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Chapter 9
Medical Devices Tribology
NipunJain , YusufOlatunjiWaidi , SaswatChowdhury , RanjitBarua , SamirDas , ArbindPrasad , andSudiptoDatta
Abstract In this book chapter, we will discuss the signicance of tribology in vari-
ous surgical and medical devices and instruments like dental implants, contact lenses, cardiovascular devices, surgical instruments, orthodontic and dental implants, articial joints, and teeth. Also, we have briey discussed the present condition and the future progress of these medical devices from the tribological viewpoint, along with the fundamental mechanism.
Keywords Medical devices · Orthopedic · Dental implants · Surgical instrument · Contact lenses

9.1 Introduction

Medical appliances are used in everyday life for various reasons, including medical care, injury healing, anatomical guidance, and biological functions. The worldwide market has grown steadily, reaching $456.9 billion in 2019 [1]. Medical devices
N. Jain · Y. O. Waidi · S. Datta (*) Department of Materials Engineering, Indian Institute of Science, Bangalore, Karnataka, India e-mail: nipunjain@iisc.ac.in; yusufwaidi@iisc.ac.in
S. Chowdhury Department of Bioengineering, Indian Institute of Science, Bangalore, Karnataka, India e-mail: saswatc@iisc.ac.in
R. Barua Centre for Healthcare Science and Technology, Indian Institute of Engineering Science and Technology, Howrah, West Bengal, India
S. Das Biomaterials and Tissue Engineering Lab, School of Medical Science and Technology Indian Institute of Technology, Kharagpur, West Bengal, India
A. Prasad Mechanical Engineering Department, Katihar Engineering College (Under Department of Science, Technology and Technical Education, Government of Bihar), Katihar, Bihar, India
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Kumar et al. (eds.), Applications of Biotribology in Biomedical Systems,
https://doi.org/10.1007/978-3-031-58327-8_9
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offer certain benets and help improve the quality of life. Nevertheless, they also carry a substantial built-in risk; thus, safety and efcacy become priorities in design consideration. Different interfaces are also created when these devices are utilized in the body to carry out specic tasks.
Device failure occurs at these formed interfaces, such as excessive wear, loosen­ing, or fretting. For this reason, the effectiveness of these depends on the way these interfaces interact with one another. Tribology is the science that studies interacting surfaces. Dowson and Wright rst coined the word “bio-tribology,” which has been used to study the behavior and mechanism of interfaces in biological systems [2]. Many studies have been carried out to look at the bio-tribological behavior and workings of medical devices.
In this article, we review current knowledge regarding the bio-tribology of medi­cal devices from various perspectives and offer insightful data regarding the com­prehension of bio-tribological conduct and function. Medical devices have a variety of applications, and their underlying principles and working mechanisms differ greatly. The tribological problems associated with widely used medical equipment are outlined, and the latest developments in the eld are scrutinized. The difculties and potential advancements for tribological effectiveness are emphasized.

9.2 Bio-Tribological Issues

Joint replacement is becoming more popular as the population ages and demands an active lifestyle. A variety of devices have surfaced as a result of technological advancements and an increase in clinical expertise [3]. Patients benet greatly from joint replacement, but some hazards, such as tribological dysfunction, are also involved. An articial joint normally has three different kinds of interfaces: articu­lating, modular, and xation (refer to Fig.9.1). In daily operations, articulating interfaces offer simultaneous movement and bearing loads. Wear particles mostly cause articial hip and knee joint revisions from sliding friction. One crucial reason for a revision is aseptic loosening brought on by xation failure, which is
Fig. 9.1 Schematic of an articial joint with three different interfaces. (Adapted from Zhang etal. [1])
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particularly dangerous in younger patients [4]. A prosthetic hip joint with various modular head and neck combinations has been studied to enhance biomechanical functions and restore anatomical features. Nonetheless, physical accelerations fre­quently result in fretting corrosion, which leads to the breakdown of modular inter­faces [5].
