The currently used biomaterials for surgical implantation include stainless
steel, titanium and its alloys. However, due to the non-degradability and the
mismatch of the mechanical properties between these metallic implants and
human bone, there maybe a long-term adverse effect of inflammation or stress
shielding effect. This may lead to bone loss which brings with a higher risk of
implant failure. To avoid this problem, implants made of biodegradable
materials are the alternatives. Due to the poor mechanical properties of
biodegradable polymer especially for load-bearing area, biodegradable metal is
used instead. Magnesium is the potential candidate since it is degradable with
mechanical properties similar to human bone whilst magnesium ion is an
essential element to human bodies.
With the advantages of using magnesium for implantations, it can be
potentially used for fracture fixation implant and bone substitutes. However, its
rapid degradation and release of hydrogen gas may inhibit its use. Hence,
modification is required. In this project, plasma immersion ion implantation
and deposition (PIII&D) using aluminium oxide as the plasma source was
conducted on the magnesium alloys. The corrosion resistance properties of the
plasma-treated magnesium alloy were found to display significant
improvement in immersion test especially at early time points. The
plasma-treated sample was compatible with osteoblasts. Cells attached and
grew on the treated sample but not the untreated sample. The animal study
showed consistent results with the cell study, and there was a significant
increase in bone formation around the treated sample when compared to the
untreated sample.
The other potential application of magnesium is its usage as a bone
substitute. Due to the limitations of autografts and allografts, synthetic bone
substitutes are developed. The ideal bone substitutes should have similar
properties to those found with autografts. However, no such bone substitutes
presently exist; hence, a novel hybrid material is fabricated in this project
through the addition of magnesium granules into a biodegradable polymer
polycaprolactone (PCL). The immersion test showed that an apatite layer
composed of magnesium, calcium, phosphate and hydroxide was formed on the
hybrids but not on pure PCL, which suggested that the hybrids were
osteoinductive and osteoconductive. The compression test showed that the
mechanical properties were enhanced with the incorporation of magnesium
granules into pure PCL and were still maintained after 2 months of immersion.
Osteoblasts grew well on the PCL-Mg hybrids. The addition of smaller
amounts of magnesium granules (0.1g PCL-Mg) resulted in higher ALP
activity and up-regulation of different bone markers when compared to the
pure PCL. Finally, the animal studies showed that more new bone formation
was found around the 0.1g PCL-Mg hybrids especially at early time points,
which suggested that the healing time could be shortened.
In conclusion, fracture fixation implants and novel bone substitutes based
on magnesium were developed in this project. The aluminium oxide coating
was able to improve the corrosion resistance properties of magnesium alloy by
suppressing the release of magnesium ions. The PCL-Mg hybrids were found
to be biodegradable, biocompatible, osteoconductive, osteoinductive and
mechanically matched to human bone properties. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/161513 |
| Date | January 2011 |
| Creators | Wong, Hoi-man., 黃凱文. |
| Contributors | Yeung, KWK, Cheung, KMC, Luk, KDK |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47869549 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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