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1.
J Phys Chem B ; 126(42): 8588-8595, 2022 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-36255856

RESUMO

Platinum (Pt) nanocrystals hold the key to a variety of catalytic applications, and those with a cubic shape are attractive as a reference catalyst due to their well-defined {100} facets on the surface. Here we demonstrate the use of droplet reactors as a viable platform for the continuous and scalable production of Pt nanocubes with uniform and controllable sizes. The synthesis was found to be sensitive to the O2 from air because of the oxidative etching associated with the O2/Br- pair. As such, either silicone oil or an inert gas had to be employed as the carrier phase to keep the droplets isolated from air. By controlling the amounts of the precursor and halide ions, the edge length of the Pt nanocubes could be tuned from 5-7 nm. In the setting of a millifluidic device, the droplet reactors could be used to achieve a production rate as high as 31.8 mg min-1, about 10-100 times greater than what has been reported in the literature. We also evaluated the electrocatalytic properties of the as-obtained Pt nanocubes toward the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). For the Pt nanocubes of 6 nm in edge length, they showed a specific activity of 0.27 mA cm-2 toward ORR at 0.9 V and a specific activity of 0.96 mA cm-2 toward MOR at the anodic potential.


Assuntos
Metanol , Platina , Platina/química , Metanol/química , Óleos de Silicone , Catálise , Oxigênio/química
2.
Part Part Syst Charact ; 39(4)2022 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-36091327

RESUMO

Scaffolds capable of promoting cell migration from the periphery towards the center along the radial direction hold promises for tissue regeneration. Here we report a simple and general method based on masked electrospray for the fabrication of such scaffolds by depositing collagen nanoparticles on radially-aligned nanofibers in a radial density gradient. Placed between the metallic needle and the collector, an aperture with tunable opening sizes serves as the mask. By increasing the size of the opening at a fixed speed, the electrosprayed particles take a radial density gradient that decreases from the center to the periphery. When deposited on a glass slide, the radial density gradient of collagen nanoparticles promotes the migration of fibroblasts from the periphery towards the center. By replacing the glass slide with a scaffold comprised of radially-aligned nanofibers, a synergetic effect arises to further accelerate cell migration along the radial direction. The synergistic effect can be attributed to a unique combination of the topographic cue arising from the aligned nanofibers and the haptotactic cue enabled by the graded nanoparticles. This work demonstrates a method to maximize cell migration from the periphery towards the center through a combination of topographic and haptotactic cues.

3.
Small ; 18(42): e2204278, 2022 10.
Artigo em Inglês | MEDLINE | ID: mdl-36071024

RESUMO

The dissolution of a polymeric solid typically starts with the absorption of solvent molecules, followed by swelling and volume expansion. Only when the extent of swelling reaches a threshold can the polymer chains be disentangled and then dissolved into the solvent. When the polymeric solid is encapsulated in a rigid shell, the swelling process will be impeded. Despite the widespread use of this process, it is rarely discussed in the literature how the polymeric solid is dissolved from the core for the generation of colloidal hollow particles. Recent studies have started to shed light on the mechanistic details involved in the formation of hollow particles through a template-directed process. Depending on the nature of the material used for the template, the removal of the template may involve different mechanisms and pathways, leading to the formation of distinct products. Here, a number of examples are used to illustrate this important phenomenon that is largely neglected in the literature. This article also discusses how the swelling of a polymeric template encapsulated in a rigid shell can be leveraged to fabricate new types of functional colloidal particles.


Assuntos
Polímeros , Tamanho da Partícula , Solventes
4.
Adv Healthc Mater ; 11(9): e2200701, 2022 05.
Artigo em Inglês | MEDLINE | ID: mdl-35506255
5.
Nano Lett ; 22(9): 3591-3597, 2022 05 11.
Artigo em Inglês | MEDLINE | ID: mdl-35439017

