Properties of scaffolds prepared by fused deposition modeling of poly(hydroxyalkanoates).

Poly(hydroxyalkanoates) are biodegradable and biocompatible polymers suitable for tissue engineering. Fused deposition modeling (FDM) belongs to modern rapid prototyping techniques for the fabrication of scaffolds. In this work, poly(3-hydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) were tested for FDM. Thermal and rheological properties of industrial PHAs were compared with poly(lactic acid) (PLA), which is a biodegradable polymer commonly used for FDM. The massive decrease in viscosity and loss of molecular weight of PHB and PHBV precluded their use for FDM. On the other hand, the thermal stability of PHBH was comparable to that of PLA. PHBH scaffolds prepared by FDM exhibited excellent mechanical properties, no cytotoxicity and large proliferation of mouse embryonic fibroblast cells within 96 h. The hydrolytic degradation of PHBH and PLA scaffolds tested in synthetic gastric juice for 52 days confirmed a faster degradation of PHBH than PLA. The decrease in molecular weight confirmed the first-order kinetics with a slightly higher (0.0169 day-1) degradation rate constant for PHBH as compared to the value (0.0107 day-1) obtained for PLA. These results indicate that PHBH could be used to produce scaffolds by FDM with application in tissue engineering.

Residual wood polymers facilitate compounding of microfibrillated cellulose with poly(lactic acid) for 3D printer filaments.

Microfibrillated cellulose (MFC) is a fascinating material with an obvious potential for composite reinforcement due to its excellent mechanics together with high specific surface area. However, in order to use this potential, commercially viable solutions to important technological challenges have to be found. Notably, the distinct hydrophilicity of MFC prevents efficient drying without loss in specific surface area, necessitating storage and processing in wet condition. This greatly hinders compounding with important technical polymers immiscible with water. Differently from cellulose, the chemistry of the major wood polymers lignin and hemicellulose is much more diverse in terms of functional groups. Specifically, the aromatic moieties present in lignin and acetyl groups in hemicellulose provide distinctly less polar surface-chemical functionality compared to hydroxyl groups which dominate the surface-chemical character of cellulose. It is shown that considerable advantages in the production of MFC-filled poly(lactic acid) filaments for three-dimensional printing can be obtained through the use of MFC containing residual lignin and hemicellulose due to their advantageous surface-chemical characteristics. Specifically, considerably reduced agglomerations of MFC in the filaments in combination with improved printability and improved toughness of printed objects are achieved.This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.