Poly(hydroxy alkanoate)s in Medical Applications

A Review of Current Achievements and Recent Challenges in Bacterial Medium-Chain-Length Polyhydroxyalkanoates: Production and Potential Applications

Using petroleum-derived plastics has contributed significantly to environmental issues, such as greenhouse gas emissions and the accumulation of plastic waste in ecosystems. Researchers have focused on developing ecofriendly polymers as alternatives to traditional plastics to address these concerns. This review provides a comprehensive overview of medium-chain-length polyhydroxyalkanoates (mcl-PHAs), biodegradable biopolymers produced by microorganisms that show promise in replacing conventional plastics. The review discusses the classification, properties, and potential substrates of less studied mcl-PHAs, highlighting their greater ductility and flexibility compared to poly(3-hydroxybutyrate), a well-known but brittle PHA. The authors summarize existing research to emphasize the potential applications of mcl-PHAs in biomedicine, packaging, biocomposites, water treatment, and energy. Future research should focus on improving production techniques, ensuring economic viability, and addressing challenges associated with industrial implementation. Investigating the biodegradability, stability, mechanical properties, durability, and cost-effectiveness of mcl-PHA-based products compared to petroleum-based counterparts is crucial. The future of mcl-PHAs looks promising, with continued research expected to optimize production techniques, enhance material properties, and expand applications. Interdisciplinary collaborations among microbiologists, engineers, chemists, and materials scientists will drive progress in this field. In conclusion, this review serves as a valuable resource to understand mcl-PHAs as sustainable alternatives to conventional plastics. However, further research is needed to optimize production methods, evaluate long-term ecological impacts, and assess the feasibility and viability in various industries.

PHB production by Bacillus megaterium strain MNSH1-9K-1 using low-cost media

Plastics are widely used for diverse applications due to their versatility. However, their negative impact on ecosystems is undeniable due to their long-term degradation. Thus, there is a rising need for developing eco-friendlier alternatives to substitute fossil-based plastics, like biopolymers. PHA are synthesized intracellularly by microorganisms under stressful conditions of growth and have similar characteristics to conventional polymers, like their melting point, transition temperatures, crystallinity, and flexibility. Although it is feasible to use biopolymers for diverse industrial applications, their elevated production cost due to the supplies needed for microbiological procedures and the low productivity yields obtained have been the main limiting factors for their commercial success. The present study assessed the ability of Bacillus megaterium strain MNSH1-9K-1 to produce biopolymers using low-cost media from different kinds of fruit-peel residues. The results show that MNSH1-9K-1 can produce up to 58 g/L of PHB when grown in a medium prepared from orange-peel residues. The data obtained provide information to enhance the scalability of these kinds of biotechnological processes.

Production of poly (3-hydroxybutyrate) and extracellular polymeric substances from glycerol by the acidophile Acidiphilium cryptum

Acidiphilium cryptum is an acidophilic, heterotrophic, and metallotolerant bacteria able to use dissolved oxygen or Fe(III) as an electron sink. The ability of this extremophile to accumulate poly(3-hydroxybutyrate) (PHB) and secrete extracellular polymeric substances (EPS) has also been reported. Hence, the aim of this work is to characterize the production of PHB and EPS by the wild strain DSM2389 using glycerol in shaken flasks and bioreactor. Results showed that maximum PHB accumulation (37-42% w/w) was obtained using glycerol concentrations of 9 and 15 g L-1, where maximum dry cell weight titers reached 3.6 and 3.9 g L-1, respectively. The culture in the bioreactor showed that PHB accumulation takes place under oxygen limitation, while the redox potential of the culture medium could be used for online monitoring of the PHB production. Recovered EPS was analyzed by Fourier-transform infrared spectroscopy and subjected to gas chromatography-mass spectrometry after cleavage and derivatization steps. These analyses showed the presence of sugars which were identified as mannose, rhamnose and glucose, in a proportion near to 3.2:2.3:1, respectively. Since glycerol had not been used in previous works, these findings suggest the potential of A. cryptum to produce biopolymers from this compound at a large scale with a low risk of microbial contamination due to the low pH of the fermentation process.

