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1.
ACS Appl Bio Mater ; 7(2): 787-790, 2024 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-38324992

RESUMO

Living probiotic bacteria can be used as an alternative treatment to fight antibiotic-resistant, pathogenic bacteria. Electrospinning probiotics into nanofibers allows the probiotics to be conveniently applied like a wound dressing to protect open wounds while providing antimicrobial activity. In this letter, we encapsulated Lactococcus lactis into biocompatible, alginate-based nanofiber scaffolds. After cross-linking the scaffold to increase the chemical stability of the fibers, the encapsulated L. lactis cells maintained their ability to inhibit the growth of Staphylococcus aureus. This living wound dressing was especially effective at inhibiting the growth of clinically relevant methicillin-resistant S. aureus.


Assuntos
Anti-Infecciosos , Staphylococcus aureus Resistente à Meticilina , Nanofibras , Probióticos , Alginatos/farmacologia , Anti-Infecciosos/farmacologia , Bactérias , Bandagens , Probióticos/farmacologia , Probióticos/uso terapêutico
2.
Proc Natl Acad Sci U S A ; 120(51): e2311396120, 2023 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-38079554

RESUMO

Cationic polymers have been identified as a promising type of antibacterial molecules, whose bioactivity can be tuned through structural modulation. Recent studies suggest that the placement of the cationic groups close to the core of the polymeric architecture rather than on appended side chains might improve both their bioactivity and selectivity for bacterial cells over mammalian cells. However, antibacterial main-chain cationic polymers are typically synthesized via polycondensations, which do not afford precise and uniform molecular design. Therefore, accessing main-chain cationic polymers with high degrees of molecular tunability hinges upon the development of controlled polymerizations tolerating cationic motifs (or cation progenitors) near the propagating species. Herein, we report the synthesis and ring-opening metathesis polymerization (ROMP) of N-methylpyridinium-fused norbornene monomers. The identification of reaction conditions leading to a well-controlled ROMP enabled structural diversification of the main-chain cationic polymers and a study of their bioactivity. This family of polyelectrolytes was found to be active against both Gram-negative (Escherichia coli) and Gram-positive (Methicillin-resistant Staphylococcus aureus) bacteria with minimal inhibitory concentrations as low as 25 µg/mL. Additionally, the molar mass of the polymers was found to impact their hemolytic activity with cationic polymers of smaller degrees of polymerization showing increased selectivity for bacteria over human red blood cells.


Assuntos
Staphylococcus aureus Resistente à Meticilina , Polímeros , Animais , Humanos , Polímeros/química , Polimerização , Antibacterianos/farmacologia , Antibacterianos/química , Norbornanos/química , Cátions , Mamíferos
3.
ACS Eng Au ; 3(6): 527-536, 2023 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-38144681

RESUMO

Nanofiber mats containing poly(3,4-ethylenedioxythiophene) (PEDOT) hold potential for use in wearable electronic applications. Unfortunately, the use of PEDOT is often limited by the acidic nature of polystyrenesulfonate (PSS), a common dispersant for PEDOT. In this study, we explored the impact of increasing the pH value of PEDOT:PSS/poly(vinyl alcohol) (PVA) precursors on the morphological and electrical properties of the resultant electrospun fibers. Specifically, electrospun nanofibers were analyzed using scanning electron microscopy, bright-field microscopy, and two-point probe measurements. We discovered that neutral and even slightly basic PEDOT:PSS/PVA precursors could be electrospun without affecting the resultant electrical properties. While cross-linking effectively stabilized the fibers, their electrical properties decreased after exposure to solutions with pH values between 5 and 11, as well as with agitated soap washing tests. Additionally, we report that the fiber mats maintained their stability after more than 3000 cycles of voltage application. These findings suggest that PEDOT:PSS-based fibers hold potential for use in wearable textile and sensor applications, where long-term durability is needed.

