Highly Aligned Bacterial Nanocellulose Films Obtained During Static Biosynthesis in a Reproducible and Straightforward Approach

Bacterial nanocellulose (BNC) is usually produced as randomly-organized highly pure cellulose nanofibers films. Its high water-holding capacity, porosity, mechanical strength, and biocompatibility make it unique. Ordered structures are found in nature and the properties appearing upon aligning polymers fibers inspire everyone to achieve highly aligned BNC (A-BNC) films. This work takes advantage of natural bacteria biosynthesis in a reproducible and straightforward approach. Bacteria confined and statically incubated biosynthesized BNC nanofibers in a single direction without entanglement. The obtained film is highly oriented within the total volume confirmed by polarization-resolved second-harmonic generation signal and Small Angle X-ray Scattering. The biosynthesis approach is improved by reusing the bacterial substrates to obtain A-BNC reproducibly and repeatedly. The suitability of A-BNC as cell carriers is confirmed by adhering to and growing fibroblasts in the substrate. Finally, the thermal conductivity is evaluated by two independent approaches, i.e., using the well-known 3 ω -method and a recently developed contactless thermoreflectance approach, confirming a thermal conductivity of 1.63 W mK −1 in the direction of the aligned fibers versus 0.3 W mK −1 perpendicularly. The fivefold increase in thermal conductivity of BNC in the alignment direction forecasts the potential of BNC-based devices outperforming some other natural polymer and synthetic materials. Bacteria confined and statically incubated for a few days biosynthesized bacterial nanocellulose (BNC) nanofibers in a single direction without entanglement. The obtained film is highly oriented within the total volume of the film, and it shows a five-fold increase in thermal conductivity in the parallel direction forecasting the potential of BNC-based devices outperforming some other natural polymer and synthetic materials

Insights on the amphiphillicity of cellulose: competitive wetting by polar and apolar solvents

Due to its molecular structure, cellulose shows both hydrophilic and lipophilic behaviour. However, the relative importance of both affinities and the extend to which cellulose can be considered amphiphillic remains the subject of conflicting and opposite views. We address this question by considering the behaviour of cellulose when exposed to immiscible solvents, water and apolar solvents (toluene or decane). We have performed molecular dynamics (MD) simulations of the competition between water/toluene and water/decane to cellulose. We consider two cellulose surfaces (from different crystalline planes) with different roughness and different accessibility to hydrophilic and hydrophobic groups. We also use bacterial cellulose to perform wetting and solvent exchange experiments. Both MD and experimental results show that cellulose has high affinity for all solvents considered. The MD simulations for the studied cellulose surfaces predict a clear preference for water over toluene. Toluene can be replaced by water but a water hydration layer cannot be replaced by toluene, an effect that can be traced back to the molecular features of cellulose. This preference is confirmed experimentally by solvent exchange experiments. In the case of water-decane mixtures, MD simulations indicate that the competition between decane and water is more complex, due to the high surface tension of the water-decane interface