Multilayer Film Comprising Polybutylene Adipate Terephthalate and Cellulose Nanocrystals with High Barrier and Compostable Properties.

In the present study, a multilayer, high-barrier, thin blown film based on a polybutylene adipate terephthalate (PBAT) blend with polyhydroxyalkanoate (PHA), and composed of four layers including a cellulose nanocrystal (CNC) barrier layer and an electrospun poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) hot-tack layer, was characterized in terms of the surface roughness, surface tension, migration, mechanical and peel performance, barrier properties, and disintegration rate. The results showed that the film exhibited a smooth surface. The overall migration tests showed that the material is suitable to be used as a food contact layer. The addition of the CNC interlayer had a significant effect on the mechanical properties of the system, drastically reducing the elongation at break and, thus, the flexibility of the material. The film containing CNCs and electrospun PHBV hot-tack interlayers exhibited firm but not strong adhesion. However, the multilayer was a good barrier to water vapor (2.4 ± 0.1 × 10-12 kg·m-2·s-1·Pa-1), and especially to oxygen (0.5 ± 0.3 × 10-15 m3·m-2·s-1·Pa-1), the permeance of which was reduced by up to 90% when the CNC layer was added. The multilayer system disintegrated completely in 60 days. All in all, the multilayer system developed resulted in a fully compostable structure with significant potential for use in high-barrier food packaging applications.

Additive Free Crosslinking of Poly-3-hydroxybutyrate via Electron Beam Irradiation at Elevated Temperatures.

When applying electron or gamma irradiation to poly-3-hydroxybutyrate (P3HB), main chain scissions are the dominant material reactions. Though propositions have been made that crosslinking in the amorphous phase of P3HB occurs under irradiation, a conclusive method to achieve controlled additive free irradiation crosslinking has not been shown and no mechanism has been derived to the best of our knowledge. By applying irradiation in a molten state at 195 °C and doses above 200 kGy, we were able to initiate crosslink reactions and achieved gel formation of up to 16%. The gel dose Dgel was determined to be 200 kGy and a range of the G values, the number of scissions and crosslinks for 100 eV energy deposition, is given. Rheology measurements, as well as size exclusion chromatography (SEC), showed indications for branching at doses from 100 to 250 kGy. Thermal analysis showed the development of a bimodal peak with a decrease in the peak melt temperature and an increase in peak width. In combination with an increase in the thermal degradation temperature for a dose of 200 kGy compared to 100 kGy, thermal analysis also showed phenomena attributed to branching and crosslinking.

Advances in Polyhydroxyalkanoate (PHA) Production, Volume 3.

Steadily increasing R&D activities in the field of microbial polyhydroxyalkanoate (PHA) biopolyesters are committed to growing global threats from climate change, aggravating plastic pollution, and the shortage of fossil resources. These prevailing issues paved the way to launch the third Special Issue of Bioengineering dedicated to future-oriented biomaterials, characterized by their versatile plastic-like properties. Fifteen individual contributions to the Special Issue, written by renowned groups of researchers from all over the world, perfectly mirror the current research directions in the PHA sector: inexpensive feedstock like carbon-rich waste from agriculture, mitigation of CO2 for PHA biosynthesis by cyanobacteria or wild type and engineered "knallgas" bacteria, powerful extremophilic PHA production strains, novel tools for rapid in situ determination of PHA in photobioreactors, modelling of the dynamics of PHA production by mixed microbial cultures from inexpensive raw materials, enhanced bioreactor design for high-throughput PHA production by sophisticated cell retention systems, sustainable and efficient PHA recovery from biomass assisted by supercritical water, enhanced processing of PHA by application of novel antioxidant additives, and the development of compatible biopolymer blends. Moreover, elastomeric medium chain length PHA (mcl-PHA) are covered in-depth, inter alia, by introduction of a novel class of bioactive mcl-PHA-based networks, in addition to the first presentation of the new rubber-like polythioester poly(3-mercapto-2-methylpropionate). Finally, the present Special Issue is concluded by a critical essay on past, ongoing, and announced global endeavors for PHA commercialization.