4.
Artigo em Inglês | MEDLINE | ID: mdl-37922414

RESUMO

The growing prevalence of methicillin-resistant Staphylococcus aureus (S. aureus) infections necessitates a greater understanding of their initial adhesion to medically relevant surfaces. In this study, the influence of the mechanical properties and oligomer content of polydimethylsiloxane (PDMS) gels on the initial attachment of Gram-positive S. aureus was explored. Small-amplitude oscillatory shear rheological measurements were conducted to verify that by altering the base to curing (B:C) ratio of the commonly used Sylgard 184 silicone elastomer kit (B:C ratios of 60:1, 40:1, 10:1, and 5:1), PDMS gels could be synthesized with Young's moduli across four distinct regimes: ultrasoft (15 kPa), soft (30 kPa), standard (400 kPa), and stiff (1500 kPa). These as-prepared gels (unextracted) were compared to gels prepared from the same B/C ratios that underwent Soxhlet extraction to remove any unreacted oligomers. While the Young's moduli of unextracted and extracted PDMS gels prepared from the same B:C ratio were statistically equivalent, the associated adhesion failure energy statistically decreased for the ultrasoft gels after extraction (from 25 to 8 J/mm2). The interactions of these eight well-characterized gels with bacteria were tested by using S. aureus SH1000, a commonly studied laboratory strain, as well as S. aureus ATCC 12600, which was isolated from a human lung infection. Increased S. aureus inactivation occurred only when the bacteria were incubated directly on top of the unextracted gels prepared at high B:C ratios (40:1 and 60:1), whereas none of the extracted gels (no unreacted oligomers) had significant levels of inactivated bacteria. S. aureus adhered the least to the stiffest extracted PDMS gels (no unreacted oligomers) and the most to soft, unextracted PDMS gels (with ∼17% unreacted oligomers). These findings suggest that both unreacted oligomers and Young's moduli are important material factors to consider when exploring the attachment behavior of Gram-positive S. aureus to hydrophobic elastomer gels.

5.
ACS Appl Bio Mater ; 6(7): 2905-2915, 2023 07 17.
Artigo em Inglês | MEDLINE | ID: mdl-37384901

RESUMO

In this manuscript, we report the synthesis of zwitterionic copolymers and their ability to form antifouling coatings on porous hydroxyapatite as a mimic of dental coatings. Specifically, we systematically investigated how altering the composition of copolymers of catechol methacrylate (Cat-MA or 2) and methacryloyloxyethyl phosphorylcholine (2-MPC) with varying catechol-to-zwitterion ratios impacted their adhesive and antifouling properties, allowing for the rational design of functional coatings. Characterization by ellipsometry, contact angle goniometry, and X-ray photoelectron spectroscopy revealed the presence of hydrophilic copolymer coatings of ∼10 nm thickness. Notably, these copolymers adhered to hydroxyapatite and reduced the level of attachment of both Gram-negative Escherichia coli and Gram-positive Streptococcus oralis. Additionally, in vitro experiments that mimicked the complex mouth environment (i.e., swallowing and using mouthwash) were employed to evaluate S. oralis adhesion, finding that the copolymer coatings reduced the quantity of adhered bacteria. We suggest that these copolymers provide insights into the design of antifouling coatings that are appropriate for use in oral care.


Assuntos
Aderência Bacteriana , Polímeros , Polímeros/farmacologia , Polímeros/química , Metacrilatos/farmacologia , Metacrilatos/química , Durapatita , Catecóis/farmacologia
6.
Biomacromolecules ; 24(6): 2908-2917, 2023 06 12.
Artigo em Inglês | MEDLINE | ID: mdl-37183416

RESUMO

The use of alginate nanofibers in certain biomedical applications, including targeted delivery to the gut, is limited because an ethanol-free, biocompatible cross-linking method has not been demonstrated. Here, we developed water-stable, alginate-based nanofibers by systematically exploring post-electrospinning cross-linking approaches that used calcium ions dissolved in (1) a glycerol/water cosolvent system and (2) acidic, neutral, or basic aqueous solutions. Scanning electron microscopy proved that the fibers cross-linked in a glycerol cosolvent or pH-optimized solutions had maintained the same morphology as the ethanol-based literature control. Notably, cross-linked fibers were generally smaller in diameter than the as-spun fibers due to both chemical interactions and mass loss during cross-linking, which was supported by mass measurements, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. During stability tests wherein the cross-linked fibers were exposed to three aqueous solutions, the cross-linked fibers were stable in water and acid buffer yet swelled in phosphate buffer saline, making them useful scaffolds for pH-controlled release applications. Proof-of-concept release experiments were conducted using a simulated gastrointestinal tract model. As desired, the cargo remained encapsulated within the cross-linked nanofibers when exposed to an acidic solution that modeled the stomach. Upon exposure to a solution that mimicked the intestines, the cargo was released. We suggest that these cross-linked, alginate-based nanofiber mats hold the potential to be broadly used in biomedical and environmental applications.


