09-11-2012, 03:21 PM
INCREMENTAL SHEET FORMING (ISF) IN THE MANUFACTURING OF TITANIUM BASED PLATE IMPLANTS IN THE BIO-MEDICAL SECTOR
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ABSTRACT
Titanium, recognized by its high strength-to-weight ratio, is a material previously
disregarded as a result of its high cost and difficult formability. Recent projects undertake
the usage and manufacturing of titanium as a replacement material in certain components in
the aerospace and mining sectors. The biomedical industry has also shown great favor
towards titanium as a result of its corrosive resistance and great biocompatibility with the
human body.
Incremental sheet forming (ISF) is a forming method capable of forming intricate,
asymmetrical components as a result of highly localized deformations. The ISF process forms
the component using stretching and bending while maintaining the material’s crystal
structure. The process can be performed using any 3-axis (and higher) Computer Numeric
Controlled (CNC) machine, making it highly available and cost effective to the
manufacturing industry.
This paper investigates the forming of bio-medical titanium plate implants for minimal
invasive surgical procedures. It proposes a customizable process chain capability for the
production of patient-specific bio-medical implants using the incremental forming
technology.
INTRODUCTION
Osteoarthritis (OA), also known as degenerative joint disease is a progressive disorder of the
joints caused by gradual loss of cartilage and resulting in the development of bony spurs and
cysts at the margins of the joints. The degradation of the musculoskeletal system, which is
mainly caused by joint injury, obesity (leading to musculoskeletal fatigue) and aging can also
lead to osteoarthritis. The hands, feet, spine, and large weight-bearing joints, such as the
hips and knees are commonly affected [1].
The only medical solution to severe cases of osteoarthritis is the surgical reconstruction or
replacement of a malformed or degenerated joint, better known as arthroplasty.
Arthroplasty makes use of biomedical implants and replacements to restore functionality of
the joints. Biomedical engineering in arthroplasty is an ever increasing field of interest as a
result of its innovative improvements to surgical quality.
Certain cases of partial osteoarthritis require less surgical action. Partial knee replacement
surgery, also known as unicondylar (or unicompartmental) knee arthroplasty involves a
covering which is placed over the affected area to resurface the affected bone and protect
the patient from further degeneration. Advantages of partial replacement include faster
recovery time and less post-operative pain. The biomedical implants used for these
operations consist of a standardized implant that is fit onto the bone by modifying (cutting
away) the outer structure of the bone. The result is known to cause post-operative
discomfort among some patients. Figure 1 shows the basic steps in Total Knee Replacement
(TKR).
BACKGROUND LITERATURE
The implementation of incrementally formed bio-medical implants in knee arthroplasty
requires sufficient background knowledge of both current surgical procedures and of current
ISF research conducted in this field.
Current Surgical Methodology
Surgeons choose a standard design implant based on the measurement of a patient's
morphological aspects from x-ray images for the traditional surgical implementation of knee
replacement surgery. The standard implants require interfering bone structures to be cut
away using a series of different bone removal tools so that the implant would fit. Due to the
variation in morphological aspects of the human femur, complications can arise as the
currently available mass manufactured implants offer limited ranges of geometry [7].
Pain and discomfort experienced by the patient during the post-operational and recovery
phases of surgery is probably the one major drawback of currently implemented knee
replacement surgery scheme. Traditional surgery causes damage to unaffected cartilage and
bone matter as well as ligaments [8]. A high concentration of nerves is disturbed as result of
the removal or damage implied to unaffected matter in the joint. The removal of the outer,
harder bone surface leads to the increase in pain and discomfort in the post operational
phases. The disturbed ligaments contain more than just strands of tensile collagen fibres.
Blood vessels as well as nerve endings are integrated into the ligaments of the knee. The
nerve endings in the ligaments of the knee are essential to optimal muscle activation and
certain reflex actions. Damage of these ligaments, as in cases of total knee arthoplasty
where the ACL and PCL are severed, result in the loss of proprioceptive function and reflex
triggering of the hamstrings [8].
APPROACH (PROCESS CHAIN)
The introduction of modern day manufacturing methods with the increased fields of
application shifts the limitation of production from the prototype manufacturability to the
digital design. The application of reverse engineering (RE) introduces a method of design
capable to produce a reliable 3D model of almost any object [12].
This project applies the techniques of reverse engineering to scan the knee joint and design
a customised implant. The implant will be manufactured out of titanium using the
incremental forming technique. The process chain proposed in Figure 4 seeks to standardize
and include all procedures that are followed in the implementation of the new knee
arthroplasty process.