An orthopedic surgeon performing a “reduction” procedure is called upon to rebuild the fractured bone. Several structures are employed in fracture xation. Fracture-xing devices are commonly made of titanium alloys, cobalt-chromium alloys, stainless steel, and NiTi shape-memory alloys [6]. Micro-action is created at the interface between the screw and the bone plate, which encourages fretting wear. Fatigue fracture frequently happens under cyclic loading. Micro-motion damages the bone by hastening the formation of cracks. It may cause the synthetic effects of corrosion and cause them to become unstable. Additionally, the wear debris and ion release from bone plates can cause inammation and perhaps cancer-causing conse­quences [7]. The eld of dentistry is experiencing a surge in tribological investiga­tions, driven by its rapid growth and advancements. This research delves into dental materials’ frictional and wear behavior, which is crucial for ensuring their long-term functionality. Dental restoration tribology itself encompasses two main areas: den­tal implant and tooth restoration tribology [8]. Tooth restoration materials face a unique challenge; hence, they must exhibit optimal wear resistance. Ideally, they should neither wear themselves excessively nor cause undue wear to their opposing surfaces, whether natural teeth or other restorations (dental implants), presenting distinct tribological concerns. The primary considerations are preventing modular interface fretting corrosion and maintaining the bone-implant interface’s long-term stability [8].
Cardiovascular diseases, the world’s leading non-communicable killer, have seen tremendous therapeutic progress thanks to innovative devices like stents, heart valves, and assist devices. However, these advancements are not without challenges [9]. Tribological issues, particularly in mechanical heart valves and VADs, can trig­ger complications like hemolysis and thrombus formation, leading to device failure. Moving parts cause wear and friction, while additional contact with blood intro­duces further friction at the interface. This interface requires careful design to mini­mize potential blood cell damage and ensure adequate clearance of blood products [10]. Similarly, due to their inherent interaction with blood vessels, stents and cath­eters also fall under the purview of tribology. Catheters, for example, can damage the vessel’s endothelium through unavoidable contact [11]. Addressing these tribo­logical challenges is crucial for ensuring cardiovascular devices’ long-term success and safety, ultimately improving patients’ lives suffering from these debilitating diseases. While stenting can lead to tissue damage and unpredictable migration due to imbalanced friction and hemodynamic forces, minimally invasive surgery (MIS) procedures like endoscopic surgery have become increasingly prevalent, introduc­ing a new set of tribological challenges. These include friction between needles and endoscope-tissue interactions, device-tissue interactions, and soft tissue. These friction-related challenges complicate precise positioning and force control during MIS, impacting key factors like grasp, needle insertion, transmission hysteresis, and
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haptic feedback [12]. While transmission hysteresis due to cam pulley or tendon­sheath mechanisms falls outside bio-tribology, it’s important to acknowledge its potential impact on surgical accuracy.
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9.3 Research Advances intheBio-Tribology
9.3.1 Articial Joints
Although wear resistance and friction coefcient are crucial for the long-term sur­vival of articial joints, improper tribological design leading to excessive wear and aseptic loosening poses the greatest threat to their performance and effectiveness [13]. Optimizing the articulating surfaces’ tribological properties has become a key focus in bio-tribology research. Two main material combinations are employed: hard-on-hard and soft-on-hard. The exceptional combination of impact resistance and tensile strength exhibited by Ultra-high molecular weight polyethylene (UHMWPE) and its modied forms renders them the material of choice for “soft” components with demanding mechanical requirements. At the same time, the “hard” counterpart often comprises titanium alloys, stainless steel, cobalt-chromium alloys, zirconia-toughened alumina composite ceramics (ZTA) or zirconia, and alumina. However, UHMWPE’s softness is the primary cause of wear and debris, as evi­denced by normal wear characteristics in retrieved acetabular cups [14]. Consequently, extensive research has been dedicated to enhancing UHMWPE’s wear resistance, with