A comparative investigation of biodegradable polyhydroxyalkanoate films as matrices for in vitro cell cultures

Polyhydroxyalkanoate recovery overview: properties, characterizations, and extraction strategies

Due to their excellent properties, polyhydroxyalkanoates are gaining increasing recognition in the biodegradable polymer market. These biogenic polyesters are characterized by high biodegradability in multiple environments, overcoming the limitation of composting plants only and their versatility in production. The most consolidated techniques in the literature or the reference legislation for the physical, chemical and mechanical characterisation of the final product are reported since its usability on the market is still linked to its quality, including the biodegradability certificate. This versatility makes polyhydroxyalkanoates a promising prospect with the potential to replace fossil-based thermoplastics sustainably. This review analyses and compares the physical, chemical and mechanical properties of poly-β-hydroxybutyrate and poly-β-hydroxybutyrate-co-β-hydroxyvalerate, indicating their current limitations and strengths. In particular, the copolymer is characterised by better performance in terms of crystallinity, hardness and workability. However, the knowledge in this area is still in its infancy, and the selling prices are too high (9-18 $ kg-1). An analysis of the main extraction techniques, established and in development, is also included. Solvent extraction is currently the most widely used method due to its efficiency and final product quality. In this context, the extraction phase of the biopolymer production process remains a major challenge due to its high costs and the need to use non-halogenated toxic solvents to improve the production of good-quality bioplastics. The review also discusses all fundamental parameters for optimising the process, such as solubility and temperature.

A 3D-Printed Scaffold for Repairing Bone Defects

The treatment of bone defects has always posed challenges in the field of orthopedics. Scaffolds, as a vital component of bone tissue engineering, offer significant advantages in the research and treatment of clinical bone defects. This study aims to provide an overview of how 3D printing technology is applied in the production of bone repair scaffolds. Depending on the materials used, the 3D-printed scaffolds can be classified into two types: single-component scaffolds and composite scaffolds. We have conducted a comprehensive analysis of material composition, the characteristics of 3D printing, performance, advantages, disadvantages, and applications for each scaffold type. Furthermore, based on the current research status and progress, we offer suggestions for future research in this area. In conclusion, this review acts as a valuable reference for advancing the research in the field of bone repair scaffolds.

Recent Development of Polyhydroxyalkanoates (PHA)-Based Materials for Antibacterial Applications: A Review

The diseases caused by microorganisms are innumerable existing on this planet. Nevertheless, increasing antimicrobial resistance has become an urgent global challenge. Thus, in recent decades, bactericidal materials have been considered promising candidates to combat bacterial pathogens. Recently, polyhydroxyalkanoates (PHAs) have been used as green and biodegradable materials in various promising alternative applications, especially in healthcare for antiviral or antiviral purposes. However, it lacks a systematic review of the recent application of this emerging material for antibacterial applications. Therefore, the ultimate goal of this review is to provide a critical review of the state of the art recent development of PHA biopolymers in terms of cutting-edge production technologies as well as promising application fields. In addition, special attention was given to collecting scientific information on antibacterial agents that can potentially be incorporated into PHA materials for biological and durable antimicrobial protection. Furthermore, the current research gaps are declared, and future research perspectives are proposed to better understand the properties of these biopolymers as well as their possible applications.

3D Disease Modelling of Hard and Soft Cancer Using PHA-Based Scaffolds

Simple Summary

Tumour progression in vivo was able to be well mimicked in 3D culture by utilizing biodegradable 10 mm × 10 mm × 8 mm P(3HO-co-3HD) and P(3HB)-based 3D scaffolds with a pore size of 30 to 300 µm. Both hard (MCF7 and MDA-MB-231) and soft (HCT116) tumour-related cells were successfully grown on the scaffolds, and their growth patterns were studied for 5 days. MDA-MB-231 tend to grow in clusters, and MCF7 cells form an evenly dispersed layer, which covered most of the 3D PHA scaffolds, while HCT116 formed large colonies within the pockets of the 3D PHA scaffold. Epithelial mesenchymal transition (EMT) marker genes, including Wnt-11, E-cadherin, Vim and Snail expression profiles, were like those seen in real tumour samples, which confirmed that the cancer models were exhibiting real tumour-like characteristics with high fidelity. These models are important in mimicking hypoxic tumours and in studying gene expression, cellular signalling, angiogenesis and drug response for translational research.

