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Study of nucleation and growth dynamic events of cubic-phase ice crystals at TiO2–water nanointerface.

The synthesis of high entropy oxide (HEO) nanoparticles (NPs) possesses many challenges in terms of process complexity and cost, scalability, tailoring nanoparticle morphology, and rapid synthesis. Herein, we report the synthesis of novel single-phase solid solution (Mn, Fe, Ni, Cu, Zn)3(O)4 quinary HEO NPs produced by a flame spray pyrolysis route. The aberration-corrected scanning transmission electron microscopy (STEM) technique is utilized to investigate the spinel crystal structure of synthesized HEO NPs, and energy-dispersive X-ray spectroscopy analysis confirmed the high entropy configuration of five metal elements in their oxide form within a single HEO nanoparticle. Selected area electron diffraction, X-ray diffraction, and Raman spectroscopy analysis results are in accordance with STEM results, providing the key attributes of a spinel crystal structure of HEO NPs. X-ray photoelectron spectroscopy results provide the insightful understanding of chemical oxidation states of individual elements and their possible cation occupancy sites in the spinel-structured HEO NPs.

PURPOSE: Bioactive substrates can be used therapeutically to enhance wound healing. Here, we evaluated the effect of an in-situ thermoresponsive hydrogel from decellularized porcine cornea ECM, COMatrix (COrnea Matrix), for application as an ocular surface bandage for corneal epithelial defects. METHODS: COMatrix hydrogel was fabricated from decellularized porcine corneas. The effects of COMatrix hydrogel on attachment and proliferation of human corneal epithelial cells (HCECs) were evaluated in vitro. The effect of COMatrix on the expressions of the inflammatory genes, IL-1β, TNF-α, and IL-6 was assessed by RT-PCR. The in-situ application and also repairing effects of COMatrix hydrogel as an ocular bandage was studied in a murine model of corneal epithelial wound. The eyes were examined by optical coherence tomography (OCT) and slit-lamp microscopy in vivo and by histology and immunofluorescence post-mortem. RESULTS: In vitro, COMatrix hydrogel significantly enhanced the attachment and proliferation of HCECs relative to control. HCECs exposed to COMatrix had less induced expression of TNF-α (P

Over the past two decades, numerous studies have investigated and characterized the transient and amorphous phases in early stages of mineralization as well as their transition mechanisms to apatite crystals in buffered solutions. Recently more attention has been drawn to the identification and characterization of collagen structure and how it can affect mineralization in contact with non-collagenous protein and calcium phosphate clusters. This review highlights some of the pathways and mechanisms through which amorphous calcium phosphate clusters form. The conversion of these clusters into hydroxyapatite crystals is also reviewed. The thermodynamic aspects of nucleation and growth processes based on classical and non-classical nucleation theories related to hydroxyapatite are discussed. In addition, this paper is written to address the significant progress on mechanisms and pathways engaged in mineralization of collagen fibrils. Finally, it addresses some of the breakthroughs and limitations in the field of collagen biomineralization studies and new challenges in this field of study.

The use of magnetic nanoparticles in association with scaffolds is considered an important way to transform typical passive scaffolds into active scaffolds. Manganese can develop magnetic properties in hydroxyapatites, as can iron, copper, cobalt and samarium, but lacks the high toxicity of these latter compounds. Because the magnetic properties exhibited by transition metal-containing hydroxyapatite are entirely dependent on site occupation and on the formation of magnetic oxides under heating, it is extremely important to understand how manganese behaves when inserted into hydroxyapatite. In this paper, we demonstrated by using X-ray difference Fourier maps that the insertion of Mn into the hydroxyapatite structure induces several perturbations in its hexagonal channels, with a preference for occupying Ca(2) sites, particularly when the hydroxyapatite lattice is poorly ordered and has CO32− inserted at PO43− sites. When CO32− is released at high temperature and the structure is better ordered, Ca(1) sites become more susceptible to occupation by Mn atoms, while the occupation of PO43− sites by MnO43− is reduced. However, with increasing time and calcination temperature, Mn atoms tend to be released from the hydroxyapatite structure in the form of Mn3O4 nanoparticles through the hydroxyl channels, occupying Ca(2) sites in the final stage of the segregation pathway. These findings are fundamental to the development of new strategies to synthesize active hydroxyapatite-based scaffolds under remote control by a magnetic field.

