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Laser powder bed fusion-centred approach to enable local drug delivery from a cementless hip stem
ENGLISH ABSTRACT: Periprosthetic joint infection (PJI) resulting from colonisation of implant surfaces by pathogenic bacteria and subsequent biofilm formation is a devastating complication following total hip arthroplasty. It significantly reduces a patient’s quality of life and, in severe cases,...
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2021
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| Summary: | ENGLISH ABSTRACT: Periprosthetic joint infection (PJI) resulting from colonisation of implant surfaces by pathogenic bacteria
and subsequent biofilm formation is a devastating complication following total hip arthroplasty. It
significantly reduces a patient’s quality of life and, in severe cases, can result in amputation or mortality.
Treatment of PJI is associated with a substantial burden on healthcare and economic resources. The
importance of research towards innovations in PJI prevention and treatment is emphasised.
Local delivery of antimicrobial drugs is an effective approach to prevent and treat PJI as it enables high
local drug concentrations while avoiding systemic side effects. Current practice is considered sub-optimal
and appreciable research exists on the improvement of local drug delivery strategies. For cementless hip
stems the focus tends to be on coatings and conditioning of the external implant surface. A significant
research gap exists between external and internal drug delivery strategies where ‘internal’ refers to the
incorporation of reservoir structures within the implant. Therefore, a prototype strategy utilising the
internal volume of a cementless stem for a reservoir from which an antimicrobial drug can be delivered
directly to the implant surface was investigated. The challenge of fabricating a cementless hip stem with
intricate internal geometries can be effectively addressed through metal additive manufacturing (MAM).
Industry is steadily incorporating MAM into process chains as the main production technology for the
fabrication of high-value functional components. Laser powder bed fusion (LPBF) was applied in this
study as MAM technology to fabricate a Ti6Al4V ELI demonstrator cementless hip stem with local drug
delivery functionality. This required an interdisciplinary approach, for which a problem solving
framework has been synthesised to aid in process chain development from an LPBF-centred perspective. The overall problem was decomposed into integrated partial and single problems which were
systematically investigated through literature study and experimentation. An LPBF-centred solution was
developed for the direct integration of permeable structures in a dense part using an in-process assembly
method. Different levels of porosity were induced into permeable thin walls according to a systematically
identified window for ranges of the process parameters, laser power and scanning speed. This resulted in
tailorable release profiles for the model antibiotic vancomycin from an aqueous formulation. Released
vancomycin retained its antibiotic efficacy against Staphylococcus aureus Xen 36 (methicillin sensitive)
and Staphylococcus aureus Xen 31 (methicillin resistant), representing two of the most frequent pathogens
in PJI. Solutions for single problems were recomposed for integrated solutions to partial problems, and
subsequently for an overall prototype solution. The overall solution cementless hip stem prototype
effectively prevented surface colonisation by Staphylococcus aureus Xen 31, confirming the efficacy of
the developed local drug delivery strategy. These results were used to inductively refine the LPBF-centred
interdisciplinary problem solving framework.
The original contribution of the research corresponds to the experimentation and framework development
phases respectively. This involves the systematic investigation of LPBF to enable local drug delivery and
an LPBF-centred approach for interdisciplinary problem solving. Lastly, it contributes to the advancement
of LPBF by demonstrating the application efficacy of the prototype solution. |
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