Two-Stage Bio-Hydrogen and Polyhydroxyalkanoate Production: Upcycling of Spent Coffee Grounds

Coffee waste is an abundant biomass that can be converted into high value chemical products, and is used in various renewable biological processes. In this study, oil was extracted from spent coffee grounds (SCGs) and used for polyhydroxyalkanoate (PHA) production through Pseudomonas resinovorans. The oil-extracted SCGs (OESCGs) were hydrolyzed and used for biohydrogen production through Clostridium butyricum DSM10702. The oil extraction yield through n-hexane was 14.4%, which accounted for 97% of the oil present in the SCGs. OESCG hydrolysate (OESCGH) had a sugar concentration of 32.26 g/L, which was 15.4% higher than that of the SCG hydrolysate (SCGH) (27.96 g/L). Hydrogen production using these substrates was 181.19 mL and 136.58 mL in OESCGH and SCGH media, respectively. The consumed sugar concentration was 6.77 g/L in OESCGH and 5.09 g/L in SCGH media. VFA production with OESCGH (3.58 g/L) increased by 40.9% compared with SCGH (2.54 g/L). In addition, in a fed-batch culture using the extracted oil, cell dry weight was 5.4 g/L, PHA was 1.6 g/L, and PHA contents were 29.5% at 24 h.

Advancement in "Garbage In Biomaterials Out (GIBO)" concept to develop biomaterials from agricultural waste for tissue engineering and biomedical applications

Presently on a global scale, one of the major concerns is to find effective strategies to manage the agricultural waste to protect the environment. One strategy that has been drawing attention among the researchers is the development of biocompatible materials from agricultural waste. This strategy implies successful conversion of agricultural waste products (e.g.: cellulose, eggshell etc.) into building blocks for biomaterial development. Some of these wastes contain even bioactive compounds having biomedical applications. The replacement and augmentation of human tissue with biomaterials as alternative to traditional method not only bypasses immune-rejection, donor scarcity, and maintenance; but also provides long term solution to damaged or malfunctioning organs. Biomaterials development as one of the key challenges in tissue engineering approach, resourced from natural origin imparts better biocompatibility due to closely mimicking composition with cellular microenvironment. The "Garbage In, Biomaterials Out (GIBO)" concept, not only recycles the agricultural wastes, but also adds to biomaterial raw products for further product development in tissue regeneration. This paper reviews the conversion of garbage agricultural by-products to the biocompatible materials for various biomedical applications.

GRAPHICAL ABSTRACT

The agro-waste biomass processed, purified, modified, and further utilized for the fabrication of biomaterials-based support system for tissue engineering applications to grow living body parts in vitro or in vivo.

Effect of Different Plasticizers on Thermal, Crystalline, and Permeability Properties of Poly(3–hydroxybutyrate–co−3–hydroxyhexanoate) Films

Poly(3−hydroxybutyrate−co−3−hydroxyhexanoate) (PHBH) films were prepared using a cast film technique. Dioxane was chosen over other polymer solvents as it resulted in homogenous films with better morphology. Several plasticizers with different molecular weights and concentrations were added to the biopolymer solution prior to casting. Thermal, crystalline, and permeability properties were analyzed by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X−ray diffraction (XRD), and both water vapor and oxygen transmission rate analysis. In general, the addition of plasticizers decreased the glass transition temperature (Tg), cold crystallization temperatures (Tcc), melting temperatures, as well as crystallinity degrees and increased the crystallite sizes and water vapor and oxygen transmission rates. The use of isosorbide and low-molecular-weight poly(ethylene glycol) (PEG) lowered the Tg around 30 °C at the highest used concentration, also being the most effective in increasing the crystallite size. When considering isosorbide and low-molecular-weight poly(ethylene glycol) (PEG) as very good plasticizers for PHBH, the question of which plasticizer to use strongly relies on the desired PHBH application.

Hydrogen-oxidizing bacteria and their applications in resource recovery and pollutant removal

Hydrogen oxidizing bacteria (HOB), a type of chemoautotroph, are a group of bacteria from different genera that share the ability to oxidize H₂ and fix CO₂ to provide energy and synthesize cellular material. Recently, HOB have received growing attention due to their potential for CO₂ capture and waste recovery. This review provides a comprehensive overview of the biological characteristics of HOB and their application in resource recovery and pollutant removal. Firstly, the enzymes, genes and corresponding regulation systems responsible for the key metabolic processes of HOB are discussed in detail. Then, the enrichment and cultivation methods including the coupled water splitting-biosynthetic system cultivation, mixed cultivation and two-stage cultivation strategies for HOB are summarized, which is the critical prerequisite for their application. On the basis, recent advances of HOB application in the recovery of high-value products and the removal of pollutants are presented. Finally, the key points for future investigation are proposed that more attention should be paid to the main limitations in the large-scale industrial application of HOB, including the mass transfer rate of the gases, the safety of the production processes and products, and the commercial value of the products.

