designing the surface of medical devices
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Designing the surface of
medical devices
Tullio Monetta, Annalisa Acquesta
Department of Chemical Engineering, Materials and Industrial Production
University of Napoli Federico II
GOAL study an ad hoc surface treatment on
dental implants to obtain medical devices showing improved performances.
Titanium
•Low density (4.5 g/cm3 against 7.9 g/cm3 for steel, 8.3 g/cm3 for VitalliumR and 9.2 g/cm3 for Co/Ni/Mo/Cr alloys );
•Excellent mechanical properties;
•Poor toxicity;
•Good biocompatibility;
•Non-magnetic;
•Good resistance to acids and alkalis;
•Good heat transmission;
•Great resistance to erosion, cavitation and impact attacks.
The rate of spontaneous oxide formation is very high.
Titanium-Titanium oxides
There are different types of oxides on the surface, including: Ti3O, Ti2O, Ti3O2, TiO, Ti2O3, Ti3O5 e TiO2.
The aim is to form TiO2, which is the most stable oxide.
Cells growth
by Steve Gschmeissner
SEM view of TiUnite surface when osteoblasts
have filled pores (Current Concepts in Dental Implantology, book Ilser Turkyilmaz,)
Osteoblast «fill in the hole»
• Micro/macro roughness is required to increase the implant osseointegration rate
• Surface showing “more valleys than peaks” for
cells adhesion and spreading is necessary • A reservoir on implant surface is needed for drug
delivery
Needs
Designing the surface
A «production process» has to be settled up allowing to obtain a surface with:
Large valleys
Small valleys
Small tanks to store chemicals
Surface
treatments
Chemical
Electrochemical
(anodization)
Acid etching
Physical
Thermal
Co-deposition
Nanostructured
oxide (Titania
Nanotubes)
Porous oxide
(Anodic Spark
Oxidation)
Compact oxide
Chemical Vapor
Deposition Cold Plasma
Sol-gel
H2O2
Thermal
Spraying
Plasma
Spraying
Physical Vapor
Deposition
Ion / Laser
beam Sandblasting
Surface Engineering
Sandblasting-acid etching
SEM IMAGES (1000X) OF Ti CP2 SANDBLASTED 1 MIN (A), Ti CP2 SANDBLASTED 1 MIN AND ACID ETCHED (B), Ti CP2 SANDBLASTED 8 MIN (C), TiI CP2 SANDBLASTED 8 MIN AND ACID ETCHED (D).
A
C
B
D
Sa(a) =Sa(b) =Sa(c)
Sa = average roughness;
Sq = root mean squared roughness;
Sku = describes the “peakedness” of the surface
topography (Kurtosis);
Ssk= describes the asymmetry of the height
distribution histogram (Skewness).
Roughness
The anodizing titanium is connected to the positive pole of the DC power supply, where an oxidation process occurs. At the negative pole there is a reduction process of species present in the electrolyte. As a result of the anodic polarization, the oxide film increases and the immediate effect, resulting from the thickening of the layer, is the titanium staining. The growth of anodic oxide does not occur by expanding the porous layer outward, but by continuous oxidation and metal dissolution within the layer.
Titanium anodizing
Example of surface obtained by anodizing
Compact oxide Porous oxide
(Anodic Spark Oxidation)
Nanostructured oxide
(Titania Nanotubes)
Porous oxide
Oxide behaviour Titanium not treated «Inorganic» nanotubes in Hank’s solution «Organic» nanotubes in Hank’s solution 10
2
103
104
105
106
10-2
10-1
100
101
102
103
104
0
24h
29h
96h
216h
360h
Imp
ed
an
ce
mo
du
lus |
Z|,
cm
2
Frequency, Hz
102
103
104
105
106
10-2
10-1
100
101
102
103
104
0
24h
29h
96h
216h
360h
Imp
ed
an
ce
mo
du
lus
|Z
|,
cm
2
Frequency, Hz
102
103
104
105
106
10-2
10-1
100
101
102
103
104
0
24h
29h
96h
216h
360h
Imp
ed
an
ce
mo
du
lus
|Z
|, o
hm
*cm
2
Frequency, Hz
Rotation speed: 10 rpm Screw: nanotubes diameter 50-60 nm, lenght 350 nm. Flat samples: nanotubes diameter 100 nm, lenght 800 nm. The nanotubes morphology could be due to the complex geometry of the screw and could be attributed to the different distribution of the electric field that occurs when using a screw instead of a flat sample. Unexpectedly, the average diameter of nanotubes does not differ if measured on the crest, on the side or on the bottom of the threads. In the assumption that the electric field assumes significantly different values between the points mentioned, it would be expected to get dissimilar structures, but this event has not been verified. The increase in anodizing time, from 90 min to 120 min, has little influence on diameter, wall thickness and nanotube length.
Anodized screw
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
1,1
5 10 15 20 25 30
Rodamina 6G
talqualenanotubi
Fra
zio
ne d
i m
ole
cola
elu
ita [ug/c
m^2
]
ore^0.5 [h^0.5]
Dru
g F
ract
ion
Rel
ease
d,
µg/c
m2
Time, h2
Titanium flat sample
Nanotubes sample
Rhodamine
Drug delivery
The untreated titanium sample restrained
7μg/cm2 of the absorbed drug, while the
nanotubes-covered sample restrained 12
μg/cm2.
After 5 days, the untreated titanium
sample released 80% of the absorbed
drug, while the nanotubes covered
sample released 60%.
After 13 days, the untreated titanium sample
released all the absorbed drug.
Nanotubes covered sample released the
overall amount of drug after 26 days.
0
2
4
6
8
10
12
14
0 5 10 15 20 25 30 35 40
Tal quale Nanotubi
y = 1,348 + 0,18174x R= 0,97414
y = 2,1818 + 0,30808x R= 0,9694
Fra
zion
e d
i fa
rmaco
elu
ita [
ug
/cm
^2]
Ore^0.5 [h^0.5]
Dru
g F
ract
ion
Rel
ease
d,
µg/c
m2
Titanium flat sample
Nanotubes sample
Time, h2
Doxorubicin Hydrochloride
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