Abstract

Tumour cells are shown to change shape and lose polarity when they are cultured in 3D, a feature typically associated with tumour progression in vivo, thus making it significant to study cancer cells in an environment that mimics the in vivo milieu. In this study we established hard (MCF7 and MDA-MB-231, breast cancer) and soft (HCT116, colon cancer) 3D cancer tumour models utilizing a blend of P(3HO-co-3HD) and P(3HB). P(3HO-co-3HD) and P(3HB) belong to a group of natural biodegradable polyesters, PHAs, that are synthesised by microorganisms. The 3D PHA scaffolds produced, with a pore size of 30 to 300 µm, allow for nutrients to diffuse within the scaffold and provide the cells with the flexibility to distribute evenly within the scaffold and grow within the pores. Interestingly, by Day 5, MDA-MB-231 showed dispersed growth in clusters, and MCF7 cells formed an evenly dispersed dense layer, while HCT116 formed large colonies within the pockets of the 3D PHA scaffolds. Our results show Epithelial Mesenchymal Transition (EMT) marker gene expression profiles in the hard tumour cancer models. In the 3D-based PHA scaffolds, MDA-MB-231 cells expressed higher levels of Wnt-11 and mesenchymal markers, such as Snail and its downstream gene Vim mRNAs, while MCF7 cells exhibited no change in their expression. On the other hand, MCF7 cells exhibited a significantly increased E-Cadherin expression as compared to MDA-MB-231 cells. The expression levels of EMT markers were comparative to their expression reported in the tumour samples, making them good representative of cancer models. In future these models will be helpful in mimicking hypoxic tumours, in studying gene expression, cellular signalling, angiogenesis and drug response more accurately than 2D and perhaps other 3D models.

Effect of Polyhydroxyalkanoate (PHA) Concentration on Polymeric Scaffolds Based on Blends of Poly-L-Lactic Acid (PLLA) and PHA Prepared via Thermally Induced Phase Separation (TIPS)

Hybrid porous scaffolds composed of both natural and synthetic biopolymers have demonstrated significant improvements in the tissue engineering field. This study investigates for the first time the fabrication route and characterization of poly-L-lactic acid scaffolds blended with polyhydroxyalkanoate up to 30 wt%. The hybrid scaffolds were prepared by a thermally induced phase separation method starting from ternary solutions. The microstructure of the hybrid porous structures was analyzed by scanning electron microscopy and related to the blend composition. The porosity and the wettability of the scaffolds were evaluated through gravimetric and water contact angle measurements, respectively. The scaffolds were also characterized in terms of the surface chemical properties via Fourier transform infrared spectroscopy in attenuated total reflectance. The mechanical properties were analyzed through tensile tests, while the crystallinity of the PLLA/PHA scaffolds was investigated by differential scanning calorimetry and X-ray diffraction.

Biomedical Applications of Polyhydroxyalkanoate in Tissue Engineering

Tissue engineering technology aids in the regeneration of new tissue to replace damaged or wounded tissue. Three-dimensional biodegradable and porous scaffolds are often utilized in this area to mimic the structure and function of the extracellular matrix. Scaffold material and design are significant areas of biomaterial research and the most favorable material for seeding of in vitro and in vivo cells. Polyhydroxyalkanoates (PHAs) are biopolyesters (thermoplastic) that are appropriate for this application due to their biodegradability, thermo-processability, enhanced biocompatibility, mechanical properties, non-toxicity, and environmental origin. Additionally, they offer enormous potential for modification through biological, chemical and physical alteration, including blending with various other materials. PHAs are produced by bacterial fermentation under nutrient-limiting circumstances and have been reported to offer new perspectives for devices in biological applications. The present review discusses PHAs in the applications of conventional medical devices, especially for soft tissue (sutures, wound dressings, cardiac patches and blood vessels) and hard tissue (bone and cartilage scaffolds) regeneration applications. The paper also addresses a recent advance highlighting the usage of PHAs in implantable devices, such as heart valves, stents, nerve guidance conduits and nanoparticles, including drug delivery. This review summarizes the in vivo and in vitro biodegradability of PHAs and conducts an overview of current scientific research and achievements in the development of PHAs in the biomedical sector. In the future, PHAs may replace synthetic plastics as the material of choice for medical researchers and practitioners.