Polyhydroxyalkanoates, the bioplastics of microbial origin: Properties, biochemical synthesis, and their applications

The rising plastic pollution deteriorates the environment significantly as these petroleum-based plastics are not biodegradable, and their production requires natural fuels (energy source) and other resources. Polyhydroxyalkanoates (PHAs) are bioplastic and a sustainable and eco-friendly alternative to synthetic plastics. PHAs can be entirely synthesized using various microorganisms such as bacteria, algae, and fungi. These value-added biopolymers show promising properties such as enhanced biodegradability, biocompatibility, and other chemo-mechanical properties. Further, it has been established that the properties of PHA polymers depend on the substrates and chemical composition (monomer unit) of these polymers. PHAs hold great potential as an alternative to petroleum-based polymers, and further research for economic production and utilization of these biopolymers is required. The review describes the synthesis mechanism and different properties of microbially synthesized PHAs for various applications. The classification of PHAs and the multiple techniques necessary for their detection and evaluation have been discussed. In addition, the synthesis mechanism involving the genetic regulation of these biopolymers in various microbial groups has been described. This review provides information on various commercially available PHAs and their application in multiple sectors. The industrial production of these microbially synthesized polymers and the different extraction methods have been reviewed in detail. Furthermore, the review provides an insight into the potential applications of this biopolymer in environmental, industrial, and biomedical applications.

Sustainability Evaluation of Polyhydroxyalkanoate Production from Slaughterhouse Residues Utilising Emergy Accounting

High raw material prices and rivalry from the food industry have hampered the adoption of renewable resource-based goods. It has necessitated the investigation of cost-cutting strategies such as locating low-cost raw material supplies and adopting cleaner manufacturing processes. Exploiting waste streams as substitute resources for the operations is one low-cost option. The present study evaluates the environmental burden of biopolymer (polyhydroxyalkanoate) production from slaughtering residues. The sustainability of the PHA production process will be assessed utilising the Emergy Accounting methodology. The effect of changing energy resources from business as usual (i.e., electricity mix from the grid and heat provision utilising natural gas) to different renewable energy resources is also evaluated. The emergy intensity for PHA production (seJ/g) shows a minor improvement ranging from 1.5% to 2% by changing only the electricity provision resources. This impact reaches up to 17% when electricity and heat provision resources are replaced with biomass resources. Similarly, the emergy intensity for PHA production using electricity EU27 mix, coal, hydropower, wind power, and biomass is about 5% to 7% lower than the emergy intensity of polyethylene high density (PE-HD). In comparison, its value is up to 21% lower for electricity and heat provision from biomass.

Biomedical applications of environmental friendly poly-hydroxyalkanoates

Biological polyesters of hydroxyacids are known as polyhydroxyalkanoates (PHA). They have proved to be an alternative, environmentally friendly and attractive candidate for the replacement of petroleum-based plastics in many applications. Many bacteria synthesize these compounds as an intracellular carbon and energy compound usually under unbalanced growth conditions. Biodegradability and biocompatibility of different PHA has been studied in cell culture systems or in an animal host during the last few decades. Such investigations have proposed that PHA can be used as biomaterials for applications in conventional medical devices such as sutures, patches, meshes, implants, and tissue engineering scaffolds as well. Moreover, findings related to encapsulation capability and degradation kinetics of some PHA polymers has paved their way for development of controlled drug delivery systems. The present review discusses about bio-plastics, their characteristics, examines the key findings and recent advances highlighting the usage of bio-plastics in different medical devices. The patents concerning to PHA application in biomedical field have been also enlisted that will provide a brief overview of the status of research in bio-plastic. This would help medical researchers and practitioners to replace the synthetic plastics aids that are currently being used. Simultaneously, it could also prove to be a strong step in reducing the plastic pollution that surged abruptly due to the COVID-19 medical waste.

P(3HB-co-4HB) as high value polyhydroxyalkanoate: its development over recent decades and current advances

Polyhydroxyalkanoate (PHA) is a biogenic polymer that has the potential to substitute synthetic plastic in numerous applications. This is due to its unique attribute of being a biodegradable and biocompatible thermoplastic, achievable through microbial fermentation from a broad utilizable range of renewable resources. Among all the PHAs discovered, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] stands out as a next generation healthcare biomaterial for having high biopharmaceutical and medical value since it is highly compatible to mammalian tissue. This review provides a critical assessment and complete overview of the development and trend of P(3HB-co-4HB) research over the last few decades, highlighting aspects from the microbial strain discovery to metabolic engineering and bioprocess cultivation strategies. The article also outlines the relevance of P(3HB-co-4HB) as a material for high value-added products in numerous healthcare-related applications.

