Biomedical Engineering Reference
In-Depth Information
SAMs by both processes, functionalisation of SAMs after its adsorption to the
surface is preferred. This is because, in certain cases, it will be dicult to
control the reactivity of the head group towards the functional molecules.
There are a number of ways in which the functional group of SAMs can be
modified. SAMs can be adsorbed to a surface and then dip coated with the
active/functional ingredient. In other ways, the functional group of SAMs are
made to react directly with the molecules to be attached. When performing
this, there are possibilities for both the monolayers and the drug to possess
the same functional groups such as alcohols, carboxylic groups etc. In these
cases, the SAMs can be converted to their corresponding acid chlorides by
reacting the surface adsorbed SAMs with thionyl chloride. Converting the
functional group of SAMs to an acid chloride will enhance the reactivity and
will effectively bind the desired molecule to the SAM. A case study on the
additive manufacturing and surface modification of parts using SAMs is
described below.
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2.4 Case Study
2.4.1 Functionalisation of Selective Laser Melted Parts with
Ciprofloxacin using Self-assembled Monolayers
Cuboidal samples with dimensions 10
10
3 mm were fabricated from
Ti6Al4V powder using a Renishaw SLM 250 machine. These samples were
fabricated using previously optimised parameters.
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The fabricated samples
were mechanically polished using silicon carbide grits (200 mm, 400 mm, 600
mm, 800 mm and 1200 mm) and diamond pastes (6 mm and 1 mm). After
polishing the samples were rinsed with deionised water and the samples
were immersed in a mixture of sulphuric acid, hydrogen peroxide and water
in the ratio of 1 : 1 : 5 for 15 minutes to remove any surface contaminants.
The samples were then rinsed in deionised water for 30 minutes (twice) to
remove any residues of the chemical mixture.
16-Phosphanohexadecanoic acid (16-PhDA), a phosphonic acid SAM with
carboxylic acid as its functional/tail group, was used to modify the SLM
fabricated part. Assembly of 16-PhDA SAMs was performed using a previ-
ously optimised procedure.
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In short, surface cleaned samples were rinsed
with tetrahydrofuran (THF) and immediately immersed in 100 mL of 16-
PhDA SAM solution (1 mM). After 24 hours, the samples were taken out and
allowed to dry at room temperature and transferred to an oven at 120 1C.
After 24 hours, the samples were taken out of the oven and allowed to cool
before rinsing with THF and deionised water for 1 minutes each to remove
any physisorbed molecules.
.
2.4.2 Surface Functionalisation using Ciprofloxacin
Functionalisation of the 16-PhDA SAMs adsorbed to the SLM fabricated
Ti6Al4V surface was performed in an inert atmosphere. The apparatus
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