recent advancements like highly cross-linked UHMWPE showing signicant promise. Notably, irradiated UHMWPE exhibits a substantial decrease in wear rate with increasing cross-linking gamma irradiation [15]. While hard-on-hard pairings (metal-on-metal and ceramic-on-ceramic) hold promise for articial joints, their durability presents distinct challenges. Thanks to effective lubrication, metal-on-metal boasts impressive initial wear rates under ideal condi­tions. However, its vulnerability to lm breakdown under stress drastically increases wear, raising concerns about its long-term viability and contributing to its clinical decline. Ceramic-on-ceramic’s superior hardness and scratch resistance, leading to sustained low wear, have driven its wider clinical adoption, particularly in knee replacements [16]. However, further research is needed to ensure the long-term durability of surface coatings used on metallic counter-faces, as their potential impact on soft surfaces remains unclear. Polyether-ether-ketone (PEEK) boasts impressive biocompatibility, radiation permeability, and enhanced wear resistance via carbon or glass ber reinforcement (CFR-PEEK, GFR-PEEK) [17]. However, the clinical benets of traditional total hip designs remain elusive compared to established alternatives like HXLPE or ceramic liners. The emergence of Ultra-low­wear polyethylene (ULWPE), with its superior wear properties due to its highly linear structure and narrow molecular weight distribution, further challenges PEEK’s dominance in the eld. Fixation methods for articial joints primarily rely
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on bone cement or biological approaches. Additionally, Joint replacement surgery relies on two main methods to secure the prosthesis: cementless and cemented xa­tion. In cemented xation, the prosthesis is “glued” directly to the bone using quick­drying bone cement. In contrast, cementless xation relies on press-tting, specially textured or porous prostheses that encourage bone ingrowth over time. The optimal approach has been debated for decades. While cementless xation offers the theo­retical advantage of long-term biological integration, where host bone grows into the prosthesis, it requires precise t. It can be impacted by excessive micro- motion, which hinders bone growth and weakens the bond [18]. Ultimately, the success of both methods hinges on a balance between micro-motion that allows bone forma­tion and excessive motion that leads to instability and failure.

9.3.2 Bone Fracture Fixation

On the surface where screws and bone plates connect, corrosion and abrasion com­monly appear. The mechanical and tribological properties of Ti6Al4V were exam­ined in research by Bartolomeu etal. using various processing techniques, including standard casting, SLM, and hot pressing [19]. Due to a very diverse microstructure, their research showed that SLM produced the best toughness and wear resistance levels. Proteins and reactive oxygen species are among the many living elements in the invivo milieu of bone complex dish surfaces. Zhang etal.’s study examined Ti6Al4V’s corrosion behavior in physiological saline, emphasizing the effects of albumin and H2O2 [20]. According to their ndings, albumin greatly speeds up cor­rosion over a longer time (120h) but rst prevents dissolving over brief periods (less than 24h). This phenomenon is associated with a thinner oxide coating that results from the erosion-producing coating dissolving under the action of albumin. The slipping frictional behaviors of bovine cortical bone and Ti–6Al–4 V plates were studied in a range of bio-lubricants, such as physical saline, simulated bodily uids, and fetal bovine serum [21]. It was observed that the friction pair with the highest wear rate and friction coefcient was lubricated with fetal bovine serum. Bio-lubricants caused corrosion wear, which increased the rate at which bones wore out at greater sliding velocities and normal loads. Attabi etal. examined the tribo­logical behavior of Ti6Al4V alloy treated with ion nitriding in different research [22]. They found notable improvements in microhardness and a decreased coef­cient of friction. The wear behavior of TiO2 nanotube-coated Ti6Al4V bone plates was studied by Wang etal. Their ndings showed a reduction in wear volume and friction coefcient, which they attributed to better lubrication by increased hydro­philicity and decreased elasticity [23]. More recently, topology optimization was used by Al-Tamimi etal. to enhance the xation plate’s mechanical, biological, and tribological performance. Their results demonstrated a respectable level of wear resistance and a signicant improvement in biological function [7].
