Polyhydroxyalkanoate (PHA): Properties and Modifications

Advancements in genetic engineering for enhanced Polyhydroxyalkanoates (PHA) production: a comprehensive review of metabolic pathway manipulation and gene deletion strategies

Polyhydroxyalkanoates (PHA) are bioplastics produced by few bacteria as intracellular lipid inclusions under excess carbon source and nutrient-deprived conditions. These polymers are biodegradable and resemble petroleum-based plastics. The rising environmental concerns have increased the demand for PHA, but the low yield in wild-type bacterial strains limits large-scale production. An improvement in the PHA production can be achieved by genetically engineering the wild-type bacterial strains by removing competitive pathways that divert the metabolites away from PHA biosynthesis, cloning strong promotors to overexpress the genes involved in PHA biosynthesis and constructing non-native metabolic pathways that feed the metabolites for PHA production. The desired monomers in the PHA polymers were obtained by elimination of genes involved in PHA biosynthetic pathway. The chain length degradation specific-gene deletion of β-oxidation pathway resulted in the accumulation of PHA monomers having high carbon chain length. A controlled accumulation of monomers in the PHA polymer was achieved by constructing novel pathways in the bacteria and deleting native genes of competitive pathways from the genome of non-PHA producers. The present review attempts to showcase the novel genetic modification approaches conducted so far to enhance the PHA production with a special focus on metabolic pathway gene deletion in various bacteria.

Bamboo: A neglected candidate for polyhydroxyalkanoate production-A review

In light of growing concerns about climate change, energy crises, and waste management due to the excessive reliance on fossil resources, there is an increasing emphasis on sustainability and the circular economy. Polyhydroxyalkanoates (PHAs), microbial polyesters synthesized from various feedstocks, offer a promising alternative to conventional plastics due to their comparable physicochemical characteristics, biological degradability, and biocompatibility. Lignocellulosic biomass, known for its abundance, renewability, and affordability, represents a particularly suitable carbon source for commercial PHA production. This review provides a comprehensive overview of the bioconversion of lignocellulosic feedstocks into PHAs, encompassing pretreatment, hydrolysis, and fermentation strategies. It highlights biosynthetic pathways from cellulose and hemicellulose via reducing sugars and volatile fatty acids fermentation, and also evaluates the feasibility of utilizing lignin as a substrate for PHA biosynthesis. Additionally, the review underscores the advantages of bamboo-a rapid-growing, renewable plant with high biomass yield, rich lignocellulosic composition, and strong carbon sequestration capacity-as a promising yet underexplored feedstock for industrial-scale PHA production.

Bioplastics and biodegradable plastics: A review of recent advances, feasibility and cleaner production

As awareness of plastic pollution increases, there is a growing emphasis on sustainable alternatives. Bioplastics and biodegradable plastics have surfaced as potential substitutes. Yet, their limited properties and high production costs hinder their practicality. This paper systematically reviews more than 280 articles to comprehensively outline the advantages and drawbacks of emerging bioplastics and biodegradable plastics, alongside advancements in cleaner production methods. Bioplastics, sourced from renewable materials, decrease dependency on fossil fuels and help lower carbon footprints during production and disposal. Some bioplastics, such as polylactic acid (PLA) and polyhydroxyalkanoates, are compostable, but their manufacturing costs usually surpass that of conventional plastics. Additionally, certain bioplastics exhibit lower mechanical strength, heat resistance, or durability. PLA and bio-polybutylene succinate (bio-PBS) are viable for single-use items and biodegradable products, with scalable production using established technologies, although bio-PBS is somewhat pricier than PLA. Biodegradable plastics lessen environmental impact by naturally degrading and can be composted in industrial settings, providing an eco-friendly disposal option. However, they require specific industrial composting conditions for complete degradation, which can lead to microplastic formation in the environment. PBS, polybutylene adipate terephthalate, and polybutylene succinate-co-adipate seem to be the most promising options, with PBS being a strong contender for replacing traditional plastics due to its biodegradable and compostable nature. It has the potential to be partially or entirely bio-based (bio-PBS). Innovative technologies, especially next-generation industrial biotechnology and microbial cell factories, offer cleaner methods for synthesizing these plastics. This review aids in identifying feasible and sustainable alternatives to conventional plastics.

Production, isolation, optimization, and characterization of microbial PHA from Bacillus australimaris

Population explosion in recent years has driven the environment to overuse nondegradable substances. Microbial polyesters known as polyhydroxyalkanoates (PHAs) are generated and retained as cytoplasmic granules in microorganisms with restricted nutritional availability and can be used to manufacture bioplastics. The current study attempts to screen soil isolates for PHA production and optimize their media parameters. Among all the isolates, 17 were identified and confirmed by Sudan black staining, as they are screening for PHA production and are identified by their colony characteristics. The isolation of the most promising strain, GS-14, was achieved through the sodium hypochlorite method, and subsequent quantification involved establishing a standard curve of crotonic acid. Notably, isolate GS-14 presented the highest yield, which was determined by extrapolating its data onto the standard curve. Characterization of the PHA polymer was subsequently performed, and the results were used to discern its properties. FTIR confirmed characteristic PHA absorption bands, with a prominent C = O stretching peak at 1732 cm⁻¹. LC-MS detected a molecular mass of 641.6 g/mol, indicative of an oligomeric species, while the actual polymer molecular weight is estimated between 5,000 and 20,000 Da. DSC revealed an exothermic peak at 174 °C, allowing the calculation of crystallinity, a key determinant of mechanical properties. Furthermore, the PHA-producing organism was identified as Bacillus australimaris through the sequencing of 16 S ribosomal RNA. The media optimization was performed via Minitab software, with statistical analyses employed to interpret the resulting data comprehensively.

Polyhydroxyalkanoates production from microalgae for sustainable bioplastics: A review

Microalgae have emerged as a promising and sustainable source for polyhydroxyalkanoates (PHA), which are increasingly recognized for their potential in bioplastics production. However, the widespread application of microalgae-derived PHA faces challenges related to economic feasibility and scalability. This review provides a comprehensive analysis of recent advancements in the cultivation and optimization of microalgae for PHA production, highlighting the critical role of nutrient limitation, particularly nitrogen and phosphorus, in enhancing PHA accumulation. This review also explores the effectiveness of various cultivation systems, including autotrophic, heterotrophic, and mixotrophic approaches, in maximizing PHA yields. Environmental factors such as light intensity, salinity, and pH are examined for their influence on PHA synthesis pathways. Additionally, it identifies key technical and economic challenges that must be addressed to commercialize microalgae-based bioplastics to fully harness the potential of microalgae in sustainable bioplastic production.

Controlled release of trifluralin herbicide using luminescent Vibrio-derived polyhydroxyalkanoate (PHA) microcapsules

The controlled release of herbicides using new and safe materials can mitigate environmental pollution. Polyhydroxyalkanoate (PHA) is a type of biopolymer that can be produced by various bacteria. It has properties that make it suitable for encapsulation and controlled release applications. A luminescent bacterium, Vibrio sp. VLC strain was used as the PHA producer in this study. Initially, the polymer was synthesized by the bacterium following optimization of the culture medium, resulting in an approximate yield of 25 %. Subsequently, the produced polymer was analyzed using TEM, FTIR, and H-NMR techniques. Microcapsules were produced using the emulsion method. FE-SEM imaging revealed spherical microcapsules with an average diameter of 0.5-2 μm. The herbicide loading content and encapsulation efficiency were determined to be 16.64 % and 66.56 %, respectively. The herbicidal effect of the microcapsules containing trifluralin was investigated using Amaranthus retroflexus and Setaria viridis plants, demonstrating a significant reduction in various parameters after application. Furthermore, the impact of encapsulated herbicide on soil microbial population was assessed, revealing a less negative effect compared to its free form. These findings suggest that the PHA from a luminescent vibrio holds promise as an eco-friendly, biodegradable, nontoxic material for the controlled release of herbicides.