Development of zinc oxide/hydroxyapatite/poly(D,L-lactic acid) fibrous scaffold for tissue engineering applications.

Scaffolds based on polymeric fibers represent an engaging biomedical device due to their particular morphology and similarity with extracellular matrices. The biggest challenge to use fibrous materials in the biomedical field is related to their favorable platform for the adhesion of pathogenic microorganisms. Therefore, their optimum performance not only depends on their bioactive potential but also on their antimicrobial properties. The aim of this work was the design of antimicrobial (zinc oxide, ZnO) and bioactive (hydroxyapatite, Hap) fibrous materials using poly(D, L-lactic acid) (PDLLA) as the polymer fiber substrate. Fiber based composite scaffolds were developed using the Forcespinning® technique. For analysis purposes, the morphological, thermal, antimicrobial and biological properties of the fibrous hybrid system obtained at a concentration of 5 wt% of ZnO and 5 wt% of Hap were studied. The incorporation of the aforementioned nanoparticles (NPs) mixture in PDLLA led to an increase in viscosity and a pseudo-plastic tendency of the precursor solution, which caused an increase in fiber diameters and their dispersion of values. Small cavities and certain roughness were the main surface morphology observed on the fibers before and after NPs incorporation. The fiber thermal stability decreased due to the presence of the NPs. The antimicrobial properties of the hybrid fibrous scaffold presented a growth inhibition (GI) of 70 and 85% for E. coli and S. aureus strains, respectively. Concerning the osteoblast-cell compatibility, PDLLA and hybrid PDLLA scaffold showed low toxicity (cell viabilities above 80%), allowing cell growth inside its three-dimension structure and favorable cell morphology extended along the fibers. This behavior suggests a promising potential of this hybrid PDLLA scaffold for bone application.

Enzymatic Degradation of the Most Common Aliphatic Bio-Polyesters and Evaluation of the Mechanisms Involved: An Extended Study.

Commercial hydrolytic enzymes belonging to different subclasses (several lipases, proteinase k, cutinase) were investigated for their ability to degrade different aliphatic polyesters, i.e., poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA), two poly(caprolactone), having two different molecular weights, poly(lactic acid) (PLA) and poly(propylene carbonate) (PPC). The enzyme screening was first carried out by investigating the capacity of fully degrading the target polymers in 24 h, then weight loss measurements of selected polyesters and target enzymes were performed. Solid residues after enzyme degradation were characterized by proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetry (TGA). Liquid fractions were studied via GPC, 1H NMR and high-performance liquid chromatography (HPLC). PCL and PBSA were found to be the most biodegradable polyesters, under the conditions used in this study. PBS was fully degraded only by cutinase, whereas none of the tested enzymes were able to completely degrade PLA and PPC, in the conditions assessed here. Cutinase exhibited the highest hydrolytic activity on PBSA, while lipase from Candida sp. (CALB) on low molecular weight PCL. Chemical analyses on residual solids showed that the enzymatic degradation occurred homogeneously from the surface through an erosion mechanism and did not significantly affect the macromolecular structure and thermal stability. Cleaving action mode for each enzyme (endo- and/or exo-type) on the different polyesters were also proposed based on the evaluation of the degradation products in the liquid fraction.

Ambient Temperature Stable, Scalable COVID-19 Polymer Particle Vaccines Induce Protective Immunity.