Purpose Recently, two-dimensional (2D) nanomaterials are gaining tremendous attention as novel antibacterial platforms to combat against continuously evolving antimicrobial resistance levels. Among the family of 2D nanomaterials, black phosphorus (BP) nanosheets have demonstrated promising potential for biomedical applications. However, there is a need to gain nanoscale insights of the antibacterial activity of BP nanosheets which lies at the center of technical challenges. Methods Ultra-large BP nanosheets were synthesized by liquid-exfoliation method in the eco-friendly deoxygenated water. Synthesized BP nanosheets were characterized by TEM, AFM, and Raman spectroscopy techniques and their chemical stability was evaluated by EDS and EELS elemental analysis. The antibacterial activity of BP nanosheets was evaluated at nanoscale by the ultramicrotome TEM technique. Further, HAADF-STEM image and EDS elemental line map of the damaged bacterium were utilized to analyze the presence of diagnostic ions. Supportive SEM and ATR-FTIR studies were carried out to confirm the bacterial cell wall damage. In vitro colony counting method was utilized to evaluate the antibacterial performance of ultra-large BP nanosheets. Results Elemental EELS and EDS analysis of BP nanosheets stored in deoxygenated water confirmed the absence of oxygen peak. TEM studies indicate the various events of bacterial cell damage with the lost cellular metabolism and structural integrity. Colony counting test results show that as-synthesized BP nanosheets (100 μg/mL) can kill ~95% bacteria within 12 hours. Conclusion TEM studies demonstrate the various events of E. coli membrane damage and the loss of structural integrity. These events include the BP nanosheets interaction with the bacterial cell wall, cytoplasmic leakage, detachment of cytoplasm from the cell membrane, reduced density of lipid bilayer and agglomerated DNA structure. The EDS elemental line mapping of the damaged bacterium confirms the disrupted cell membrane permeability and the lost cellular metabolism. SEM micrographs and ATR-FTIR supportive results confirm the bacterial cell wall damage.

Ferritin biomineralization is essential to regulate the toxic Fe2+ iron ions in the human body. Unravelling the mechanism of biomineralization in ferritin facilitates our understanding of the cause...

The ions found in biological environment during biomineralization as well as the counterions present in syntheses, i.e., the reagents employed, play an important role in the precipitation and stabilization of apatites. In this work, precipitation of strontium-containing hydroxyapatites at different concentrations (0, 20, 40, 60, 80 and 100% Sr2+) was performed in the presence of two counterions typically present in biological environments: Na+ and Cl−. It was demonstrated that the presence of Na+/Cl− in the synthesis environment led to the precipitation of a biphasic hydroxyapatite (HAp) system formed by two non-miscible phases: Ca-rich HAp and Sr-rich HAp. The biphasic system was observed for intermediate Sr2+ concentrations (20, 40 and 60%) and exhibited greater lattice microstrain compared with the single-phase systems of Ca HAp (0%) and Sr HAp (100%). Although Na+/Cl− were inserted into both Ca- and Sr-rich HAp phases, Cl− ions were preferentially accommodated into the enlarged Sr-rich HAp structure. The presence of Cl− ions in the Sr-rich HAp phase decreased microstrain compared to the Ca-rich phase. After calcination, the biphasic system was transformed into a completely miscible Ca/Sr HAp phase without the formation of other phosphates or oxides.

Background Nanoscale surface roughness has been suggested to have antibacterial and antifouling properties. Several existing models have attempted to explain the antibacterial mechanism of nanoscale rough surfaces without direct observation. Here, conventional and liquid-cell TEM are implemented to observe nanoscale bacteria/surface roughness interaction. The visualization of such interactions enables the inference of possible antibacterial mechanisms. Methods and results Nanotextures are synthesized on biocompatible polymer microparticles (MPs) via plasma etching. Both conventional and liquid-phase transmission electron microscopy observations suggest that these MPs may cause cell lysis via bacterial binding to a single protrusion of the nanotexture. The bacterium/protrusion interaction locally compromises the cell wall, thus causing bacterial death. This study suggests that local mechanical damage and leakage of the cytosol kill the bacteria first, with subsequent degradation of the cell envelope. Conclusion Nanoscale surface roughness may act via a penetrative bactericidal mechanism. This insight suggests that future research may focus on optimizing bacterial binding to individual nanoscale projections in addition to stretching bacteria between nanopillars. Further, antibacterial nanotextures may find use in novel applications employing particles in addition to nanotextures on fibers or films.