Engineering xylose utilization in Cupriavidus necator for enhanced poly(3-hydroxybutyrate) production from mixed sugars

Lignocellulosic biomass is a promising renewable feedstock for biodegradable plastics like polyhydroxyalkanoates (PHAs). Cupriavidus necator, a versatile microbial host that synthesizes poly(3-hydroxybutyrate) (PHB), the most abundant type of PHA, has been studied to expand its carbon source utilization. Since C. necator NCIMB11599 cannot metabolize xylose, we developed xylose-utilizing strains by introducing synthetic xylose metabolic pathways, including the xylose isomerase, Weimberg, and Dahms pathways. Through rational and evolutionary engineering, the RXI22 and RXW62 strains were able to efficiently utilize xylose as the sole carbon source, producing 64.2 wt% (wt%) and 61.4 wt% PHB, respectively. Among the engineered strains, the xylose isomerase-based RXI22 strain demonstrated the most efficient co-fermentation performance, with a PHB content of 75.7 wt% and a yield of 0.32 (g PHB/g glucose and xylose) from mixed sugars. The strains developed in this study represent an enhanced PHA producer, offering a sustainable route for converting lignocellulosic biomass into bioplastics.

Advances in polyhydroxyalkanoate (PHA) production from renewable waste materials using halophilic microorganisms: A comprehensive review

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polymers that can replace conventional plastics in different sectors. However, PHA commercialization is hampered due to their high production cost resulting from the use of high purity substrates, their low conversion into PHAs by using conventional microbial chassis and the high downstream processing cost. Taking these challenges into account, researchers are focusing on the use of waste by-products as alternative low-cost feedstocks for fast-growing and contamination-resistant halophilic microorganisms (Bacteria, Archaea…). This is of great importance since these extremophiles can use low-cost substrates, produce high PHA content of copolymers or different PHA monomer compositions. They can present high potential for reducing the costs of PHA fermentation and recovery processes, making their use in commercial applications easier. However, little is known about the potential of halophiles in advancing the PHA production from renewable waste materials at lab-scale and their successful implementation at industrial-scale. This review presents actual advances in PHA production by halophilic pure/engineered species (e.g. Haloferax mediterranei, Halomonas spp.) and mixed microbial consortia (MMC) using organic waste streams. The development of optimal PHA production process involves robust genetic engineering strategies, advanced fermentation processes using mixed microbial consortia versus pure/engineered strains as well as algal biomass as feedstocks.

Waste to wealth: Polyhydroxyalkanoates (PHA) production from food waste for a sustainable packaging paradigm

The growing demand for sustainable food packaging and the increasing concerns regarding environmental pollution have driven interest in biodegradable materials. This paper presents an in-depth review of the production of Polyhydroxyalkanoates (PHA), a biodegradable polymer, from food waste. PHA-based bioplastics, particularly when derived from low-cost carbon sources such as volatile fatty acids (VFAs) and waste oils, offer a promising solution for reducing plastic waste and enhancing food packaging sustainability. Through optimization of microbial fermentation processes, PHA production can achieve significant efficiency improvements, with yields reaching up to 87 % PHA content under ideal conditions. This review highlights the technical advancements in using PHA for food packaging, emphasizing its biodegradability, biocompatibility, and potential to serve as a biodegradable alternative to petroleum-based plastics. However, challenges such as high production costs, mechanical limitations, and the need for scalability remain barriers to industrial adoption. The future of PHA in food packaging hinges on overcoming these challenges through further research and innovation in production techniques, material properties, and cost reduction strategies, along with necessary legislative support to promote widespread use.

New model compounds for the efficient colorimetric screening of medium chain length polyhydroxyalkanoate (mcl-PHA) depolymerases reveal mechanism of activity

Plastic pollution presents a significant environmental problem contributing to increased CO2 emissions and persistently accumulation in ecosystems. Biobased polymers, like polyhydroxyalkanoates (PHAs), offer a part of a solution with their biodegradability and reduced carbon footprint. However, effective end-of-life strategies, such as controlled enzymatic depolymerization, are crucial for sustainability, relying on efficient PHA depolymerases (PHAases). Here we describe the synthesis of two new chromogenic compounds derived from polyhydroxyoctanoate (PHO) and their application in a continuous, quantitative spectrophotometric assay for PHO depolymerase and other medium chain lengths PHAase activity within 10 min. These substrates allow activity measurement at temperatures above 45 °C, simplifying the comparison of PHAases and aiding enzymatic degradation progress. The study also explores enzyme specificity and identifies key amino acids involved in PHO recognition by PfPHOase. The 3-hydroxyoctanoyl moieties of both compounds were found to bind specifically to a groove formed by the amino acids Phe96, Phe125, Ile171, and Val230, which are highly conserved in known mcl-PHA depolymerases.

A state-of-the-art review of environmental behavior and potential risks of biodegradable microplastics in soil ecosystems: Comparison with conventional microplastics

As the use of biodegradable plastics becomes increasingly widespread, their environmental behaviors and impacts warrant attention. Unlike conventional plastics, their degradability predisposes them to fragment into microplastics (MPs) more readily. These MPs subsequently enter the terrestrial environment. The abundant functional groups of biodegradable MPs significantly affect their transport and interactions with other contaminants (e.g., organic contaminants and heavy metals). The intermediates and additives released from depolymerization of biodegradable MPs, as well as coexisting contaminants, induce alterations in soil ecosystems. These processes indicate that the impacts of biodegradable MPs on soil ecosystems might significantly diverge from conventional MPs. However, an exhaustive and timely comparison of the environmental behaviors and effects of biodegradable and conventional MPs within soil ecosystems remains scarce. To address this gap, the Web of Science database and bibliometric software were utilized to identify publications with keywords containing biodegradable MPs and soil. Moreover, this review comprehensively summarizes the transport behavior of biodegradable MPs, their role as contaminant carriers, and the potential risks they pose to soil physicochemical properties, nutrient cycling, biota, and CO2 emissions as compared with conventional MPs. Biodegradable MPs, due to their great transport and adsorption capacity, facilitate the mobility of coexisting contaminants, potentially inducing widespread soil and groundwater contamination. Additionally, these MPs and their depolymerization products can disrupt soil ecosystems by altering physicochemical properties, increasing microbial biomass, decreasing microbial diversity, inhibiting the development of plants and animals, and increasing CO2 emissions. Finally, some perspectives are proposed to outline future research directions. Overall, this study emphasizes the pronounced effects of biodegradable MPs on soil ecosystems relative to their conventional counterparts and contributes to the understanding and management of biodegradable plastic contamination within the terrestrial ecosystem.

All-organic transistors printed on a biodegradable and bioderived substrate for sustainable bioelectronics

Biodegradable electronics is an incipient need in order to mitigate the alarming increase of electronic waste worldwide caused by capillary penetration of electronic devices and sensors. Flexibility, solution processability, low capital expenditure, and energy-efficient processes, which are distinctive features of organic printed electronics, have to be complemented by a sustainable sourcing and end-of-life of materials employed. This requirement calls for solutions where materials, especially substrates that typically represent the largest volume, can be biodegraded in the environment with no harm, yet assuring that no precious resources are dispersed. In this work, the bioderived and biodegradable biopolymer polyhydroxybutyrate (PHB) was used as a substrate, cast from an acetic acid solution, for all-organic field effect transistors (OFETs) based on an inkjet printed polymer semiconductor. The OFETs showed small device-to-device variation, a proper current modulation with I ON /I OFF of about 1.2·103, mobility values as high as 0.07 cm2/Vs in saturation regime and channel length/width normalized leakage currents in the order of nA, which remained almost unaltered also after intensive mechanical stresses upon bending and rolling. Such mechanical stability and flexibility, together with the biodegradability and bioderivation, make PHB an appealing candidate for the development of sustainable printed bioelectronics, with widespread future applications in the biomedical and food packaging sector.