Assuntos
Nanofibras , Nanofibras/química , Preparações de Ação Retardada , Alginatos/química , Etanol , Glicerol , Água/química , Trato Gastrointestinal , Espectroscopia de Infravermelho com Transformada de Fourier
7.
ACS Appl Bio Mater ; 6(3): 951-964, 2023 03 20.
Artigo em Inglês | MEDLINE | ID: mdl-36791266

RESUMO

Living bacteria are used in biotechnologies that lead to improvements in health care, agriculture, and energy. Encapsulating bacteria into flexible and modular electrospun polymer fabrics that maintain their viability will further enable their use. This review will first provide a brief overview of electrospinning before examining the impact of electrospinning parameters, such as precursor composition, applied voltage, and environment on the viability of encapsulated bacteria. Currently, the use of nanofiber scaffolds to deliver live probiotics into the gut is the most researched application space; however, several additional applications, including skin probiotics (wound bandages) and menstruation products have also been explored and will be discussed. The use of bacteria-loaded nanofibers as seed coatings that promote plant growth, for the remediation of contaminated wastewaters, and in energy-generating microbial fuel cells are also covered in this review. In summary, electrospinning is an effective method for encapsulating living microorganisms into dry polymer nanofibers. While these living composite scaffolds hold potential for use across many applications, before their use in commercial products can be realized, numerous challenges and further investigations remain.


Assuntos
Bandagens , Polímeros , Bactérias , Atenção à Saúde , Agricultura
8.
ACS Appl Mater Interfaces ; 14(45): 50543-50556, 2022 Nov 16.
Artigo em Inglês | MEDLINE | ID: mdl-36331290

RESUMO

The COVID-19 pandemic has revealed the importance of the detection of airborne pathogens. Here, we present composite air filters featuring a bioinspired liquid coating that facilitates the removal of captured aerosolized bacteria and viruses for further analysis. We tested three types of air filters: commercial polytetrafluoroethylene (PTFE), which is well known for creating stable liquid coatings, commercial high-efficiency particulate air (HEPA) filters, which are widely used, and in-house-manufactured cellulose nanofiber mats (CNFMs), which are made from sustainable materials. All filters were coated with omniphobic fluorinated liquid to maximize the release of pathogens. We found that coating both the PTFE and HEPA filters with liquid improved the rate at which Escherichia coli was recovered using a physical removal process compared to uncoated controls. Notably, the coated HEPA filters also increased the total number of recovered cells by 57%. Coating the CNFM filters did not improve either the rate of release or the total number of captured cells. The most promising materials, the liquid-coated HEPA, filters were then evaluated for their ability to facilitate the removal of pathogenic viruses via a chemical removal process. Recovery of infectious JC polyomavirus, a nonenveloped virus that attacks the central nervous system, was increased by 92% over uncoated controls; however, there was no significant difference in the total amount of genomic material recovered compared to that of controls. In contrast, significantly more genomic material was recovered for SARS-CoV-2, the airborne, enveloped virus, which causes COVID-19, from liquid-coated filters. Although the amount of infectious SARS-CoV-2 recovered was 58% higher, these results were not significantly different from uncoated filters due to high variability. These results suggest that the efficient recovery of airborne pathogens from liquid-coated filters could improve air sampling efforts, enhancing biosurveillance and global pathogen early warning.


