Biosynthesis of poly(3-hydroxybutyrate) copolymers by Azotobacter chroococcum 7B: A precursor feeding strategy

Adhesion of Escherichia coli and Lactobacillus fermentum to Films and Electrospun Fibrous Scaffolds from Composites of Poly(3-hydroxybutyrate) with Magnetic Nanoparticles in a Low-Frequency Magnetic Field

The ability of materials to adhere bacteria on their surface is one of the most important aspects of their development and application in bioengineering. In this work, the effect of the properties of films and electrospun scaffolds made of composite materials based on biosynthetic poly(3-hydroxybutyrate) (PHB) with the addition of magnetite nanoparticles (MNP) and their complex with graphene oxide (MNP/GO) on the adhesion of E. coli and L. fermentum under the influence of a low-frequency magnetic field and without it was investigated. The physicochemical properties (crystallinity; surface hydrophilicity) of the materials were investigated by X-ray structural analysis, differential scanning calorimetry and "drop deposition" methods, and their surface topography was studied by scanning electron and atomic force microscopy. Crystal violet staining made it possible to reveal differences in the surface charge value and to study the adhesion of bacteria to it. It was shown that the differences in physicochemical properties of materials and the manifestation of magnetoactive properties of materials have a multidirectional effect on the adhesion of model microorganisms. Compared to pure PHB, the adhesion of E. coli to PHB-MNP/GO, and for L. fermentum to both composite materials, was higher. In the magnetic field, the adhesion of E. coli increased markedly compared to PHB-MNP/GO, whereas the effect on the adhesion of L. fermentum was reversed and was only evident in samples with PHB-MNP. Thus, the resultant factors enhancing and impairing the substrate binding of Gram-negative E. coli and Gram-positive L. fermentum turned out to be multidirectional, as they probably have different sensitivity to them. The results obtained will allow for the development of materials with externally controlled adhesion of bacteria to them for biotechnology and medicine.

Poly(3-hydroxybutyrate) 3D-Scaffold-Conduit for Guided Tissue Sprouting

Scaffold biocompatibility remains an urgent problem in tissue engineering. An especially interesting problem is guided cell intergrowth and tissue sprouting using a porous scaffold with a special design. Two types of structures were obtained from poly(3-hydroxybutyrate) (PHB) using a salt leaching technique. In flat scaffolds (scaffold-1), one side was more porous (pore size 100-300 μm), while the other side was smoother (pore size 10-50 μm). Such scaffolds are suitable for the in vitro cultivation of rat mesenchymal stem cells and 3T3 fibroblasts, and, upon subcutaneous implantation to older rats, they cause moderate inflammation and the formation of a fibrous capsule. Scaffold-2s are homogeneous volumetric hard sponges (pore size 30-300 μm) with more structured pores. They were suitable for the in vitro culturing of 3T3 fibroblasts. Scaffold-2s were used to manufacture a conduit from the PHB/PHBV tube with scaffold-2 as a filler. The subcutaneous implantation of such conduits to older rats resulted in gradual soft connective tissue sprouting through the filler material of the scaffold-2 without any visible inflammatory processes. Thus, scaffold-2 can be used as a guide for connective tissue sprouting. The obtained data are advanced studies for reconstructive surgery and tissue engineering application for the elderly patients.

Cell Behavior Changes and Enzymatic Biodegradation of Hybrid Electrospun Poly(3-hydroxybutyrate)-Based Scaffolds with an Enhanced Piezoresponse after the Addition of Reduced Graphene Oxide

This is the first comprehensive study of the impact of biodegradation on the structure, surface potential, mechanical and piezoelectric properties of poly(3-hydroxybutyrate) (PHB) scaffolds supplemented with reduced graphene oxide (rGO) as well as cell behavior under static and dynamic mechanical conditions. There is no effect of the rGO addition up to 1.0 wt% on the rate of enzymatic biodegradation of PHB scaffolds for 30 d. The biodegradation of scaffolds leads to the depolymerization of the amorphous phase, resulting in an increase in the degree of crystallinity. Because of more regular dipole order in the crystalline phase, surface potential of all fibers increases after the biodegradation, with a maximum (361 ± 5 mV) after the addition of 1 wt% rGO into PHB as compared to pristine PHB fibers. By contrast, PHB-0.7rGO fibers manifest the strongest effective vertical (0.59 ± 0.03 pm V^-1 ) and lateral (1.06 ± 0.02 pm V^-1 ) piezoresponse owing to a greater presence of electroactive β-phase. In vitro assays involving primary human fibroblasts reveal equal biocompatibility and faster cell proliferation on PHB-0.7rGO scaffolds compared to pure PHB and nonpiezoelectric polycaprolactone scaffolds. Thus, the developed biodegradable PHB-rGO scaffolds with enhanced piezoresponse are promising for tissue-engineering applications.

