From spherical compartments to polymer films: exploiting vesicle fusion to generate solid supported thin polymer membranes

Solid supported polymer membranes as scaffold for the insertion of functional biomolecules provide the basis for mimicking natural membranes. They also provide the means for unraveling biomolecule-membrane interactions and engineering platforms for biosensing. Vesicle fusion is an established procedure to obtain solid supported lipid bilayers but the more robust polymer vesicles tend to resist fusion and planar membranes rarely form. Here, we build on vesicle fusion to develop a refined and efficient way to produce solid supported membranes based on poly(dimethylsiloxane)-poly(2-methyl-2-oxazoline) (PMOXA-b-PDMS-b-PMOXA) amphiphilic triblock copolymers. We first create thiol-bearing polymer vesicles (polymersomes) and anchor them on a gold substrate. An osmotic shock then provokes polymersome rupture and drives planar film formation. Prerequisite for a uniform amphiphilic planar membrane is the proper combination of immobilized polymersomes and osmotic shock conditions. Thus, we explored the impact of the hydrophobic PDMS block length of the polymersome on the formation and the characteristics of the resulting solid supported polymer assemblies by quarz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). When the PDMS block is short enough, attached polymersomes restructure in response to osmotic shock, resulting in a uniform planar membrane. Our approach to rapidly form planar polymer membranes by vesicle fusion brings many advantages to the development of synthetic planar membranes for bio-sensing and biotechnological applications

Polymer-Lipid Hybrid Membranes as a Model Platform to Drive Membrane-Cytochrome c Interaction and Peroxidase-like Activity

Controllable attachment of proteins to material surfaces is very attractive for many applications including biosensors, bioengineered scaffolds or drug screening. Especially, redox proteins have received considerable attention as a model system not only to understand the mechanism of electron transfer in biological systems, but also the development of novel biosensors. However, current research attempts suffer from denaturation of the protein after its attachment to solid substrates. Here, we present how lipid, polymer and hybrid membranes based on mixtures of lipids and copolymers on a solid support provide a more favorable environment to drive selective and functional attachment of a model redox protein, cytochrome c (cyt c). Polymer membranes provided chemical versatility to support covalent attachment of cyt c, whereas lipid membranes provided flexibility and biocompatibility to support insertion of cyt c through its hydrophobic part. Hybrid membranes combine the most promising characteristics of both lipids and polymers and allowed attachment of cyt c with both covalent attachment and insertion driven by hydrophobic interactions. We then investigated the effect of different attachment strategies on the accessibility and peroxidase-like activity of cyt c, in the presence of different membranes. The real-time combination of cyt c with the planar membranes was investigated by quartz crystal microbalance with dissipation. It was possible to selectively drive the insertion of cyt c into a specific lipid domain of hybrid membranes. In addition, protein accessibility and its functionality were dependent on the specificity of the combination strategy: covalent conjugation of cyt c to polymer and hybrid membranes promoted higher accessibility and supported higher peroxidase-like activity. Taking together, the combination of biomolecules with planar membranes can be modulated in such a way to improve the accessibility of the biomolecules and their resulting functionality for the development of efficient âEuro�active surfacesâEuro�

Design of Bio-Conjugated Hydrogels for Regenerative Medicine Applications: From Polymer Scaffold to Biomolecule Choice

Bio-conjugated hydrogels merge the functionality of a synthetic network with the activity of a biomolecule, becoming thus an interesting class of materials for a variety of biomedical applications. This combination allows the fine tuning of their functionality and activity, whilst retaining biocompatibility, responsivity and displaying tunable chemical and mechanical properties. A complex scenario of molecular factors and conditions have to be taken into account to ensure the correct functionality of the bio-hydrogel as a scaffold or a delivery system, including the polymer backbone and biomolecule choice, polymerization conditions, architecture and biocompatibility. In this review, we present these key factors and conditions that have to match together to ensure the correct functionality of the bio-conjugated hydrogel. We then present recent examples of bio-conjugated hydrogel systems paving the way for regenerative medicine applications

Recent Advances in Hybrid Biomimetic Polymer-Based Films: from Assembly to Applications