Assuntos
Filtros de Ar , COVID-19 , Vírus , Humanos , Pandemias , SARS-CoV-2 , COVID-19/prevenção & controle , Bactérias , Poeira , Politetrafluoretileno
9.
ACS Appl Mater Interfaces ; 14(33): 38116-38131, 2022 Aug 24.
Artigo em Inglês | MEDLINE | ID: mdl-35947443

RESUMO

Biofouling is a serious problem in ultrafiltration (UF) membrane applications. Modifying the surface of membranes with low molecular weight, commercially available antibacterial chemistries is an excellent strategy to mitigate biofouling. Herein, we report a new strategy to impart antibacterial and anti-biofouling behavior without changing the support membrane's size selectivity and pure water permeance (PWP). To this end, a strong antibacterial agent, cetyltrimethylammonium bromide (CTAB), was codeposited with dopamine onto commercial polyethersulfone (PES) UF membranes in the presence of nitrogen (N2) gas backflow. The PWP and pore size of the support membrane did not change with codeposition, confirming the benefit of N2 backflow in mitigating the solution intrusion phenomenon. X-ray photoelectron spectroscopy (XPS), surface ζ potentials, and contact angle measurements confirmed the successful codeposition of polydopamine (PDA) and CTAB onto the membrane. Among three different CTAB concentrations systematically investigated, the membrane functionalized with CTAB at the critical micelle concentration (CMC) provided the best anti-biofouling activity against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and retained its surface ζ potential after being stored in 1 M NaCl (pH = 6.8) for 3 months. Our results demonstrate the potential of using a facile, one-step approach to modify commercial UF membranes without compromising their pore size or flux, while simultaneously endowing antibacterial activity.


Assuntos
Dopamina , Ultrafiltração , Antibacterianos/química , Antibacterianos/farmacologia , Cetrimônio , Escherichia coli , Membranas Artificiais , Ultrafiltração/métodos , Água
10.
ACS Appl Mater Interfaces ; 14(34): 38471-38482, 2022 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-35975683

RESUMO

Perovskite quantum dots (PQDs) offer high photoluminescence quantum yields; however, due to their limited stability in aqueous media, to date their utilization in biomedical applications has been limited. The present work demonstrates highly fluorescent and stable aqueous PQDs that were synthesized using a facile engineered phase transfer method. Ligands were engineered to have a dual functionality, i.e., they could simultaneously mediate the strong binding of PQDs and the interactions with water molecules. The resultant water-soluble PQDs demonstrated robust structural and optical properties. The extracted aqueous PQDs remained stable in pellet form for 8 months, which was the entire test duration. Notably, 100% of their fluorescence was also retained. As a proof-of-concept experiment, the water-soluble PQDs were successfully tagged to polyclonal antibodies and used to image Escherichia coli cells in aqueous media. No structural or optical disturbance in PQDs was detected throughout the process. This work marks the beginning of the use of nonpolymeric aqueous PQDs and shows their strong potential to be used in biological applications.


Assuntos
Pontos Quânticos , Compostos de Cálcio/química , Fluorescência , Óxidos , Pontos Quânticos/química , Titânio , Água/química
11.
Biomater Sci ; 10(6): 1596, 2022 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-35199114

RESUMO

Correction for 'Encapsulating bacteria in alginate-based electrospun nanofibers' by Emily Diep et al., Biomater. Sci., 2021, 9, 4364-4373, DOI: 10.1039/D0BM02205E.