RESUMO

Despite the successful control of crystal phase using template-directed growth, much remains unknown about the underlying mechanisms. Here, we demonstrate that the crystal phase taken by the deposited metal depends on the lateral size of face-centered cubic (fcc)-Pd nanoplate templates with 12 nm plates giving fcc-Ru while 18-26 nm plates result in hexagonal closed-packed (hcp)-Ru. Although Ru overlayers with a metastable fcc- (high in bulk energy) or stable hcp-phase (low in bulk energy) can be epitaxially deposited on the basal planes, the lattice mismatch will lead to jagged hcp- (high in surface energy) and smooth fcc-facets (low in surface energy), respectively, on the side faces. As the proportion of basal and side faces on the nanoplates varies with lateral size, the crystal phase will change depending on the relative contributions from the surface and bulk energies. The Pd@fcc-Ru outperforms the Pd@hcp-Ru nanoplates toward ethylene glycol and glycerol oxidation reactions.


Assuntos
Nanopartículas , Oxirredução , Fenômenos Físicos
6.
Adv Healthc Mater ; 11(7): e2200412, 2022 04.
Artigo em Inglês | MEDLINE | ID: mdl-35385227
7.
J Am Chem Soc ; 144(6): 2556-2568, 2022 02 16.
Artigo em Inglês | MEDLINE | ID: mdl-35108015

RESUMO

Palladium is one of the few metals capable of forming hydrides, with the catalytic properties being dependent on the elemental composition and spatial distribution of H atoms in the lattice. Herein, we report a facile method for the complete transformation of Pd nanocubes into a stable phase made of PdH0.706 by treating them with aqueous hydrazine at a concentration as low as 9.2 mM. Using formic acid oxidation (FAO) as a model reaction, we systematically investigated the structure-catalytic property relationship of the resultant nanocubes with different degrees of hydride formation. The current density at 0.4 V was enhanced by four times when the nanocubes were completely converted from Pd to PdH0.706. On the basis of a set of slab models with PdH(100) overlayers on Pd(100), we conducted density functional theory calculations to demonstrate that the degree of hybrid formation could influence both the activity and selectivity toward FAO by modulating the relative stability of formate (HCOO) and carboxyl (COOH) intermediates. This work provides a viable strategy for augmenting the performance of Pd-based catalysts toward various reactions without altering the loading of this scarce metal.

8.
J Orthop Res ; 40(12): 2754-2762, 2022 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-35212415

RESUMO

Intrasynovial flexor tendon lacerations of the hand are clinically problematic, typically requiring operative repair and extensive rehabilitation. The small-molecule connective tissue growth factor (CTGF) mimics, oxotremorine M (Oxo-M) and 4-PPBP maleate (4-PPBP), have been shown to improve tendon healing in small animal models by stimulating the expansion and differentiation of perivascular CD146+ cells. To enhance intrasynovial flexor tendon healing, small-molecule CTGF mimics were delivered to repaired canine flexor tendons via porous sutures. In vitro studies demonstrated that Oxo-M and 4-PPBP retained their bioactivity and could be released from porous sutures in a sustained manner. However, in vivo delivery of the CTGF mimics did not improve intrasynovial tendon healing. Histologic analyses and expression of tenogenic, extracellular matrix, inflammation, and remodeling genes showed similar outcomes in treated and untreated repairs across two time points. Although in vitro experiments revealed that CTGF mimics stimulated robust responses in extrasynovial tendon cells, there was no response in intrasynovial tendon cells, explaining the lack of in vivo effects. The results of the current study indicate that therapeutic strategies for tendon repair must carefully consider the environment and cellular makeup of the particular tendon for improving the healing response.


Assuntos
Fator de Crescimento do Tecido Conjuntivo , Tendões , Cães , Animais , Fator de Crescimento do Tecido Conjuntivo/farmacologia , Fator de Crescimento do Tecido Conjuntivo/uso terapêutico , Fator de Crescimento do Tecido Conjuntivo/metabolismo , Suturas , Diferenciação Celular
9.
Biomaterials ; 283: 121421, 2022 04.
Artigo em Inglês | MEDLINE | ID: mdl-35219147