Development of Biodegradable Delivery Systems Containing Novel 1,2,4-Trioxolane Based on Bacterial Polyhydroxyalkanoates

In this work, delivery systems in the form of microparticles and films containing 1,2,4-trioxolane (ozonide, OZ) based on polyhydroxyalkanoates (PHAs) were developed. Main systems’ characteristics were investigated: the particle yield, average diameter, zeta potential, surface morphology, loading capacity, and drug release profile of microparticles, as well as surface morphology and release profiles of OZ-containing films. PHA-based OZ-loaded microparticles have been found to have satisfactory size, zeta potential, and ozonide loading-release behavior. It was noted that OZ content influenced the surface morphology of obtained systems.

Polyhydroxyalkanoates (PHAs) as Biomaterials in Tissue Engineering: Production, Isolation, Characterization

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible biopolymers. These biomaterials have grown in importance in the fields of tissue engineering and tissue reconstruction for structural applications where tissue morphology is critical, such as bone, cartilage, blood vessels, and skin, among others. Furthermore, they can be used to accelerate the regeneration in combination with drugs, as drug delivery systems, thus reducing microbial infections. When cells are cultured under stress conditions, a wide variety of microorganisms produce them as a store of intracellular energy in the form of homo- and copolymers of [R]—hydroxyalkanoic acids, depending on the carbon source used for microorganism growth. This paper gives an overview of PHAs, their biosynthetic pathways, producing microorganisms, cultivation bioprocess, isolation, purification and characterization to obtain biomaterials with medical applications such as tissue engineering.

Development and Advantages of Biodegradable PHA Polymers Based on Electrospun PHBV Fibers for Tissue Engineering and Other Biomedical Applications

Biodegradable polymeric biomaterials offer a significant advantage in disposable or fast-consuming products in medical applications. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is an example of a polyhydroxyalkanoate (PHA), i.e., one group of natural polyesters that are byproducts of reactions taking place in microorganisms in conditions with an excess carbon source. PHA polymers are a promising material for the production of everyday materials and biomedical applications. Due to the high number of monomers in the group, PHAs permit modifications enabling the production of copolymers of different compositions and with different proportions of individual monomers. In order to change and improve the properties of polymer fibers, PHAs are combined with either other natural and synthetic polymers or additives of inorganic phases. Importantly, electrospun PHBV fibers and mats showed an enormous potential in both the medical field (tissue engineering scaffolds, plasters, wound healing, drug delivery systems) and industrial applications (filter systems, food packaging). This Review summarizes the current state of the art in processing PHBV, especially by electrospinning, its degradation processes, and biocompatibility studies, starting from a general introduction to the PHA group of polymers.

Microbial Polyhydroxyalkanoates and Nonnatural Polyesters

Microorganisms produce diverse polymers for various purposes such as storing genetic information, energy, and reducing power, and serving as structural materials and scaffolds. Among these polymers, polyhydroxyalkanoates (PHAs) are microbial polyesters synthesized and accumulated intracellularly as a storage material of carbon, energy, and reducing power under unfavorable growth conditions in the presence of excess carbon source. PHAs have attracted considerable attention for their wide range of applications in industrial and medical fields. Since the first discovery of PHA accumulating bacteria about 100 years ago, remarkable advances have been made in the understanding of PHA biosynthesis and metabolic engineering of microorganisms toward developing efficient PHA producers. Recently, nonnatural polyesters have also been synthesized by metabolically engineered microorganisms, which opened a new avenue toward sustainable production of more diverse plastics. Herein, the current state of PHAs and nonnatural polyesters is reviewed, covering mechanisms of microbial polyester biosynthesis, metabolic pathways, and enzymes involved in biosynthesis of short-chain-length PHAs, medium-chain-length PHAs, and nonnatural polyesters, especially 2-hydroxyacid-containing polyesters, metabolic engineering strategies to produce novel polymers and enhance production capabilities and fermentation, and downstream processing strategies for cost-effective production of these microbial polyesters. In addition, the applications of PHAs and prospects are discussed.

