical-relevant surface characteristics, has been thoroughly evaluated, underscoring the increasing acknowledgment of EDM-based methodologies as surface engineering instruments rather than just machining methods. ¹⁴² Le and his colleagues ²¹ examined and improved the machining of X40CrMoV51 steel in both heat-treated and non-heat-treated conditions under finishing conditions. The researchers found that the state of the steel affects how it discharges, how it removes material, and the quality of the output. In a detailed study, Le ¹⁴³ looked at the surface metal properties and changes in the microstructure of the re-solidified layer during finishing-PMEDM, highlighting the connections between discharge settings, the powder-mixed dielectric medium, and the formation of the white layer. These results indicate that PMEDM serves not only as a material removal technique but also as a technology for the precise modulation of surface microstructure.

The research released from 2020 to 2025 unequivocally illustrates that PMEDM has developed into a multifaceted production and surface modification method for biological materials. Contemporary research increasingly emphasizes the correlation between process parameters, powder properties, and thermo-physical processes with surface integrity and biocompatibility results, while novel data-driven approaches further improve process optimization and dependability. These contributions affirm the growing body of evidence supporting PMEDM as a transformative technology in biomedical manufacturing. Through collaborative efforts involving computational modeling, experimental validation, and biological evaluation, researchers are unlocking PMEDM's full potential as a non-contact, multifunctional machining and surface functionalization technique tailored for next-generation implants.

Additionally, Figure 11 shows the number of publications on the keyword PMEDM over the last 15 years.

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Figure 11.

Number of publications related to the keyword PMEDM in the last 15 years.