Applications and environmental impact of biodegradable polymers in textile industry: A review

With the increasing global population, the disposal of waste has risen, especially over the last century. The Environmental Protection Agency (EPA) reported that 11 million tons of textile-related waste were landfilled in the USA in 2018, and this amount is projected to increase to 4.5 billion tons by 2040. Bio-based polymers have gained attention due to their remarkable properties. The most important biodegradable polymers include PLA, PHA, PHB, PCL, PBS, bamboo fibers, and banana fibers. Global biopolymer production capacity is expected to rise significantly, from around 2.18 million tons in 2023 to approximately 7.43 million tons by 2028. In the textile industry, the linear waste model presents numerous challenges, such as environmental damage and resource shortages. Shifting from a linear to a circular economy is essential to address these issues. Reducing, reusing, and recycling are the three key actions and strategies that form the foundation of the circular economy. This paper presents the current state of knowledge and technological advancements in biodegradable polymers in the textile industry, along with their products and applications. The study explores the cost-effectiveness, limitations, opportunities, and advancements in their manufacturing technologies. Biodegradable polymers in the textile sector are regarded as green alternatives to non-biodegradable polymers.

Polyhydroxyalkanoates: Medical Applications and Potential for Use in Dentistry

Polyhydroxyalkanoates (PHAs) are promising biopolymers as an alternative to traditional synthetic polymers due to their biodegradability and biocompatibility. The PHA market is blooming in response to the growing demand for biodegradable and environmentally friendly plastics. These biopolyesters are produced and degraded by a variety of microorganisms, making them environmentally friendly, while offering benefits such as biocompatibility (when adequately processed) and biodegradability. Their versatility extends to various areas, from biomedicine to agriculture and composite materials, where they pave the way for significative innovations. In the field of regenerative medicine, some PHAs have key applications, namely in vascular grafts, oral tissue regeneration, and development of self-healing polymers. In addition, PHAs have the potential to be used in the creation of dental implant materials and dental medical devices. PHAs can also be used to encapsulate hydrophobic drugs, providing an approach for more targeted and effective treatments. To summarize, PHAs open new perspectives in the field of medicine by improving drug delivery and offering ecologically biocompatible solutions for medical devices. The aim of this review is to present the medical and dental applications of PHA, their advantages, disadvantages, and indications.

Bio-Based and Biodegradable Polymeric Materials for a Circular Economy

Nowadays, plastic contamination worldwide is a concerning reality that can be addressed with appropriate society education as well as looking for innovative polymeric alternatives based on the reuse of waste and recycling with a circular economy point of view, thus taking into consideration that a future world without plastic is quite impossible to conceive. In this regard, in this review, we focus on sustainable polymeric materials, biodegradable and bio-based polymers, additives, and micro/nanoparticles to be used to obtain new environmentally friendly polymeric-based materials. Although biodegradable polymers possess poorer overall properties than traditional ones, they have gained a huge interest in many industrial sectors due to their inherent biodegradability in natural environments. Therefore, several strategies have been proposed to improve their properties and extend their industrial applications. Blending strategies, as well as the development of composites and nanocomposites, have shown promising perspectives for improving their performances, emphasizing biopolymeric blend formulations and bio-based micro and nanoparticles to produce fully sustainable polymeric-based materials. The Review also summarizes recent developments in polymeric blends, composites, and nanocomposite plasticization, with a particular focus on naturally derived plasticizers and their chemical modifications to increase their compatibility with the polymeric matrices. The current state of the art of the most important bio-based and biodegradable polymers is also reviewed, mainly focusing on their synthesis and processing methods scalable to the industrial sector, such as melt and solution blending approaches like melt-extrusion, injection molding, film forming as well as solution electrospinning, among others, without neglecting their degradation processes.

A Review of Polyhydroxyalkanoates: Characterization, Production, and Application from Waste

The search for alternatives to petrochemical plastics has intensified, with increasing attention being directed toward bio-based polymers (bioplastics), which are considered healthier and more environmentally friendly options. In this review, a comprehensive overview of polyhydroxyalkanoates (PHAs) is provided, including their characterization, applications, and the mechanisms underlying their biosynthesis. PHAs are natural polyesters produced by a wide range of prokaryotic and some eukaryotic organisms, positioning them as a significant and widely studied type of bioplastic. Various strategies for the production of PHAs from agroindustrial waste, such as cacao shells, cheese whey, wine, wood, and beet molasses, are reviewed, emphasizing their potential as sustainable feedstocks. Industrial production processes for PHAs, including the complexities associated with extraction and purification, are also examined. Although the use of waste materials offers promise in reducing costs and environmental impact, challenges remain in optimizing these processes to enhance efficiency and cost-effectiveness. The need for continued research and development to improve the sustainability and economic viability of PHA production is emphasized, positioning PHAs as a viable and eco-friendly alternative to conventional petroleum-based plastics.

Innovative biomaterials for food packaging: Unlocking the potential of polyhydroxyalkanoate (PHA) biopolymers

Polyhydroxyalkanoate (PHA) biopolyesters show a good balance between sustainability and performance, making them a competitive alternative to conventional plastics for ecofriendly food packaging. With an emphasis on developments over the last decade (2014-2024), this review examines the revolutionary potential of PHAs as a sustainable food packaging material option. It also delves into the current state of commercial development, competitiveness, and the carbon footprint associated with PHA-based products. First, a critical examination of the challenges experienced by PHAs in terms of food packaging requirements is undertaken, followed by an assessment of contemporary strategies addressing permeability, mechanical properties, and processing considerations. The various PHA packaging end-of-life options, including a comprehensive overview of the environmental impact and potential solutions will also be discussed. Finally, conclusions and future perspectives are elucidated with a view of prospecting PHAs as future green materials, with a blend of performance and sustainability of food packaging solutions.

Cloning, Overexpression and Application of Lipase from Thermotolerant Bacillus subtilis TTP-06 in the Degradation of Polyhydroxyalkanoate

Polyhydroxyalkanoates (PHAs) constitute a principal group of bio-degradable polymers that are produced by certain microbes under limited supply of nutrients. PHA is a linear polyester that comprises of 3-hydroxy fatty acid monomers. Triacylglycerol acylhydrolases are known to catalyze the hydrolysis of ester linkages and in turn they are beneficial in the degradation of PHA. In present study, lipase-catalyzed degradation of PHA synthesized by Priestia megatarium POD1 was monitored. A gene from thermotolerant Bacillus subtilis TTP-06 that was capable of expressing lipase enzyme was amplified by PCR, cloned into a pTZ57R/T-vector, transferred to an expression vector pET-23a (+) and expressed in Escherichia coli BL21 (DE3) cells. The recombinant enzyme purified to 19.37-fold had a molecular weight of 30 kDa (SDS-PAGE analysis). Scanning Electron Microscopy (SEM) revealed changes in the surface morphology of native and treated PHA films. Further, changes in molecular vibrations were confirmed by Fourier Transform Infrared Spectroscopy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-024-01329-z.

