Polymer/drug films as a model system for a drug eluting coronary stent coating layer Valeria Ciarnelli Prof. Clive Roberts Prof. Morgan Alexander, Prof. Martyn Davies School of Pharmacy The University of Nottingham 14 September 212 PharmSci_APS
Introduction: what is a coronary stent? The coronary artery stent is a tubular device, in the form of a coil or mesh, that is inserted at the site of arterial obstruction via a catheter. This device widens the coronary artery improving blood flow to the ischemic heart muscle. 2 types: Bare metal stent (BMS) Drug eluting stent (DES) A Obstruction: plaque. The stent is placed via catheter B Balloon inflated The artery is expanded C Scaffolding action The blood flow is re-established
Targets Drug eluting stent + Drug/Polymer coating layer Characterization of films as models for drug eluting coronary stent coating layer Characterization of the actual drug eluting coronary stent coating layer This work is a part of analytical support to develop a medical device Optimization of manufactoring process
Methods. Spun cast film preparation and equipments used Spin casting Spray coating AFM (XPS) 3 (ToF-SIMS) Spun cast or spray coated film Sample ID Casting Procedure Drying Step Series 1* Spun cast Room condition Series 2* Spun cast Bake in oven (5 C for 45 min) Series 3* Spray coated Warm air (5 C for 15 sec each 2 nd spray cycle) Series 4* Spun cast in argon atmosphere Bake in oven (5 C for 45 min under vacuum) *The films were made from solutions at different drug polymer weigh ratio precisely at 1:3; 1:1 and 3:1. Pure polymer and drug films were also made as references models.
Methods. Atomic Force Microscopy (AFM) A) Ball and stick model of pentacene B) STM images, C) and D) NC-AFM image of pentacene A B 1.3 Å C 5 Å 5 Å -2 Hz D Å + 1 Hz 5 Å 2 Å -7 Hz Leo Gross et al, Science, 29 Leo Gross et al, Science, 29, 324, 1428-5 Hz
Methods. Time of flight Secondary Ion Mass Spectroscopy (ToF-SIMS) Analysis Ion Beam Sputter Ion Beam 1 µm 3 µm y x Intensity Depth z Anna Belu et al. Chemical imaging of drug eluting coatings: Combining surface analysis and confocal Raman microscopy
Methods. X-Ray Photo-electron Spectroscopy (XPS) Photoemission peak Photo emission X-rays Inelastic scattering tail Free electron X-Ray Valence electrons ev Core electrons Nucleus X-Ray Coronene Molecule (C 24 H 12 )
Results. AFM characterization. Series 1 and 2 Series 1. Spun cast film without heating step. Tapping mode. 22nm Phase 63 15nm Phase 41 134nm Phase 6 2 µm Increasing drug loading - 9-9 1:3 d:p wr 1: 1 d:p wr 3: 1 d:p wr Film at 1:3 wr shows circular pit features (diameter approximately 1-25). Clear evidence of phase separation Film at 3:1 drug polymer weight ratio shows globular surface features - 9 Series 2. Spun cast film with heating step (5 C for 45 min). QNM mode. 33nm DMT modulus 25 MPa DMT modulus DMT modulus 2 137 MPa 145 nm 3 GPa c 2 µm MPa 1:3 d:p wr 1: 1 d:p wr 3: 1 d:p wr Film at 1:1 shows network structure surrounding deeper areas, globular features with a diameter of approximately 1 MPa GPa
Results. AFM characterization. Series 2 and 3 Series 3. Spray coated film on silicon wafer with heating step. (QNM mode) 167 nm DMT modulus 5.8 GPa 551 nm DMT modulus 2.6 GPa 216 nm DMT modulus 1 GPa 2.4 GPa GPa 1:3 d:p wr 1: 1 d:p wr 3: 1 d:p wr 75 MPa Increasing drug loading Presence of globular features (diameter 1) showing mechanical heterogeneity Features organized in globular domains also observed in the spun cast films. These features occur at a higher incidence with increasing drug concentration Series 4. Spun cast film on silicon prepared in argon atmosphere with heating step (5 C for 45 min) under vacuum. ( tapping mode RH = 5%) 2nm Phase 12 8 nm Phase -15 33 nm Phase -15 2µm 1-27 1:3 d:p wr 1: 1 d:p wr 3: 1 d:p wr Different morphology although still presence of globular domains with diameter ranging from 1 to 35-21
