Medical Device and Orthopaedic Implant Engineering & Surface Finishing

Medical devices and orthopaedic implant engineering is becoming popular day by day providing ease to mankind. There is always a need to improve the working and reliability of medical devices. It not only involves the study of biological needs but also demands intricate engineering that is very close to perfection. Orthopaedic implants are also very important as they recreate a body structure and help the injured to get back to their original form. Therefore, both medical devices and orthopaedic implants need a lot more attention to have higher efficiency and excellent performance. It requires experienced surface finishing routes, choice of the right technique, accurate implementation, and dimensional control. All these requirements have made it important to ensure the right surface finishing technique for the concerned medical device or implant. It will help reduce the cost of the overall equipment and provide better results.

Medical Engineering

Medical engineering is the application of engineering knowledge to develop medicine and healthcare products, devices, and procedures. Multiple directions are present in this field to work for therapeutic, treatment, diagnosis, or prevention techniques. It combines the knowledge of biology and medicine with that of engineering. It is an interdisciplinary field that has high demand in the future. Better is the engineering technology, better will be the health-care and medicine department. It will improve and revise the traditional healthcare methods with advanced and efficient ones.

Surface Finishing Techniques for Orthopaedic Implant Engineering

Surface finishing techniques play a vital role in the development of both medical devices and orthopaedic implants. No medical equipment can shine better without being finished efficiently by choosing the right surface finishing tool. For orthopaedic implants, there is a high demand for dimensional accuracy that can be achieved precisely by using lathe surface finishing, lapping, polishing, and drag finishing processes. Medical devices also have intricate parts such as blades that needs to be finished perfectly to achieve professional performance. There is no chance of risk in these devices in terms of dimensions, sharpness, roughness, alignment, etc. It, therefore, requires an accurate measurement that is possible using the surface finishing techniques mentioned above.

Manufacturing Process for Orthopaedic implants

Orthopaedic implants are defined as the support or replacement for hard connective tissues such as bones and joints. Orthopaedic implants are made with metals, alloys, ceramics, polymers, or composites depending on the application. But mostly metals are used because they provide extra support and compatibility with the body. These can be temporary or permanent depending on the reason for using them. Orthopaedic implants serve a crucial role for people who have fractured or broken their arm or leg or even backbone. These implants are specifically designed according to the patient and then implanted with great care and safety. Coatings are also done to save the body from unwanted reactions and problems that may arise. These implants include screws, nails, plates, sticks, and wires.

Orthopaedic implants are made by multiple engineering techniques. Automation and simulation processes have made manufacturing far easier and more efficient than before. Mostly, titanium and stainless-steel alloys are used for orthopaedic implants. The following steps are carried out:

  1. Selection of the right material depending on the type of implant and duration.
  2. After this, CNC machining with pre-programmed instructions is used. A vertical machine center (VMC) is also utilised for this purpose.
  3. After getting the required implant shaped by CNC or VMC, the next processes are carried out to meet the accuracy demands and surface finishing. This buffing process (also called polishing) is used. It has two types namely cutting buff and finishing buff.
  4. After buffing, electrochemical polishing is done to remove any extra matter or particles from the surface of the implant. Micro peaks and hollow surfaces are being smoothed to increase the smoothness of the surface.
  5. At the end, there is an ultrasonic cleaning process to remove any remaining particles from the implant.

Manufacturing Process for Orthopaedic implants

Non-destructive Testing for the Medical Industry

NDT is playing a very important role in checking the durability, reliability, and quality of manufactured implants. Any flaws will be detected before use and thus lessening the vulnerability of the patient. Visual testing is first carried out to confirm there are no visible flaws in the implant by using visual aids. Liquid Penetrant Testing or magnetic particle imaging is performed to find any defect or crack in the implant. Eddy current detection can also be used to find any additional components or changed behavior of the implant. NDT is important because it leaves the implant unchanged and safe after the testing.

What are orthopaedic implants made of

Following are the materials and alloys that are biocompatible and are being used in making implants:


Cobalt Chrome

It is an alloy (Co-Cr) that has high wear resistance, strength, and temperature endurance. Other elements such as molybdenum are also added to improve its performance. Mostly, it is used in dental and orthopaedic implants. Removable partial dentures and porcelain fused to metal fabrication structures are done using Co-Cr alloys. It is used to treat spinal deformity and stability of the spine. These are lightweight and comfortable alloys that fit perfectly into the mouth and do not irritate much. In vitro and in vivo tests have proved that it can be used in surgical implants and is biocompatible. It shows excellent corrosion resistance due to the presence of chromium.