Bio-based modification of polyhydroxyalkanoates (PHA) towards increased antimicrobial activities and reduced cytotoxicity

With the increased occurrence of bacteria resistance to conventional antibiotics, the development of novel antimicrobials is urgently needed. Traditional biomaterials used for delivering these agents often struggle to achieve sustained release while maintaining non-cytotoxic properties. In this study, we present an innovative approach using bacterial polyhydroxyalkanoates (PHA) as a carrier for antimicrobial delivery, specifically designed for wound healing applications. Octenidine dihydrochloride (OCT), a widely used antimicrobial agent, served as our model drug. To achieve the desired balance of OCT release and low cytotoxicity, we introduced a novel bio-derived additive, 3-hydroxy-pentadecanoic acid (3OHC15), extracted from bacteria. This additive significantly improved the hydrophilicity of PHA films, resulting in enhanced and sustained release of OCT. Importantly, the additive did not adversely affect the material's tensile strength or thermal properties. The increased OCT release led to improved antibacterial activity against both Gram-negative and -positive strains. Most notably, the incorporation of 3OHC15 in PHA mitigated the cytotoxic effects of the released drug on human fibroblasts, ensuring biocompatibility. This work represents a novel strategy in the design of biomaterials for the delivery of bioactive compounds, achieving a critical balance between efficacy and cytocompatibility, and marks a significant advancement in the field of antimicrobial delivery systems.

Potential for curdlan recovery from aerobic granular sludge wastewater treatment systems - A review

The aerobic granular sludge (AGS) biotechnology has been explored for wastewater treatment for over two decades. AGS is gaining increased interest due to its enhanced treatment performance ability and the potential for resource recovery from AGS-based wastewater treatment systems. Resource recovery from AGS is a promising approach to sustainable wastewater treatment and attaining a circular economy in the wastewater management industry. Currently, research is at an advanced stage on recovering value-added resources such as phosphorus, polyhydroxyalkanoates, alginate-like exopolysaccharides, and tryptophan from waste aerobic granules. Recently, other value-added resources, including curdlan, have been identified in the aerobic granule matrix, and this may increase the sustainability of biotechnology in the wastewater industry. This paper provides an overview of AGS resource recovery potential. In particular, the potential for enhanced curdlan biosynthesis in the granule matrix and its recovery from AGS wastewater treatment systems is outlined.

Exploring polyhydroxyalkanoates biosynthesis using hydrocarbons as carbon source: a comprehensive review

Environmental pollution caused by petrochemical hydrocarbons (HC) and plastic waste is a pressing global challenge. However, there is a promising solution in the form of bacteria that possess the ability to degrade HC, making them valuable tools for remediating contaminated environments and effluents. Moreover, some of these bacteria offer far-reaching potential beyond bioremediation, as they can also be utilized to produce polyhydroxyalkanoates (PHAs), a common type of bioplastics. The accumulation of PHAs in bacterial cells is facilitated in environments with high C/N or C/P ratio, which are often found in HC-contaminated environments and effluents. Consequently, some HC-degrading bacteria can be employed to simultaneously produce PHAs and conduct biodegradation processes. Although bacterial bioplastic production has been thoroughly studied, production costs are still too high compared to petroleum-derived plastics. This article aims to provide a comprehensive review of recent scientific advancements concerning the capacity of HC-degrading bacteria to produce PHAs. It will delve into the microbial strains involved and the types of bioplastics generated, as well as the primary pathways for HC biodegradation and PHAs production. In essence, we propose the potential utilization of HC-degrading bacteria as a versatile tool to tackle two major environmental challenges: HC pollution and the accumulation of plastic waste. Through a comprehensive analysis of strengths and weaknesses in this aspect, this review aims to pave the way for future research in this area, with the goal of facilitating and promoting investigation in a field where obtaining PHAs from HC remains a costly and challenging process.

Investigating chemical pre-treatment methods: Valorization of wheat straw to enhance polyhydroxyalkanoate (PHA) production with novel isolate Bacillus paranthracis RSKS-3

Wheat is a crucial food crop worldwide, generating straw upon post-harvest. The straw is often burned to enhance soil fertility, leading to massive air pollution. In this study, wheat straw was investigated for the production of Polyhydroxyalkanoate (PHA) using the novel isolate Bacillus paranthracis RSKS-3. The wheat straw was pulverized and valorized with different acids (2 % and 4 % H2SO4, acetic acid, and hydrochloric acid) and alkalis (2 % and 4 % NaOH, calcium carbonate, and potassium hydroxide). The validation of carbohydrates was done using the Molisch test by analyzing purple-ring production and the DNS test which concluded 4 % H2SO4 as an effective treatment with a maximal sugar yield of 5.04 mg/mL at P < 0.05. The bioconversion efficiency of the extract to PHA resulted in 0.87 g/L by Bacillus paranthracis RSKS-3, later characterized by Ultraviolet (UV)-spectroscopy and FT-IR assessment. The findings of the research offer a potential strategy to mitigate airborne pollutants that result from smouldering wheat straw, thereby contributing significant improvements to sustainable development.

Development of PBS/Nano Composite PHB-Based Multilayer Blown Films with Enhanced Properties for Food Packaging Applications

Biobased and biodegradable plastics have emerged as promising alternatives to conventional plastics offering the potential to reduce environmental impacts while promoting sustainability. This study focuses on the production of multilayer blown films with enhanced functional properties suitable for food packaging applications. Films were developed through co-extrusion in a three-layer film configuration, with Polybutylene Succinate (PBS) and Polybutylene Succinate Adipate (PBSA) as the external and internal layers, respectively. The functional layer consisted of Polyhydroxybutyrate (PHB) enhanced with nanoclays Cloisite® 30B at varying weight ratios. Films were also processed by manipulating the extruder screw speed of the functional layer to investigate its impact on the functional properties. Rheology, mechanical strength, and barrier performance were characterised to establish correlations between processing conditions and functional layer blends (Cloisite® 30B/PHB) on the properties of the resultant films. Rheological test results indicated that the system with 5% Cloisite® had the best polymer/nanofiller matrix dispersion. Mechanical and permeability tests showed that by varying the process conditions (the alteration of the thickness of the functionalized layer) resulted in an improvement in mechanical and barrier properties. Furthermore, the addition of the nanofiller resulted in a stiffening of the film with a subsequent decrease in permeability to oxygen and water vapour.

Topography hierarchy of biocompatible polyhydroxyalkanoate film

Polyhydroxyalkanoates (PHAs) are used for various biomedical applications due to their biocompatibility. Surface properties, such as surface roughness, are crucial for PHAs performance. Traditional parameters used for the characterization of surface roughness, such as R a, are often insufficient to capture the complex and hierarchical (multiscale) topography of PHA films. We measure the topography and surface roughness of thin PHA films with atomic force microscopy and analyze the topography data using several relatively novel data processing methods, including the calculation of autocorrelation functions, topological data analysis, and the distribution of minimum and maximum values of pixels over the topography data. The results provide details of multiscale and anisotropic surface properties that are crucial to PHAs biocompatibility but often overlooked by traditional topography analysis methods.