There is an unmet need for safe and effective severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines that are stable and can be cost-effectively produced at large scale. Here, a biopolymer particle (BP) vaccine technology that can be quickly adapted to new and emerging variants of SARS-CoV-2 is used. Coronavirus antigen-coated BPs are described as vaccines against SARS-CoV-2. The spike protein subunit S1 or epitopes from S and M proteins (SM) plus/minus the nucleocapsid protein (N) are selected as antigens to either coat BPs during assembly inside engineered Escherichia coli or BPs are engineered to specifically ligate glycosylated spike protein (S1-ICC) produced by using baculovirus expression in insect cell culture (ICC). BP vaccines are safe and immunogenic in mice. BP vaccines, SM-BP-N and S1-ICC-BP induced protective immunity in the hamster SARS-CoV-2 infection model as shown by reduction of virus titers up to viral clearance in lungs post infection. The BP platform offers the possibility for rapid design and cost-effective large-scale manufacture of ambient temperature stable and globally available vaccines to combat the coronavirus disease 2019 (COVID-19) pandemic.

Small changes in PDMMLA structure influence the adsorption behavior of ECM proteins and syndecan-4 on PDMMLA derivative surfaces: Experimental validation by tensiometric surface force measurements.

Cardiovascular diseases are the leading cause of death around the world according to the World Health Organization. In-stent restenosis is an inflammatory response of the immune system to endovascular stent implantation in atherosclerotic patients. Biocompatible and biodegradable polymers are of great interest in this field in order to limit the side effects of stent treatments. Poly([R,S]-3,3-dimethylmalic acid) (PDMMLA) is a new biodegradable statistical polyester which presents promising properties as a stent coating. In this work, we studied by dynamic tensiometry, the adhesion of extracellular matrix proteins (bovine serum albumin, fibronectin, fibrinogen, and vitronectin) and plasma membrane proteoglycan (syndecan-4) on three PDMMLA derivatives with different hydrophilicity levels. The results show that proteins have different adhesion profiles and affinity on these surfaces. They show similar behavior on the most hydrophilic surface, making hydrophilic, ionic and hydrogen type bonds. Then we compared each protein's individual profile to that of a mixture of all studied proteins. The comparison shows that vitronectin and syndecan-4 are the quantitatively dominating proteins adsorbed by specific interactions. Based on the results from previous studies, this work allowed us to identify the most important PDMMLA surface as a promising biomaterial for bioactive stent-coating.

Forensic Engineering of Advanced Polymeric Materials-Part VII: Degradation of Biopolymer Welded Joints.

Welding technology may be considered as a promising processing method for the formation of packaging products from biopolymers. However, the welding processes used can change the properties of the polymer materials, especially in the region of the weld. In this contribution, the impact of the welding process on the structure and properties of biopolymer welds and their ability to undergo hydrolytic degradation will be discussed. Samples for the study were made from polylactide (PLA) and poly(3-hydroxyalkanoate) (PHA) biopolymers which were welded using two methods: ultrasonic and heated tool welding. Differential scanning calorimetry (DSC) analysis showed slight changes in the thermal properties of the samples resulting from the processing and welding method used. The results of hydrolytic degradation indicated that welds of selected biopolymers started to degrade faster than unwelded parts of the samples. The structure of degradation products at the molecular level was confirmed using mass spectrometry. It was found that hydrolysis of the PLA and PHA welds occurs via the random ester bond cleavage and leads to the formation of PLA and PHA oligomers terminated by hydroxyl and carboxyl end groups, similarly to as previously observed for unwelded PLA and PHA-based materials.

Skin-Compatible Biobased Beauty Masks Prepared by Extrusion.

In the cosmetic sector, natural and sustainable products with a high compatibility with skin, thus conjugating wellness with a green-oriented consumerism, are required by the market. Poly(hydroxyalkanoate) (PHA)/starch blends represent a promising alternative to prepare flexible films as support for innovative beauty masks, wearable after wetting and releasing starch and other selected molecules. Nevertheless, preparing these films by extrusion is difficult due to the high viscosity of the polymer melt at the temperature suitable for processing starch. The preparation of blends including poly(butylene succinate-co-adipate) (PBSA) or poly(butylene adipate-co-terephthalate) (PBAT) was investigated as a strategy to better modulate melt viscosity in view of a possible industrial production of beauty mask films. The release properties of films in water, connected to their morphology, was also investigated by extraction trials, infrared spectroscopy and stereo and electron microscopy. Then, the biocompatibility with cells was assessed by considering both mesenchymal stromal cells and keratinocytes. All the results were discussed considering the morphology of the films. This study evidenced the possibility of modulating thanks to the selection of composition and the materials processing of the properties necessary for producing films with tailored properties and processability for beauty masks.

