Preparation of Porous Scaffold Based on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) and FucoPol.

This work focused on the development of porous scaffolds based on biocomposites comprising two biodegradable and biocompatible biopolymers: a terpolyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (PHBHVHHx), and the bacterial polysaccharide FucoPol. The PHBHVHHx terpolymer was composed of 3-hydroxybutyrate (55 wt%), 3-hydroxyvalerate (21 wt%), and 3-hydroxyhexanoate (24 wt%). This hydrophobic polyester has low crystallinity and can form elastic and flexible films. Fucopol is a fucose-containing water-soluble polysaccharide that forms viscous solutions with shear thinning behavior and has demonstrated emulsion-forming and stabilizing capacity and wound healing ability. Emulsion-templating was used to fabricate PHA-based porous structures in which FucoPol acted as a bioemulsifier. Compared with the scaffolds obtained from emulsions with only water, the use of FucoPol aqueous solutions resulted in structures with improved mechanical properties, namely higher tensile strength (4.4 MPa) and a higher Young's Modulus (85 MPa), together with an elongation at break of 52%. These features, together with the scaffolds' high porosity and pore interconnectivity, suggest their potential to sustain cell adhesion and proliferation, which is further supported by FucoPol's demonstrated wound healing ability. Therefore, the developed PHBHVHHx:FucoPol scaffolds arise as innovative porous bioactive structures with great potential for use in tissue engineering applications.

Subcritical Water as a Pre-Treatment of Mixed Microbial Biomass for the Extraction of Polyhydroxyalkanoates.

Polyhydroxyalkanoate (PHA) recovery from microbial cells relies on either solvent extraction (usually using halogenated solvents) and/or digestion of the non-PHA cell mass (NPCM) by the action of chemicals (e.g., hypochlorite) that raise environmental and health hazards. A greener alternative for PHA recovery, subcritical water (SBW), was evaluated as a method for the dissolution of the NPCM of a mixed microbial culture (MMC) biomass. A temperature of 150 °C was found as a compromise to reach NPCM solubilization while mostly preventing the degradation of the biopolymer during the procedure. Such conditions yielded a polymer with a purity of 77%. PHA purity was further improved by combining the SBW treatment with hypochlorite digestion, in which a significantly lower hypochlorite concentration (0.1%, v/v) was sufficient to achieve an overall polymer purity of 80%. During the procedure, the biopolymer suffered some depolymerization, as evidenced by the lower molecular weight (Mw) and higher polydispersity of the extracted samples. Although such changes in the biopolymer's molecular mass distribution impact its mechanical properties, impairing its utilization in most conventional plastic uses, the obtained PHA can find use in several applications, for example as additives or for the preparation of graft or block co-polymers, in which low-Mw oligomers are sought.

Characterization of the Thermostable Biosurfactant Produced by Burkholderia thailandensis DSM 13276.

Biosurfactants synthesized by microorganisms represent safe and sustainable alternatives to the use of synthetic surfactants, due to their lower toxicity, better biodegradability and biocompatibility, and their production from low-cost feedstocks. In line with this, the present study describes the physical, chemical, and functional characterization of the biopolymer secreted by the bacterium Burkholderia thailandensis DSM 13276, envisaging its validation as a biosurfactant. The biopolymer was found to be a glycolipopeptide with carbohydrate and protein contents of 33.1 ± 6.4% and 23.0 ± 3.2%, respectively. Galactose, glucose, rhamnose, mannose, and glucuronic acid were detected in the carbohydrate moiety at a relative molar ratio of 4:3:2:2:1. It is a high-molecular-weight biopolymer (1.0 × 107 Da) with low polydispersity (1.66), and forms aqueous solutions with shear-thinning behavior, which remained after autoclaving. The biopolymer has demonstrated a good emulsion-stabilizing capacity towards different hydrophobic compounds, namely, benzene, almond oil, and sunflower oil. The emulsions prepared with the biosurfactant, as well as with its autoclaved solution, displayed high emulsification activity (>90% and ~50%, respectively). Moreover, the almond and sunflower oil emulsions stabilized with the biosurfactant were stable for up to 4 weeks, which further supports the potential of this novel biopolymer for utilization as a natural bioemulsifier.

Bioconversion of Terephthalic Acid and Ethylene Glycol Into Bacterial Cellulose by Komagataeibacter xylinus DSM 2004 and DSM 46604.