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9.3.3 Dental Restoration andImplants
Chewing exposes the teeth to a great deal of wear and tear. Therefore, a dental replacement material’s wear resistance is crucial. Various materials have been employed for tooth restoration, including polymers, ceramics, metals, and alloys [24]. Because dental restorations must consider aesthetics, the value of the metal and its alloys has declined over time due to its unappealing hue. Amalgam llings are utilized as dental repair materials in very small quantities. Dental implants and orthodontic equipment are the primary uses for the bulk of metal and alloy dental materials. While polymeric materials are also utilized for dental restorations, they frequently exhibit poor gloss retention and a high wear rate [25]. The crystalline and glassy phases that make up dental ceramics are closely connected regarding their mechanical and tribological characteristics. Dental ceramics offer superior wear resistance in addition to a look that is similar to that of natural teeth. This makes them a popular choice for repair ingredients [26]. One of the drawbacks of ceramics is that they might break easily, which could lead to the restoration failing. Dental ceramics have a stronger wear resistance than natural teeth, which can lead to sig­nicant wear on the opposite natural tooth’s occlusal surface.
Organic ller materials (like alumina, zirconia, quartz, borosilicate glass, etc.) are mixed with organic monomers (like Bisphenol Bis-GMA, 2-hydroxyethyl meth­acrylate, A-glycidyl methacrylate, TEGDMA, HEMA, Urethane dimethacrylate, and Bis-EMA, ethoxylated bisphenol A-dimethacrylate) in resin-based dental com­posites [27]. As such, materials are often used to repair decaying tooth tissues and x cavities because they closely resemble the properties of genuine teeth. Instead of dental ceramics, composite-based materials may be applied directly, signicantly increasing clinical competence [28]. Initial resin composites show a high wear rate because of the big ller particles they contain. The introduction of micro/nano­hybrid composites has greatly increased the wear resistance [29]. The wear behav­ior of a composite based on Bis-GMA/TEGDMA with varying weight fractions of silane-treated micro zirconia particles was examined by Kumar etal. Their dental composite, lled with 3-weight percent nano zirconia ller, demonstrated excep­tional wear resistance, minimal wear rate, and maximum hardness compared to con­ventional dental composites [30]. Chadda etal. examined the wear behavior and fracture toughness of hydroxyapatite and silica/hydroxyapatite-lled Bis-GMA/ TEGDMA composite. The composites with the lowest ller content (20wt%) show the best wear resistance and increased fracture toughness, whereas those with a ller level ranging from 30 to 40wt% show the best wear resistance [31]. Materials with polymer-inltrated ceramic networks (PICNs) offer superior wear resistance and improved mechanical qualities. The wear behavior and mechanism of a PICN material (commercial ENAMIC) were examined by Xu etal. They discovered that whereas the ENAMIC and tooth enamel have comparable Vickers hardness, they differ in Young’s moduli [32]. Moreover, the ENAMIC has less wear resistance than tooth enamel yet displays a comparable wear damage mode. The impact of acidic substances on the wear behavior of a PICN material (Vita Enamic, Vita Zahnfabrik,
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Fig. 9.2 Dental restoration implants. (a) A diagrammatic illustration of human teeth. (b) An actual image of dental restoration implant assembly. (Adapted from Armentia etal. [34])
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Bad Sackingen, Germany) was investigated by Yu etal. While acid erosion had a notable impact on the PICN’s early wear behavior, it did not appear to have any discernible inuence on the wear property over the long run [33].
A strong base for permanent or removable replacement teeth that mimic natural teeth is provided by implants [34]. Dental implants have several benets, including improved aesthetics, increased durability, and ease of use (Fig.9.2). Even with these advantages, there are also cases of clinical failure. Potential reasons include inter­face fretting and corrosion [35], which can directly affect bone ingrowth during the rst phase of implant placement and the long-term survival of dental implants. Mastication pressures cause fretting at the dental implant/bone contact, and for osseointegration to be effective, the implant’s micro-motion amplitude must be kept below a certain threshold. Micro-motions between 50 and 150μm for stability are the ideal range [36]. As implantation technology develops, customized thresholds impacted by surface treatment, implant materials, and superstructure design will be expected to replace the traditional upper limit for micromotion amplitude. Various alloying elements have been investigated to advance the tribological characteristics of CP-Ti; titanium alloys with β and near-β showing promise are among them. Other surface alterations have also been used, including anodic oxidation, sandblasting, plasma-spraying, and etching [37]. Following sandblasting and acid etching (SLA), ultrane-grain pure titanium (UFG-Ti) has a surface with a hierarchical porous structure that offers good wettability. Ti-6Al-4V with PEEK covering has improved wear resistance and biocompatibility [38]. Porous materials, such as porous tita­nium and porous tantalum, have been introduced for dental implants. For long-term stability, porosity increases the coefcient of friction between implants and the sur­rounding tissues, which promotes osseointegration and bone ingrowth [39]. The pores’ size, shape, and porosity strongly impact the tight integration of the implant and growing bone tissue. Earlier bone ingrowth and added constant bone addition
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are encouraged by porous tantalum, which has been modied on the surface to increase biocompatibility [40].
