Fabrication of new biobased composites with remarkable properties offers an attractive pathway for producing environmentally friendly materials. Here, a reinforcement for poly­(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) with functionalized cellulose nanocrystals (CNCs) is presented and used to successfully 3D-print such composites by fused deposition modeling (FDM). Acetylated CNC content varies from 5 to 20 wt % in order to evaluate the effect of the reinforcing agent on thermal and mechanical properties in the composites. The reinforcing effect of CNC is investigated by dynamic mechanical, thermal, and rheological analysis. Thermogravimetric analysis and infrared spectroscopy allow one to assert the success of chemical functionalization, whereas transmission electron microscopy is used to evaluate the impact of chemical modification on the morphology of the crystals. 3D-printability of biobased composites is proved by developing structures of complex designs with a FDM printer. Finally, the degree of disintegration under composting conditions is studied. Findings from these tests serve as an important step forward toward the development of ecofriendly materials for 3D-printing complex architectures with tailored mechanical properties and functionalities.

In recent years, biopolymers have been attracting the attention of researchers and specialists from different fields, including biotechnology, material science, engineering, and medicine. The reason is the possibility of combining sustainability with scientific and technological progress. This is an extremely broad research topic, and a distinction has to be made among different classes and types of biopolymers. Polyhydroxyalkanoate (PHA) is a particular family of polyesters, synthetized by microorganisms under unbalanced growth conditions, making them both bio-based and biodegradable polymers with a thermoplastic behavior. Recently, PHAs were used more intensively in biomedical applications because of their tunable mechanical properties, cytocompatibility, adhesion for cells, and controllable biodegradability. Similarly, the 3D-printing technologies show increasing potential in this particular field of application, due to their advantages in tailor-made design, rapid prototyping, and manufacturing of complex structures. In this review, first, the synthesis and the production of PHAs are described, and different production techniques of medical implants are compared. Then, an overview is given on the most recent and relevant medical applications of PHA for drug delivery, vessel stenting, and tissue engineering. A special focus is reserved for the innovations brought by the introduction of additive manufacturing in this field, as compared to the traditional techniques. All of these advances are expected to have important scientific and commercial applications in the near future.

This research evaluates the effects of filler content and silanization on thermal, morphological and mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH)-based composites. Microfibrillated cellulose (MFC) was obtained by a mechanical treatment of high-pressure homogenization, starting from oat hull fiber, a byproduct of the agri-food sector. MFC reinforced PHBH composites were prepared by melt compounding. SEM and FT-IR analysis showed a good dispersion of the filler in the polymeric matrix, denoting the effectiveness of the surface silanization process. The thermal stability of PHBH composites remains substantially unchanged, and the glass transition temperature marginally increases with the increase of the filler content. Furthermore, silanized MFC shows slightly reinforcing mechanical effects on PHBH composites, such as the increase of 10% of the Young modulus with an increase of the maximum tensile stress as well. This finding has an economical interest since the results showed that MFC, deriving from a byproduct, can be successfully used as filler, decreasing the cost of the bio-based compound leaving substantially unaltered its mechanical and thermal properties.

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