Immunomodulatory biomaterials and their application in therapies for chronic inflammation-related diseases

The degree of tissue injuries such as the level of scarring or organ dysfunction, and the immune response against them primarily determine the outcome and speed of healing process. The successful regeneration of functional tissues requires proper modulation of inflammation-producing immune cells and bioactive factors existing in the damaged microenvironment. In the tissue repair and regeneration processes, different types of biomaterials are implanted either alone or by combined with other bioactive factors, which will interact with the immune systems including immune cells, cytokines and chemokines etc. to achieve different results highly depending on this interplay. In this review article, the influences of different types of biomaterials such as nanoparticles, hydrogels and scaffolds on the immune cells and the modification of immune-responsive factors such as reactive oxygen species (ROS), cytokines, chemokines, enzymes, and metalloproteinases in tissue microenvironment are summarized. In addition, the recent advances of immune-responsive biomaterials in therapy of inflammation-associated diseases such as myocardial infarction, spinal cord injury, osteoarthritis, inflammatory bowel disease and diabetic ulcer are discussed.

Improved fermentation strategies in a bioreactor for enhancing poly(3-hydroxybutyrate) (PHB) production by wild type Cupriavidus necator from fructose

Poly(3-hydroxybutyrate) (PHB) belongs to the family of polyhydroxyalkanoates, biopolymers used for agricultural, industrial, or even medical applications. However, scaling up the production is still an issue due to the myriad of parameters involved in the fermentation processes. The present work seeks, firstly, to scale up poly(3-hydroxybutyrate) (PHB) production by wild type C. necator ATCC 17697 from shaken flasks to a stirred-tank bioreactor with the optimized media and fructose as carbon source. The second purpose is to improve the production of PHB by applying both the batch and fed-batch fermentation strategies in comparison with previous works of wild type C. necator with fructose. Furthermore, thinking of biomedical applications, physicochemical, and cytotoxicity analyses of the produced biopolymer, are presented.

Fed-batch fermentation with an exponential feeding strategy enabled us to achieve the highest values of PHB concentration and productivity, 25.7 g/l and 0.43 g/(l h), respectively. The PHB productivity was 3.3 and 7.2 times higher than the one in batch strategy and shaken flask cultures, respectively. DSC, FTIR, ¹H, and ¹³C NMR analysis led to determine that the biopolymer produced by C. necator ATCC 17697 has a molecular structure and characteristics in agreement with the commercial PHB. Additionally, the biopolymer does not induce cytotoxic effects on the NIH/3T3 cell culture.

Due to the improved fermentation strategies, PHB concentration resulted in 40 % higher of the already reported one for wild type C. necator using other fed-batch modes and fructose as a carbon source. Thus the produced PHB could be attractive for biomedical applications, which generate a rising interest in polyhydroxyalkanoates during recent years.

Transcriptome Changes in Pseudomonas putida KT2440 during Medium-Chain-Length Polyhydroxyalkanoate Synthesis Induced by Nitrogen Limitation

Pseudomonas putida’s versatility and metabolic flexibility make it an ideal biotechnological platform for producing valuable chemicals, such as medium-chain-length polyhydroxyalkanoates (mcl-PHAs), which are considered the next generation bioplastics. This bacterium responds to environmental stimuli by rearranging its metabolism to improve its fitness and increase its chances of survival in harsh environments. Mcl-PHAs play an important role in central metabolism, serving as a reservoir of carbon and energy. Due to the complexity of mcl-PHAs’ metabolism, the manner in which P. putida changes its transcriptome to favor mcl-PHA synthesis in response to environmental stimuli remains unclear. Therefore, our objective was to investigate how the P. putida KT2440 wild type and mutants adjust their transcriptomes to synthesize mcl-PHAs in response to nitrogen limitation when supplied with sodium gluconate as an external carbon source. We found that, under nitrogen limitation, mcl-PHA accumulation is significantly lower in the mutant deficient in the stringent response than in the wild type or the rpoN mutant. Transcriptome analysis revealed that, under N-limiting conditions, 24 genes were downregulated and 21 were upregulated that were common to all three strains. Additionally, potential regulators of these genes were identified: the global anaerobic regulator (Anr, consisting of FnrA, Fnrb, and FnrC), NorR, NasT, the sigma⁵⁴-dependent transcriptional regulator, and the dual component NtrB/NtrC regulator all appear to play important roles in transcriptome rearrangement under N-limiting conditions. The role of these regulators in mcl-PHA synthesis is discussed.

