Mechanisms of Deformation in Fully Conjugated Conducting Gels. Stretching and Swelling

Improved mechanical and electronic properties of co-assembled folic acid gel with aniline and polyaniline

Co-assembled folic acid (F) gel with aniline (ANI) (ANI:F = 1:2, w/w) is produced at 2% (w/v) concentration in water/DMSO (1:1, v/v) mixture. The gel is rigid and on polymerization of the gel pieces in aqueous ammonium persulfate solution co-assembled folic acid - polyaniline (F-PANI) gel is formed. Both the co-assembled F-ANI and F-PANI gels have fibrillar network morphology, the fiber diameter and its degree of branching increase significantly from those of F gel. WAXS pattern indicates co-assembled structure with the F fiber at the core and ANI/PANI at its outer surface and the co-assembly is occurring in both F-ANI and F-PANI systems through noncovalent interaction of H-bonding and π stacking processes between the components. FTIR and UV-vis spectra characterize the doped PANI formation and the MALDI mass spectrometry indicates the degree of polymerization of polyaniline in the range 24-653. The rheological experiments support the signature of gel formation in the co-assembled state and the storage (G') and loss (G″) modulii increase in the order F gel< F-ANI gel < F-PANI gel, showing the highest increase in G' ≈ 1100% for the F-PANI gel. The stress at break, elasticity, and stiffness also increase in the same order. The dc-conductivity of F-ANI and F-PANI xerogels is 2 and 7 orders higher than that of F xerogel. Besides, the current (I)-voltage (V) curves indicate that the F-xerogel is insulator, but F-ANI xerogel is semiconductor showing both electronic memory and rectification; on the other hand, the F-PANI xerogel exhibits a negative differential resistance (NDR) property with a NDR ratio of 3.0.

31P and 13C solid-state NMR spectroscopy to study collagen synthesis and biomineralization in polymer-based bone implants

A combination of solid-state NMR spectroscopy and MRI was used to evaluate the formation of extracellular matrix in poly(D,L-lactide-co-glycolide) (PLGA) bone implants. Porous PLGA scaffolds were implanted into rat tibiae and analysed after 2, 4 or 8 weeks. MRI clearly delineated the implants within the cancellous bone. Differences in the trabecular structure of the implanted material and native bone were demonstrated. In addition, implants were analyzed by solid-state NMR spectroscopy under magic angle spinning. (13)C NMR spectra showed the unambiguous signature of collagen formed in the scaffolds, but also the characteristic signals of the PLGA matrix, indicating that resorption was not complete after 8 weeks. Furthermore, (31)P NMR spectroscopy detected the inorganic component of the matrix, which is composed of bioapatite. (31)P NMR spectra were quantified and this analysis revealed that the amount of inorganic extracellular matrix formed de novo was significantly lower than in native bone. This demonstrates that solid-state NMR spectroscopy, in particular in combination with MRI, can provide useful information on the composition and structure of the extracellular matrix, and serve as a tool to evaluate the quality of tissue engineering strategies.