Lapping and Polishing Cobalt Chrome

Test Requirements: To mirror polish cobalt chrome balls, 28mm diameter. Ra < 2µinches and Roundness < 0.0004”

Equipment used: 1. Kemet Spherical polisher, 2. Cast iron lap, 3. NLH cloth, 4. Kemet Diamond compound 1-KC547, 5. OS lubricating fluid, 6. CO-42 cleaning fluid, 7 .Precise tooling

Process breakdown: The lap was fitted to drive boss on spherical polisher, a square of NLH cloth was placed on top with 1-KC547 diamond compound applied to the middle, the machined ball was pushed onto the machined shaft and inserted into the yoke holder and placed onto cloth, a slight spray of OS lubricating fluid was applied and was run for 15 minutes till polished up.

Results: Surface finish requirement < 2 µinches (0.051 µm)
Surface finish achieved: 0.0119 µm
Roundness required: 0.0004” (10.16 µm)
Roundness achieved: 2.365 µm

Before Polishing Cobalt Chrome

before polishing Cobalt Chrome ball

After Polishing Cobalt Chrome

after polishing Cobalt Chrome ball


Aluminium is generally used in conjunction with titanium. It is added as an alloying element and is widely used in orthopaedic implants. Aluminium forms Aluminium oxide coating on the surface that is impervious and can be used to protect the inner layers from corrosion. Therefore, Aluminium is used to increase the lifetime of implants. Being readily available and cost-effective, it is used along with other metals to make effective and durable implants. But it does not stand alone as an implant material due to its low strength.
Iron has shown a great opportunity for making degradable implants. It is a promising biodegradable implant material with good mechanical strength and biological properties. The time of its degradation can be controlled by using coatings and the addition of other elements. It reduces the risks of long-term compatibility of the implant with the body. When degrading, it converts to iron atoms that are already present in the body and perform multiple functions. It can therefore add to the body and lower the problems of mineral deficiency systematically. Some concerns are still shown because chloride ions can attack the iron implants and cause quick degradation with sharp and deep pits resulting in mechanical strength failure.

Cobalt-based Alloys

They are widely used alloys for biomedical implants for hip joints, knee joints, and others. These are used to make a metal-on-metal hip joint for resurfacing. They also have highly corrosion-resistant properties with efficient wear resistance in a biological environment that even contains high chloride ions. It is because of the crystallographic nature of cobalt. Other properties are imparted by alloying it with elements such as chromium, molybdenum, and tungsten. These alloys are used to make dental restorations. Although the price of these alloys is a bit higher the performance under a corrosive environment and stability can compensate for it.

Lapping and Polishing Tibial

Test Requirements: To mirror polish a Tibial with pin
Component/Material: Machined Tibial with pin

Machine Type: Kemet 15” diamond lapping/polishing machine
Lap Plate: Kemet Iron & Copper composite lapping plate, annular grooved, CHEM – H polishing pad
Abrasive Type/Grade: Kemet Diamond Slurry Type K micron Standard & COL-K (NC)
Additional Pressure: 4 Kg hand weights

Process Breakdown
Stage Plate/cloth type Abrasive type/grade Process time
1 Kemet Iron Type K Standard Diamond slurry 40 minutes
2 Kemet Copper 20 minutes
3 CHEM-H COL-K (NC) 40 minutes

Comments: A special fixture would need to be made to hold the Tibial with pin.

Fixture on Polishing Machine with Annular grooved Lapping Plate

Lapping and Polishing Tibial

Polished Tibial

Lapped Polished Tibial


Titanium and its alloys are widely used in medical implants, especially dental implants. It is highly biocompatible. It has been in use since 1960 and serves as a viable option for dental implants due to its durability and compatible functionality mode. It is mostly used for replacing damaged or missing teeth. The prerequisite to using this as a replacement is the good health of a person. It has an excellent bone formation and bonding ability that makes it perfect for implants. It can be manufactured by using programmed processes followed by surface finishing techniques. It also shows excellent corrosion resistance in the body resulting in long-term use and non-toxicity.


It is an important material that has excellent strength and mechanical properties comparable to those of bones. It is a biodegradable material that is used for a new generation of orthopaedic implants. They degrade in the physiobiological environment and provide much better results as a substitute for permanent implants. It has highly controllable dimensional accuracy due to its excellent machinability. It has a high damping capacity. It gives the advantage of removing the need for a second surgery. But its high corrosion rate is still limiting its use as an implant. Therefore, surface modifications and coatings are widely used to improve their corrosion performance.

Steel Alloys

These are the most common and old alloys that are used as implants ranging from dental implants to orthopaedic applications. Stainless steel finds its applications where the implant is in direct contact with a biological fluid. Its type 316L is regarded as the most corrosion-resistant material for implants. It has minimum chances of causing the infection. Mostly it is used for temporary implants due to its short-term corrosion resistance. One reason for making steel implants is its lower cost, easy manufacturing, and testing. Also, they have high elasticity modulus that makes them suitable for orthopaedic implants.