RESUMO

Autologous cardiac cell therapy is a promising treatment for combating the right ventricular heart failure (RVHF) that can occur in patients with congenital heart disease (CHD). However, autologous cell therapies suffer from low cell retention following injection and patient-to-patient variability in cell quality. Here, we demonstrate how computational methods can be used to identify mechanisms of cardiac-derived c-Kit+ cell (CPC) reparative capacity and how biomaterials can be designed to improve cardiac patch performance by engaging these mechanisms. Computational modeling revealed the integrin subunit αV (ITGAV) as an important mediator of repair in CPCs with inherently low reparative capacity (CPCslow). We could engage ITGAV on the cell surface and improve reparative capacity by culturing CPCs on electrospun polycaprolactone (PCL) patches coated with fibronectin (PCL + FN). We tested CPCs from 4 different donors and found that only CPCslow with high ITGAV expression (patient 956) had improved anti-fibrotic and pro-angiogenic paracrine secretion on PCL + FN patches. Further, knockdown of ITGAV via siRNA led to loss of this improved paracrine secretion in patient 956 on PCL + FN patches. When implanted in rat model of RVHF, only PCL + FN + 956 patches were able to improve RV function, while PCL +956 patches did not. In total, we demonstrate how cardiac patches can be designed in a patient-specific manner to improve in vitro and in vivo outcomes.


Assuntos
Cardiopatias Congênitas , Insuficiência Cardíaca , Animais , Terapia Baseada em Transplante de Células e Tecidos , Criança , Cardiopatias Congênitas/terapia , Insuficiência Cardíaca/terapia , Ventrículos do Coração , Humanos , Células-Tronco Multipotentes , Ratos
10.
Adv Healthc Mater ; 11(9): e2100828, 2022 05.
Artigo em Inglês | MEDLINE | ID: mdl-34050610

RESUMO

A facile method is described herein for generating a mineral gradient in a biodegradable polymer scaffold. The gradient is achieved by swelling a composite film made of polycaprolactone (PCL) and hydroxyapatite (HAp) nanoparticles with a PCL solution. During the swelling process, the solvent and PCL polymer chains diffuse into the composite film, generating a gradient in HAp density at their interface. The thickness of the mineral gradient can be tuned by varying the extent of swelling to match the length scale of the natural tendon-to-bone attachment (20-60 µm). When patterned with an array of funnel-shaped channels, the mineral gradient presents stem cells with spatial gradations in both biochemical cues (e.g., osteoinductivity and conductivity associated with the HAp nanoparticles) and mechanical cues (e.g., substrate stiffness) to stimulate their differentiation into a graded distribution of cell phenotypes. This new class of biomimetic scaffolds holds great promise for facilitating the regeneration of the injured tendon-to-bone attachment by stimulating the formation of a functionally graded interface.


Assuntos
Osteogênese , Tecidos Suporte , Biomimética , Durapatita , Poliésteres , Engenharia Tecidual/métodos
11.
Adv Mater ; 34(1): e2102591, 2022 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-34648198

RESUMO

Bimetallic Janus nanocrystals have received considerable interest in recent years owing to their unique properties and niche applications. The side-by-side distribution of two distinct metals provides a flexible platform for tailoring the optical and catalytic properties of nanocrystals. First, a brief introduction to the structural features of bimetallic Janus nanocrystals, followed by an extensive discussion of the synthetic approaches, is given. The strategies and experimental controls for achieving the Janus structure, as well as the mechanistic understandings, are specifically discussed. Then, a number of intriguing properties and applications enabled by the Janus nanocrystals are highlighted. Finally, this article is concluded with future directions and outlooks with respect to both syntheses and applications of this new class of functional nanomaterials.

12.
Nanoscale ; 13(44): 18498-18506, 2021 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-34730167

RESUMO

The catalytic behaviors or properties of bimetallic catalysts are highly dependent on the surface composition, but it has been a grand challenge to acquire such information. In this work, we employ Pd@PtnL core-shell nanocrystals with an octahedral shape and tunable Pt shell thickness as a model system to elucidate their surface compositions using catalytic reactions based upon the selective hydrogenation of butadiene and acetylene. Our results indicate that the surface of the core-shell nanocrystals changed from Pt-rich to Pd-rich when they were subjected to calcination under oxygen, a critical step involved in the preparation of many industrial catalysts. The inside-out migration can be attributed to both atomic interdiffusion and the oxidation of Pd atoms during the calcination process. The changes in surface composition were further confirmed using infrared and X-ray photoelectron spectroscopy. This work offers insightful guidance for the development and optimization of bimetallic catalysts toward various reactions.