Biological membranes, in addition to being a cell boundary, can host a variety of proteins that are involved in different biological functions, including selective nutrient transport, signal transduction, inter- and intra-cellular communication, and cell-cell recognition. Due to their extreme complexity, there has been an increasing interest in developing model membrane systems of controlled properties based on combinations of polymers and different biomacromolecules, i.e., polymer-based hybrid films. In this review, we have highlighted recent advances in the development and applications of hybrid biomimetic planar systems based on different polymeric species. We have focused in particular on hybrid films based on (i) polyelectrolytes, (ii) polymer brushes, as well as (iii) tethers and cushions formed from synthetic polymers, and (iv) block copolymers and their combinations with biomacromolecules, such as lipids, proteins, enzymes, biopolymers, and chosen nanoparticles. In this respect, multiple approaches to the synthesis, characterization, and processing of such hybrid films have been presented. The review has further exemplified their bioengineering, biomedical, and environmental applications, in dependence on the composition and properties of the respective hybrids. We believed that this comprehensive review would be of interest to both the specialists in the field of biomimicry as well as persons entering the field

How Do the Properties of Amphiphilic Polymer Membranes Influence the Functional Insertion of Peptide Pores?

Pore-forming peptides are of high biological relevance particularly as cytotoxic agents, but their properties are also applicable for the permeabilization of lipid membranes for biotechnological applications, which can then be translated to the more stable and versatile polymeric membranes. However, their interactions with synthetic membranes leading to pore formation are still poorly understood, hampering the development of peptide-based nanotechnological applications, such as biosensors or catalytic compartments. To elucidate these interactions, we chose the model peptide melittin, the main component of bee venom. Here, we present our systematic investigation on how melittin interacts with and inserts into synthetic membranes, based on amphiphilic block copolymers, to induce pore formation in three different setups (planar membranes and micrometric and nanometric vesicles). By varying selected molecular properties of block copolymers and resulting membranes (e.g., hydrophilic to hydrophobic block ratio, membrane thickness, surface roughness, and membrane curvature) and the stage of melittin addition to the synthetic membranes, we gained a deeper understanding of melittin insertion requirements. In the case of solid-supported planar membranes, melittin interaction was favored by membrane roughness and thickness, but its insertion and pore formation were hindered when the membrane was excessively thick. The additional property provided by micrometric vesicles, curvature, increased the functional insertion of melittin, which was evidenced by the even more curved nanometric vesicles. Using nanometric vesicles allowed us to estimate the pore size and density, and by changing the stage of melittin addition, we overcame the limitations of peptideâEuro"polymer membrane interaction. Mirroring the functionality assay of planar membranes, we produced glucose-sensing vesicles. The design of synthetic membranes permeabilized with melittin opens a new path toward the development of biosensors and catalytic compartments based on pore-forming peptides functionally inserted in synthetic planar or three-dimensional membranes

Peningkatan Nilai Kalori pada Batubara Lignit dengan Metode Aglomerasi Air dan Minyak Sawit pada PT. Indonesia Power Ujp Pltu Barru

Penggunaan batubara di PLTU sangat bergantung kepada kualitas batubara yang digunakan, karena semakin tinggi kualitas batubara maka akan memaksimalkan pembakaran dan secara langsung akan berdampak pada produksi listrik yang dihasilkan. Penelitian ini bertujuan untuk mengetahui peningkatan nilai kalori pada batubara lignit. Pada penelitian ini digunakan metode aglomerasi dengan media air dan minyak sawit yang pada setiap sampel diberi perlakukan yang sama namun mengalami peningkatan yang berbeda. Ada tiga sampel yang digunakan pada penelitian ini dimana pada setiap sampel memiliki komposisi batubara lignit seberat 1 gram, minyak sawit sebanyak 10,20,30 ml dan air sebanyak 100 ml. Hasil penelitian ini menunjukkan bahwa semakin banyak konsentrasi minyak maka semakin tinggi kadar karbon yang diikat, sehingga dapat meningkatkan nilai kalori batubara. Dilihat dari konsentrasi 30% pada setiap sampel batubara mengalami peningkatan nilai kalori yang sebelumnya 3.765,23 cal/gr menjadi 5.279,46 cal/gr pada sampel pertama, 3.567,44 cal/gr menjadi 4.989,07 cal/gr pada sampel kedua dan 4.026,07 cal/gr menjadi 5.166,98 cal/gr pada sampel ketiga. Dari hasil penelitian ini dapat disimpulkan bahwa batubara lignit yang digunakan di PLTU dapat ditingkatkan nilai kalorinya menggunakan metode aglomerasi air dan minyak sawit

