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Content archived on 2024-06-18

Multifunctional Conducting Polymer Devices for Electroresponsive Cell Regeneration

Final Report Summary - MULTIFUN CP (Multifunctional Conducting Polymer Devices for Electroresponsive Cell Regeneration.)

The objectives of the project were to develop and assess electrically conductive scaffolds for use as supporting multifunctional platforms for electrically responsive cell regeneration. This included:

1. Designing the appropriate architecture with tailored interfacial chemistries for cell attachment.
2. Assessing the effect of the conductive properties of the material in physiologically relevant conditions.
3. Optimizing electrical stimulation conditions and assessing their effect on cell growth and proliferation.

Three different conductive scaffolds have been developed, fully characterized and tested for applications in regenerative medicine. These include a bilayer polyaniline (PANI) film, a functionalized poly(ethylene dioxythiophene) (f-PEDOT) foam and a 3D-f-PEDOT hydrogel.

1. Bilayer PANI film: PANI was chemically polymerised on the surface of prefabricated chitosan films in the presence of phytic acid resulting in a free-standing conductive film. Phytic acid is highly negatively charged and binds strongly to protonated amine. Taking advantage of the protonated amines found in both the chitosan and PANI backbones, phytic acid behaved as a cross-linker between the amine groups of both these polymers leading to a cross-linked network. This approach induced a significant electrical stability in the films during incubation in physiologically relevant conditions. One of the main limitations of CPs is that they lose their oxidized state upon incubation in cell media converting to the reduced state, which is the non-conductive form of CP. By introducing the dopant in the system via chemical crosslinking, the developed bilayer films maintained their oxidized state in physiological media over extended periods (~30 days). Of significance as well is the ex-vivo work conducted to assess this bilayer film as a patch for myocardium infarction (MI) treatment. The conductive patch is showing promising results in lowering the arrhythmia of infarcted hearts. Also, there are no reports of similar studies in the literature assessing the effect of conducting polymers on the contractility and conduction velocity of cardiac tissue.

2. f-PEDOT foam: PEDOT functionalised with carboxylic groups has been chemically synthesised as proposed in MultiFun CP (PEDOT-COOH). A protocol has been developed and optimised for the crosslinking of PEDOT-COOH with the amine groups of the gelatin foam using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). Following the crosslinking of PEDOT-COOH onto the scaffold, the internal porous structure was maintained as confirmed by scanning electron microscopy (SEM). Upon doping in 0.1M HClO4, swollen scaffolds exhibited a resistance of 7.88 ± 0.10 kΩ, which is comparable to reported values of other widely investigated conducting polymers in the literature. Chondrocytes were seeded in the 3D structure and their metabolic activity was tested. Both doped and undoped scaffolds showed good biocompatibility with an increase in both the metabolic activity and DNA comparable to the control gelatin foam.

3. 3D-f-PEDOT hydrogel: an electroconductive hydrogel based on f- PEDOT has been fabricated. PEDOT-COOH was reacted with N-(3-aminopropyl)methacrylamide hydrochloride to introduce double bonds on the side chains of the polymeric backbone. Then the modified polymer was polymerised with acrylic acid using polyethylene glycol diacrylate (PEG-DA) as a crosslinker and azobisisobutyronitrile (AIBN) as an initiator. This resulted in a hydrogel with high swelling ratio (~ 3500%), porous internal structure, and robust mechanical integrity (Young’s Moduli ~ 73.96 ± 20.72 kPa). Despite the high ratio of insulator in the network, the electroactivity of the hydrogel was remarkable in phosphate buffer solution (PBS) as an electrolyte and the redox peaks were in agreement with those of the pristine polymer. C2C12 muscle cells attached to the scaffold without the need to coat with any proteins. Additionally, cells proliferated and were alive after 7 days of culture. Due to the porous structure of the hydrogel, it was found that cells infiltrated into the matrix and remained viable.

The scientific results obtained during the period of the fellowship are envisioned to be published in high impact journals. A major hurdle in the application of conducting polymers in the biomedical field has been addressed and that is increasing their stability in the conductive state in physiologically relevant conditions. The bilayer film has huge potential to be applied in cardiac regeneration. The results so far are very promising. The patch has been shown to decrease the arrhythmia in infarcted hearts. If the on-going in vivo results lead to positive effect, the patch could have a huge socio-economic impact in the clinic. Heart failure is a huge burden on society and the fabrication of the patch is easy, scalable and most important cheap.

Additionally, the chemical synthesis of a functional PEDOT (f-PEDOT) resolved the rigidity issue often associated with CPs limiting their potential to form 3D hydrated scaffolds that require both flexible and hydrophilic polymer. The f-PEDOT polymer chemically synthesised will be the first reported water soluble functional PEDOT. f-PEDOT paves the way for introducing new chemistries and applying different fabrication techniques to produce electoconductive systems tailored to suit different clinical needs. Additionally, the 3D scaffolds based on this polymer are novel in that potentially they are biodegradable, and allow cell seeding in a 3D structure. The hydrogel is electroactive in physiological buffer and allows cell adhesion without any pre-treatment with proteins. Also, cells proliferate and infiltrate in the porous structure.