Algal-based bioplastics: global trends in applied research, technologies, and commercialization

The excessive global demand for plastic materials has resulted in severe plastic waste pollution. Conventional plastics derived from non-renewable fossil fuels are non-biodegradable, leading to significant environmental problems. Algal-based bioplastics represent a more viable, renewable, and sustainable alternative to conventional plastics. They have identical properties and characteristics as conventional plastics while being naturally biodegradable. The potential of the algal biomass value chain has already been well-established by researchers. Here, we review the novel insights on research, technology, and commercialization trends of algal-based bioplastics, encompassing macroalgae and green microalgae/cyanobacteria. Data showed that within the last decade, there has been substantial interest in utilizing microalgae for biopolymer production, with more focus on using cyanobacterial species compared to green algae. Moreover, most of the research conducted has largely focused on the production of PHA or its co-polymers. Since 2011, there have been a total of 55 patents published related to algal-based bioplastics production. To date, ~ 81 entities worldwide (commercial and private businesses) produce bioplastics from algae. Overall results of this study emphasized that even with the economic and social challenges, algae possess a substantial potential for the sustainable development of bioplastics while also addressing the UN's SDGs.

Benchmarking Unsupervised Clustering Algorithms for Atomic Force Microscopy Data on Polyhydroxyalkanoate Films

Surface of polyhydroxyalkanoate (PHA) films of varying monomer compositions are analyzed using atomic force microscopy (AFM) and unsupervised machine learning (ML) algorithms to investigate and classify films based on global attributes such as the scan size, film thickness, and monomer type. The experiment provides benchmarked results for 12 of the most widely used clustering algorithms via a hybrid investigation approach while highlighting the impact of using the Fourier transform (FT) on high-dimensional vectorized data for classification on various pools of data. Our findings indicate that the use of a one-dimensional (1D) FT of vectorized data produces the most accurate outcome. The experiment also provides insights into case-by-case investigations of algorithm performances and the impact of various data pools. Lastly, we show an early version of our tool aimed at investigating surfaces using ML approaches and discuss the results of our current experiment to configure future improvements.

Embracing Sustainability: The World of Bio-Based Polymers in a Mini Review

The proliferation of polymer science and technology in recent decades has been remarkable, with synthetic polymers derived predominantly from petroleum-based sources dominating the market. However, concerns about their environmental impacts and the finite nature of fossil resources have sparked interest in sustainable alternatives. Bio-based polymers, derived from renewable sources such as plants and microbes, offer promise in addressing these challenges. This review provides an overview of bio-based polymers, discussing their production methods, properties, and potential applications. Specifically, it explores prominent examples including polylactic acid (PLA), polyhydroxyalkanoates (PHAs), and polyhydroxy polyamides (PHPAs). Despite their current limited market share, the growing awareness of environmental issues and advancements in technology are driving increased demand for bio-based polymers, positioning them as essential components in the transition towards a more sustainable future.

Production of poly-3-hydroxybutyrate (PHB) nanoparticles using grape residues as the sole carbon source

The production of poly-3-hydroxybutyrate (PHB) on an industrial scale remains a major challenge due to its higher production cost compared to petroleum-based plastics. As a result, it is necessary to develop efficient fermentative processes using low-cost substrates and identify high-value-added applications where biodegradability and biocompatibility properties are of fundamental importance. In this study, grape residues, mainly grape skins, were used as the sole carbon source in Azotobacter vinelandii OP cultures for PHB production and subsequent nanoparticle synthesis based on the extracted polymer. The grape residue pretreatment showed a high rate of conversion into reducing sugars (fructose and glucose), achieving up to 43.3 % w w-1 without the use of acid or external heat. The cultures were grown in shake flasks, obtaining a biomass concentration of 2.9 g L-1 and a PHB accumulation of up to 37.7 % w w-1. PHB was characterized using techniques such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The formation of emulsified PHB nanoparticles showed high stability, with a particle size between 210 and 240 nm and a zeta potential between -12 and - 15 mV over 72 h. Owing to these properties, the produced PHB nanoparticles hold significant potential for applications in drug delivery.

Production and characterization of polyhydroxybutyrate bioplastic precursor from Parageobacillus toebii using low-cost substrates and its potential antiviral activity

There is an increasing desire for bioplastics produced from renewable resources as an alternative to their petrochemical counterparts. These biopolymers have long-unnoticed antiviral properties. This study aimed to produce and characterize bioplastics by Parageobacillus toebii using low-cost substrates and determine their antiviral activity against coxsackievirus B4. Seven low-cost substrates (bagasse, water hyacinth, rice straw, rice water, sesame husks, molasses, and corn syrup) were compared with glucose for bioplastic precursor production. The highest bioplastic produced was from water hyacinth and glucose, followed by molasses, rice straw, rice water, sesame husks, and bagasse. Water hyacinth and glucose media were further optimized to increase the bioplastic precursor yield. The optimization of the media leads to increases in bioplastic precursor yields of 1.8-fold (3.456 g/L) and 1.496-fold (2.768 g/L), respectively. These bioplastics were further characterized by thermogravimetric analysis (TGA), Fourier-transformed infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR), and gas chromatography-mass spectrometry (GC-MS). They are thermostable, and their characterizations confirm the presence of polyhydroxybutyrate. The antiviral assay showed reasonable antiviral effects for bioplastics from water hyacinth (80.33 %) and glucose (55.47 %) media at 250 μg/mL maximum non-toxic concentrations (MNTC). The present investigation demonstrates a low-cost model for producing polyhydroxybutyrate bioplastic precursor for antiviral applications.

Accelerated Weathering Testing (AWT) and Bacterial Biodegradation Effects on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/Rapeseed Microfiber Biocomposites Properties

In the context of sustainable materials, this study explores the effects of accelerated weathering testing and bacterial biodegradation on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/rapeseed microfiber biocomposites. Accelerated weathering, simulating outdoor environmental conditions, and bacterial biodegradation, representing natural degradation processes in soil, were employed to investigate the changes in the mechanical, thermal and morphological properties of these materials during its post-production life cycle. Attention was paid to the assessment of the change of structural, mechanical and calorimetric properties of alkali and N-methylmorpholine N-oxide (NMMO)-treated rapeseed microfiber (RS)-reinforced plasticized PHBV composites before and after accelerated weathering. Results revealed that accelerated weathering led to an increase in stiffness, but a reduction in tensile strength and elongation at break, of the investigated PHBV biocomposites. Additionally, during accelerated weathering, the crystallinity of PHBV biocomposites increased, especially in the presence of RS, due to both the hydrolytic degradation of the polymer matrix and the nucleating effect of the filler. It has been observed that an increase in PHBV crystallinity, determined by DSC measurements, correlates with the intensity ratio I1225/1180 obtained from FTIR-ATR data. The treatment of RS microfibers increased the biodegradation capability of the developed PHBV composites, especially in the case of chemically untreated RS. All the developed PHBV composites demonstrated faster biodegradation in comparison to neat PHBV matrix.

Physicochemical cell disruption of Bacillus sp. for recovery of polyhydroxyalkanoates: future bioplastic for sustainability

Polyhydroxybutyrate (PHB) is known for wide applications, biocompatibility, and degradability; however, it cannot be commercialized due to conventional recovery using solvents. The present study employed mechanical cell-disruption methods, such as Pestle and mortar, sonication, and glass bead vortexing, for solvent-free extraction of PHA from Bacillus sp. Different time intervals were set for grinding (5, 10, 15 min), sonicating (1, 3 and 5 min), and vortexing (2, 5 and 8 g glass beads with 5, 10 and 15 min each) hence studying their effect on cell lysis to release PHA. Tris buffer containing phenylmethyl sulfonyl fluoride (PMSF) (20 mM Tris-HCl, pH 8.0, 1 mM PMSF) was employed as a lysis buffer to study its action over Bacillus cells. Its presence was checked with the above methods in cell lysis. Sonicating cells for 5 min in the presence of lysis buffer achieved a maximum PHA yield of 45%. Cell lysis using lysis buffer yielded 35% PHA when vortexing with 5 g glass beads for 15 min. Grinding cells for 15 min showed a maximum yield of 34% but lacked a lysis buffer. The overall results indicated that the action of lysis buffer and physical extraction methods improved PHA yield by %. Therefore, the study sought to evaluate the feasibility of applying laboratory methods for cell disruption. These methods can showcase possible opportunities in large-scale applications. The polymer yield results were compared with standard sodium hypochlorite extraction. Confirmation of obtained polymers as polyhydroxy butyrate (PHB) was made through FTIR and 1HNMR characterization.