13.
Adv Mater ; 33(49): e2103801, 2021 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-34623694

RESUMO

A relatively unexplored aspect of noble-metal nanomaterials is polymorphism, or their ability to crystallize in different crystal phases. Here, a method is reported for the facile synthesis of Ru@Pd core-shell nanocrystals featuring polymorphism, with the core made of hexagonally close-packed (hcp)-Ru while the Pd shell takes either an hcp or face-centered cubic (fcc) phase. The polymorphism shows a dependence on the shell thickness, with shells thinner than ≈1.4 nm taking the hcp phase whereas the thicker ones revert to fcc. The injection rate provides an experimental knob for controlling the phase, with one-shot and drop-wise injection of the Pd precursor corresponding to fcc-Pd and hcp-Pd shells, respectively. When these nanocrystals are tested as catalysts toward formic acid oxidation, the Ru@Pdhcp nanocrystals outperform Ru@Pdfcc in terms of both specific activity and peak potential. Density functional theory calculations are also performed to elucidate the origin of this performance enhancement.

14.
Adv Mater ; 33(45): e2104729, 2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34535918

RESUMO

Nanobottles refer to colloidal particles featuring a hollow body connected to a single opening on the surface. This unique feature makes them ideal carriers for the encapsulation and controlled release of various types of cargos. Here a facile route to the fabrication of uniform nanobottles made of polydopamine by leveraging swelling-induced pressure is reported. When polystyrene spheres are coated with polydopamine and then incubated with a toluene/water emulsion, the polystyrene will be swollen to automatically poke a single hole in the shell because of the pressure inside the shell. After quenching the swelling with ethanol and then removing all the polystyrene with tetrahydrofuran, polydopamine nanobottles are obtained. The dimensions of the hollow body are determined by the polystyrene template, while the size of the opening can be tuned by varying the shell thickness. Through the opening, different types of cargos, including small molecules and biomacromolecules, can be easily loaded with a thermoresponsive material into the cavity. The cargos can be released in a controllable manner through direct heating or polydopamine-enabled photothermal heating. In a proof-of-concept experiment, the polydopamine nanobottles are used for temperature-controlled release of thrombin to trigger the formation of fibrin gels in situ.


Assuntos
Indóis/química , Nanoestruturas/química , Polímeros/química , Portadores de Fármacos/química , Fibrina/metabolismo , Corantes Fluorescentes/química , Furanos/química , Indóis/metabolismo , Polímeros/metabolismo , Poliestirenos/química , Temperatura , Trombina/química , Trombina/metabolismo
15.
Adv Healthc Mater ; 10(15): e2101282, 2021 08.
Artigo em Inglês | MEDLINE | ID: mdl-34352151
16.
Artigo em Inglês | MEDLINE | ID: mdl-34296606

RESUMO

Carbon-supported Pt-M (M = Co, Ni, and Fe) alloy nanocrystals are widely used as catalysts toward oxygen reduction, a reaction key to the operation of proton-exchange membrane fuel cells. Here we report a colloidal method for the in situ growth of Pt-Co nanocrystals on various commercial carbon supports. The use of different carbon supports resulted in not only variations in size and composition for the nanocrystals but also their catalytic activity and durability toward oxygen reduction in acidic media. Among the nanocrystals, those grown on Vulcan XC72 and Ketjenblack EC300J showed the highest specific and mass activities in the 0.1 M HClO4 and 0.05 M H2SO4 electrolytes, respectively. Additionally, the catalysts also showed different durability depending on the strength of the interaction between the nanocrystals and the carbon support. Our analysis demonstrated that the difference in catalytic performance could be ascribed to the distinct effects of carbon support on both the synthetic and catalytic processes.