Results. ToF-SIMS characterization. Depth profiling of spun cast films series 1 Series 1. Spun cast film on silicon wafer 1:3 d:p weight ratio 1:1 d:p weight ratio 3:1 d:p weight ratio 16 14 12 8 6 4 Film at 1:3 drug polymer weight ratio without heating step Bulk Polymer PLA Interface Drug Everolimus Silicon x 5 18 16 14 12 8 6 4 Film at 1:1 drug polymer weight ratio without heating step Polymer PLA Drug Everolimus Silicon x 1 9 8 7 6 5 4 3 2 Film at 3:1 drug polymer weight ratio without heating step Polymer PLA Drug Everolimus Silicon x 5 2 2 1 Surface 1 2 3 4 5 Depht (nm) 1 2 3 4 5 Depht (nm) Polymer Drug Silicon x n (n= 5,1 and 5 for 1:3, 1:1 and 3:1 respectively) This indicates that the drug migrates to the surface and to an extent at the substrate interface leaving the polymer relatively concentrated in the bulk. Overall relative ion peak intensities for drug and polymer markers are consistent with the respective concentration Sample ID Thickness (nm) Sputter time Sputter rate (sec) (nm/sec) 1:3 d:p wr 25 277.9 1:1 d:p wr 315 351.9 3:1 d:p wr 288 342.85 1 2 3 4 5 6 Depht (nm)
Results. ToF-SIMS characterization. Depth profiling of spun cast films series 2 Series 2. Spun cast film on glass slide. The films underwent a drying step in the oven at 5 C for 45 min 1:3 d:p weight ratio 1:1 d:p weight ratio 3:1 d:p weight ratio Intensity Counts (ion (ions) count) 9 8 7 6 5 4 3 Film at 1:3 drug polymer weight ratio with heating step Silicon Polymer PLA Drug Everolimus Count (ions) 6 5 4 3 Film at 1:1 drug polymer weight ratio with heating step Silicon Polymer PLA Drug Everolimus Intensity Counts (ion (ions) count) 7 6 5 4 3 Film at 3:1 drug polymer weight ratio with heating step Silicon Polymer PLA Drug Everolimus 5 1 15 2 25 3 5 1 15 2 25 3 35 5 1 15 2 25 3 35 Polymer Drug Silicon The polymer is concentrated in the bulk region of the film The drug migrates to the surface forming a surface-enriched drug region for all the films at different loadings Polymer Drug 1:1 d:p wr
Results. ToF-SIMS characterization. Depth profiling of spun cast films series 3 Series 3. Spray coated film on silicon. The films underwent a drying step (warm air 5 C) 1:3 d:p weight ratio 1:1 d:p weight ratio 7 Spray coated film at 1:3 drug polymer wr. 18 4 Spray coated film at 1:1drug polymer wr Silicon 1 Polymer Drug Silicon 8 6 4 5 Polymer 4 Drug Silicon x 5 14 3 5 1 15 2 Drug Polymer Polymer The drug surface enrichment is less pronounced than the one observed for the spun cast films 1:1 d:p wr Polymer 25 Drug 15 25 3 5 Spray coated film at 3:1 drug polymer wr 35 6 16 3:1 d:p weight ratio 5 1 15 2 Drug 25 3 1 Silicon 2 3 4
Results. XPS characterization. Surface analysis of spun cast films series 2 and spray coated films series 3 XPS spectra of drug powder XPS spectra of polymer powder x 1 2 x 1 3 8 O 1s C 1s 25 O 1s 7 6 2 5 CPS 4 CPS 15 3 1 C 1s 2 N 1s 5 1 12 9 6 3 Bi ndi ng E nergy (ev) 12 9 6 3 Bi ndi ng E nergy (ev) C S( hi i b di d i C S / i ) Spun cast films (series 2) Spray coated films (series 3) Spun cast films (series 4) Drug/polymer wr (Drug loading) 1:3 (25%) 1:1 (5%) 3:1 (75%) 1:3 (25%) 1:1 (5%) 3:1 (75%) 1:3 (25%) 1:1 (5%) 3:1 (75%) N % (theoretical).37.74 1.1.37.74 1.1.37.74 1.1 N % (experimental) ± SD 1.3 ±.2 1.2 ±.4 1.1 ±.1.4 ±.4 1. ±.1 1.3 ±.5 1.29 ±.6 1.44 ±.4 1.39 ±.3 Experimental Drug % (w/w) ± SD 85.4 ± 1. 83.3 ± 2.4 76.4 ±.7 27.2 ± 2.7 64.7 ± 7. 88.5 ±.2 88.5 ± 4. 99.5± 2.4 96.3± 1.7 Drug enrichment Less pronounced drug enrichment