Poly(3-hydroxybutyrate): Promising biomaterial for bone tissue engineering

Poly(3-hydroxybutyrate) is a natural polymer, produced by different bacteria, with good biocompatibility and biodegradability. Cardiovascular patches, scaffolds in tissue engineering and drug carriers are some of the possible biomedical applications of poly(3-hydroxybutyrate). In the past decade, many researchers examined the different physico-chemical modifications of poly(3-hydroxybutyrate) in order to improve its properties for use in the field of bone tissue engineering. Poly(3-hydroxybutyrate) composites with hydroxyapatite and bioglass are intensively tested with animal and human osteoblasts in vitro to provide information about their biocompatibility, biodegradability and osteoinductivity. Good bone regeneration was proven when poly(3-hydroxy-butyrate) patches were implanted in vivo in bone tissue of cats, minipigs and rats. This review summarizes the recent reports of in vitro and in vivo studies of pure poly(3-hydroxy-butyrate) and poly(3-hydroxybutyrate) composites with the emphasis on their bioactivity and biocompatibility with bone cells.

Chondrocyte Co-cultures with the Stromal Vascular Fraction of Adipose Tissue in Polyhydroxybutyrate/Poly-(hydroxybutyrate-co-hydroxyhexanoate) Scaffolds: Evaluation of Cartilage Repair in Rabbit

Chondral defects are challenging to repair because of the poor self-healing capacity of articular cartilage. The aim of this study was to compare and investigate the cartilage regeneration of stromal vascular fraction (SVF) cells and adipose-derived stem cells (ASCs) co-cultured with chondrocytes seeding on scaffolds composed of polyhydroxybutyrate (PHB)/poly-(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx). In this study, the cellular morphologies and proliferation capabilities on scaffolds were evaluated. Next, scaffolds with 1:1 co-culture of ASCs/SVF and chondrocytes were implanted into the full-thickness cartilage defects in rabbit knee for 10 weeks. Cells seeded on the scaffolds showed better adhesion, migration, and proliferation in vitro. Importantly, implantation with scaffolds with SVF and chondrocytes revealed more desirable in vivo healing outcomes. Our results illustrate a one-step surgical procedure for the regeneration of focal cartilage defects using a mixture of SVF from adipose tissue and uncultured chondrocytes.

Potential of Electrospun Poly(3-hydroxybutyrate)/Collagen Blends for Tissue Engineering Applications

In this work, tunable nonwoven mats based on poly(3-hydroxybutyrate) (PHB) and type I collagen (Coll) were successfully produced by electrospinning. The PHB/Coll weight ratio (fixed at 100/0, 70/30, and 50/50, resp.) was found to control the morphological, thermal, mechanical, and degradation properties of the mats. Increasing collagen amounts led to larger diameters of the fibers (in the approximate range 600-900 nm), while delaying their thermal decomposition (from 245°C to 262°C). Collagen also accelerated the hydrolytic degradation of the mats upon incubation in aqueous medium at 37°C for 23 days (with final weight losses of 1%, 15%, and 23% for 100/0, 70/30, and 50/50 samples, resp.), as a result of increased mat wettability and reduced PHB crystallinity. Interestingly, 70/30 meshes were the ones displaying the lowest stiffness (~116 MPa; p < 0.05 versus 100/0 and 50/50 meshes), while 50/50 samples had an elastic modulus comparable to that of 100/0 ones (~250 MPa), likely due to enhanced physical crosslinking of the collagen chains, at least at high protein amounts. All substrates were also found to allow for good viability and proliferation of murine fibroblasts, up to 6 days of culture. Collectively, the results evidenced the potential of as-spun PHB/Coll meshes for tissue engineering applications.