12.
ACS Appl Mater Interfaces ; 14(4): 6148-6156, 2022 Feb 02.
Artigo em Inglês | MEDLINE | ID: mdl-35042335

RESUMO

Antifouling membranes that offer excellent operational lifetimes are critical technologies needed to meet the growing demand for clean water. In this study, we demonstrate antifouling membranes featuring an ultrathin oil layer that stayed immobilized on the surface and in the pore walls of poly(vinylidene fluoride) membranes for multiple cycles of operation at industrially relevant transmembrane pressures. An optimized quantity of a commercial Krytox oil with either a low (K103) or a high viscosity (K107) was infused onto the active surface and into the pores of membranes with a 0.45 µm pore size. The presence of the oil layer was qualitatively confirmed using crystal violet staining and variable pressure scanning electron microscopy. Using a dead-end stirred cell, a consistent pure water permeance value of 3000 L m-2 h-1 bar-1 was achieved for the K103 liquid-infused membranes for at least 10 operation cycles, which was expectedly lower than the permeance of bare control membranes (∼16 000 L m-2 h-1 bar-1), suggesting that a stable oil layer was formed on all membrane-active sites. To quantify if oil was lost during membrane operation, extensive thermogravimetric analysis was conducted on both the as-prepared and used membranes. When challenged with the microorganism, Escherichia coli K12, the liquid-infused membranes statistically reduced microbial attachment by ∼50% versus the control membranes. For the first time, we have demonstrated that by forming an immobilized, robust, and stable oil-coated membrane, we can generate high-performance membranes with stable permeance values that can be operated at relevant transmembrane pressures and provide long-lasting antifouling properties.

13.
Chem Commun (Camb) ; 57(100): 13740-13743, 2021 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-34847573

RESUMO

Herein, we report a controllable pathway to accelerate the polymerization kinetics of dopamine using ultrasound as a trigger. The use of ultrasound was demonstrated to dramatically accelerate the slow liquid phase reaction kinetics and increase the deposition rate of the polydopamine coating on the surface of polymeric membranes.


Assuntos
Dopamina/química , Indóis/química , Membranas Artificiais , Polímeros/química , Indóis/síntese química , Cinética , Permeabilidade , Polimerização , Polímeros/síntese química , Porosidade , Sulfonas/química , Propriedades de Superfície , Ondas Ultrassônicas , Água/química
14.
ACS Appl Mater Interfaces ; 13(42): 50358-50367, 2021 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-34648279

RESUMO

We designed and synthesized epoxy-encapsulated microparticles with core-shell structures via suspension polymerization to enable high-efficiency, room-temperature cold spray processing. The soft core of the microparticles was comprised of a thermoset resin, diglycidyl ether of bisphenol A (DGEBA), which was optionally blended with the thermoplastic, poly(butyl acrylate); the protective shell was formed using polyurea. The composition, morphology, and thermal behavior of the microparticles were investigated. An inverse relationship between deposition efficiency and particle size was demonstrated by varying the surfactant concentration that was used during particle synthesis. We also determined that the microparticles that had pure resin as the core had the lowest viscosity, exhibited a decrease in the critical impact velocity required for adhesion, had the best flowability, and yielded a dramatic increase in deposition efficiency (56%). We have demonstrated that our in-house synthesized particles can form homogeneous, smooth, and fully coalesced coatings using room-temperature cold spray.

15.
Ind Eng Chem Res ; 60(25): 9179-9188, 2021 Jun 30.
Artigo em Inglês | MEDLINE | ID: mdl-34602741

RESUMO

In this study, we systematically investigated the flux performance of ultrafiltration (UF) membranes functionalized with randomly-accumulated nanofibers. By electrospinning nanofibers from hydrophobic polysulfone (PSf) and hydrophilic cellulose (CL), we were able to explore the role that bulk nanofiber (NF) layer thickness, individual NF diameter, and intrinsic chemistry have on composite membrane flux. Additional parameters that we systematically tested include the molecular weight cut-off (MWCO) of the base membrane (10, 100, and 200 kDa), flow orientation (cross-flow versus dead-end), and the feed solution (hydrophilic water versus hydrophobic oil). Structurally, the crosslinked PSf nanofibers were more robust than the CL nanofibers, which lead to the PSfNF-UF membranes having a greater flux performance. To decouple the structural robustness from the water affinity of the fibers, we chemically modified the PSf fibers to be hydrophilic and indeed, the flux of these new composite membranes featuring hydrophilic crosslinked nanofibers were superior. In summary, the greatest increase in flux performance arises from the smallest diameter, hydrophilic nanofibers that are mechanically robust (crosslinked). We have demonstrated that electrospun nanofiber layers improve the flux performance of ultrafiltration membranes.

