SAST II - Novel Electrochemical Scaffolding Technique for SAST

Transcription

1 SAST II - Novel Electrochemical Scaffolding Technique for SAST Luigi De Nardo luigi.denardo@polimi.it Dipartimento di Chimica, Materiali e Ingegneria Chimica G. Natta

2 Outline 1. Why scaffolding in medicine? i. Clinical needs ii. Material/device approach and limitations 2. Scaffolding on medical devices i. Electrochemical fabrication technologies ii. Morphology tuning of chitosan scaffolds via cathodic deposition 3. Stability modulation 4. Future studies 2

3 Scaffolding at a glance 3

4 Surface Assisted Approach Tissue engineering approach Implantable devices Material Surface Assisted Drug Delivery Surface Assisted Tissue Engineering Surface Assisted Selective Transfection 4

5 Chitosan Chitin is a natural polysaccharide of major importance synthesized by an enormous number of living organisms the most abundant polymer after cellulose Chitin Chitosan Chitosan is a deacetylated chitin-derivative the only pseudonatural cationic polymer solubilization by NH 2 protonation Chitosan 5

6 Chitosan as biomaterial Applications Wound healing Tissue engineering Gene therapy Benefits Chemo-attract macrophages and neutrophils Stimulate granulation tissue and re-epithelization Carry growth factors to accelerate the healing Limitation of scar formation and retraction Intrinsic antimicrobial activity/controlled release of exogenous antimicrobial agents to anti-infection Rapid degradation, non-toxic and biodegradable Easy to develop various forms Cytokines, extracellular matrix, antibiotics controlled release Retain cell morphology, promote attachment, proliferation and viability of living tissues, cells and even stem cells Provide cell immunoisolation Biodegradable and biocompatible with high cationic charge potential Protect DNA from degradation by nucleases High transfection efficiency 6

7 ELD of Chitosan Electrochemical Deposition (ELD) of Chitosan has been proposed by Redepenning et al. (JBMR 2002) ELD is based on Cathodic electrophoresys of Chitosan Local increase of ph 2H 3 O + + 2e - 2H 2 O + H 2 2H 2 O + 2e - H 2 + 2(OH) - Chit NH 3+ +OH - Chit NH 2 +H 2 O 7

8 ELD on Titanium - Experimental ELD on Titanium specimens Ti CP ASTM grade 2 (Ø = 12 mm, 0.5 mm thick) Acid etched ([HNO 3 ] = 20% v/v + [HF] = 3% v/v) and water rinsed [Chitosan] = 1% w/v (practical grade, DA >75%, Aldrich) acid solution in: Acetic acid Malonic acid Citric acid Phosphoric acid Deposition on Ti Galvanostatic mode J = 1-20 ma cm -2 Ambient conditions 8

9 Deposition rate 9

10 Morphology tuning Acetic acid (17.48 mm) Phosphoric acid (57.55 mm) Malonic acid (9.61 mm) Citric acid (14.27 mm) 10

11 Morphology vs. deposition time J = 5 ma cm -2, t = 2 min J = 5 ma cm -2, t = 4 min Acetic acid (17.48 mm) J = 20 ma cm -2, t = 2 min J = 20 ma cm -2, t = 2 min 11

12 Molarity and Anion effects ACID ph [M] Acetic mM Phosphoric mM Citric ,27mM Malonic mM _ Chitosan film + Effects of molarity and anions on deposition: Deposition increases by increasing ph Deposition depends on Anions molarity µg cm -2 Boccaccini et al. Mat Lett 2009 ph 12

13 Buffering effect [CH 3 COO - ]=262.3mM ph = 4 (NH 4 OH buffer) [CH 3 COO - ]= 17.48mM Major role of ions concentration vs. ph Acetic acid buffering effect Competitive reduction proce 13

14 Stability tuning crosslinking Phosphate (PHOS) Tripoliphosphate (TPP) DI Water solutions of [PHOS], [TPP] = (10-30)% Crossliking time = 4-24 H T = 4 C 14

15 Crosslinking morphology effects As deposited t = 4H, [TPP] = 10% w/v t = 4H, [Phos] =10% w/v 15

16 Crosslinking morphology effects [PHOS] = 10% w/v [PHOS] = 30% w/v No major morphological differences between crosslinkers Crosslinking doesn t affect the overall morphology Pore dimension and interconnection are preserved Cracks are evident at low crosslinker concentration Increasing the crosslinker concentration results in absence of cracks 16

17 Coating stability evaluation Coating stability evaluation in Phosphate Buffered Saline (PBS) T = 37 C ph = 7.2 Coating stability improvement via TPP crosslinking: Increasing in water uptake Time-shift in dissolution 17

18 Surface Assisted Approach Tissue engineering approach Implantable devices Surface Assisted Selective Transfection DNA strand codeposition? Polyplexes deposition? Effects of Chitosan derivatives on deposition process? 18

19 Surface Assisted Approach Tissue engineering approach Implantable devices Surface Assisted Tissue Engineering Foundamental of electrodeposition process Co-deposition of Chemical and Physical tissue signals Self standing scaffolds?? 19

20 Surface Assisted Approach Tissue engineering approach Implantable devices Surface Assisted Drug Delivery Improving chitosan crosslinking Dissolution/stability kinetics? 20

21 Acknowledgments Group People Federica Rubini, M. Sc. Lorenzo Ulivi, M. Sc. Gabriele Candiani, Ph. D Prof. Roberto Chiesa Prof. Alberto Cigada Grants Fondo 5x1000 Giovani Ricercatori Politecnico di Milano Contratto Nanotecnologia per il Medicale - Istituto Italiano di Tecnologie Contratto Industriale EuroCoatings, Pergine.Grazie a tutti voi per il futuro supporto 21

22 .Grazie a tutti voi per il futuro supporto 22

23 SAST II - Novel Electrochemical Scaffolding Technique for SAST Luigi De Nardo luigi.denardo@polimi.it Dipartimento di Chimica, Materiali e Ingegneria Chimica G. Natta