Experimental wound dressings of degradable PHA for skin defect repair

The present study reports construction of wound dressing materials from degradable natural polymers such as hydroxy derivatives of carboxylic acids (PHAs) and 3-hydroxybutyrate/4-hydroxybutyrate [P(3HB/4HB)] as copolymer. The developed polymer films and electrospun membranes were evaluated for its wound healing properties with Grafts-elastic nonwoven membranes carrying fibroblast cells derived from adipose tissue multipotent mesenchymal stem cells. The efficacy of nonwoven membranes of P(3HB/4HB) carrying the culture of allogenic fibroblasts was assessed against model skin defects in Wistar rats. The morphological, histological and molecular studies revealed the presence of fibroblasts on dressing materials which facilitated wound healing, vascularization and regeneration. Further it was also observed that cells secreted extracellular matrix proteins which formed a layer on the surface of membranes and promoted the migration of epidermal cells from the neighboring tissues surrounding the wound. The wounds under the P(3HB/4HB) membrane carrying cells healed 1.4 times faster than the wounds under the cell-free membrane and 3.5 times faster than the wounds healing under the eschar (control).The complete wound healing process was achieved at Day 14. Thus the study highlights the importance of nonwoven membranes developed from degradable P(3HB/4HB) polymers in reducing inflammation, enhancing angiogenic properties of skin and facilitating better wound healing process.

Opsonisation of nanoparticles prepared from poly(β-hydroxybutyrate) and poly(trimethylene carbonate)-b-poly(malic acid) amphiphilic diblock copolymers: Impact on the in vitro cell uptake by primary human macrophages and HepaRG hepatoma cells

The present work reports the investigation of the biocompatibility, opsonisation and cell uptake by human primary macrophages and HepaRG cells of nanoparticles (NPs) formulated from poly(β-malic acid)-b-poly(β-hydroxybutyrate) (PMLA-b-PHB) and poly(β-malic acid)-b-poly(trimethylene carbonate) (PMLA-b-PTMC) diblock copolymers, namely PMLA₈₀₀-b-PHB₇₃₀₀, PMLA₄₅₀₀-b-PHB₄₄₀₀, PMLA₂₅₀₀-b-PTMC₂₈₀₀ and PMLA₄₃₀₀-b-PTMC₁₄₀₀. NPs derived from PMLA-b-PHB and PMLA-b-PTMC do not trigger lactate dehydrogenase release and do not activate the secretion of pro-inflammatory cytokines demonstrating the excellent biocompatibility of these copolymers derived nano-objects. Using a protein adsorption assay, we demonstrate that the binding of plasma proteins is very low for PMLA-b-PHB-based nano-objects, and higher for those prepared from PMLA-b-PTMC copolymers. Moreover, a more efficient uptake by macrophages and HepaRG cells is observed for NPs formulated from PMLA-b-PHB copolymers compared to that of PMLA-b-PTMC-based NPs. Interestingly, the uptake in HepaRG cells of NPs formulated from PMLA₈₀₀-b-PHB₇₃₀₀ is much higher than that of NPs based on PMLA₄₅₀₀-b-PHB₄₄₀₀. In addition, the cell internalization of PMLA₈₀₀-b-PHB₇₃₀₀ based-NPs, probably through endocytosis, is strongly increased by serum pre-coating in HepaRG cells but not in macrophages. Together, these data strongly suggest that the binding of a specific subset of plasmatic proteins onto the PMLA₈₀₀-b-PHB₇₃₀₀-based NPs favors the HepaRG cell uptake while reducing that of macrophages.

Preparation and characterization of biodegradable polyhydroxybutyrate-co-hydroxyvalerate/polyethylene glycol-based microspheres

The in vivo effectiveness of biomolecules may be limited by their rapid diffusion in the body and short half-life time. Encapsulation of these biomolecules allows protecting them against degradation and ensuring a controlled release over time. In this work, the production of polyhydroxybutyrate-co-hydroxyvalerate/polyethylene glycol-based microspheres loaded with heparin by double emulsion-solvent evaporation is investigated. Significant improvements are achieved after blending PHB-HV microspheres with PEG. First of all, an important decrease of the initial burst effect is ensured. Moreover, lower degradation of the microspheres is observed after 30days in the release medium. Finally, the release rate could be controlled using different PEG molecular weights and concentrations. A toxic effect of PHB-HV 30% PEG 1100gmol^-1 microspheres is observed whereas PHB-HV and PHB-HV 30% PEG 10,000gmol^-1 microspheres are not toxic. These microspheres seem to be most suited for further tissue engineering applications. The effectiveness of direct PEG blending to PHB-HV is proved, limiting the use of chemical reagents for PHB-HV/PEG copolymer synthesis and steps for chemical reagents removal from the copolymer.