Various investigations are also available where bioresorbable composites were used for orthopedic implants such as cancellous screws, cortical screws, staples and pins [4150]. Bioresorbable implants have a lot of advantages over metallic implants [46, 5154]. The patient does not need to visit the doctor for the removal of the metallic implants after bone healing. Resorbable-based polymeric implants are nowadays used in various biomedical applications [5557].

9.3.4 Cardiovascular Devices

Concerns about wear and friction, especially at the hinge area of titling-disc and bileaet valves and between the ball and cage in cage-ball valves, have led to much research on mechanical heart valves. Valve failure may result from strut fracture or leaet escape due to excessive wear. As documented by Zhang etal., a low-prole bileaet prosthesis experienced leaet escape due to severe wear at the leaet out­ow edge [58].
Ventricular assist devices (VADs) support heart function and come in pulsatile and rotary pump designs, utilizing different bearing systems like rolling elements, pivot, and journal bearings [59]. While rolling element bearings don’t directly con­tact blood, friction heat can induce hemolysis in sealed ball-bearing systems. Additionally, shaft seals are necessary to prevent blood from entering bearing voids, preventing bearing seizure.
Although uid shear stress can cause hemolysis, pivot bearings immersed in blood depend on boundary lubrication and need a signicant blood uid layer for washout [60]. Journal bearings are less prone to wear, but they frequently require extra thrust bearings, which increases complexity. Using a blood saline solution in journal bearings is a typical x that calls for a reservoir and a ow cycling line. Nevertheless, using blood as the bearing uid carries a risk of coagulation-related pump seizure. Sundareswaran etal. determined the ball bearing wear rate to be less than 1.46μm/yr using a surface prolometer [59].
In their investigation on apical aortic blood pumps, Da Silva etal. discovered that bearing component wear reduction is essential for durability [61]. Their testing demonstrated a direct correlation between load and wear at this pivot point, with wear at the lower bearing pivot being the primary cause of device failure. The fric­tion that occurs during stent installation is important between blood arteries and stents [62]. Because re-endothelized tissue frequently malfunctions and raises the likelihood of in-stent thrombosis and restenosis, endothelial damage during this process leads to restenosis-related failures [63]. Blood uid friction has been con­nected to stent migration and corrosion after placement. Friction between porcine aorta and aortic stent-grafts was investigated by Chen etal., along with the use of polyvinyl alcohol (PVA) and polydimethylsiloxane (PDMS) cryogels [64].
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9.3.5 Minimal Invasive Surgical Devices

Traditional surgeries generally depend on accessing the open wound created through a planned incision, which often leads to certain postoperative complications, such as granular tissue formation and longer healing periods [65]. Minimally invasive sur­gery (MIS) minimizes some of these complications, increasing patient compliance and quality of life. This involves inserting the endoscopy lens and surgery accesso­ries at the target site. This set of systems helps perform critical tasks through exte­rior surroundings without directly accessing the interior system. In contrast to conventional “open” surgeries, minimally invasive surgical techniques offer certain clinical advantages, such as limited tissue disruption, lower pain, and improved healing and recovery [66]. Moreover, it offers reduced hospitalization times and remains economically viable. However, some shortcomings are associated with it, such as minimal dexterity, absence of 3D imaging modalities, and minimal design parameters, subsequently leading to improper feedback from the operated tissue site [67].