Commercial poly methyl methacrylate (PMMA)-based cement is currently used in the field of orthopedics. However, it suffers from lack of bioactivity, mechanical weakness, and monomer toxicity. In this study, a PMMA-based cement nanocomposite reinforced with hydroxyapatite (HA) nanofibers and two-dimensional (2D) magnesium phosphate MgP nanosheets was synthesized and optimized in terms of mechanical property and cytocompatibility. The HA nanofibers and the MgP nanosheets were synthesized using a hydrothermal homogeneous precipitation method and tuning the crystallization of the sodium-magnesium-phosphate ternary system, respectively. Compressive strength and MTT assay tests were conducted to evaluate the mechanical property and the cytocompatibility of the PMMA-HA-MgP nanocomposites prepared at different ratios of HA and MgP. To optimize the developed nanocomposites, the standard response surface methodology (RSM) design known as the central composite design (CCD) was employed. Two regression models generated by CCD were analyzed and compared with the experimental results, and good agreement was observed. Statistical analysis revealed the significance of both factors, namely, the HA nanofibers and the MgP nanosheets, in improving the compressive strength and cell viability of the PMMA-MgP-HA nanocomposite. Finally, it was demonstrated that the HA nanofibers of 7.5% wt and the MgP nanosheets of 6.12% wt result in the PMMA-HA-MgP nanocomposite with the optimum compressive strength and cell viability.

When dental implants become infected, the progression of the disease is rapid. Commercially available dental implant surfaces can be easily contaminated, resulting in rapid progression of peri-mucositis and peri-implantitis. The aim of this study was to evaluate, in vitro, the pattern of doxycycline release from by dental implants with titanium nanotube surface (DINS) at different pHs to examine novel drug loading and chemical coating techniques. Nine DINS were loaded with doxycycline and subsequently coated with polylactic-co-glycolic acid (PLGA). High-performance liquid chromatography (HPLC) was used to measure the amounts of released doxycycline in a 30-day period. Cytotoxicity of the DINS was evaluated by an assay using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT). The results showed that the experimental DINS coated with doxycycline and PLGA showed a mean drug release during the experimental period for the groups: pH 7.4 (8.39 μg/mL), pH 6.4 (8.63 μg/mL). The pH 5.4 (15.18 μl/mL) doxycycline release from DINS was faster at pH 5.4 than those at pHs 6.4 and 7.4 (P = .0031 and .0034, respectively). This new surface treatment of dental implants with titanium nanotubes and subsequent drug loading demonstrated biocompatibility and sustained doxycycline release over a 30-day period. Additional studies are needed in order to adopt a stable drug release at neutral pH environment while warranting a constant drug release in an acidic pH environment.

Water is ubiquitous in natural systems, ranging from the vast oceans to the nanocapillaries in the earth crust or cellular organelles. In bulk or in intimate contact with solid surfaces, water molecules arrange themselves according to their hydrogen (H) bonding, which critically affects their short- and long-range molecular structures. Formation of H-bonds among water molecules designates the energy levels of certain nonbonding molecular orbitals of water, which are quantifiable by spectroscopic techniques. While the molecular architecture of water in nanoenclosures is of particular interest to both science and industry, it requires fine spectroscopic probes with nanometer spatial resolution and sub-eV energy sensitivity. Graphene liquid cells (GLCs), which feature opposing closely spaced sheets of hydrophobic graphene, facilitate high-resolution transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) measurements of attoliter water volumes encapsulated tightly in the GLC nanovessels. We perform in situ TEM and EELS analysis of water encased in thin GLCs exposed to room and cryogenic temperatures to examine the nanoscale arrangement of the contained water molecules. Simultaneous quantification of GLC thickness leads to the conclusion that H-bonding strengthens under increased water confinement. The present results demonstrate the feasibility of nanoscale chemical characterization of aqueous fluids trapped in GLC nanovessels and offer insights on water molecule arrangement under high-confinement conditions.

Glucose biosensors play an important role in the diagnosis and continued monitoring of the disease, diabetes mellitus. This report proposes the development of a novel enzymatic electrochemical glucose biosensor based on TiO$_2$ nanotubes modified by AgO and Prussian blue (PB) nanoparticles (NPs), which has an additional advantage of possessing antimicrobial properties for implantable biosensor applications. In this study, we developed two high performance glucose biosensors based on the immobilization of glucose oxidase (GOx) onto Prussian blue (PB) modified TiO$_2$ nanotube arrays functionalized by Au and AgO NPs. AgO-deposited TiO$_2$ nanotubes were synthesized through an electrochemical anodization process followed by Ag electroplating process in the same electrolyte. Deposition of PB particles was performed from an acidic ferricyanide solution. The surface morphology and elemental composition of the two fabricated biosensors were investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) which indicate the successful deposition of Au and AgO nanoparticles as well as PB nanocrystals. Cyclic voltammetry and chronoamperometry were used to investigate the performance of the modified electrochemical biosensors. The results show that the developed electrochemical biosensors display excellent properties in terms of electron transmission, low detection limit as well as high stability for the determination of glucose. Under the optimized conditions, the amperometric response shows a linear dependence on the glucose concentration to a detection limit down to 4.91 $\mu$M with sensitivity of 185.1 mA M$^{-1}$ cm$^{-2]$ in Au modified biosensor and detection limit of 58.7 $\mu$M with 29.1 mA M$^{-1}$ cm$^{-2]$ sensitivity in AgO modified biosensor.