Third generation poly(hydroxyacid) composite scaffolds for tissue engineering

Bone tissue engineering based on scaffolds is quite a complex process as a whole gamut of criteria needs to be satisfied to promote cellular attachment, proliferation and differentiation: biocompatibility, right surface properties, adequate mechanical performance, controlled bioresorbability, osteoconductivity, angiogenic cues, and vascularization. Third generation scaffolds are more of composite types to maximize biological-mechanical-chemical properties. In the present review, our focus is on the performance of micro-organism-derived polyhydroxyalkanoates (PHAs)-polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV)-composite scaffolds with ceramics and natural polymers for tissue engineering applications with emphasis on bone tissue. We particularly emphasize on how material properties of the composites affect scaffold performance. PHA-based composites have demonstrated their biocompatibility with a range of tissues and their capacity to induce osteogenesis due to their piezoelectric properties. Electrospun PHB/PHBV fiber mesh in combination with human adipose tissue-derived stem cells (hASCs) were shown to improve vascularization in engineered bone tissues. For nerve and skin tissue engineering applications, natural polymers such as collagen and chitosan remain the gold standard but there is scope for development of scaffolds combining PHAs with other natural polymers which can address some of the limitations such as brittleness, lack of bioactivity and slow degradation rate presented by the latter. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1667-1684, 2017.

Polyhydroxyalkanoates - what are the uses? Current challenges and perspectives

Over the past few decades, a considerable attention has been focused on the microbial polyhydroxyalkanoates (PHAs) owing to its multifaceted properties, i.e. biodegradability, biocompatibility, non-toxicity and thermo-plasticity. This article presents a critical review of the foregoing research, current trends and future perspectives on the value added applications of PHAs in the biomedical, environmental and industrial domains of life.

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)-based scaffolds for tissue engineering

Development and selection of an ideal scaffold is of importance for tissue engineering. Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) is a biocompatible bioresorbable copolymer that belongs to the polyhydroxyalkanoate family. Because of its good biocompatibility, PHBHHx has been widely used as a cell scaffold for tissue engineering. This review focuses on the utilization of PHBHHx-based scaffolds in tissue engineering. Advances in the preparation, modification, and application of PHBHHx scaffolds are discussed.

Advances in the applications of polyhydroxyalkanoate nanoparticles for novel drug delivery system

Drug delivery technology is emerging as an interdisciplinary science aimed at improving human health. The controlled delivery of pharmacologically active agents to the specific site of action at the therapeutically optimal rate and dose regimen has been a major goal in designing drug delivery systems. Over the past few decades, there has been considerable interest in developing biodegradable drug carriers as effective drug delivery systems. Polymeric materials from natural sources play an important role in controlled release of drug at a particular site. Polyhydroxyalkanoates, due to their origin from natural sources, are given attention as candidates for drug delivery materials. Biodegradable and biocompatible polyhydroxyalkanoates are linear polyesters produced by microorganisms under unbalanced growth conditions, which have emerged as potential polymers for use as biomedical materials for drug delivery due to their unique physiochemical and mechanical properties. This review summarizes many of the key findings in the applications of polyhydroxyalkanoates and polyhydroxyalkanoate nanoparticles for drug delivery system.

Manipulation of Ralstonia eutropha carbon storage pathways to produce useful bio-based products

Ralstonia eutrophais a Gram-negative betaproteobacterium found natively in soils that can utilize a wide array of carbon sources for growth, and can store carbon intracellularly in the form of polyhydroxyalkanoate. Many aspects of R. eutrophamake it a good candidate for use in biotechnological production of polyhydroxyalkanoate and other bio-based, value added compounds. Manipulation of the organism's carbon flux is a cornerstone to success in developing it as a biotechnologically relevant organism. Here, we examine the methods of controlling and adapting the flow of carbon in R. eutrophametabolism and the wide range of compounds that can be synthesized as a result. The presence of many different carbon utilization pathways and the custom genetic toolkit for manipulation of those pathways gives R. eutrophaa versatility that allows it to be a biotechnologically important organism.