16.
Biomater Sci ; 9(12): 4364-4373, 2021 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-34128000

RESUMO

Encapsulation technologies are imperative for the safe delivery of live bacteria into the gut where they regulate bodily functions and human health. In this study, we develop alginate-based nanofibers that could potentially serve as a biocompatible, edible probiotic delivery system. By systematically exploring the ratio of three components, the biopolymer alginate (SA), the carrier polymer poly(ethylene oxide) (PEO), and the FDA approved surfactant polysorbate 80 (PS80), the surface tension and conductivity of the precursor solutions were optimized to electrospin bead-free fibers with an average diameter of 167 ± 23 nm. Next, the optimized precursor solution (2.8/1.2/3 wt% of SA/PEO/PS80) was loaded with Escherichia coli (E. coli, 108 CFU mL-1), which served as our model bacterium. We determined that the bacteria in the precursor solution remained viable after passing through a typical electric field (∼1 kV cm-1) employed during electrospinning. This is because the microbes are pulled into a sink-like flow, which encapsulates them into the polymer nanofibers. Upon electrospinning the E. coli-loaded solutions, beads that were much smaller than the size of an E. coli were initially observed. To compensate for the addition of bacteria, the SA/PEO/PS80 weight ratio was reoptimized to be 2.5/1.5/3. Smooth fibers with bulges around the live microbes were formed, as confirmed using fluorescence and scanning electron microscopy. By dissolving and plating the nanofibers, we found that 2.74 × 105 CFU g-1 of live E. coli cells were contained within the alginate-based fibers. This work demonstrates the use of electrospinning to encapsulate live bacteria in alginate-based nanofibers for the potential delivery of probiotics to the gut.


Assuntos
Nanofibras , Alginatos , Escherichia coli , Humanos , Polietilenoglicóis , Tensão Superficial
17.
ACS Appl Mater Interfaces ; 13(18): 21635-21644, 2021 May 12.
Artigo em Inglês | MEDLINE | ID: mdl-33938727

RESUMO

Recent advances in memristive nanocrystal assemblies leverage controllable colloidal chemistry to induce a broad range of defect-mediated electrochemical reactions, switching phenomena, and modulate active parameters. The sample geometry of virtually all resistive switching studies involves thin film layers comprising monomodal diameter nanocrystals. Here we explore the evolution of bipolar and threshold resistive switching across highly ordered, solution-processed nanoribbon assemblies and mixtures comprising BaZrO3 (BZO) and SrZrO3 (SZO) nanocrystals. The effects of nanocrystal size, packing density, and A-site substitution on operating voltage (VSET and VTH) and switching mechanism were studied through a systematic comparison of nanoribbon heterogeneity (i.e., BZO-BZO vs BZO-SZO) and monomodal vs bimodal size distributions (i.e., small-small and small-large). Analysis of the current-voltage response confirms that tip-induced, trap-mediated space-charge-limited current and trap-assisted tunneling processes drive the low- and high-resistance states, respectively. Our results demonstrate that both smaller nanocrystals and heavier alkaline earth substitution decrease the onset voltage and improve stability and state retention of monomodal assemblies and bimodal nanocrystal mixtures, thus providing a base correlation that informs fabrication of solution-processed, memristive nanocrystal assemblies.

18.
ACS Appl Mater Interfaces ; 13(1): 48-66, 2021 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-33356093

RESUMO

With an ever increasing scientific, technological, and industrial interest in high surface area, porous nanofiber mats, electrospinning has emerged as a popular method to produce fibrous assemblies for use across biomedical, energy, and environmental applications. However, not all precursor solutions nor complex geometries can be easily fabricated using the traditional single-nozzle apparatus. Therefore, coaxial electrospinning, a modified version of electrospinning that features a concentrically aligned dual nozzle, has been developed. This review will first describe the mechanism of electrospinning two precursor solutions simultaneously and the operational parameters that need to be optimized to fabricate continuous fibers. Modifications that can be made to the coaxial electrospinning process, which enable the fabrication of uniform fibers with improved properties, as well as the fabrication of fibers that are hollow, functionalized, and from "nonspinnable precursors" will be discussed as a means of promoting the advantages of using a coaxial setup. Examples of how coaxially electrospun nanofibers are employed in diverse applications will be provided throughout this review. We conclude with a timely discussion about the current limitations and challenges of coaxial electrospinning.

