Designing the surface of medical devices

Transcription

1 Designing the surface of medical devices Tullio Monetta, Annalisa Acquesta Department of Chemical Engineering, Materials and Industrial Production University of Napoli Federico II

2 GOAL study an ad hoc surface treatment on dental implants to obtain medical devices showing improved performances.

3 Titanium Low density (4.5 g/cm 3 against 7.9 g/cm 3 for steel, 8.3 g/cm 3 for VitalliumR and 9.2 g/cm 3 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.

4 Titanium-Titanium oxides The rate of spontaneous oxide formation is very high. There are different types of oxides on the surface, including: Ti 3 O, Ti 2 O, Ti 3 O 2, TiO, Ti 2 O 3, Ti 3 O 5 e TiO 2. The aim is to form TiO2, which is the most stable oxide.

5 Cells growth Osteoblast «fill in the hole» SEM view of TiUnite surface when osteoblasts have filled pores (Current Concepts in Dental Implantology, book Ilser Turkyilmaz,) by Steve Gschmeissner

6 Needs 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

7 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

8 Surface Engineering Surface treatments Chemical Acid etching H 2 O 2 Sol-gel Cold Plasma Chemical Vapor Deposition Electrochemical (anodization) Compact oxide Porous oxide (Anodic Spark Oxidation) Nanostructured oxide (Titania Nanotubes) Co-deposition Thermal Physical Thermal Spraying Plasma Spraying Physical Vapor Deposition Ion / Laser beam Sandblasting

9 Sandblasting-acid etching A B C D 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).

10 Roughness Sa(a) =Sa(b) =Sa(c) S a = average roughness; S q = root mean squared roughness; S ku = describes the peakedness of the surface topography (Kurtosis); S sk = describes the asymmetry of the height distribution histogram (Skewness).

11 Roughness

12 Titanium anodizing 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.

13 Example of surface obtained by anodizing Compact oxide Porous oxide (Anodic Spark Oxidation) Nanostructured oxide (Titania Nanotubes) Porous oxide

14 Titanium (oxide) Nanotubes «Inorganic nanotubes» «Organic nanotubes»

15 Oxide behaviour Titanium not treated «Inorganic» nanotubes in Hank s solution «Organic» nanotubes in Hank s solution 10 2 Impedance modulus Z, cm h 29h 96h 216h 360h Frequency, Hz Impedance modulus Z, ohm*cm h 29h 96h 216h 360h Impedance modulus Z, cm h 29h 96h 216h 360h Frequency, Hz Frequency, Hz

16 Anodized screw

17 Anodized screw

18 Anodized screw Rotation speed: Screw: Flat samples: 10 rpm nanotubes diameter nm, lenght 350 nm. 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.

19 Drug delivery 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. Drug Fraction Released, µg/cm 2 Frazione di farmaco eluita [ug/cm^2] Doxorubicin Hydrochloride y = 1, ,18174x R= 0,97414 y = 2, ,30808x R= 0, Time, h 2 Ore^0.5 [h^0.5] Tal quale Titanium flat sample Nanotubi Nanotubes sample Frazione di molecola eluita [ug/cm^2] Drug Fraction Released, µg/cm 2 1,1 1 0,9 0,8 0,7 0,6 0,5 0,4 Rhodamine Rodamina 6G Titanium flat sample talquale Nanotubes sample nanotubi 0, ore^0.5 [h^0.5] Time, h 2 The untreated titanium sample restrained 7μg/cm 2 of the absorbed drug, while the nanotubes-covered sample restrained 12 μg/cm 2.

20 Conclusions Item performances can be improved by a proper design of the surface. Needs, aims, cost, added value, product shelf-life, should be considered when choosing the production process to modify the surface. A multidisciplinary approach is required.