The Preparation and Biomedical Application of Biopolyesters.

Biopolyesters represent a large family that can be obtained by polymerization of variable bio-derived hydroxyalkanoic acids. The monomer composition, molecular weight of the biopolyesters can affect the properties and applications of the polyesters. The majority of biopolyesters can either be biosynthesized from natural biofeedstocks or semi-synthesized (biopreparation of monomers followed by the chemical polymerization of the monomers). With the fast development of synthetic biology and biosynthesis techniques, the biosynthesis of unnatural biopolyesters (like lactate containing and aromatic biopolyesters) with improved performance and function has been a tendency. The presence of novel preparation methods, novel monomer composition has also significantly affected the properties, functions and applications of the biopolyesters. Due to the properties of biodegradability and biocompatibility, biopolyesters have great potential in biomedical applications (as implanting or covering biomaterials, drug carriers). Moreover, biopolyesters can be fused with other functional ingredients to achieve novel applications or improved functions. This study summarizes and compares the updated preparation methods of representative biopolyesters, also introduces the current status and future trends of their applications in biomedical fields.

Block Copolyesters Containing 2,5-Furan and trans-1,4-Cyclohexane Subunits with Outstanding Gas Barrier Properties.

Biopolymers are gaining increasing importance as substitutes for plastics derived from fossil fuels, especially for packaging applications. In particular, furanoate-based polyesters appear as the most credible alternative due to their intriguing physic/mechanical and gas barrier properties. In this study, block copolyesters containing 2,5-furan and trans-1,4-cyclohexane moieties were synthesized by reactive blending, starting from the two parent homopolymers: poly(propylene furanoate) (PPF) and poly(propylene cyclohexanedicarboxylate) (PPCE). The whole range of molecular architectures, from long block to random copolymer with a fixed molar composition (1:1 of the two repeating units) was considered. Molecular, thermal, tensile, and gas barrier properties of the prepared materials were investigated and correlated to the copolymer structure. A strict dependence of the functional properties on the copolymers' block length was found. In particular, short block copolymers, thanks to the introduction of more flexible cyclohexane-containing co-units, displayed high elongation at break and low elastic modulus, thus overcoming PPF's intrinsic rigidity. Furthermore, the exceptionally low gas permeabilities of PPF were further improved due to the concomitant action of the two rings, both capable of acting as mesogenic groups in the presence of flexible aliphatic units, and thus responsible for the formation of 1D/2D ordered domains, which in turn impart outstanding barrier properties.

Biomedical applications of microbially engineered polyhydroxyalkanoates: an insight into recent advances, bottlenecks, and solutions.

