Louth, Sophie Elizabeth Thompson 
ORCID: 0000-0003-3065-8201
(2024).
Exploiting additively manufactured lattices to control mechanical properties and drug delivery in bone implants.
University of Birmingham.
Eng.D.
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Louth2024EngD.pdf
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Abstract
Metal bone implants are used extensively to provide mechanical support, fixation or to fill defects due to disease, aging or trauma. Examples of implant include joint replacement, fracture plates, and fusion cages. These are very successful surgeries; however, failures do occur. The most common causes of bone implant failure are infection and aseptic loosening which can be caused by stress shielding or poor fixation.
Additive manufacturing enables the creation of implants with complex geometries such as lattices which cannot be easily made with conventional manufacturing techniques. Despite lattices being used in medical devices for fixation, and extensively researched for stress shielding their potential to be exploited as drug delivery vehicles has not been fully explored. In this work the novel technique of manipulating lattice geometry to control drug release is proposed.
The mechanical properties of lattices manufactured from Ti-6Al-4V by laser powder bed fusion was investigated. Four lattice designs provided sufficient compressive strength to be weight bearing while having sufficient void volume to fill with a drug loaded biomaterial.
For example BCCZ lattices with a 350 μm strut thickness had an offset stress of 365 ± 7 MPa with a volume fraction of 0.583 ± 0.001. Additionally the effects of strut and wall thickness, lattice rotations during building, loading and a combination of the two, and unit cell size were investigated; to understand which factors were important when designing additively manufactured medical devices.
Secondly, BCCZ and gyroid lattices with volume fractions of 0.2, 0.4 and 0.6 were filled with brushite cement containing 2.5% w/w gentamicin sulphate. The drug release fitted the Korsmeyer-Peppas model with R2 values of at least 0.98 and could be controlled by changing the lattice geometry. There were also statistical differences in the size of inhibition zones of Staphylococcus aureus and Pseudomonas aeruginosa. The presence of brushite cement in the lattice structure did not reduce the compressive strength.
Finally, a coating was developed to immobilise therapeutics to the surface of implants. Albumin was used as a model therapeutic, it was covalently attached via amide bond coupling to PCL which was dip coated onto Ti-6Al-4V coupons. This process was optimised and albumin continued to intrinsically fluoresce on coupon surfaces after immersion for four months in phosphate buffered saline at 37°C.
This thesis focuses on the exploitation of lattices manufactured by laser powder bed fusion to control drug delivery while manipulating the mechanical properties, with a view to using them in hip replacements to treat infection, and spinal interbody fusion cages to improve bone ingrowth.
| Type of Work: | Thesis (Doctorates > Eng.D.) | |||||||||||||||
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| Award Type: | Doctorates > Eng.D. | |||||||||||||||
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| Licence: | All rights reserved | |||||||||||||||
| College/Faculty: | Colleges > College of Engineering & Physical Sciences | |||||||||||||||
| School or Department: | School of Chemical Engineering | |||||||||||||||
| Funders: | Engineering and Physical Sciences Research Council | |||||||||||||||
| Subjects: | R Medicine > RD Surgery R Medicine > RM Therapeutics. Pharmacology T Technology > TJ Mechanical engineering and machinery |
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| URI: | http://etheses.bham.ac.uk/id/eprint/14841 |
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