Komagataeibacter xylinus strains DSM 2004 and DSM 46604 were evaluated for their ability to grow and produce bacterial cellulose (BC) upon cultivation on terephthalic acid (TA) and ethylene glycol (EG), which are monomers of the petrochemical-derived plastic polyethylene terephthalate (PET). Both strains were able to utilize TA, EG, and their mixtures for BC synthesis, with different performances. K. xylinus DSM 2004 achieved higher BC production from TA (0.81 ± 0.01 g/L), EG (0.64 ± 0.02 g/L), and TA + EG mixtures (0.6 ± 0.1 g/L) than strain DSM 46604. The latter was unable to utilize EG as the sole carbon source and reached a BC production of 0.16 ± 0.01 g/L and 0.23 ± 0.1 g/L from TA alone or TA + EG mixtures, respectively. Further supplementing the media with glucose enhanced BC production by both strains. During cultivation on media containing TA and EG, rapid pH drop due to metabolization of EG into acidic compounds led to some precipitation of TA that was impregnated into the BC pellicles. An adaptation of the downstream procedure involving BC dissolution in NaOH was used for the recovery of pure BC. The different medium composition tested, as well as the downstream procedure, impacted the BC pellicles' physical properties. Although no variation in terms of the chemical structure were observed, differences in crystallinity degree and microstructure of the produced BC were observed. The BC produced by K. xylinus DSM 2004 had a higher crystallinity (19-64%) than that of the strain DSM 46604 (17-53%). Moreover, the scanning electron microscopy analysis showed a higher fiber diameter for K. xylinus DSM 2004 BC (46-56 nm) than for K. xylinus DSM 46604 (37-49 nm). Dissolution of BC in NaOH did not influence the chemical structure; however, it led to BC conversion from type I to type II, as well as a decrease in crystallinity. These results demonstrate that PET monomers, TA and EG, can be upcycled into a value-added product, BC, presenting an approach that will contribute to lessening the environmental burden caused by plastic disposal in the environment.

Preparation and Characterization of Porous Scaffolds Based on Poly(3-hydroxybutyrate) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

Poly(hydroxyalkanoates) (PHAs) with different material properties, namely, the homopolymer poly(3-hydroxybutyrate), P(3HB), and the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate, P(3HB-co-3HV), with a 3HV of 25 wt.%, were used for the preparation of porous biopolymeric scaffolds. Solvent casting with particulate leaching (SCPL) and emulsion templating were evaluated to process these biopolymers in porous scaffolds. SCPL scaffolds were highly hydrophilic (>170% swelling in water) but fragile, probably due to the increase of the polymer's polydispersity index and its high porosity (>50%). In contrast, the emulsion templating technique resulted in scaffolds with a good compromise between porosity (27-49% porosity) and hydrophilicity (>30% water swelling) and without impairing their mechanical properties (3.18-3.35 MPa tensile strength and 0.07-0.11 MPa Young's Modulus). These specifications are in the same range compared to other polymer-based scaffolds developed for tissue engineering. P(3HB-co-3HV) displayed the best overall properties, namely, lower crystallinity (11.3%) and higher flexibility (14.8% elongation at break. Our findings highlight the potency of our natural biopolyesters for the future development of novel porous scaffolds in tissue engineering, thanks also to their safety and biodegradability.

Oxygen Plasma Treated-Electrospun Polyhydroxyalkanoate Scaffolds for Hydrophilicity Improvement and Cell Adhesion.

Poly(hydroxyalkanoates) (PHAs) with differing material properties, namely, the homopolymer poly(3-hydroxybutyrate), P(3HB), the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate), P(3HB-co-3HV), with a 3HV content of 25 wt.% and a medium chain length PHA, and mcl-PHA, mainly composed of 3-hydroxydecanoate, were studied as scaffolding material for cell culture. P(3HB) and P(3HB-co-3HV) were individually spun into fibers, as well as blends of the mcl-PHA with each of the scl-PHAs. An overall biopolymer concentration of 4 wt.% was used to prepare the electrospinning solutions, using chloroform as the solvent. A stable electrospinning process and good quality fibers were obtained for a solution flow rate of 0.5 mL h-1, a needle tip collector distance of 20 cm and a voltage of 12 kV for P(3HB) and P(3HB-co-3HV) solutions, while for the mcl-PHA the distance was increased to 25 cm and the voltage to 15 kV. The scaffolds' hydrophilicity was significantly increased under exposure to oxygen plasma as a surface treatment. Complete wetting was obtained for the oxygen plasma treated scaffolds and the water uptake degree increased in all treated scaffolds. The biopolymers crystallinity was not affected by the electrospinning process, while their treatment with oxygen plasma decreased their crystalline fraction. Human dermal fibroblasts were able to adhere and proliferate within the electrospun PHA-based scaffolds. The P(3HB-co-3HV): mcl-PHA oxygen plasma treated scaffold highlighted the most promising results with a cell adhesion rate of 40 ± 8%, compared to 14 ± 4% for the commercial oxygen plasma treated polystyrene scaffold AlvetexTM. Scaffolds based on P(3HB-co-3HV): mcl-PHA blends produced by electrospinning and submitted to oxygen plasma exposure are therefore promising biomaterials for the development of scaffolds for tissue engineering.