Biocompatibility of polyhydroxyalkanoate as a potential material for ligament and tendon scaffold material

There is a strong need for new biodegradable materials that are suitable for scaffolds in tissue engineering of tendons and ligaments. In many cases, quick degradation rates are favorable, however, with respect to ligament and tendon replacement, slowly degrading polymers are clearly favored. Prime candidates are members of the large class of polyhydroxyalkanoates (PHAs), which are thermoplastic/elastomeric biopolyesters that are slowly degraded by surface erosion. Moreover, their physico-mechanical properties can be tailored during biosynthesis in bacteria or by chemical modifications. They may be spun into fibers, coated on surfaces or be part of composites. This study has investigated the biocompatability of seven different thermoplastic or elastomeric PHAs using L929 murine fibroblast cells. Cell viability and proliferation over 7 days was analyzed with live/dead staining and a picogreen assay. In addition, extracellular matrix production was measured with the hydroxyproline assay after 14 days. It was found that cell attachment to the PHA film ranged from 85-99% after 7 days. Three PHA films (PHBV (92/8), PHOUE-POSS and PHUE-O3) supported similar cell viability in comparison to the controls performed on tissue culture plastic (polystyrene), whereas the biomaterials (PHUA, PHUE, PHB and PHOUE) showed fewer viable cells than in controls. PHB, PHUE-O3, and PHBV with a water contact angle below 85 degrees supported a similar amount of collagen production in comparison to the tissue culture plastic controls. PHUA, PHUE, PHOUE, and PHOUE-POSS showed a decrease in collagen production in comparison to the controls after 14 days. Overall, PHB, PHBV, and PHUE-O3 demonstrated good performance with regards to potential use as a tissue-engineering scaffold.

Preparation of a novel biodegradable nanocomposite scaffold based on poly (3-hydroxybutyrate)/bioglass nanoparticles for bone tissue engineering

One of the most important challenges in composite scaffolds is pore architecture. In this study, poly (3-hydroxybutyrate) with 10% bioglass nanoparticles was prepared by the salt leaching processing technique, as a nanocomposite scaffold. The scaffolds were characterized by SEM, FTIR and DTA. The SEM images demonstrated uniformed porosities of appropriate sizes (about 250-300 microm) which are interconnected. Furthermore, higher magnification SEM images showed that the scaffold possesses less agglomeration and has rough surfaces that may improve cell attachment. In addition, the FTIR and DTA results showed favorable interaction between polymer and bioglass nanoparticles which improved interfaces in the samples. Moreover, the porosity of the scaffold was assessed, and the results demonstrated that the scaffold has uniform and high porosity in its structure (about 84%). Finally it can be concluded that this scaffold has acceptable porosity and morphologic character paving the way for further studies to be conducted from the perspective of bone tissue engineering.

A Novel Biocompatible Poly (3-hydroxy-co-4-hydroxybutyrate) Blend as a Potential Biomaterial for Tissue Engineering

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) P(3HB-co-4HB) biopolymer was subjected to a depyrogenation treatment followed by blending with vitamin E (P(3HB-co-4HB)/Vit E blend), collagen (Col blend) or both (P(3HB-co-4HB)/Vit E/Col hybrid blend) to improve its biological performance. The cytocompatibility and pro-inflammatory response to the biopolymer after the treatment and blending were evaluated by cellular responses in vitro. Cell attachment and spreading of murine NIH 3T3 fibroblasts seeded on the films were found to be the highest on the hybrid P(3HB-co-4HB)/Vit E/Col blend film. The P(3HB-co-4HB) blends showed increased cell proliferation and negligible cytotoxicity. The pro-inflammatory cytokines, IL6 and TNF α expression in the murine macrophage cell line J774 A-1 monocyte/macrophage cells cultured on the biopolymer films were assessed by immunoblotting and RT-PCR analyses which revealed that the combined blending strategy was the most effective in reducing the pro-inflammatory activity. The depyrogenated P(3HB-co-4HB) blends significantly extend the range of biomaterials suitable for tissue engineering.