The impact of pretreatment with simvastatin on kidney tissue of rats with acute sepsis

It has been reported that changes in cytokine levels affect mitochondrial functions, levels of hypoxia-inducible factor α (HIF-1α), and tissue damage during sepsis. We aimed to investigate the effects of simvastatin pretreatment on mitochondrial enzyme activities, and on levels of ghrelin, HIF-1α, and thiobarbituric acid reactive substances (TBARS) in kidney tissue during sepsis. Rats were separated into four groups, namely, control, lipopolysaccharides (LPS) (20 mg/kg), simvastatin (20 mg/kg), and simvastatin + LPS. We measured the levels of mitochondrial enzyme activities and TBARS in the kidney using spectrophotometry. The histological structure of the kidney sections was examined after staining with hematoxylin and eosin. Tumor necrosis factor α (TNF-α), IL-10, HIF-1α, and ghrelin immunoreactivity were examined using proper antibodies. In tissue, TNF-α (p  0.05). Ghrelin immunoreactivity was lower in the LPS group (p  0.05). We observed that pretreatment of simvastatin caused favorable changes on ghrelin and TBARS levels in rats with sepsis

Biomolecules Turn Self-Assembling Amphiphilic Block Co-polymer Platforms Into Biomimetic Interfaces

Biological membranes constitute an interface between cells and their surroundings and form distinct compartments within the cell. They also host a variety of biomolecules that carry out vital functions including selective transport, signal transduction and cell-cell communication. Due to the vast complexity and versatility of the different membranes, there is a critical need for simplified and specific model membrane platforms to explore the behaviors of individual biomolecules while preserving their intrinsic function. Information obtained from model membrane platforms should make invaluable contributions to current and emerging technologies in biotechnology, nanotechnology and medicine. Amphiphilic block co-polymers are ideal building blocks to create model membrane platforms with enhanced stability and robustness. They form various supramolecular assemblies, ranging from three-dimensional structures (e.g., micelles, nanoparticles, or vesicles) in aqueous solution to planar polymer membranes on solid supports (e.g., polymer cushioned/tethered membranes,) and membrane-like polymer brushes. Furthermore, polymer micelles and polymersomes can also be immobilized on solid supports to take advantage of a wide range of surface sensitive analytical tools. In this review article, we focus on self-assembled amphiphilic block copolymer platforms that are hosting biomolecules. We present different strategies for harnessing polymer platforms with biomolecules either by integrating proteins or peptides into assemblies or by attaching proteins or DNA to their surface. We will discuss how to obtain synthetic structures on solid supports and their characterization using different surface sensitive analytical tools. Finally, we highlight present and future perspectives of polymer micelles and polymersomes for biomedical applications and those of solid-supported polymer membranes for biosensing

Academic student satisfaction and perceived performance in the e-learning environment during the COVID-19 pandemic: Evidence across ten countries

The outbreak of the COVID-19 pandemic has dramatically shaped higher education and seen the distinct rise of e-learning as a compulsory element of the modern educational landscape. Accordingly, this study highlights the factors which have influenced how students perceive their academic performance during this emergency changeover to e-learning. The empirical analysis is performed on a sample of 10,092 higher education students from 10 countries across 4 continents during the pandemic’s first wave through an online survey. A structural equation model revealed the quality of e-learning was mainly derived from service quality, the teacher’s active role in the process of online education, and the overall system quality, while the students’ digital competencies and online interactions with their colleagues and teachers were considered to be slightly less important factors. The impact of e-learning quality on the students’ performance was strongly mediated by their satisfaction with e-learning. In general, the model gave quite consistent results across countries, gender, study fields, and levels of study. The findings provide a basis for policy recommendations to support decision-makers incorporate e-learning issues in the current and any new similar circumstances.info:eu-repo/semantics/publishedVersio