Lapping and Polishing Steel alloy

Test Requirements: To develop a process to polish a spherical cap

Equipment used: Kemet SpheriMatch machine, NLH cloth, 3 micron type k slurry, Customised lap, 15” pressure weight, Co42 cleaning fluid

Process breakdown: The spherical cap was fixed on to a 15” pressure weight using foam tape, then the pressure weight was placed into the jaws of the SpheriMatch chuck and tightened using the key. Tthe customised lap was placed on the sweep arm and positioned covering half the area of the cap, the sweep length was then adjusted to give a slight sweep of about 10mm. The machine was then run for 10 minute cycles while applying 3 micron type k from a trigger spray every 2 minutes. It was run for a total of around 6 cycles to achieve the finish. Part was then cleaned with Co42 cleaning fluid.

After Polishing Steel Alloy Cap

After Polishing Steel Alloy Cap



Polyethylene is a commonly used biological polymer that is not biodegradable and is porous. Dental implant abutment can be made from Polyetheretherketone (PEEK). Moreover, polymers can change the structure by interacting with human body fluids. Hence, their functionality can be controlled. Medical devices such as catheters are made from polymers due to flexibility.


Polytetrafluoroethylene (PTFE) is used in implants for soft and delicate body parts such as vocal cord defect correction, arterial graft, facial plastic surgery, and even in orthopaedic joints. It is also regarded as a reliable permanent implant for certain applications. It is used in dental treatments and implants to improve the shape and alignment of teeth. If there is an offending artery, then instead of removing it, a Teflon sponge is inserted. Thus, a variety of uses can be seen for Teflon in medical applications.


It is a biomaterial that is used in dentistry and orthopaedic implants. It is widely used in dentistry due to its strength and aesthetics. It is also used for bone replacement due to its high strength, wear resistance, and endurance. It is mostly used in load-bearing joints such as hip joints, and knee and ankle joints. It is also used efficiently in ball and socket joints owing to its wear resistance. Different manufacturing processes are used to stiffen the alumina implants and use them as a replacement for costly zirconia implants.


It exists in the form of zirconium oxide and has a strong ceramic crystal structure. It has a very high tensile strength and modulus of elasticity that makes it appropriate to be used in load-bearing implants. They also have a good aesthetic look that makes them more attractive rather than titanium. Also, it has higher biocompatibility with the human body.

Silicon Nitride

This is a new class of materials in implants. Mostly, the studies are being conducted for their use in orthopaedics and dentistry. Spinal implants have been made by using this compound. It is a very strong and inert material that would find applications in implants in the future. They are considered safe materials to be used inside the human body and are nontoxic. Coatings of silicon nitride are also used for other implants to make them efficient while controlling the cost.


Carbon Fibers

Carbon fibers are used in conjunction with polymers for orthopaedic and spinal surgery. It is used for the treatment of nonhealing bone. Mostly, it is used as a reinforcement for making medical implants. It adds to the strength of materials and can aid the fixation of extremity fractures. Carbon fibers originally have a bendable small diameter, high strength, and also a high-modulus fabric that can be molded with adaptation into complicated curved areas for a couple of versions in utilised use. The new carbon fiber has additionally been used in the therapy of tibial non-union (non-recovery bone); which has proven fine outcomes. A clear benefit over titanium implants.

Medical Implants Surface Finishing Standards

Following are the standards that have been set to provide excellent quality implants:

  1. ISO 7206 (1, 2, and 6) for surgical implants including criteria for dimensions, articulation, and endurance for partial or total implants in the regions of the head, neck, and hip joint.
  2. ISO 7207 (1 and 2) for dimensional accuracy and articulation of surgical implants of partial or total knee joints.
  3. ISO 9583 and ISO 9584 for magnetic particle imaging and radiographic testing respectively.
  4. ISO 14243 (1 and 3) for wear of total knee joint with load control and environmental impact on dimensions.
  5. ASTM F746, F797, F1223, and F1147 are designed for crevice corrosion, fretting corrosion, constraints, and tension testing of metal coatings and calcium phosphates joints.

Nanoscale Surface Modifications

Nanoscale surface modifications are required to change the behavior of materials as they interact with human tissues. Hence nanoscale modifications can change the surface of implants can generate efficient results. There are two types of modifications that can be done:

  1. Chemical Modifications - It includes electrochemical modifications such as anodic oxidation that can be controlled by existing voltage values and related parameters. Another method is chemical patterning which can add nano-pits on the surface thus changing the properties such as wettability, roughness, porosity, and thickness of the layer. Selected elements can also be incorporated by using multiple solvents in an etching process. Chemical vapor deposition and sol-gel processes can also be used to alter the surface of implants.
  2. Physical modifications - It includes thermal oxidation and ion implantation that can change the atomic arrangement in the implants. These techniques allow depth control of biological elements and ions.

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