Chitosan-BaTiO3 nanostructured piezopolymer for tissue engineering.

Herein we report the synthesis of a piezopolymer composed of chitosan (CS)/hydroxylated BaTiO3 (OH-BTO) nanoparticles with enhanced biocompatibility, non-toxicity, and piezoelectric behavior that can be advantageously used in biomedical applications. Our CS/OH-BTO nanocomposites exhibit piezoelectric coefficient (d33 = 11.29 pC/N) between those of dry skin (0.05-0.19 pC/N) and bone (4-11 pC/N), demonstrating biocompatibility in contact with human fibroblasts (HF) cells after 24 h. SEM, XRD, FTIR and Raman measurements were performed to assess the mechanism of interaction between CS matrix and OH-BTO NPs and their correlation with the biological responses. Cytotoxicity assays with HF cells reveal that hydroxylation of BTO NPs does not affect the cell viability of CS/OH-BTO films with NPs concentration from 1 to 30 wt.%. In contrast, non-hydroxylated BTO NPs showed significant cell damage, which could be traced to uncontrollable NPs agglomeration. This behavior suggests that CS/OH-BTO nanocomposites can act as active material that promotes cell growth and can be used for biomedical purposes.

Stochastic excitation for high-resolution atomic force acoustic microscopy imaging: a system theory approach.

In this work, a high-resolution atomic force acoustic microscopy imaging technique is developed in order to obtain the local indentation modulus at the nanoscale level. The technique uses a model that gives a qualitative relationship between a set of contact resonance frequencies and the indentation modulus. It is based on white-noise excitation of the tip-sample interaction and uses system theory for the extraction of the resonance modes. During conventional scanning, for each pixel, the tip-sample interaction is excited with a white-noise signal. Then, a fast Fourier transform is applied to the deflection signal that comes from the photodiodes of the atomic force microscopy (AFM) equipment. This approach allows for the measurement of several vibrational modes in a single step with high frequency resolution, with less computational cost and at a faster speed than other similar techniques. This technique is referred to as stochastic atomic force acoustic microscopy (S-AFAM), and the frequency shifts of the free resonance frequencies of an AFM cantilever are used to determine the mechanical properties of a material. S-AFAM is implemented and compared with a conventional technique (resonance tracking-atomic force acoustic microscopy, RT-AFAM). A sample of a graphite film on a glass substrate is analyzed. S-AFAM can be implemented in any AFM system due to its reduced instrumentation requirements compared to conventional techniques.