Project thoughts / plans

1. Project thoughts / plans John Hardy February 2011

2. Overview • Conducting polymer-based materials • Hyaluronic acid-based materials • Glucose sensing hydrogels

3. Motivation • Conducting polymer-based materials

4. Overview • Introduction • Why do materials conduct electricity? • State of the art • Conducting polymers • Potential for future research • Non-biodegradable conducting polymers • Biodegradable conducting polymers

5. Atomic Structure • Electron orbitals • 8th grade

6. Atomic Structure • Electron orbitals • University • y1

7. Molecular Structure + s s s-s overlap = s bond + s p s-p overlap = s bond + p p p-p overlap = s bond + p p p-p overlap = p bond

8. Molecular Structure s* p* p Energy 2p s s* 2s s

9. Band structures n: 1 2 3 4 ∞ y4 11 y3 Energy y2 y1

10. Band structures Eg Eg Eg Eg or or

11. Semiconductors • Improving the conductivity • Approach 1: Transfer energy to the system Eg

12. Semiconductors • Improving the conductivity • Approach 1: Transfer energy to the system • Approach 2: ‘Doping’ Eg

13. Semiconductors • Improving the conductivity • Approach 1: Transfer energy to the system • Approach 2: ‘Doping’ Eg

14. Semiconductors • Improving the conductivity • Approach 1: Transfer energy to the system • Approach 2: ‘Doping’ Eg ‘allegedly’

15. Semiconductors • Improving the conductivity • Approach 1: Transfer energy to the system • Approach 2: ‘Doping’ Eg Eg Eg • Remove electrons • Insert ‘holes’ • P-type doping • Add electrons • Insert a ‘mid-gap orbital’ • N-type doping

16. Carbon and Silicon Carbon – 1s2 2s2 2p2 Silicon - 1s2 2s22p6 3s2 3p2 Silicon is a semiconductor • Diamond is an insulator Si Si Si C C C Si Si Si Si Si Si C C C C C C Eg Eg

17. Doping Silicon P-type doping N-type doping Phosphorous - …3s2 3p3 • Boron - 1s2 2s22p1 Si Si Si Si Si Si . Si Si Si Si Si Si Si Si Si Si B P Eg Eg • Remove electrons • Insert ‘holes’ • P-type doping • Add electrons • Insert a ‘mid-gap orbital’ • N-type doping

18. Doping conducting polymers • Parapolyphenylene (PPP) P-type doping (oxidation) Polaron Polaron Polaron Further doping Polaron combination

19. Doping conducting polymers • Polyaniline Oxidation Oxidation Reduction Reduction Leuco-emeraldine base Non-conducting Emeraldine base Non-conducting Base Acid Base Acid Emeraldine salt Conducting form Leuco-emeraldine salt Non-conducting

20. De-doping conducting polymers • Polypyrrole (PPy) • Conductivity (σ) of film 3to 60 S/cm Literature: Schmidt and co-workers, Biomed. Mater. 2008, 3 (3), 034124-

21. Self-doped conducting polymers • Polythiophene • Water soluble • Conductivity (σ) of film 10-7 to 10-2 S/cm • Exposure to Br2 vapor – σ ≈ 10 S/cm Oxidation (- M+) Reduction (+ M+) Literature: Wudl and co-workers, JACS. 1987, 109, 1858-

22. Problems with conductive polymers • Chemical stability • Sensitivity to air / moisture • High crystallinity • Solubility / processability / mechanical properties Polyacetyleneσup to 105S/cm Polyacetyleneσup to 50 S/cm Literature: Grubbs and co-workers, Adv. Mat. 1989, 1 (11), 362-

23. Problems with conductive polymers • Biodegradability Polythiophene Polyacene Polyfluorene Ester bond Biodegradable polythiophene copolymer Literature: Schmidt and co-workers, Macromol. 2009, 42, 502-

24. Proposed research • Supramolecular polymers • Functionalization of biodegradable materials with SDCPs • Silk proteins • Polycaprolactone (PCL) • Non-biodegradable SDCPs • Neural electrodes

25. Supramolecular polymers • Oligothiophene-based • H-bonding, van der Waals interactions & π-π stacking • Oligoaniline-based • Peptide-directed assembly Literature: Schmidt and co-workers, Macromol. 2009, 42, 502- & Yang and co-workers, Tet. Lett. 1996, 37, 731-

26. Silk-based materials • Silk • Commercially available protein • Processable in solution • Chemically modifiable • ‘Biocompatible’ • Collaborative project: David Kaplan (Tufts)

27. Silk-based materials • Visit Tufts (03/28-04/11) • Upon my return to Austin Literature: Schmidt and co-workers, Macromol. 2009, 42, 502-

28. PCL-based materials • PCL • Commercially available biodegradable polymer • Processable in melt/solution • Chemically modifiable • ‘Biocompatible’ • UG project: RushiSukhavasi

29. PCL-based materials

30. Neural electrodes • Self-doped polymer films • Non-biodegradable polymers • Simple (2 steps) • Electropolymerization of: • Self-dope by sulfonation with HSO3F • σ up to 72 S/cm • UG project: Tushar Garg Literature: Yildiz and co-workers, J. Solid State Electrochem. 2006, 10, 110-

31. Hyaluronic acid-based materials • Collaboration with Sarah Mayes • Collaboraiton with Zin Khaing

32. Collaboration with Sarah • In-situ cross-linking hydrogels • Simple chemistry • UV free • UG project: Phillip Lin

33. Collaboration with Zin • In-situ cross-linking hydrogels • Complex chemistry • Absolutely bioorthogonal • UG project: Jesus Maldonado Literature: Schmidt/Khaing and co-workers…

34. Glucose sensing hydrogels • Collaboration with Austin McElroy, Chris Condit, Jordan Dwelle & Tom Milner

35. Glucose sensing hydrogels • Boronic acid-based hydrogels • Prepare hydrogels that swell/shrink in the presence of glucose High boronic acid content hydrogel Low boronic acid content hydrogel

36. Conclusion • Prepare further in advance