Biomaterials / Medical Devices

Patient-Specific Mandibular Prosthesis for Osteosarcoma Reconstruction

A custom jaw implant for a 23 year old cancer patient who cannot tolerate metal, using a plastic composite that behaves more like bone than titanium does.

Implant stiffness of 14 GPa against titanium's 110 GPa, closer to real bone

Group case study. I owned materials selection and the mechanical case.

The implant in place, modelled from the patient's CT scans. Ceramic teeth and ceramic coated fixation screws mean no metal surface touches tissue anywhere on the device.

14 GPa: implant stiffness, near cortical bone
110 GPa: titanium, roughly 8x stiffer
Zero: exposed metal surfaces
186 MPa: ultimate strength, far above bite loads

Overview

This patient had bone cancer in the jaw and needed part of it removed. The standard fix is a titanium plate.

Titanium was ruled out. The patient reacts badly to metal, so an implant shedding even trace metal as it wears would inflame constantly and eventually fail. Every metal part of the usual solution had to be replaced, while still leaving a 23 year old with a normal face and a working jaw.

Bar chart comparing hardness and modulus of PEEK and fibre-reinforced grades — Hardness and stiffness across the five grades tested. Carbon fibre lifts both, and the 30% grade gave the closest match to cortical bone while staying well inside its strength limits.

What I did

Modelled the implant in 3D from the patient's CT scans as a carbon fibre reinforced PEEK plate following the original jaw line.
Compared five grades of PEEK on modulus, strength, hardness, wear and creep, and set out why the chosen grade won.
Matched stiffness to bone deliberately instead of maximising it, because an over stiff implant shields bone from load and the bone then resorbs.
Tested creep under sustained load at 37 °C, since a jaw sees decades of chewing cycles rather than one load to failure.
Specified the biological interface and the manufacturing, cost and regulatory route so the design could actually be delivered.

Tensile load against displacement curve for CF10 PEEK — Load against displacement for the composite: it stretches, yields at around 122 MPa, then breaks at 186 MPa. Chewing loads keep the implant far down the elastic part of this curve.

Methods

3D modelling from patient CT scans
Biocompatibility and metal sensitivity assessment
Mechanical comparison of five PEEK and carbon fibre PEEK grades
Creep and fatigue testing at body temperature under chewing loads
Bioactive coating and autologous stem cell specification for osseointegration
Design for manufacture, unit cost and regulatory pathway

Key results

01
Stiffness matches bone instead of overwhelming it. Carbon fibre PEEK sits at 14 GPa against titanium's 110 GPa, which is what drives the bone loss seen around conventional plates.
02
Strength is still well ahead of the load. Yield around 122 MPa, ultimate 186 MPa and fatigue strength 120 MPa, with bite forces far below all three.
03
Alternatives were ruled out on numbers. A phenolic carbon fibre composite at roughly 20 GPa was stiffer than needed and worse in flexure, so it lost to the 14 GPa grade.
04
No metal means no failure mode from a scratch. On a coated metal implant one scratch exposes the substrate. This releases no metal ions, and being radiolucent it keeps follow up scans for recurrence readable.

Outcome

The case ends with an implant that can be made and that solves the problem which ruled out standard treatment. It matches bone stiffness, contains no metal, encourages the patient's own bone to grow into it and keeps imaging clear. The trade offs are stated: it costs more than an off the shelf titanium plate and takes longer to produce.

Tools & techniques

CADMaterials selectionPEEK compositesBiomechanicsMedical device design