Polysaccharide-Based Injectable Hydrogels with Fast Gelation and Self-Strengthening Mechanical Kinetics for Oral Tissue Regeneration.

Oral defects lead to a series of function disorders, severely threatening the patients' health. Although injectable hydrogels are widely studied in tissue regeneration, their mechanical performance is usually stationary after implant, without further self-adaption toward the microenvironment. Herein, an injectable hydrogel with programmed mechanical kinetics of instant gelation and gradual self-strengthening along with outstanding biodegradation ability is developed. The fast gelation is realized through rapid Schiff base reaction between biodegradable chitosan and aldehyde-modified sodium hyaluronate, while self-strengthening is achieved via slow reaction between redundant amino groups on chitosan and epoxy-modified hydroxyapatite. The resultant hydrogel also possesses multiple functions including (1) bio-adhesion, (2) self-healing, (3) bactericidal, (4) hemostasis, and (5) X-ray in situ imaging, which can be effectively used for oral jaw repair. We believe that the strategy illustrated here will provide new insights into dynamic mechanical regulation of injectable hydrogels and promote their application in tissue regeneration.

Three-Dimensional Printed Titanium Scaffolds Enhance Osteogenic Differentiation and New Bone Formation by Cultured Adipose Tissue-Derived Stem Cells Through the IGF-1R/AKT/Mammalian Target of Rapamycin Complex 1 (mTORC1) Pathway.

BACKGROUND This study aimed to investigate the effects of three-dimensional (3D) printed titanium (3DTi) scaffolds on osteogenic differentiation and new bone formation by 3D cultured adipose tissue-derived stem cells (ADSCs) in vitro, and the effects of bone regeneration in vivo using a full-thickness mandibular defect rat model, and the mechanisms involved. MATERIAL AND METHODS Alpha-beta titanium alloy (Ti6Al4V) 3DTi scaffolds were prepared with Cellmatrix hydrogel and 3D culture medium. ADSCs were impregnated into the 3DTi scaffolds. ADSC viability and proliferation were assessed using the cell counting kit-8 (CCK-8) assay, and alkaline phosphatase (ALP) levels were measured. Real-time polymerase chain reaction (RT-PCR) and Western blot were performed to assess the expression of osteogenesis-related mRNA for RUNX2, OPN, OCN, and IGF-1 genes and proteins. A rat model of full-thickness mandibular defect was evaluated with micro-computed tomography (microCT) scanning, and histochemistry with Alizarin red and von Giesen's stain were used to evaluate osteogenesis. RESULTS ADSC viability and proliferation were not affected by culture with 3DTi scaffolds. Expression of osteogenesis-related mRNA and proteins for RUNX2, OPN, OCN, and IGF-1, expression of ALP, and histochemical findings showed that the use of 3DTi scaffolds enhanced osteogenic differentiation and new bone formation by ADSCs, with upregulation of components of the IGF-1R/AKT/mTORC1 pathway. CONCLUSIONS The 3D culture of ADSCs with 3DTi scaffolds enhanced osteogenic differentiation and new bone formation through the IGF-1R/AKT/mTORC1 pathway. This improved method of osteointegration may have clinical application in the preparation of bone grafts before implantation for improved repair of mandibular bone defects.

Construction of Compact Polyelectrolyte Multilayers Inspired by Marine Mussel: Effects of Salt Concentration and pH As Observed by QCM-D and AFM.

Biomimetic multilayers based on layer-by-layer (LbL) assembly were prepared as functional films with compact structure by incorporating the mussel-inspired catechol cross-linking. Dopamine-modified poly(acrylic acid) (PAADopa) was synthesized as a polyanion to offer electrostatic interaction with the prelayer polyethylenimine (PEI) and consecutively cross-linked by zinc to generate compact multilayers with tunable physicochemical properties. In situ layer-by-layer growth and cross-linking were monitored by a quartz crystal microbalance with dissipation (QCM-D) to reveal the kinetics of the process and the influence of Dopa chemistry. Addition of Dopa enhanced the mass adsorption and led to the formation of a more compact structure. An increase of ionic strength induced an increase in mass adsorption in the Dopa-cross-linked multilayers. This is a universal approach for coating of various surfaces such as Au, SiO2, Ti, and Al2O3. Roughness observed by AFM in both wet and dry conditions was compared to confirm the compact morphology of Dopa-cross-linked multilayers. Because of the pH sensitivity of Dopa moiety, metal-chelated Dopa groups can be turned into softer structure at higher pH as revealed by reduction of Young's modulus determined by MFP-3D AFM. A deeper insight into the growth and mechanical properties of Dopa-cross-linked polyelectrolyte multilayers was addressed in the present study. This allows a better control of these systems for bioapplications.