Polyhydroxyalkanoates production in biorefineries: A review on current status, challenges and opportunities

The need for a sustainable and circular bioeconomy model is imperative due to petroleum non-renewability, scarcity and environmental impacts. Biorefineries systems explore biomass to its maximum, being an important pillar for the development of circular bioeconomy. Polyhydroxyalkanoates (PHAs) can take advantage of biorefineries, as they can be produced using renewable feedstocks, and are potential substitutes for petrochemical plastics. The present work aims to evaluate the current status of the industrial development of PHAs production in biorefineries and PHAs contributions to the bioeconomy, along with future development points. Advancements are noticed when PHA production is coupled in wastewater treatment systems, when residues are used as substrate, and also when analytical methodologies are applied to evaluate the production process, such as the Life Cycle and Techno-Economic Analysis. For the commercial success of PHAs, it is established the need for dedicated investment and policies, in addition to proper collaboration of different society actors.

Unlocking growth potential in Halomonas bluephagenesis for enhanced PHA production with sulfate ions

The mutant strain Halomonas bluephagenesis (TDH4A1B5P) was found to produce PHA under low-salt, non-sterile conditions, but the yield was low. To improve the yield, different nitrogen sources were tested. It was discovered that urea was the most effective nitrogen source for promoting growth during the stable stage, while ammonium sulfate was used during the logarithmic stage. The growth time of H. bluephagenesis (TDH4A1B5P) and its PHA content were significantly prolonged by the presence of sulfate ions. After 64 hr in a 5-L bioreactor supplemented with sulfate ions, the dry cell weight (DCW) of H. bluephagenesis weighed 132 g/L and had a PHA content of 82%. To promote the growth and PHA accumulation of H. bluephagenesis (TDH4A1B5P), a feeding regimen supplemented with nitrogen sources and sulfate ions with ammonium sodium sulfate was established in this study. The DCW was 124 g/L, and the PHA content accounted for 82.3% (w/w) of the DCW, resulting in a PHA yield of 101 g/L in a 30-L bioreactor using the optimized culture strategy. In conclusion, stimulating H. bluephagenesis (TDH4A1B5P) to produce PHA is a feasible and suitable strategy for all H. bluephagenesis.

Polyhydroxyalkanoates and exopolysaccharides: An alternative for valuation of the co-production of microbial biopolymers

Polyhydroxyalkanoates (PHAs) and exopolysaccharides (EPSs) belong to a class of abundant biopolymers produced by various fermenting microorganisms. These biocompounds have high value-added potential and can be produced concurrently. Co-production of PHAs and EPSs is a strategy employed by researchers to reduce costs associated with large-scale production. EPSs and PHAs are non-toxic, biocompatible, and biodegradable, making them suitable for various industrial sectors, including packaging and the medical and pharmaceutical industries. These biopolymers can be derived from agro-industrial residues, thus contributing to the bioeconomy by producing high-value-added products. This review investigates approaches for simultaneously synthesizing PHAs and EPSs using different carbon sources and microorganisms.

Current advances and emerging trends in sustainable polyhydroxyalkanoate modification from organic waste streams for material applications

The current processes for producing polyhydroxyalkanoates (PHAs) are costly, owing to the high cost of cultivation feedstocks, and the need to sterilise the growth medium, which is energy-intensive. PHA has been identified as a promising biomaterial with a wide range of potential applications and its functionalization from waste streams has made significant advances recently, which can help foster the growth of a circular economy and waste reduction. Recent developments and novel approaches in the functionalization of PHAs derived from various waste streams offer opportunities for addressing these issues. This study focuses on the development of sustainable, efficient, and cutting-edge methods, such as advanced bioprocess engineering, novel catalysts, and advances in materials science. Chemical techniques, such as epoxidation, oxidation, and esterification, have been employed for PHA functionalization, while enzymatic and microbial methods have indicated promise. PHB/polylactic acid blends with cellulose fibers showed improved tensile strength by 24.45-32.08 % and decreased water vapor and oxygen transmission rates while PHB/Polycaprolactone blends with a 1:1 ratio demonstrated an elongation at break four to six times higher than pure PHB, without altering tensile strength or elastic modulus. Moreover, PHB films blended with both polyethylene glycol and esterified sodium alginate showed improvements in crystallinity and decreased hydrophobicity.

Fabrication and biological properties of artificial tendon composite from medium chain length polyhydroxyalkanoate

Medium chain length polyhydroxyalkanoate (MCL-PHA), a biodegradable and biocompatible material, has a mechanical characteristic of hyper-elasticity, comparable to elastomeric material with similar properties to human tendon flexibility. These MCL-PHA properties gave rise to applying this material as an artificial tendon or ligament implant. In this study, the material was solution-casted in cylinder and rectangular shapes in the molds with the designated small holes. A portion of the torn human tendon was threaded into the holes as a suture to generate a composite tendon graft. The tensile testing of the three types of MCL-PHA/tendon composite shows that the cylinder material shape with the zigzag threaded three holes has the highest value of maximum tensile strength at 56 MPa, closing to the ultimate tendon tensile stress (50-100 MPa). Fibroblast cells collected from patients were employed as primary tendon cells for growing to attach to the surface of the MCL-PHA material to prove the concept of the composite tendon graft. The cells could attach and proliferate with substantial viability and generate collagen, leading to chondrogenic induction of tendon cells. An in vivo biocompatibility was also conducted in a rat subcutaneous model in comparison with medical-grade silicone. The MCL-PHA material was found to be biocompatible with the surrounding tissues. For surgical application, after the MCL-PHA material is decomposed, tendon cells should develop into an attached tendon and co-generated as a tendon graft.

Biosynthesis and properties of polyhydroxyalkanoates synthesized from mixed C5 and C6 sugars obtained from hardwood hydrolysis

Glucose and xylose are fermentable sugars readily available from lignocellulosic biomass, and are a sustainable carbon substrate supporting industrial biotechnology. Three strains were assessed in this work - Paraburkholderia sacchari, Hydrogenophaga pseudoflava, and Bacillus megaterium - for their ability to uptake both C5 and C6 sugars contained in a hardwood hydrolysate produced via a thermomechanical pulping-based process with concomitant production of poly(3-hydroxyalkanoate) (PHA) biopolymers. In batch conditions, B. megaterium showed poor growth after 12 h, minimal uptake of xylose throughout the cultivation, and accumulated a maximum of only 25 % of the dry biomass as PHA. The other strains simultaneously utilized both sugars, although glucose uptake was faster than xylose. From hardwood hydrolysate, P. sacchari accumulated 57 % of its biomass as PHA within 24 h, whereas H. pseudoflava achieved an intracellular PHA content of 84 % by 72 h. The molecular weight of the PHA synthesized by H. pseudoflava (520.2 kDa) was higher than that of P. sacchari (265.5 kDa). When the medium was supplemented with propionic acid, the latter was rapidly consumed by both strains and incorporated as 3-hydroxyvalerate subunits into the polymer, demonstrating the potential for production of polymers with improved properties and value. H. pseudoflava incorporated 3-hydroxyvalerate subunits with at least a 3-fold higher yield, and produced polymers with higher 3-hydroxyvalerate content than P. sacchari. Overall, this work has shown that H. pseudoflava can be an excellent candidate for bioconversion of lignocellulosic sugars to PHA polymers or copolymers as part of an integrated biorefinery.

