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Analysis of

Failed BiomaterialsA biomaterial is a structure that can be used to

replace or augment part of the human body.

Common biomaterials are contact lenses, knee and hip

replacements (Figures 1 and 2). The material

specifications are dictated by the shape, mechanical

and physiological requirements of the original tissue.

Hard composite tissue such as bone can be replaced by

metals and ceramics, and softer connective tissue

such as tendons and ligaments can be replaced by

polymeric materials.

The design of an optimum biomaterial, amongst other

things, requires consideration of mechanical

properties and biocompatibility.

The mechanical property, which defines the stiffness

of a biomaterial is called the elastic modulus (EM). If

the EM of the biomaterial does not match the EM of

the original tissue that it is replacing, the implant may

fail. Likewise, if the material is not biocompatible an

inflammatory response may be elicited, possibly

leading to loosening or rejection of the implant.

Similarly, design flaws can lead to uneven load

distributions on the implant. Such design shortcomings

may lead to premature failure of the biomaterial

possibly necessitating revision surgery.

Figure 1 Total Knee Replacement.

Figure 2 Total Hip Replacement.

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One of the most common failure mechanisms for metal biomaterials is fatigue. Over time, cyclic

loading of the material can cause cracks to propagate and the material to fracture before the end of its

engineering lifespan (Photograph 1). Another common failure in softer biomaterials is engineering

wear. This involves two uneven surfaces articulating past each other, releasing wear particles that

facilitate the abrasion and eventual failure of one or more surfaces, as shown in the failure of the

polymeric portion of a total knee replacement (Photograph 2).

The ways in which cracks propagate are characteristic and as a result can be used to identify the

specific failure mechanism. Mechanical tests can be carried out to determine if the failed material met

its original engineering specifications and chemical analysis shows if the material was manufactured to

the required grade

Once the failure mechanism is identified, the analyst can determine the cause of the failure, for

example, investigating why a hip implant failed in-vivo. The cause may be due to improper

implantation, manufacturing defects, design deficiencies, operational damage, abuse by the patient or

the use of defective, non-biocompatible materials.

Hannaford Forensic Services has been conducting independent investigations for over 20 years and

employs a team of experienced and qualified forensic engineers and scientists. Please contact one of

the team to discuss the range of materials and biomaterials failure investigation services that we can

offer.

Tel (24 hrs): +852 2548 0577

Photograph 1 Broken Hagie Pin shown here inthe treatment of a fractured clavicle.

Photograph 2 Worn polyethylene componentfrom a total knee replacement.

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