Mussel-Inspired Photografting on Colloidal Spheres: A Generalized Self-Template Route to Stimuli-Responsive Hollow Spheres for Controlled Pesticide Release.

A thermo-controlled pesticide release system composed of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) thin film grafted polydopamine (PDA) (PDMAEMA-g-PDA) microcapsules is reported. SiO2 microparticles are used as a template to prepare PDA-coated SiO2 microparticles. The thermally-responsive PDMAEMA thin films are grafted on PDA surfaces using a metal-free surface-initiated photopolymerization approach without adding any photo-initiator or photosensitizer under UV light irradiation. The subsequent acid etching yields PDMAEMA-g-PDA hollow microcapsules. PDMAEMA-g-PDA microcapsules exhibit well-controlled release of avermectin (Av). The results show that the loading ability of PDMAEMA-g-PDA microcapsules of Av is up to 52.7% (w/w). The release kinetics of Av demonstrate that Av@PDMAEMA-g-PDA microcapsules exhibit temperature-controlled release performance. This work is significant for controlled release systems. This simple design is expected to be used in various applications, such as in controlled drug release and agriculture-related fields.

Enhancement of enzymatic activity by magnetic spherical polyelectrolyte brushes: a potential recycling strategy for enzymes.

Interactions between amyloglucosidase and magnetic spherical polyelectrolyte brushes (MSPB) were studied by turbidimetric titration, which reveals reversible and tunable behaviors of pH-dependent enzyme-SPB binding. Quantitative thermodyanmic parameters including binding affinity and stoichiometry between enzyme and SPBs were further measured by isothermal titration calorimetry (ITC). A large amount of enzyme can be loaded in MSPB without loss of MSPB stability. We demonstrated that the enzymatic activity of amyloglucosidase bound in MSPB could be greatly enhanced (catalytic reaction rate, k(bound) = 1.36k(free)) compared to free enzyme acitivity in solution. This is tremendous improvement from other carrier systems that usually lead to a significant decrease of enzymatic activity. Both the high enzyme loading capacity and the enhancement of the catalytic activity probably arise from the Coulombic interactions between the enzyme and MSPB. These findings provide a practical strategy for enhancement of enzyme activity and enzyme recycling by MSPB.

Deposition and water repelling of temperature-responsive nanopesticides on leaves.

Pesticides are widely used to increase agricultural productivity, however, weak adhesion and deposition lead to low efficient utilization. Herein, we prepare a nanopesticide formulation (tebuconazole nanopesticides) which is leaf-adhesive, and water-dispersed via a rapid nanoparticle precipitation method, flash nanoprecipitation, using temperature-responsive copolymers poly-(2-(dimethylamino)ethylmethylacrylate)-b-poly(ε-caprolactone) as the carrier. Compared with commercial suspensions, the encapsulation by the polymer improves the deposition of TEB, and the contact angle on foliage is lowered by 40.0°. Due to the small size and strong van der Waals interactions, the anti-washing efficiency of TEB NPs is increased by 37% in contrast to commercial ones. Finally, the acute toxicity of TEB NPs to zebrafish shows a more than 25-fold reduction as compared to commercial formulation indicating good biocompatibility of the nanopesticides. This work is expected to enhance pesticide droplet deposition and adhesion, maximize the use of pesticides, tackling one of the application challenges of pesticides.

Biodegradable Antibacterial Bioorthogonal Polymeric Nanocatalysts Prepared by Flash Nanoprecipitation.

Bioorthogonal activation of pro-dyes and prodrugs using transition-metal catalysts (TMCs) provides a promising strategy for imaging and therapeutic applications. TMCs can be loaded into polymeric nanoparticles through hydrophobic encapsulation to generate polymeric nanocatalysts with enhanced solubility and stability. However, biomedical use of these nanostructures faces challenges due to unwanted tissue accumulation of nonbiodegradable nanomaterials and cytotoxicity of heavy-metal catalysts. We report here the creation of fully biodegradable nanocatalysts based on an engineered FDA-approved polymer and the naturally existing catalyst hemin. Stable nanocatalysts were generated through kinetic stabilization using flash nanoprecipitation. The therapeutic potential of these nanocatalysts was demonstrated through effective treatment of bacterial biofilms through the bioorthogonal activation of a pro-antibiotic.