Biocomposite Materials Based on Poly(3-hydroxybutyrate) and Chitosan: A Review

One of the important directions in the development of modern medical devices is the search and creation of new materials, both synthetic and natural, which can be more effective in their properties than previously used materials. Traditional materials such as metals, ceramics, and synthetic polymers used in medicine have certain drawbacks, such as insufficient biocompatibility and the emergence of an immune response from the body. Natural biopolymers have found applications in various fields of biology and medicine because they demonstrate a wide range of biological activity, biodegradability, and accessibility. This review first described the properties of the two most promising biopolymers belonging to the classes of polyhydroxyalkanoates and polysaccharides-polyhydroxybutyrate and chitosan. However, homopolymers also have some disadvantages, overcome which becomes possible by creating polymer composites. The article presents the existing methods of creating a composite of two polymers: copolymerization, electrospinning, and different ways of mixing, with a description of the properties of the resulting compositions. The development of polymer composites is a promising field of material sciences, which allows, based on the combination of existing substances, to develop of materials with significantly improved properties or to modify of the properties of each of their constituent components.

Growth of Mesenchymal Stem Cells on Poly(3-Hydroxybutyrate) Scaffolds Loaded with Simvastatin

We studied the effect of porous composite scaffolds based on poly(3-hydroxybutyrate) (PHB) loaded with simvastatin on the growth and differentiation of mesenchymal stem cells. The scaffolds have a suitable microstructure (porosity and pore size) and physicochemical properties to support the growth of mesenchymal stem cells. Scaffold loading with simvastatin suppressed cell growth and increased alkaline phosphatase activity, which can attest to their osteoinductive properties.

The Growth of 3T3 Fibroblasts on PHB, PLA and PHB/PLA Blend Films at Different Stages of Their Biodegradation In Vitro

Over the past century there was a significant development and extensive application of biodegradable and biocompatible polymers for their biomedical applications. This research investigates the dynamic change in properties of biodegradable polymers: poly(3-hydroxybutyrate (PHB), poly-l-lactide (PLA), and their 50:50 blend (PHB/PLA)) during their hydrolytic non-enzymatic (in phosphate buffered saline (PBS), at pH = 7.4, 37 °C) and enzymatic degradation (in PBS supplemented with 0.25 mg/mL pancreatic lipase). 3T3 fibroblast proliferation on the polymer films experiencing different degradation durations was also studied. Enzymatic degradation significantly accelerated the degradation rate of polymers compared to non-enzymatic hydrolytic degradation, whereas the seeding of 3T3 cells on the polymer films accelerated only the PLA molecular weight loss. Surprisingly, the immiscible nature of PHB/PLA blend (showed by differential scanning calorimetry) led to a slower and more uniform enzymatic degradation in comparison with pure polymers, PHB and PLA, which displayed a two-stage degradation process. PHB/PLA blend also displayed relatively stable cell viability on films upon exposure to degradation of different durations, which was associated with the uneven distribution of cells on polymer films. Thus, the obtained data are of great benefit for designing biodegradable scaffolds based on polymer blends for tissue engineering.