Valorization of Agricultural Waste Lignocellulosic Fibers for Poly(3-Hydroxybutyrate-Co-Valerate)-Based Composites in Short Shelf-Life Applications

Biocircularity could play a key role in the circular economy, particularly in applications where organic recycling (composting) has the potential to become a preferred waste management option, such as food packaging. The development of fully biobased and biodegradable composites could help reduce plastic waste and valorize agro-based residues. In this study, extruded films made of composites of polyhydroxybutyrate-co-valerate (PHBV) and lignocellulosic fibers, namely almond shell (AS) and Oryzite® (OR), a polymer hybrid composite precursor, have been investigated. Scanning electron microscopy (SEM) analysis revealed a weak fiber-matrix interfacial interaction, although OR composites present a better distribution of the fiber and a virtually lower presence of "pull-out". Thermogravimetric analysis showed that the presence of fibers reduced the onset and maximum degradation temperatures of PHBV, with a greater reduction observed with higher fiber content. The addition of fibers also affected the melting behavior and crystallinity of PHBV, particularly with OR addition, showing a decrease in crystallinity, melting, and crystallization temperatures as fiber content increased. The mechanical behavior of composites varied with fiber type and concentration. While the incorporation of AS results in a reduction in all mechanical parameters, the addition of OR leads to a slight improvement in elongation at break. The addition of fibers improved the thermoformability of PHBV. In the case of AS, the improvement in the processing window was achieved at lower fiber contents, while in the case of OR, the improvement was observed at a fiber content of 20%. Biodisintegration tests showed that the presence of fibers promoted the degradation of the composites, with higher fiber concentrations leading to faster degradation. Indeed, the time of complete biodisintegration was reduced by approximately 30% in the composites with 20% and 30% AS.

Recent Biotechnological Applications of Polyhydroxyalkanoates (PHA) in the Biomedical Sector-A Review

Petroleum-derived plastics are materials of great importance for the contemporary lifestyle, and are widely used commercially because they are low cost, resistant, malleable, and weightless, in addition to their hydrophobic character. However, some factors that confer the qualities of these materials also cause problems, mainly environmental, associated with their use. The COVID-19 pandemic aggravated these impacts due to the high demand for personal protective equipment and the packaging sector. In this scenario, bioplastics are environmentally positive alternatives to these plastics due to their applicability in several areas ranging from packaging, to biomedicine, to agriculture. Polyhydroxyalkanoates (PHAs) are biodegradable biopolymers usually produced by microorganisms as an energy reserve. Their structural variability provides a wide range of applications, making them a viable option to replace polluting materials. PHAs can be applied in various biotechnology sectors, such as producing drug carriers and scaffolds for tissue engineering. This review aimed to survey works published in the last five years on the study and biotechnological application of PHAs in the biomedical sector, exploring the versatility and advantages of their use and helping to understand how to enhance their application.

Tailoring the Nucleation and Crystallization Rate of Polyhydroxybutyrate by Copolymerization

In the polyester family, the biopolymer with the greatest industrial potential could be poly(3-hydroxybutyrate) (PHB), which can be produced nowadays biologically or chemically. The scarce commercial use of PHB derives from its poor mechanical properties, which can be improved by incorporating a flexible aliphatic polyester with good mechanical performance, such as poly(ε-caprolactone) (PCL), while retaining its biodegradability. This work studies the structural, thermal, and morphological properties of block and random copolymers of PHB and PCL. The presence of a comonomer influences the thermal parameters following nonisothermal crystallization and the kinetics of isothermal crystallization. Specifically, the copolymers exhibit lower melting and crystallization temperatures and present lower overall crystallization kinetics than neat homopolymers. The nucleation rates of the PHB components are greatly enhanced in the copolymers, reducing spherulitic sizes and promoting transparency with respect to neat PHB. However, their spherulitic growth rates are depressed so much that superstructural growth becomes the dominating factor that reduces the overall crystallization kinetics of the PHB component in the copolymers. The block and random copolymers analyzed here also display important differences in the structure, morphology, and crystallization that were examined in detail. Our results show that copolymerization can tailor the thermal properties, morphology (spherulitic size), and crystallization kinetics of PHB, potentially improving the processing, optical, and mechanical properties of PHB.

Effect of Monomers of 3-Hydroxyhexanoate on Properties of Copolymers Poly(3-Hydroxybutyrate-co 3-Hydroxyhexanoate)

The properties of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) P(3HB-co-3HHx) copolymers with different ratios of monomers synthesized by the wild-type strain Cupriavidus necator B-10646 on sugars, and an industrial sample from Kaneka synthesized by the recombinant strain C. necator NSDG-ΔfadB1 on soybean oil, were studied in a comparative aspect and in relation to poly(3-hydroxybutyrate) P(3HB). The copolymer samples, regardless of the synthesis conditions or the ratio of monomers, had reduced values of crystallinity degree (50-60%) and weight average molecular weight (415-520 kDa), and increased values of polydispersity (2.8-4.3) compared to P(3HB) (70-76%, 720 kDa, and 2.2). The industrial sample had differences in its thermal behavior, including a lower glass transition temperature (-2.4 °C), two peaks in its crystallization and melting regions, a lower melting point (T_melt) (112/141 °C), and a more pronounced gap between T_melt and the temperature of thermal degradation (T_degr). The process, shape, and size of the spherulites formed during the isothermal crystallization of P(3HB) and P(3HB-co-3HHx) were generally similar, but differed in the maximum growth rate of the spherulites during exothermic crystallization, which was 3.5-3.7 μm/min for P(3HB), and 0.06-1.25 for the P(3HB-co-3HHx) samples. The results from studying the thermal properties and the crystallization mechanism of P(3HB-co-3HHx) copolymers are important for improving the technologies for processing polymer products from melts.

Exploring the Feasibility of Cell-Free Synthesis as a Platform for Polyhydroxyalkanoate (PHA) Production: Opportunities and Challenges

The extensive utilization of traditional petroleum-based plastics has resulted in significant damage to the natural environment and ecological systems, highlighting the urgent need for sustainable alternatives. Polyhydroxyalkanoates (PHAs) have emerged as promising bioplastics that can compete with petroleum-based plastics. However, their production technology currently faces several challenges, primarily focused on high costs. Cell-free biotechnologies have shown significant potential for PHA production; however, despite recent progress, several challenges still need to be overcome. In this review, we focus on the status of cell-free PHA synthesis and compare it with microbial cell-based PHA synthesis in terms of advantages and drawbacks. Finally, we present prospects for the development of cell-free PHA synthesis.

Sustainable Valorization of Bioplastic Waste: A Review on Effective Recycling Routes for the Most Widely Used Biopolymers

Plastics-based materials have a high carbon footprint, and their disposal is a considerable problem for the environment. Biodegradable bioplastics represent an alternative on which most countries have focused their attention to replace of conventional plastics in various sectors, among which food packaging is the most significant one. The evaluation of the optimal end-of-life process for bioplastic waste is of great importance for their sustainable use. In this review, the advantages and limits of different waste management routes-biodegradation, mechanical recycling and thermal degradation processes-are presented for the most common categories of biopolymers on the market, including starch-based bioplastics, PLA and PBAT. The analysis outlines that starch-based bioplastics, unless blended with other biopolymers, exhibit good biodegradation rates and are suitable for disposal by composting, while PLA and PBAT are incompatible with this process and require alternative strategies. The thermal degradation process is very promising for chemical recycling, enabling building blocks and the recovery of valuable chemicals from bioplastic waste, according to the principles of a sustainable and circular economy. Nevertheless, only a few articles have focused on this recycling process, highlighting the need for research to fully exploit the potentiality of this waste management route.