Multimerization and aggregation of native-state insulin: effect of zinc.

The aggregation of insulin is complicated by the coexistence of various multimers, especially in the presence of Zn(2+). Most investigations of insulin multimerization tend to overlook aggregation kinetics, while studies of insulin aggregation generally pay little attention to multimerization. A clear understanding of the starting multimer state of insulin is necessary for the elucidation of its aggregation mechanism. In this work, the native-state aggregation of insulin as either the Zn-insulin hexamer or the Zn-free dimer was studied by turbidimetry and dynamic light scattering, at low ionic strength and pH near pI. The two states were achieved by varying the Zn(2+) content of insulin at low concentrations, in accordance with size-exclusion chromatography results and literature findings (Tantipolphan, R.; Romeijn, S.; Engelsman, J. d.; Torosantucci, R.; Rasmussen, T.; Jiskoot, W. J. Pharm. Biomed. 2010, 52, 195). The much greater aggregation rate and limiting turbidity (τ(∞)) for the Zn-insulin hexamer relative to the Zn-free dimer was explained by their different aggregation mechanisms. Sequential first-order kinetic regimes and the concentration dependence of τ(∞) for the Zn-insulin hexamer indicate a nucleation and growth mechanism, as proposed by Wang and Kurganov (Wang, K.; Kurganov, B. I. Biophys. Chem. 2003, 106, 97). The pure second-order process for the Zn-free dimer suggests isodesmic aggregation, consistent with the literature. The aggregation behavior at an intermediate Zn(2+) concentration appears to be the sum of the two processes.

Engineered Polymer-Supported Biorthogonal Nanocatalysts Using Flash Nanoprecipitation.

Transition-metal catalysts (TMCs) effect bioorthogonal transformations that enable the generation of therapeutic agents in situ, minimizing off-target effects. The encapsulation of insoluble TMCs into polymeric nanoparticles to generate "polyzymes" has vastly expanded their applicability in biological environments by enhancing catalyst solubility and stability. However, commonly used precipitation approaches provide limited encapsulation efficiency in polyzyme fabrication and result in a low catalytic activity. Herein, we report the creation of polyzymes with increased catalyst loading and optimized turnover efficiency using flash nanoprecipitation (FNP). Polyzymes with controlled size and catalyst loading were fabricated by tuning the process conditions of FNP. The biological applicability of polyzymes was demonstrated by efficiently transforming a non-toxic prodrug into the active drug within cancer cells.

Fabrication of Charge-Conversion Nanoparticles for Cancer Imaging by Flash Nanoprecipitation.

Traditional charge-conversion nanoparticles (NPs) need the breakage of acid-labile groups on the surface, which impedes the rapid response to the acidic microenvironment. Here, we developed novel rodlike charge-conversion NPs with amphiphilic dextran- b-poly(lactic- co-glycolic acid), poly(2-(dimethylamino) ethylmethylacrylate)- b-poly(ε-caprolactone), and an aggregation-induced emission-active probe through flash nanoprecipitation (FNP). These NPs exhibit reversible negative-to-positive charge transition at a slightly acidic pH relying on the rapid protonation/deprotonation of polymers. The size and the critical charge-conversion pH can be further tuned by varying the flow rate and polymer ratio. Consequently, the charge conversion endows NPs with resistance to protein adsorption at physiological pH and enhanced internalization to cancer cells under acidic conditions. Ex vivo imaging on harvest organs shows that charge-conversion NPs were predominantly distributed in tumors after intravenous administration to mice due to the robust response of NPs to the acidic microenvironment in tumor tissue, whereas control NPs or free probes were broadly accumulated in tumor, liver, kidney, and lung. These results suggest the great potential of the current FNP strategy in the facile and generic fabrication of charge-conversion NPs for tumor-targeting delivery of drugs or fluorescent probes.

Morphology Tuning of Aggregation-Induced Emission Probes by Flash Nanoprecipitation: Shape and Size Effects on in Vivo Imaging.