PHB/PHBHHx scaffolds and human adipose-derived stem cells for cartilage tissue engineering

The goal of this study was to investigate the potential of polyhydroxybutyrate (PHB)/poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) (PHB/PHBHHx) to produce neocartilage upon seeding with differentiated human adipose-derived stem cells (hASCs). hASCs were grown on a three-dimensional PHB/PHBHHx scaffold in vitro with or without chondrogenic media for 14 days. Scanning electron microscopy showed that differentiated cells produced abundant extracellular matrices with increasing culture time. No cytotoxicity was observed by the live/dead cell viability assay. GAG and total collagen content in the differentiated cells increased significantly with in vitro culture time. After 14 days of in vitro culture, the differentiated cells grown on the (PHB/PHBHHx) scaffold (differentiated cells/(PHB/PHBHHx)) were implanted into the subcutaneous layer nude mice for 12 or 24 weeks, non-differentiated cells/(PHB/PHBHHx) were implanted as the control group. The differentiated cells/(PHB/PHBHHx) implants formed cartilage-like tissue after 24 weeks of implantation, and stained positive for collagen type II, safranin O, and toluidine blue. In addition, typical cartilage lacuna was observed, and there were no remnants of PHB/PHBHHx. Collagen type II was detected by Western blot at 12 and 24 weeks of implantation. In the control group, no cartilage formation was observed. This study demonstrated that PHB/PHBHHx is a suitable material for cartilage tissue engineering.

Biocompatibility of polyhydroxybutyrate microspheres: in vitro and in vivo evaluation

Microspheres have been prepared from the resorbable linear polyester of beta-hydroxybutyric acid (polyhydroxybutyrate, PHB) by the solvent evaporation technique and investigated in vitro and in vivo. Biocompatibility of the microspheres has been proved in tests in the culture of mouse fibroblast cell line NIH 3T3 and in experiments on intramuscular implantation of the microspheres to Wistar rats for 3 months. Tissue response to the implantation of polymeric microspheres has been found to consist in a mild inflammatory reaction, pronounced macrophage infiltration that increases over time, involving mono- and poly-nuclear foreign body giant cells that resorb the polymeric matrix. No fibrous capsules were formed around polymeric microparticles; neither necrosis nor any other adverse morphological changes and tissue transformation in response to the implantation of the PHB microparticles were recorded. The results of the study suggest that polyhydroxybutyrate is a good candidate for fabricating prolonged-action drugs in the form of microparticles intended for intramuscular injection.

Increased response of Vero cells to PHBV matrices treated by plasma

The copolymers poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) are being intensely studied as a tissue engineering substrate. It is known that poly 3-hydroxybutyric acids (PHBs) and their copolymers are quite hydrophobic polyesters. Plasma-surface modification is an effective and economical surface treatment technique for many materials and of growing interest in biomedical engineering. In this study we investigate the advantages of oxygen and nitrogen plasma treatment to modify the PHBV surface to enable the acceleration of Vero cell adhesion and proliferation. PHBV was dissolved in methylene chloride at room temperature. The PHBV membranes were modified by oxygen or nitrogen-plasma treatments using a plasma generator. The membranes were sterilized by UV irradiation for 30 min and placed in 96-well plates. Vero cells were seeded onto the membranes and their proliferation onto the matrices was also determined by cytotoxicity and cell adhesion assay. After 2, 24, 48 and 120 h of incubation, growth of fibroblasts on matrices was observed by scanning electron microscopy (SEM). The analyses of the membranes indicated that the plasma treatment decreased the contact angle and increased the surface roughness; it also changed surface morphology, and consequently, enhanced the hydrophilic behavior of PHBV polymers. SEM analysis of Vero cells adhered to PHBV treated by plasma showed that the modified surface had allowed better cell attachment, spreading and growth than the untreated membrane. This combination of surface treatment and polymer chemistry is a valuable guide to prepare an appropriate surface for tissue engineering application.