In silico Assessment of Pharmacological Profile of Low Molecular Weight Oligo-Hydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are a large class of polyesters that are biosynthesized by microorganisms at large molecular weights (Mw > 80 kDa) and have a great potential for medical applications because of their recognized biocompatibility. Among PHAs, poly(3-hydroxybutyrate), poly(4-hydroxybutyrate), poly(3-hydroxyvalerate), poly(4-hydroxyvalerate), and their copolymers are proposed to be used in biomedicine, but only poly(4-hydroxybutyrate) has been certified for medical application. Along with the hydrolysis of these polymers, low molecular weight oligomers are released typically. In this study, we have used a computational approach to assess the absorption, distribution, metabolism, and excretion (ADME)-Tox profiles of low molecular weight oligomers (≤32 units) consisting of 3-hydroxybutyrate, 4-hydroxybutyrate, 3-hydroxyvalerate, 4-hydroxyvalerate, 3-hydroxybutyrate-co-3-hydroxyvalerate, and the hypothetical PHA consisting of 4-hydroxybutyrate-co-4-hydroxyvalerate. According to our simulations, these oligomers do not show cardiotoxicity, hepatotoxicity, carcinogenicity or mutagenicity, and are neither substrates nor inhibitors of the cytochromes involved in the xenobiotic's metabolism. They also do not affect the human organic cation transporter 2 (OCT2). However, they are considered to be inhibitors of the organic anion transporters OATP1B1, and OATP1B3. In addition, they may produce eye irritation, and corrosion, skin irritation and have a low antagonistic effect on the androgen receptor.

Paula ML, M. de Moraes R, Alves GM, M. Lacerda T, dos Santos JC, M. dos Santos A, Medeiros SDF. Chemical Modification of Pullulan Exopolysaccharide by Grafting Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) via Click Chemistry

Biodegradable and biocompatible copolymers have been often studied for the development of biomaterials for drug delivery systems. In this context, this work reports the synthesis and characterization of a novel pullulan-g-poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (Pull-g-PHBHV) graft copolymer using click chemistry. Well-defined and functional pullulan backbones containing azide groups (PullN₃) previously prepared by our group were successfully used for this purpose and propargyl-terminated poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was prepared via transesterification using propargyl alcohol as a chain transfer agent. By an alkyne-azide cycloaddition reaction catalyzed by copper (Cu (I)) (CuAAC), the graft copolymer Pull-g-PHBHV was obtained. The chemical structures of the polymers were accessed by ¹H NMR and ¹³C NMR FTIR. Disappearance of the bands referring to the main bonds evidenced success in the grafting reaction. Besides that, DRX, DSC and TGA were used in order to access the changes in crystallinity and thermal behavior of the material. The remaining crystallinity of the Pull-g-PHBHV structure evidences the presence of PHBHV. Pull-g-PHBHV presented lower degradation maximum temperature values than the starting materials, indicating its minor thermal stability. Finally, the synthesized material is an innovative biopolymer, which has never been reported in the previous literature. It is a bio-derived and biodegradable polymer, chemically modified, resulting in interesting properties which can be useful for their further applications as biomedical systems for controlled delivery, for example.

Statistical augmentation of polyhydroxybutyrate production by Isoptericola variabilis: Characterization, moulding, in vitro cytocompatibility and biodegradability evaluation

This study aimed to explore the production of polyhydroxybutyrate (PHB), a polyhydroxyalkanoate (PHA), which has been widely considered as a potential substitute for the synthetic polymers. Among 53 actinomycete isolates, 11 of them were found to be PHB positive and the quantity of PHB from the positive isolates varied from 10.5 to 29.82 wt% on a dry cell weight basis. A strain designated as PPLAT 012, accumulated relatively higher PHB and has been identified as Isoptericola variabilis by 16S rRNA gene sequence analysis. An effort has also been made to optimize the PHB production by the hyper-producing strain using the conventional, one-factor-at-a-time, and statistical response surface methodologies and the maximum PHB production (46.18%) in DSMZ medium, amended with 12% glucose and 9% potassium nitrate with a pH of 7.0. Further, the characteristic properties such as processability, cytocompatibility and biodegradability of the extracted PHB was also demonstrated. The physical properties of the recovered PHB was further improved by blending with PLA and the resultant blends were characterized. The present investigation has demonstrated that the isolate, Isoptericola variabilis, could be utilized as a potential source for the production of PHB with desirable characteristics, suitable for biomedical applications.