Results. XPS characterization. Depth profiling of spun cast films: series 4 Series 4. Spun cast film on silicon. 5ºC for 45 min, Ar atmosphere and controlled humidity 1:3 d:p weight ratio 1:1 d:p weight ratio 3:1 d:p weight ratio C1s, O1s & Si2p % 9 8 7 6 5 4 3 2 1 5 1 15 2 1.8 1.6 1.4 1.2 1.8 N1s %.6.4.2 C1s, O1s & Si2p % 9 8 7 6 5 4 3 2 1 1.6 1.4 1.2 1 2 4 6 8 1 12.8.6.4.2 N1s % 9 8 7 C1s, O1s & Si2p % 6 5 4 3 2 1 5 1 15 2 Etching time (sec) 1.4 1.2 1.8 N1s %.6.4.2 C 1s O 1s N 1s Si 2p Drug enrichment at the surface and interface (film/silicon). The same is observed for the other drug polymer concentrations. The drug profiles obtained from XPS and ToF-SIMS depth profiling are consistent.
Conclusions We are able to characterize this particular drug polymer coating layer using complementary surface analysis techniques. AFM shows the presence of globular features (diameter 1-15) occurring at higher incidence with increased drug loading ToF-SIMS depth profiling on the model films showed the drug and polymer distribution as a function of depth, with the drug preferentially located at the surface The XPS analysis confirmed the existence of an enrichment of drug on the surface of the model films (series 2 and 3) at higher percentage compared to the bulk drug loading. In the case of the spray coated films the drug at the surface increased with the drug loading The drug enrichment is more pronounced in the spun cast films than the spray coated films. We have gained an understanding of the distribution of the drug
Acknowledgements Supervisors Thanks to: Prof Clive J Roberts Prof Morgan R Alexander Prof Martyn C Davies Prof Chen Xinyong Dr David J Scurr Mrs Emily Smith From Kratos Analytical Chris Blomfield Simon Hutton THANKS FOR LISTENING
Results. ToF-SIMS Depth profiling of spun cast films: series 4 Series 4. Spun cast film on silicon wafer. Silicon substrate, 5 ºC for 45 min, Ar atmosphere and controlled humidity 1:3 d:p weight ratio 1:1 d:p weight ratio 3:1 d:p weight ratio 6 5 4 5 4 3 Silicon Polymer Drug 5 1 15 2 25 45 4 35 3 25 15 5 Silicon Polymer Drug 5 1 15 2 25 35 3 25 15 5 Silicon Polymer Drug 5 1 15 2 25 The drug migrates to both the surface and the interface (film/silicon) The polymer is concentrated in the bulk region. Relative ion peak intensities for drug and polymer markers are consistent with the respective concentration Sample ID Thickness (nm) Sputter time Sputter rate (sec) (nm/sec) 1:3 d:p wr 84 115.81 1:1 d:p wr 93 93 1 3:1 d:p wr 83 95.87
Results. AFM characterization Globular features Peak force QNM mode Series 3. 1:1 drug polymer wr Series 2. 1:1 drug polymer wr Deformation a 185 nm DMT modulus 3.5 GPa 1 a Diameters: 1 2 x 2 µm 1µm 1.5 x 1.5 µm 1 23 MPa b b 2 x 2 µm Diameters: 2 Series 3. 1:3 drug polymer wr 216 nm 1µm 1 GPa 1.5 x 1.5 µm Series 2. 2 areas of spun cast film at 1:1 drug polymer weight ratio. Globular features with a diameters of approximately 1-2 can be observed. Their formations is probably due to the dry step at 5 C for 45 min. 2 DMT modulus 75 MPa 2 Series 3. Granular structure of the domain. The size of the globular structure varies between 1 and 2 nm.