Clinicians routinely perform medical endoscopy due to the multiple associated benets, such as minimal pain and faster recovery. In a typical endoscopic proce­dure, the instrument itself may lead to compression, tension, and other mechanical damage, which causes great pain and triggers a cascade of anomalies. Therefore, more focused research on the tool-tissue interface becomes particularly relevant. During gastrointestinal endoscopy, the endoscope is inserted into the GI tract. As it advances, it can result in many negative repercussions, such as throat congestion, bleeding, sub-mucosal tearing, etc. [68]. All of these are caused by the tribological effects of repeated insertion, rotation, pushing, and retrieval procedures. The rst study reported on collapsed GI tract surgery was in the early 2000s. The friction coefcient at the interface of the endoscope increases proportionally with the speed and can be measured by a viscoelastic model [69]. The challenge of performing experimental investigations is evident because of the inated cost and ethical con­siderations. The complex anatomy of the digestive tract in humans has aided in the development of endoscopy. The digestive tract has altered diameters, wall thick­ness, and lengths at different locations, from the esophagus to the large intestine. The microbiota of the digestive tract also exerts additional frictional forces that have been proven experimentally, the data of which can help in considering the safety­related parameters during gastrointestinal endoscopic interventions.
Laparoscopy, i.e., MIS in the abdomen, involves relatively small cuts in the abdominal region. The endoscopic advancements aid the clinician with visual input and organ control. The design of the instruments provides a handle, tip, and a rigid shaft, which allows the surgeon to perform axial sliding, rotation, and pivoting in two perpendicular planes. This fulcrum inuence signicantly reduces exibility and connes the surgeon mostly to the frontal or sideway tissue. The Laparoscopic graspers are often used for tissue interactions, such as clamping, gripping, and drag­ging. Tissue damage is almost inevitable in these cases due to the associated friction at the tool-tissue interface. Also, there is increased pressure build-up during the
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withdrawal of the laparoscopic graspers, which remains a primary reason for exces­sive injury in a typical laparoscopic procedure. Studies suggest that such trauma caused by a pressure build-up has a 2–4% higher risk of injury to the bile duct, bowel, and vascular structures than in traditional surgical procedures [70]. It was also hinged that 66% of tissue-related damage during laparoscopic intervention was attributed to grasping action.
Another class of MISDs is vascular stents, where tribology is crucial both during the delivery and post-delivery stage. Predominantly, the stent should not drive an extensive tissue injury due to friction and does not migrate and get washed down­stream by the owing blood [71]. Stent migration can be reduced by studying dif­ferent forces involved in the stent-tissue interaction, i.e., time-dependent blood ow, normal force that the vessel exerts on the stent strut structure, and friction force. One of them is to increase the normal force by oversizing the stent, which can exert more strain on the vessel [62]. Alternative options for the same are by increasing the contact area of the stent with the vessel wall, either by broadening the contact area between struts or by introducing additional struts. (Fig.9.3). There is a chance to raise the friction coefcients, and tribology becomes relevant as stents are intended to remain static after being progressively inated [72]. The primary elements inu­encing the interaction are the chemical and physical characteristics such as Van der Waals forces, capillary forces, and electrostatic interactions.
The other related MISD is a catheter that enables the insertion of stents into con­stricted vessels and contributes to tribological contexts. A typical vascular surgery also uses guidewires to push the catheter and guide it to the deployment site. Lubrication becomes important as the catheters must adjust according to the vessel, and a low-friction material is more helpful.
9.4 Current Challenges andFuture Work
Tribological problems with biomechanical, electrochemical, and tribological inter­actions are common in fracture xation components. Because of its intricacy, the coupling mechanism in the invivo environment is yet unknown. Although material mechanical and tribological performance has been effectively improved through invitro research, more thought must be given to fracture structures invivo biome­chanical settings. Porous materials encourage bone ingrowth and cell adhesion and have a greater coefcient of friction. Nevertheless, further research is needed to optimize bone ingrowth and osseointegration by surface modication and changes to porous structure design (porosity, pore size, etc.). Further investigation is neces­sary to understand fully how oral microbial habitats affect porous implants. Although research on dental materials invitro mostly focuses on their wear characteristics, it is still unclear how long-term invivo wear occurs. The scarcity of knowledge on material wear processes may hamper dental material development.
Studying the bio-tribology of cardiovascular devices is crucial for enhancing performance and reliability. Future advancements should focus on creating