17.
Chemistry ; 27(55): 13855-13863, 2021 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-34314521

RESUMO

Colloidal synthesis of metal nanocrystals with controlled shapes and internal structures calls for a tight control over both the nucleation and growth processes. Here we report a method for the facile synthesis of Pt right bipyramids (RBPs) by separating nucleation from growth and controlling the nucleation step in a continuous flow reactor. Specifically, homogeneous nucleation was thermally triggered by introducing the reaction solution into a tubular flow reactor held at an elevated temperature to generate singly-twinned seeds. At a lower temperature, the singly-twinned seeds were protected from oxidative etching to allow their slow growth and evolution into RBPs while additional nucleation of undesired seeds could be largely suppressed to ensure RBPs as the main product. Further investigation indicated that the internal structure and growth pattern of the seeds were determined by the temperatures used for the nucleation and growth steps, respectively. The Br- ions involved in the synthesis also played a critical role in the generation of RBPs by serving as a capping agent for the Pt{100} facets while regulating the reduction kinetics through coordination with the Pt(IV) ions.


Assuntos
Nanopartículas Metálicas , Platina , Íons , Cinética , Oxirredução
18.
Nat Commun ; 12(1): 3215, 2021 Jun 02.
Artigo em Inglês | MEDLINE | ID: mdl-34078886

RESUMO

Despite the large number of reports on colloidal nanocrystals, very little is known about the mechanistic details in terms of nucleation and growth at the atomistic level. Taking bimetallic core-shell nanocrystals as an example, here we integrate in situ liquid-cell transmission electron microscopy with first-principles calculations to shed light on the atomistic details involved in the nucleation and growth of Pt on Pd cubic seeds. We elucidate the roles played by key synthesis parameters, including capping agent and precursor concentration, in controlling the nucleation site, diffusion path, and growth pattern of the Pt atoms. When the faces of a cubic seed are capped by Br-, Pt atoms preferentially nucleate from corners and then diffuse to edges and faces for the creation of a uniform shell. The diffusion does not occur until the Pt deposited at the corner has reached a threshold thickness. At a high concentration of the precursor, self-nucleation takes place and the Pt clusters then randomly attach to the surface of a seed for the formation of a non-uniform shell. These atomistic insights offer a general guideline for the rational synthesis of nanocrystals with diverse compositions, structures, shapes, and related properties.

19.
Angew Chem Int Ed Engl ; 60(36): 19643-19647, 2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-34128305

RESUMO

We report a simple route based upon seed-mediated growth to the synthesis of Pd@Aux Pd1-x (0.8≤x≤1) core-shell nanocubes. Benefiting from the well-defined {100} facets and an optimal Au/Pd ratio for the surface, the nanocubes bearing a shell made of Au0.95 Pd0.05 work as an efficient electrocatalyst toward H2 O2 production, with high selectivity of 93-100 % in the low-overpotential region of 0.4-0.7 V. When the Au0.95 Pd0.05 alloy is confined to a shell of only three atomic layers in thickness, the electrocatalyst is able to maintain its surface structure and elemental composition, endowing continuous and stable production of H2 O2 during oxygen reduction at a high rate of 1.62 mol g(Pd+Au) -1  h-1 . This work demonstrates a versatile route to the rational development of active and durable electrocatalysts based upon alloy nanocrystals.

20.
J Am Chem Soc ; 143(22): 8509-8518, 2021 06 09.
Artigo em Inglês | MEDLINE | ID: mdl-34043340

RESUMO

Despite extensive efforts devoted to the synthesis of Pt-Co bimetallic nanocrystals for fuel cell and related applications, it remains a challenge to simultaneously control atomic arrangements in the bulk and on the surface. Here we report a synthesis of Pt-Co@Pt octahedral nanocrystals that feature an intermetallic, face-centered tetragonal Pt-Co core and an ultrathin Pt shell, together with the dominance of {111} facets on the surface. When evaluated as a catalyst toward the oxygen reduction reaction (ORR), the nanocrystals delivered a mass activity of 2.82 A mg-1 and a specific activity of 9.16 mA cm-2, which were enhanced by 13.4 and 29.5 times, respectively, relative to the values of a commercial Pt/C catalyst. More significantly, the mass activity of the nanocrystals only dropped 21% after undergoing 30 000 cycles of accelerated durability test, promising an outstanding catalyst with optimal performance for ORR and related reactions.

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