Natural extracellular matrices (ECMs) have been widely used as a support for the adhesion, migration, differentiation, and proliferation of adipose-derived stem cells (ADSCs). However, poor mechanical behavior and unpredictable biodegradation properties of natural ECMs considerably limit their potential for bioapplications and raise the need for different, synthetic scaffolds. Hydrogels are regarded as the most promising alternative materials as a consequence of their excellent swelling properties and their resemblance to soft tissues. A variety of strategies have been applied to create synthetic biomimetic hydrogels, and their biophysical and biochemical properties have been modulated to be suitable for cell differentiation. In this review, we first give an overview of common methods for hydrogel preparation with a focus on those strategies that provide potential advantages for ADSC encapsulation, before summarizing the physical properties of hydrogel scaffolds that can act as biological cues. Finally, the challenges in the preparation and application of hydrogels with ADSCs are explored and the perspectives are proposed for the next generation of scaffolds.
Antimicrobial peptides (AMPs) have been attracting much attention due to their excellent antimicrobial efficiency and low rate in driving antimicrobial resistance (AMR), which has been increasing globally to alarming levels. Conjugation of AMPs into functional polymers not only preserves excellent antimicrobial activities but reduces the toxicity and offers more functionalities, which brings new insight toward developing multifunctional biomedical materials such as hydrogels, polymer vesicles, polymer micelles, and so forth. These nanomaterials have been exhibiting excellent antimicrobial activity against a broad spectrum of bacteria including multidrug-resistant (MDR) ones, high selectivity, and low cytotoxicity, suggesting promising potentials in wound dressing, implant coating, antibiofilm, tissue engineering, and so forth. This Perspective seeks to highlight the state-of-the-art strategy for the synthesis, self-assembly, and biomedical applications of AMP-polymer conjugates and explore the promising directions for future research ranging from synthetic strategies, multistage and stimuli-responsive antibacterial activities, antifungi applications, and potentials in elimination of inflammation during medical treatment. It also will provide perspectives on how to stem the remaining challenges and unresolved problems in combating bacteria, including MDR ones.
Periodontitis is a common disease caused by plaque biofilms, which are important pathogenic factors of many diseases and may be eradicated by antibiotic therapy. However, low-dose antibiotic therapy is a complicated challenge for eradicating biofilms as hundreds (even thousands) of times higher concentrations of antibiotics are needed than killing planktonic bacteria. Polymer vesicles may solve these problems via effective antibiotic delivery into biofilms, but traditional single corona vesicles lack the multifunctionalities essential for biofilm eradication. In this paper, we aim to effectively treat biofilm-induced periodontitis using much lower concentrations of antibiotics than traditional antibiotic therapy by designing a multifunctional dual corona vesicle with intrinsic antibacterial and enhanced antibiotic delivery capabilities. This vesicle is co-assembled from two block copolymers, poly(ε-caprolactone)-block-poly(lysine-stat-phenylalanine) [PCL-b-P(Lys-stat-Phe)] and poly(ethylene oxide)-block-poly(ε-caprolactone) [PEO-b-PCL]. Both PEO and P(Lys-stat-Phe) coronas have their specific functions: PEO endows vesicles with protein repelling ability to penetrate extracellular polymeric substances in biofilms (“stealthy” coronas), whereas P(Lys-stat-Phe) provides vesicles with positive charges and broad spectrum intrinsic antibacterial activity. As a result, the dosage of antibiotics can be reduced by 50% when encapsulated in the dual corona vesicles to eradicate Escherichia coli or Staphylococcus aureus biofilms. Furthermore, effective in vivo treatment has been achieved from a rat periodontitis model, as confirmed by significantly reduced dental plaque, and alleviated inflammation. Overall, this “stealthy” and antibacterial dual corona vesicle demonstrates a fresh insight for improving the antibiofilm efficiency of antibiotics and combating the serious threat of biofilm-associated diseases.
Asphaltene nanoaggregates have recently been observed in live crude oil by observation of gravitationally induced asphaltene gradients in four different reservoir sands with oil columns up to 1000 m vertical. When the liquid phase is invariant, these gradients can be fit using Archimedes buoyancy in the Boltzmann distribution; the only adjustable parameter in data fitting is the size of the asphaltene nanoaggregate; ∼2 nm is obtained in four reservoir sands and is similar to laboratory results for asphaltene nanoaggregates in toluene. Here, a live crude oil (with dissolved gases) has been spun at modest g forces for long times designed to create a large, equilibrium asphaltene gradient for the presumed 2 nm aggregates. Elevated temperatures (∼91°C) were employed during centrifugation to mimic reservoir conditions for asphaltene aggregation and prevention of a possible wax phase. Elevated pressures were employed on the hot, live crude oil to maintain dissolved gas concentrations. A total of 13 alliquots of crude oil were removed after centrifugation, and the asphaltene concentrations were determined by optical spectroscopy. Indeed, a large asphaltene gradient was observed, and a 2.6 nm diameter nanoaggregate was obtained using Archimedes buoyancy in the Boltzmann distribution. In addition, a solubility model accounting for the gas/oil ratio (GOR) gradient was used to analyze the asphaltene gradient, giving an asphaltene particle size of 2.0 nm, thus, the same as field observations. In addition, the gradient in bulk resins was shown to be quite small, showing the stark contrast of asphaltene versus bulk resin aggregation. The heaviest resins (or lightest asphaltenes) do show some gradient. These observations allow for the determination of the maximum and minimum asphaltene aggregation number; the range is roughly 3-8. Some modest resin association with asphaltenes, one resin molecule in every asphaltene nanoaggregate, is consistent with our data. These results are discussed within the increasingly successful modified Yen model of asphaltenes.
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