Biopolymeric polyhydroxyalkanoates (PHAs) are fabricated and accumulated by microbes under unbalanced growth conditions, primarily by diverse genera of bacteria. Over the last two decades, microbially engineered PHAs gained substantial interest worldwide owing to their promising wide-range uses in biomedical field as biopolymeric biomaterials. Because of non-hazardous disintegration products, preferred surface alterations, inherent biocompatibility, modifiable mechanical properties, cultivation support for cells, adhesion devoid of carcinogenic impacts, and controllable biodegradability, the PHAs like poly-3-hydroxybutyrate, 3-hydroxybutyrate and 3-hydroxyvalerate co-polymers, 3-hydroxybutyrate and 4-hydroxybutyrate co-polymers, etc., are available for various medical applications. These PHAs have been exploited to design in vivo implants like sutures as well as valves for direct tissue repairing as well as in regeneration devices like bone graft substitutes, nerve guides as well as cardiovascular patches, etc. Furthermore, they are also emerged as attractive candidates for developing effective/novel drug delivery systems because of their biocompatibility and biodegradability with the ability to deliver and release the drugs at a specific site in a controllable manner and, therefore widen the therapeutic window with reduced side effects. However, there still remain some bottlenecks related to PHA purity, mechanical properties, biodegradability, etc., that are need to be addressed so as to make PHAs a realistic biomaterial. In addition, innovative approaches like PHAs co-production with other value-added products, etc., must be developed currently for economical PHA production. This review provides an insight toward the recent advances, bottlenecks, and potential solutions for prospective biomedical applications of PHAs with conclusion that relatively little research/study has been performed presently toward the viability of PHAs as realistic biopolymeric biomaterials.

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.

Poly(propylene 2,5-thiophenedicarboxylate) vs. Poly(propylene 2,5-furandicarboxylate): Two Examples of High Gas Barrier Bio-Based Polyesters.

Both academia and industry are currently devoting many efforts to develop high gas barrier bioplastics as substitutes of traditional fossil-based polymers. In this view, this contribution presents a new biobased aromatic polyester, i.e., poly(propylene 2,5-thiophenedicarboxylate) (PPTF), which has been compared with the furan-based counterpart (PPF). Both biopolyesters have been characterized from the molecular, thermo-mechanical and structural points of view. Gas permeability behavior has been evaluated with respect to 100% oxygen, carbon dioxide and nitrogen at 23 °C. In case of CO2 gas test, gas transmission rate has been also measured at different temperatures. The permeability behavior at different relative humidity has been investigated for both biopolyesters, the thiophen-containing sample demonstrating to be better than the furan-containing counterpart. PPF's permeability behavior became worse than PPTF's with increasing RH, due to the more polar nature of the furan ring. Both biopolyesters under study are characterized by superior gas barrier performances with respect to PEF and PET. With the simple synthetic strategy adopted, the exceptional barrier properties render these new biobased polyesters interesting alternatives in the world of green and sustainable packaging materials. The different polarity and stability of heterocyclic rings was revealed to be an efficient tool to tailor the ability of crystallization, which in turn affects mechanical and barrier performances.

Manufacturing and Characterization of Toughened Poly(lactic acid) (PLA) Formulations by Ternary Blends with Biopolyesters.

Ternary blends with a constant poly(lactic acid) (PLA) content (60 wt %) and varying amounts of poly(3-hydroxybutyrate) (PHB) and poly(ε-caprolactone) (PCL) were manufactured by one step melt blending process followed by injection moulding, with the main aim of improving the low intrinsic toughness of PLA. Mechanical properties were obtained from tensile and Charpy impact tests. The miscibility and morphology of the system was studied by thermal analysis and field emission scanning electron microscopy (FESEM). The obtained results showed a clear phase separation, thus indicating poor miscibility between these three biopolyesters, i.e., PLA, the continuous component with dispersed PHB and PCL domains in the form of different sphere size. Nevertheless, the high fragility of PLA was remarkably reduced, as detected by the Charpy impact test. In accordance with the decrease in brittleness, a remarkable increase in elongation at break is achieved, with increasing PCL load due to its flexibility; in addition, increasing PCL load provides thermal stability at high temperatures. Thus, tailored materials can be manufactured by melt blending PLA, PHB, and PCL in different percentages to offer a wide range of biodegradable polymer blends.

Producing microbial polyhydroxyalkanoate (PHA) biopolyesters in a sustainable manner.

