Biomedical Engineering Reference
In-Depth Information
addressed in the literature. Therefore, there is an urgent need for the develop-
ment of a better understanding of microstructural evolution and property-
microstructure relationships in implant alloys as a function of processing.
As noted above, the need for prosthesis implants such as hip implants is
increasing at an alarming rate. While currently existing hip implants function
appropriately, they do not represent the best compromise of required properties.
Furthermore, presently the manufacturing of implants is largely via subtractive
technologies involving substantial material wastage leading to increased costs and
time of production. Therefore, an imperative need exists for functionally-graded
hip implants representing a better balance of properties and manufactured via
novel additive manufacturing technologies based on near-net shape processing.
Some specifi c problems associated with currently employed implant manu-
facturing processes and the consequent compromise in properties are listed below:
1. The manufacturing is based on conventional casting and forging of compo-
nents followed by material removal steps via subtractive technologies such
as precision machining. These technologies not only involve substantial
wastage of material but are also limited to monolithic components without
any compositional/functional changes within the same component.
2. Diverse property requirements at different locations on an implant are
satisfi ed by joining different components (for example, femoral stem and
femoral head) made of different materials in a total hip replacement sys-
tem. This always leads to the formation of chemically abrupt interfaces
that are detrimental to the properties of the implant.
The current manufacturing route for hip implants does not allow for custom-
designing for specifi c patients with rapid turnaround times. Consequently, instead
of custom-designing the implant, the surgeon is often forced to adapt the pre-
existing design to fi t the patient's requirements. This can become particularly
challenging if the required physical dimensions of the implant differ substantially
from those of the standard manufactured ones, such as implants to be used for
children.
9.3 LASER PROCESSING OF ORTHOPEDIC BIOMATERIALS
9.3.1 Novel Processing Technology—Laser Engineered Net
Shaping (LENS™)
Similar to rapid prototyping technologies such as stereolithography, the LENS™
process [3,24] begins with a CAD design fi le of a three-dimensional component,
which is electronically sliced into a series of layers. The information about each of
these layers is transmitted to the manufacturing assembly. A metal or alloy sub-
strate is used as a base for depositing the component. A high power laser (capable
of delivering several hundred watts of power) is focused on the substrate to create
a melt pool into which the powder feedstock is delivered through an inert gas
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