Bio-Based Electrospun Fibers for Wound Healing

Being designated to protect other tissues, skin is the first and largest human body organ to be injured and for this reason, it is accredited with a high capacity for self-repairing. However, in the case of profound lesions or large surface loss, the natural wound healing process may be ineffective or insufficient, leading to detrimental and painful conditions that require repair adjuvants and tissue substitutes. In addition to the conventional wound care options, biodegradable polymers, both synthetic and biologic origin, are gaining increased importance for their high biocompatibility, biodegradation, and bioactive properties, such as antimicrobial, immunomodulatory, cell proliferative, and angiogenic. To create a microenvironment suitable for the healing process, a key property is the ability of a polymer to be spun into submicrometric fibers (e.g., via electrospinning), since they mimic the fibrous extracellular matrix and can support neo- tissue growth. A number of biodegradable polymers used in the biomedical sector comply with the definition of bio-based polymers (known also as biopolymers), which are recently being used in other industrial sectors for reducing the material and energy impact on the environment, as they are derived from renewable biological resources. In this review, after a description of the fundamental concepts of wound healing, with emphasis on advanced wound dressings, the recent developments of bio-based natural and synthetic electrospun structures for efficient wound healing applications are highlighted and discussed. This review aims to improve awareness on the use of bio-based polymers in medical devices.

Esterase-Cleavable 2D Assemblies of Magnetic Iron Oxide Nanocubes: Exploiting Enzymatic Polymer Disassembling To Improve Magnetic Hyperthermia Heat Losses

Here, we report a nanoplatform based on iron oxide nanocubes (IONCs) coated with a bioresorbable polymer that, upon exposure to lytic enzymes, can be disassembled increasing the heat performances in comparison with the initial clusters. We have developed two-dimensional (2D) clusters by exploiting benchmark IONCs as heat mediators for magnetic hyperthermia and a polyhydroxyalkanoate (PHA) copolymer, a biodegradable polymer produced by bacteria that can be digested by intracellular esterase enzymes. The comparison of magnetic heat performance of the 2D assemblies with 3D centrosymmetrical assemblies or single IONCs emphasizes the benefit of the 2D assembly. Moreover, the heat losses of 2D assemblies dispersed in water are better than the 3D assemblies but worse than for single nanocubes. On the other hand, when the 2D magnetic beads (2D-MNBs) are incubated with the esterase enzyme at a physiological temperature, their magnetic heat performances began to progressively increase. After 2 h of incubation, specific absorption rate values of the 2D assembly double the ones of individually coated nanocubes. Such an increase can be mainly correlated to the splitting of the 2D-MNBs into smaller size clusters with a chain-like configuration containing few nanocubes. Moreover, 2D-MNBs exhibited nonvariable heat performances even after intentionally inducing their aggregation. Magnetophoresis measurements indicate a comparable response of 3D and 2D clusters to external magnets (0.3 T) that is by far faster than that of single nanocubes. This feature is crucial for a physical accumulation of magnetic materials in the presence of magnetic field gradients. This system is the first example of a nanoplatform that, upon exposure to lytic enzymes, such as those present in a tumor environment, can be disassembled from the initial 2D-MNB organization to chain-like assemblies with clear improvement of the heat magnetic losses resulting in better heat dissipation performances. The potential application of 2D nanoassemblies based on the cleavable PHAs for preserving their magnetic losses inside cells will benefit hyperthermia therapies mediated by magnetic nanoparticles under alternating magnetic fields.

Stereoselective Ring-Opening (Co)polymerization of β-Butyrolactone and ε-Decalactone Using an Yttrium Bis(phenolate) Catalytic System

An effective route for ring-opening copolymerization of β-butyrolactone (BBL) with ε-decalactone (ε-DL) is reported. Microstructures of the block copolymers characterized by 13C NMR spectroscopy revealed syndiotactic-enriched poly(3-hydroxybutyrate) (PHB) blocks. Several di- and triblock copolymers (PDL-b-PHB and PDL-b-PHB-b-PDL, respectively) were successfully synthesized by sequential addition of the monomers using (salan)Y(III) complexes as catalysts. The results from MALDI-ToF mass spectrometry confirmed the presence of the copolymers. Moreover, thermal properties of the block copolymers were also investigated and showed that the microphase separation of PDL-b-PHB copolymers into PHB- and PDL-rich domains has an impact on the glass transition temperatures of both blocks.