Aggregation-induced emission (AIE) imaging probes have recently received considerable attention because of their unique property of high performance in the aggregated state and their imaging capability. However, the tendency of AIE molecules to aggregate into micron long irregular shapes, which significantly limits their application in vivo, is becoming a serious issue that needs to be addressed. Here, we introduce a novel engineering strategy to tune the morphology and size of AIE nanoaggregates, based on flash nanoprecipitation (FNP). Quinolinemalononitrile (ED) is encapsulated inside properly selected amphiphilic block copolymers of varying concentration. This leads to a variety of ED particle morphologies with different sizes. The shape and size are found to have strong influences on tumor targeting both in vitro and in vivo. The current results therefore indicate that the FNP method together with optimal choice of an amphiphilic copolymer is a universal method to systematically control the aggregation state of AIE materials and hence tune the morphology and size of AIE nanoaggregates, which is potentially useful for precise imaging at specific tumor sites.

[Comparison of magnetic resonance imaging artifacts of five common dental materials].

OBJECTIVE: To compare five materials commonly used in dentistry, including three types of metals and two types of ceramics, by using different sequences of three magnetic resonance imaging (MRI) field strengths (0.35, 1.5, and 3.0 T). METHODS: Three types of metals and two types of ceramics that were fabricated into the same size and thickness as an incisor crown were placed in a plastic tank filled with saline. The crowns were scanned using an magnetic resonance (MR) machine at 0.35, 1.5, and 3.0 T field strengths. The TlWI and T2WI images were obtained. The differences of various materials in different artifacts of field MR scans were determined. RESULTS: The zirconia crown presented no significant artifacts when scanned under the three types of MRI field strengths. The artifacts of casting ceramic were minimal. All dental precious metal alloys, nickel-chromium alloy dental porcelain, and cobalt-chromium ceramic alloy showed varying degrees of artifacts under the three MRI field strengths. CONCLUSION: Zirconia and casting ceramics present almost no or faint artifacts. By contrast, precious metal alloys, nickel-chromium alloy dental porcelain and cobalt-chromium ceramic alloy display MRI artifacts. The artifact area increase with increasing magnetic field.

ß-Lactoglobulin (BLG) binding to highly charged cationic polymer-grafted magnetic nanoparticles: effect of ionic strength.

Poly(2-(methacryloyloxy)ethyltrimethyl ammonium chloride) (PMATAC) modified magnetic nanoparticles (NPs) with a high zeta potential of ca. 50mV were synthesized by atom transfer radical polymerization (ATRP). The prepared NPs consist of a magnetic core around 13nm and a PMATAC shell around 20nm attached on the surface of magnetic nanoparticles. Thermodynamic binding parameters between ß-lactoglobulin and these polycationic NPs were investigated at different ionic strengths by high-resolution turbidimetry, dynamic light scattering (DLS), and isothermal titration calorimetry (ITC). Both turbidity and ITC show that binding affinities for BLG display a non-monotonic ionic strength dependence trend and a maximum appears at ionic strength of 50mM. Such observation should arise from the coeffects of protein charge anisotropy visualized by DelPhi electrostatic modeling and the strong electrostatic repulsion among highly charged NPs at a variety of ionic strengths.

Stable and efficient loading of silver nanoparticles in spherical polyelectrolyte brushes and the antibacterial effects.

A more efficient and convenient strategy was demonstrated to immobilize silver nanoparticles (NPs) with a crystalline structure into the spherical polyelectrolyte brushes (SPB) as an antibacterial material. The SPB used for surface coating (Ag immobilized PVK-PAA SPB) consists of a poly(N-vinylcarbazole) (PVK) core and poly(acrylic acid) (PAA) chain layers which are anchored onto the surface of PVK core at one end. Well-dispersed silver nanoparticles (diameter∼3.5 nm) then formed and were electrostatically confined in the brush layer. Ag content is controlled by a repeated loading process. Thin film coatings were then constructed by layer-by-layer depositions of positive charged poly(diallyldimethylammonium chloride) (PDDA) and SPB. The multilayer composites display excellent stability as well as antibacterial performance but not for simple PVK-PAA coated surface. The results show that almost complete bacteria growth including both dispersed bacterial cells and biofilms was inhibited over a period of 24 h. This approach opens a novel strategy for stable and efficient immobilization of Ag NPs in fabrication of antibacterial materials.