19.
J Mech Behav Biomed Mater ; 114: 104168, 2021 02.
Artigo em Inglês | MEDLINE | ID: mdl-33218928

RESUMO

Changes in the elastic properties of brain tissue have been correlated with injury, cancers, and neurodegenerative diseases. However, discrepancies in the reported elastic moduli of brain tissue are persistent, and spatial inhomogeneities complicate the interpretation of macroscale measurements such as rheology. Here we introduce needle induced cavitation rheology (NICR) and volume-controlled cavity expansion (VCCE) as facile methods to measure the apparent Young's modulus E of minimally manipulated brain tissue, at specific tissue locations and with sub-millimeter spatial resolution. For different porcine brain regions and sections analyzed by NICR, we found E to be 3.7 ± 0.7 kPa and 4.8 ± 1.0 kPa for gray matter, and white matter, respectively. For different porcine brain regions and sections analyzed by VCCE, we found E was 0.76 ± 0.02 kPa for gray matter and 0.92 ± 0.01 kPa for white matter. Measurements from VCCE were more similar to those obtained from macroscale shear rheology (0.75 ± 0.06 kPa) and from instrumented microindentation of white matter (0.97 ± 0.40 kPa) and gray matter (0.86 ± 0.20 kPa). We attributed the higher stiffness reported from NICR to that method's assumption of a cavitation instability due to a neo-Hookean constitutive response, which does not capture the strain-stiffening behavior of brain tissue under large strains, and therefore did not provide appropriate measurements. We demonstrate via both analytical modeling of a spherical cavity and finite element modeling of a needle geometry, that this strain stiffening may prevent a cavitation instability. VCCE measurements take this stiffening behavior into account by employing an incompressible one-term Ogden model to find the nonlinear elastic properties of the tissue. Overall, VCCE afforded rapid and facile measurement of nonlinear mechanical properties of intact, healthy mammalian brain tissue, enabling quantitative comparison among brain tissue regions and also between species. Finally, accurate estimation of elastic properties for this strain stiffening tissue requires methods that include appropriate constitutive models of the brain tissue response, which here are represented by inclusion of the Ogden model in VCCE.


Assuntos
Encéfalo , Substância Branca , Animais , Módulo de Elasticidade , Substância Cinzenta , Reologia , Suínos
20.
Environ Sci Technol ; 54(20): 13249-13256, 2020 10 20.
Artigo em Inglês | MEDLINE | ID: mdl-32970427

RESUMO

Water filtration membranes produced sustainably through microbial cellulose production can have filtration properties altered through facile chemical treatments. Microbial cellulose is an effective membrane filtration medium, and pristine microbial membranes can serve as ultrafiltration membranes with a permeability of 143 L m-2h-1bar-1 and a particle size cut off of 35 nm. As living biofilms, these membranes consist of microbial cellulose, bacteria, and extracellular polymers. Thus, additional biofilm components may reduce the intrinsic permeability of the cellulose. Here, microbial membranes were treated with hydrogen peroxide (H2O2) and sodium hypochlorite (NaOCl, liquid bleach) to remove impurities present in microbial cellulose and increase membrane permeability. For example, permeability increased from 143 to 257 L m-2h-1bar-1 with treatment by 0.3% H2O2 for 12 min. The membranes were also treated with sodium hydroxide (NaOH) to increase membrane selectivity, and the particle size cutoff was reduced from 35 to 10 nm post-treatment with 0.8% NaOH for 20 min. Scanning electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, contact angle goniometry, and X-ray diffraction were used to characterize the physical and chemical properties of the membrane matrix. Facile chemical treatments provide a significant degree of flexibility to tailor microbial membranes to meet specific needs. Microbial membrane production is inherently accessible, and this study furthers that accessibility by utilizing only readily available components to treat microbial membranes and expand their potential applications.


Assuntos
Celulose , Ultrafiltração , Peróxido de Hidrogênio , Membranas Artificiais , Permeabilidade
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