Evaluation of culture medium on poly(3-hydroxybutyrate) production by Cupriavidus necator ATCC 17697: application of the response surface methodology

Polyhydroxyalkanoates (PHA), of which polyhydroxybutyrate (PHB) is the most abundant, are polymers of bacterial origin used for various applications in the medical, industrial and agricultural fields. In the present study we worked on the selection, evaluation and improvement of the significant variables of the medium for the production of PHB by Cupriavidus necator ATCC 17697. In order to address the selection of the main factors and optimize the culture medium, a complete factorial experimental design based on the coupled response surface methodology, was presented. The model with the best adjustment of the variables turned out to be quadratic in fructose (C), linear in ammonium sulphate (N) and pH, with interaction in pH and phosphate solution (P), where the pH was the most significant (p < 0.0001) while the micro-elements solution could be neglected. Thus, optimum carbon concentration, adequate nitrogen limitation and interaction between initial pH and phosphate solution concentration are important factors to ensure a high production of PHB. The optimal values of the selected variables were C = 20 g/l, N = 1.5 g/l, P = 8.75 g/l and pH 7.5. A maximum PHB production of 4.6 g/l, obtained under these conditions, increased almost 2.5 times. The polymer accumulated in the cytoplasm of C. necator ATCC 17697 in the form of granules showed an FTIR spectrum corresponding to that of commercial PHB.

Bioinformatics Analysis of Metabolism Pathways of Archaeal Energy Reserves

Energy storage compounds play crucial roles in prokaryotic physiology. Five chemical compounds have been identified in prokaryotes as energy reserves: polyphosphate (polyP), polyhydroxyalkanoates (PHAs), glycogen, wax ester (WE) and triacylglycerol (TAG). Currently, no systematic study of archaeal energy storage metabolism exists. In this study, we collected 427 archaeal reference sequences from UniProt database. A thorough pathway screening of energy reserves led to an overview of distribution patterns of energy metabolism in archaea. We also explored how energy metabolism might have impact on archaeal extremophilic phenotypes. Based on the systematic analyses of archaeal proteomes, we confirmed that metabolism pathways of polyP, PHAs and glycogen are present in archaea, but TAG and WE are completely absent. It was also confirmed that PHAs are tightly related to halophilic archaea with larger proteome size and higher GC contents, while polyP is mainly present in methanogens. In sum, this study systematically investigates energy storage metabolism in archaea and provides a clear correlation between energy metabolism and the ability to survive in extreme environments. With more genomic editing tools developed for archaea and molecular mechanisms unravelled for energy storage metabolisms (ESMs), there will be a better understanding of the unique lifestyle of archaea in extreme environments.

Switching from petro-plastics to microbial polyhydroxyalkanoates (PHA): the biotechnological escape route of choice out of the plastic predicament?

The benefit of biodegradable “green plastics” over established synthetic plastics from petro-chemistry, namely their complete degradation and safe disposal, makes them attractive for use in various fields, including agriculture, food packaging, and the biomedical and pharmaceutical sector. In this context, microbial polyhydroxyalkanoates (PHA) are auspicious biodegradable plastic-like polyesters that are considered to exert less environmental burden if compared to polymers derived from fossil resources.

The question of environmental and economic superiority of bio-plastics has inspired innumerable scientists during the last decades. As a matter of fact, bio-plastics like PHA have inherent economic drawbacks compared to plastics from fossil resources; they typically have higher raw material costs, and the processes are of lower productivity and are often still in the infancy of their technical development. This explains that it is no trivial task to get down the advantage of fossil-based competitors on the plastic market. Therefore, the market success of biopolymers like PHA requires R&D progress at all stages of the production chain in order to compensate for this disadvantage, especially as long as fossil resources are still available at an ecologically unjustifiable price as it does today.

Ecological performance is, although a logical argument for biopolymers in general, not sufficient to make industry and the society switch from established plastics to bio-alternatives. On the one hand, the review highlights that there’s indeed an urgent necessity to switch to such alternatives; on the other hand, it demonstrates the individual stages of the production chain, which need to be addressed to make PHA competitive in economic, environmental, ethical, and performance-related terms. In addition, it is demonstrated how new, smart PHA-based materials can be designed, which meet the customer’s expectations when applied, e.g., in the biomedical or food packaging sector.

Molecular Level Structure of Biodegradable Poly(Delta-Valerolactone) Obtained in the Presence of Boric Acid

In this study, low molecular weight poly(δ-valerolactone) (PVL) was synthesized through bulk-ring openings polymerization of δ-valerolactone with boric acid (B(OH)₃) as a catalyst and benzyl alcohol (BnOH) as an initiator. The resulting homopolymer was characterized with the aid of nuclear magnetic resonance (NMR) and mass spectrometry (MS) techniques to gain further understanding of its molecular structure. The electrospray ionization mass spectrometry (ESI-MS) spectra of poly(δ-valerolactone) showed the presence of two types of homopolyester chains-one terminated by benzyl ester and hydroxyl end groups and one with carboxyl and hydroxyl end groups. Additionally, a small amount of cyclic PVL oligomers was identified. To confirm the structure of PVL oligomers obtained, fragmentation of sodium adducts of individual polyester molecules terminated by various end groups was explored in ESI-MSⁿ by using collision induced dissociation (CID) techniques. The ESI-MSⁿ analyses were conducted both in positive- and negative ion mode. The comparison of the fragmentation spectra obtained with proposed respective theoretical fragmentation pathways allowed the structure of the obtained oligomers to be established at the molecular level. Additionally, using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), it was proven that regardless of the degree of oligomerization, the resulting PVL samples were a mixture of two types of linear PVL oligomers differing in end groups and containing just a small amount of cyclic oligomers that tended to be not visible at higher molar masses.