Sustainable production of microbial polyhydroxyalkanoate (PHA) biopolyesters on a larger scale has to consider the "four magic e": economic, ethical, environmental, and engineering aspects. Moreover, sustainability of PHA production can be quantified by modern tools of Life Cycle Assessment. Economic issues are to a large extent affected by the applied production mode, downstream processing, and, most of all, by the selection of carbon-rich raw materials as feedstocks for PHA production by safe and naturally occurring wild type microorganisms. In order to comply with ethics, such raw materials should be used which do not interfere with human nutrition and animal feed supply chains, and shall be convertible towards accessible carbon feedstocks by simple methods of upstream processing. Examples were identified in carbon-rich waste materials from various industrial braches closely connected to food production. Therefore, the article shines a light on hetero-, mixo-, and autotrophic PHA production based on various industrial residues from different branches. Emphasis is devoted to the integration of PHA-production based on selected raw materials into the holistic patterns of sustainability; this encompasses the choice of new, powerful microbial production strains, non-hazardous, environmentally benign methods for PHA recovery, and reutilization of waste streams from the PHA production process itself.

Dynamic contact angle cycling homogenizes heterogeneous surfaces.

In order to reduce restenosis, the necessity to develop the appropriate coating material of metallic stent is a challenge for biomedicine and scientific research over the past decade. Therefore, biodegradable copolymers of poly((R,S)-3,3 dimethylmalic acid) (PDMMLA) were prepared in order to develop a new coating exhibiting different custom groups in its side chain and being able to carry a drug. This material will be in direct contact with cells and blood. It consists of carboxylic acid and hexylic groups used for hydrophilic and hydrophobic character, respectively. The study of this material wettability and dynamic surface properties is of importance due to the influence of the chemistry and the potential motility of these chemical groups on cell adhesion and polymer kinetic hydrolysis. Cassie theory was used for the theoretical correction of contact angles of these chemical heterogeneous surfaces coatings. Dynamic Surface Analysis was used as practical homogenizer of chemical heterogeneous surfaces by cycling during many cycles in water. In this work, we confirmed that, unlike receding contact angle, advancing contact angle is influenced by the difference of only 10% of acidic groups (%A) in side-chain of polymers. It linearly decreases with increasing acidity percentage. Hysteresis (H) is also a sensitive parameter which is discussed in this paper. Finally, we conclude that cycling provides real information, thus avoiding theoretical Cassie correction. H(10)is the most sensible parameter to %A.

Tailoring barrier properties of thermoplastic corn starch-based films (TPCS) by means of a multilayer design.

This work compares the effect of adding different biopolyester electrospun coatings made of polycaprolactone (PCL), polylactic acid (PLA) and polyhydroxybutyrate (PHB) on oxygen and water vapour barrier properties of a thermoplastic corn starch (TPCS) film. The morphology of the developed multilayer structures was also examined by Scanning Electron Microscopy (SEM). Results showed a positive linear relationship between the amount of the electrospun coatings deposited onto both sides of the TPCS film and the thickness of the coating. Interestingly, the addition of electrospun biopolyester coatings led to an exponential oxygen and water vapour permeability drop as the amount of the electrospun coating increased. This study demonstrated the versatility of the technology here proposed to tailor the barrier properties of food packaging materials according to the final intended use.

On the Use of the Electrospinning Coating Technique to Produce Antimicrobial Polyhydroxyalkanoate Materials Containing In Situ-Stabilized Silver Nanoparticles.

Electro-hydrodynamic processing, comprising electrospraying and electrospinning techniques, has emerged as a versatile technology to produce nanostructured fiber-based and particle-based materials. In this work, an antimicrobial active multilayer system comprising a commercial polyhydroxyalkanoate substrate (PHA) and an electrospun PHA coating containing in situ-stabilized silver nanoparticles (AgNPs) was successfully developed and characterized in terms of morphology, thermal, mechanical, and barrier properties. The obtained materials reduced the bacterial population of Salmonella enterica below the detection limits at very low silver loading of 0.002 ± 0.0005 wt %. As a result, this study provides an innovative route to generate fully renewable and biodegradable materials that could prevent microbial outbreaks in food packages and food contact surfaces.