Poly(3-hydroxybutyrate)/hydroxyapatite/alginate scaffolds seeded with mesenchymal stem cells enhance the regeneration of critical-sized bone defect

A critical-sized calvarial defect in rats is employed to reveal the osteoinductive properties of biomaterials. In this study, we investigate the osteogenic efficiency of hybrid scaffolds based on composites of a biodegradable and biocompatible polymer, poly(3-hydroxybutyrate) (PHB) with hydroxyapatite (HA) filled with alginate (ALG) hydrogel containing mesenchymal stem cells (MSCs) on the regeneration of the critical-sized radial defect of the parietal bone in rats. The scaffolds based on PHB and PHB/HA with desired shapes were prepared by two-stage salt leaching technique using a mold obtained by three-dimensional printing. To obtain PHB/HA/ALG/MSC scaffolds seeded with MSCs, the scaffolds were filled with ALG hydrogel containing MSCs; acellular PHB/ALG and PHB/ALG filled with empty ALG hydrogel were prepared for comparison. The produced scaffolds have high porosity and irregular interconnected pore structure. PHB/HA scaffolds supported MSC growth and induced cell osteogenic differentiation in a regular medium in vitro that was manifested by an increase in ALP activity and expression of the CD45 phenotype marker. The data of computed tomography and histological studies showed 94% and 92%, respectively, regeneration of critical-sized calvarial bone defect in vivo at 28th day after implantation of MSC-seeded PHB/HA/ALG/MSC scaffolds with 3.6 times higher formation of the main amount of bone tissue at 22-28 days in comparison with acellular PHB/HA/ALG scaffolds that was shown at the first time by fluorescent microscopy using the original technique of intraperitoneal administration of fluorescent dyes to living postoperative rats. The obtained in vivo results can be associated with the MSC-friendly microstructure and in vitro osteogenic properties of PHB/HA base-scaffolds. Thus, the obtained data demonstrate the potential of MSCs encapsulated in the bioactive biopolymer/mineral/hydrogel scaffold to improve the bone regeneration process in critical-sized bone defects.

Effect of poly(3-hydroxyalkanoates) as natural polymers on mesenchymal stem cells

Mesenchymal stem cells (MSCs) are stromal multipotent stem cells that can differentiate into multiple cell types, including fibroblasts, osteoblasts, chondrocytes, adipocytes, and myoblasts, thus allowing them to contribute to the regeneration of various tissues, especially bone tissue. MSCs are now considered one of the most promising cell types in the field of tissue engineering. Traditional petri dish-based culture of MSCs generate heterogeneity, which leads to inconsistent efficacy of MSC applications. Biodegradable and biocompatible polymers, poly(3-hydroxyalkanoates) (PHAs), are actively used for the manufacture of scaffolds that serve as carriers for MSC growth. The growth and differentiation of MSCs grown on PHA scaffolds depend on the physicochemical properties of the polymers, the 3D and surface microstructure of the scaffolds, and the biological activity of PHAs, which was discovered in a series of investigations. The mechanisms of the biological activity of PHAs in relation to MSCs remain insufficiently studied. We suggest that this effect on MSCs could be associated with the natural properties of bacteria-derived PHAs, especially the most widespread representative poly(3-hydroxybutyrate) (PHB). This biopolymer is present in the bacteria of mammalian microbiota, whereas endogenous poly(3-hydroxybutyrate) is found in mammalian tissues. The possible association of PHA effects on MSCs with various biological functions of poly(3-hydroxybutyrate) in bacteria and eukaryotes, including in humans, is discussed in this paper.

Feeding strategies for tuning poly (3-hydroxybutyrate-co-4-hydroxybutyrate) monomeric composition and productivity using Burkholderia sacchari

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-4HB)) co-polymers were produced at bench-scale in fed-batch cultivations by Burkholderia sacchari from glucose (main carbon-source) and gamma-butyrolactone (GBL) as co-substrate. As P(3HB-4HB) properties highly depend on the 4-hydroxybutyrate (4HB) molar fraction, it is advantageous to have a thorough knowledge of the process in order to promote the production of the targeted final product. In this work, polymers with a 4HB molar percentage ranging from 1.5 to 8.4% (mol/mol) were obtained as consequence of a fine tuning of the fed-batch operation conditions, namely regarding the co-substrate feeding rate and its addition time, as GBL is toxic to B. sacchari cells. The best results regarding both the 4HB incorporation (molar%) and the co-polymer productivity (7.1% and 1.1g/(L.h) respectively) were reached when a pulse of GBL (<10g/L) was added early in the accumulation phase followed by a constant GBL addition at a rate similar to that of consumption so that a steady co-substrate concentration in the medium was maintained.