Fixation of carbon dioxide by a hydrogen-oxidizing bacterium for value-added products

With rapid technology progress and cost reduction, clean hydrogen from water electrolysis driven by renewable powers becomes a potential feedstock for CO₂ fixation by hydrogen-oxidizing bacteria. Cupriavidus necator (formally Ralstonia eutropha), a representative member of the lithoautotrophic prokaryotes, is a promising producer of polyhydroxyalkanoates and single cell proteins. This paper reviews the fundamental properties of the hydrogen-oxidizing bacterium, the metabolic activities under limitation of individual gases and nutrients, and the value-added products from CO₂, including the products with large potential markets. Gas fermentation and bioreactor safety are discussed for achieving high cell density and high productivity of desired products under chemolithotrophic conditions. The review also updates the recent research activities in metabolic engineering of C. necator to produce novel metabolites from CO₂.

Resorbable implants in pediatric fracture treatment

Pediatric osteosynthesis has developed over the last 20 years, thereby reducing medical and economic burden, including long and expensive hospitalization. Currently, conventional and rigid alloying systems such as titanium are used for stabilization of bone fractures in children. In many cases, implants must be removed, as otherwise growth would be impeded. Biodegradable implant materials exhibit beneficial properties and would make a second removal surgery unnecessary. In the following article, we will give an overview of implant materials that are currently used in pediatric traumatology with a focus on Mg-based implants. Furthermore, we will discuss current scientific knowledge on resorbable implants, including results from pre-clinics and clinics.

Biodegradable and Biocompatible Polyhydroxy-alkanoates (PHA): Auspicious Microbial Macromolecules for Pharmaceutical and Therapeutic Applications

Polyhydroxyalkanoates (PHA) are bio-based microbial biopolyesters; their stiffness, elasticity, crystallinity and degradability are tunable by the monomeric composition, selection of microbial production strain, substrates, process parameters during production, and post-synthetic processing; they display biological alternatives for diverse technomers of petrochemical origin. This, together with the fact that their monomeric and oligomeric in vivo degradation products do not exert any toxic or elsewhere negative effect to living cells or tissue of humans or animals, makes them highly stimulating for various applications in the medical field. This article provides an overview of PHA application in the therapeutic, surgical and tissue engineering area, and reviews strategies to produce PHA at purity levels high enough to be used in vivo. Tested applications of differently composed PHA and advanced follow-up products as carrier materials for controlled in vivo release of anti-cancer drugs or antibiotics, as scaffolds for tissue engineering, as guidance conduits for nerve repair or as enhanced sutures, implants or meshes are discussed from both a biotechnological and a material-scientific perspective. The article also describes the use of traditional processing techniques for production of PHA-based medical devices, such as melt-spinning, melt extrusion, or solvent evaporation, and emerging processing techniques like 3D-printing, computer-aided wet-spinning, laser perforation, and electrospinning.

Techno-economic feasibility of waste biorefinery: Using slaughtering waste streams as starting material for biopolyester production

The utilization of industrial waste streams as input materials for bio-mediated production processes constitutes a current R&D objective not only to reduce process costs at the input side but in parallel, to minimize hazardous environmental emissions. In this context, the EU-funded project ANIMPOL elaborated a process for the production of polyhydroxyalkanoate (PHA) biopolymers starting from diverse waste streams of the animal processing industry. This article provides a detailed economic analysis of PHA production from this waste biorefinery concept, encompassing the utilization of low-quality biodiesel, offal material and meat and bone meal (MBM). Techno-economic analysis reveals that PHA production cost varies from 1.41 €/kg to 1.64 €/kg when considering offal on the one hand as waste, or, on the other hand, accounting its market price, while calculating with fixed costs for the co-products biodiesel (0.97 €/L) and MBM (350 €/t), respectively. The effect of fluctuating market prices for offal materials, biodiesel, and MBM on the final PHA production cost as well as the investment payback time have been evaluated. Depending on the current market situation, the calculated investment payback time varies from 3.25 to 4.5years.