Climate and biodiversity impacts of low-density polyethylene production from CO2 and electricity in comparison to bio-based polyethylene

Plastics are essential materials for modern societies, but their production contributes to significant environmental issues. Power-to-X processes could produce plastics from captured CO₂ and hydrogen with renewable electricity, but these technologies may also face challenges from environmental perspective. This paper focuses on environmental sustainability assessment of CO₂-based low-density polyethylene (LDPE) compared to bio-based LDPE. Life cycle assessment has been applied to study climate impacts and land use related biodiversity impacts of different plastic production scenarios. According to the climate impact results, the carbon footprint of the produced plastic can be negative if the energy used is from wind, solar, or bioenergy and the carbon captured within the plastic is considered. In terms of biodiversity, land-use related biodiversity impacts seem to be lower from CO₂-based polyethylene compared to sugarcane-based polyethylene. Forest biomass use for heat production in CO₂-based polyethylene poses a risk to significantly increase biodiversity impacts. Taken together, these results suggest that CO₂-based LDPE produced with renewable electricity could reduce biodiversity impacts over 96 % while carbon footprint seems to be 6.5 % higher when compared to sugarcane-based polyethylene.

Exploiting Polyhydroxyalkanoates for Biomedical Applications

Polyhydroxyalkanoates (PHA) are biodegradable plastic. Numerous bacteria produce PHAs under environmental stress conditions, such as excess carbon-rich organic matter and limitations of other nutritional elements such as potassium, magnesium, oxygen, phosphorus, and nitrogen. In addition to having physicochemical properties similar to fossil-fuel-based plastics, PHAs have unique features that make them ideal for medical devices, such as easy sterilization without damaging the material itself and easy dissolution following use. PHAs can replace traditional plastic materials used in the biomedical sector. PHAs can be used in a variety of biomedical applications, including medical devices, implants, drug delivery devices, wound dressings, artificial ligaments and tendons, and bone grafts. Unlike plastics, PHAs are not manufactured from petroleum products or fossil fuels and are, therefore, environment-friendly. In this review, a recent overview of applications of PHAs with special emphasis on biomedical sectors, including drug delivery, wound healing, tissue engineering, and biocontrols, are discussed.

Commercialization potential of agro-based polyhydroxyalkanoates biorefinery: A technical perspective on advances and critical barriers

The exponential increase in the use and careless discard of synthetic plastics has created an alarming concern over the environmental health due to the detrimental effects of petroleum based synthetic polymeric compounds. Piling up of these plastic commodities on various ecological niches and entry of their fragmented parts into soil and water has clearly affected the quality of these ecosystems in the past few decades. Among the many constructive strategies developed to tackle this global issue, use of biopolymers like polyhydroxyalkanoates as sustainable alternatives for synthetic plastics has gained momentum. Despite their excellent material properties and significant biodegradability, polyhydroxyalkanoates still fails to compete with their synthetic counterparts majorly due to the high cost associated with their production and purification thereby limiting their commercialization. Usage of renewable feedstocks as substrates for polyhydroxyalkanoates production has been the thrust area of research to attain the sustainability tag. This review work attempts to provide insights about the recent developments in the production of polyhydroxyalkanoates using renewable feedstock along with various pretreatment methods used for substrate preparation for polyhydroxyalkanoates production. Further, the application of blends based on polyhydroxyalkanoates, and the challenges associated with the waste valorization based polyhydroxyalkanoates production strategy is elaborated in this review work.

Influence of FFF Process Conditions on the Thermal, Mechanical, and Rheological Properties of Poly(hydroxybutyrate-co-hydroxy Hexanoate)

Polyhydroxyalkanoates are natural polyesters synthesized by microorganisms and bacteria. Due to their properties, they have been proposed as substitutes for petroleum derivatives. This work studies how the printing conditions employed in fuse filament fabrication (FFF) affect the properties of poly(hydroxybutyrate-co-hydroxy hexanoate) or PHBH. Firstly, rheological results predicted the printability of PHBH, which was successfully realized. Unlike what usually happens in FFF manufacturing or several semi-crystalline polymers, it was observed that the crystallization of PHBH occurs isothermally after deposition on the bed and not during the non-isothermal cooling stage, according to calorimetric measurements. A computational simulation of the temperature profile during the printing process was conducted to confirm this behavior, and the results support this hypothesis. Through the analysis of mechanical properties, it was shown that the nozzle and bed temperature increase improved the mechanical properties, reducing the void formation and improving interlayer adhesion, as shown by SEM. Intermediate printing velocities produced the best mechanical properties.

General overview of biopolymers: structure and properties

Biopolymers are synthesized from a biological origin under natural phenomenon especially during their growth cycle, in the form of polymeric substances that portrays excellent properties such as flexibility, tensile strength, steadiness, reusability, and so on. The amalgamated form of two or more biopolymers leads to the formation of “biocomposites” with novel applications. Several mechanisms were identified for the effective production of biopolymers from diverse life forms such as microbial origin plant and animal origin. Based on their origin, biopolymer differs in their structure and functions. Biopolymers are preferred over chemically synthesized polymers due to their biodegradability and their impact on the environment. Biopolymers play a pivotal role in pharmaceutical industries. The biopolymers could be employed for, the administration of medicine as well as regenerative medicine to reach minimal immunogenicity and maximum pharmacological expressivity in a treated individual. Based on their properties biopolymers were exclusively used in medical devices, cosmaceuticals, and confectionaries, it is also used as additives in food industries, bio-sensors, textile industries, and wastewater treatment plants. Ecological support is of utmost concern nowadays due to the ever-expanding ramification over the planet by usage of plastic as packaging material, turning up scientists and researchers to focus on biodegradable biopolymer utilization. The miscibility-structural-property relation between every biopolymer must be focused on to improve the better environment. Specific biopolymers are designed for the betterment of agrarian and commoners of society. Advanced structural modifications, properties of biopolymers, and applications of biopolymers to achieve a greener environment were discussed in this chapter.

Enhanced flame retardancy and toughness of eco-friendly polyhydroxyalkanoate/bentonite composites based on in situ intercalation of P-N-containing hyperbranched macromolecules

Polyhydroxyalkanoates (PHA) is a biodegradable polyester, and its application range is limited by the poor flame retardancy and low modulus. Bentonite (BNT) as a green inorganic filler can improve the modulus and flame retardancy of PHA to a certain extent. An in situ polymerization method was designed to intercalate P-N-containing hyperbranched macromolecules (HBM) among BNT layers (HBM-B) and to improve the flame retardancy while improving the dispersion of BNT in the PHA matrix. The layer spacing of BNT was increased from 1.2 nm to 4.5 nm. The effect law of the joint action of in situ intercalation of BNT and the HBM on flame retardancy and mechanical properties of PHA was systematically studied. The HBM-B showed stronger flame retardancy when the mass ratio of HBM to BNT was 75/25. The limiting oxygen index (LOI) of the PHA/HBM-B composite was increased to 27.6 % while maintaining good toughness. Compared to the physical blend of HBM and BNT (HBM/B), the elongation at break of PHA/HBM-B₂₅ composites can be increased by up to 10 times. When the content of HBM-B is up to 15 wt%, the LOI of PHA-Based composites can reach 29.6 % and the UL-94 rating reaches V-0, which meets the standard of flame-retardant material. Therefore, the present work is expected to expand the application of PHA-based composites in the field of flame retardancy.