Occlusive thrombosis is a central pathological event in heart attack, stroke, thromboembolism, etc. Therefore, pharmacological thrombolysis or anticoagulation is used for treating these diseases. However, systemic administration of such drugs causes hemorrhagic side-effects. Therefore, there is significant clinical interest in strategies for enhanced drug delivery to clots while minimizing systemic effects. One such strategy is by using drug-carrying nanoparticles surface-decorated with clot-binding ligands. Efforts in this area have focused on binding to singular targets in clots, e.g. platelets, fibrin, collagen, vWF or endothelium. Targeting vWF, collagen or endothelium maybe sub-optimal since in vivo these entities will be rapidly covered by platelets and leukocytes, and thus inaccessible for sufficient nanoparticle binding. In contrast, activated platelets and fibrin are majorly accessible for particle-binding, but their relative distribution in clots is highly heterogeneous. We hypothesized that combination-targeting of 'platelets + fibrin' will render higher clot-binding efficacy of nanoparticles, compared to targeting platelets or fibrin singularly. To test this, we utilized liposomes as model nanoparticles, decorated their surface with platelet-binding peptides (PBP) or fibrin-binding peptides (FBP) or combination (PBP + FBP) at controlled compositions, and evaluated their binding to human blood clots in vitro and in a mouse thrombosis model in vivo. In parallel, we developed a computational model of nanoparticle binding to single versus combination entities in clots. Our studies indicate that combination targeting of 'platelets + fibrin' enhances the clot-anchorage efficacy of nanoparticles while utilizing lower ligand densities, compared to targeting platelets or fibrin only. These findings provide important insights for vascular nanomedicine design.

This chapter is an introduction to nanocomposite materials and its classifications with emphasis on orthopedic application. It covers different types of matrix nanocomposites including ceramics, metal, polymer and natural-based nanocomposites with the main features and applications in the orthopedic. In addition, it presents structure, composition, and biomechanical features of bone as a natural nanocomposite. Finally, it deliberately presents developing methods for nanocomposites bone grafting.

Emre Firlar,1,2 Meagan Ouy,1 Leigha Covnot,1 Yuan Xing,3 Daniel Lee,1,4 Alessandro Chan,1,4 Yi He,3 Boao Song,2 Solomon Afelik,4 Yong Wang,3 Reza Shahbazian-Yassar,2 Jose Oberholzer,1,3 Tolou Shokuhfar1 1Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA; 2University of Illinois at Chicago, Department of Mechanical and Industrial Engineering, Chicago, IL, USA; 3University of Virginia, Department of Surgery, Charlottesville, VA, USA; 4University of Illinois at Chicago, Department of Surgery, Chicago, IL, USA Background: Islet cell transplantation is one of the key treatments for type 1 diabetes. Understanding the mechanisms of insulin fusion and exocytosis are of utmost importance for the improvement of the current islet cell transplantation and treatment of diabetes. These phenomena have not been fully evaluated due either to the lack of proper dynamic imaging, or the lack of proper cell preservation during imaging at nanoscales. Methods: By maintaining the native environment of pancreatic β-cells between two graphene monolayer sheets, we were able to monitor the subcellular events using in situ graphene liquid cell (GLC)-transmission electron microscopy (TEM) with both high temporal and high spatial resolution. Results: For the first time, the nucleation and growth of insulin particles until the later stages of fusion were imaged at nanometer scales. The release of insulin from plasma membrane involves the degradation of plasma membrane and drastic reductions in the shorter axis of the insulin particles. Sequential exocytosis results indicated the nucleation, growth and attachment of the new insulin particles to the already anchored ones, which is thermodynamically favorable due to the reduction in total surface, further reducing the Gibbs free energy. The retraction of the already anchored insulin toward the cell is also monitored for the first time live at nanoscale resolution. Conclusion: Investigation of insulin granule dynamics in β-cells can be investigated via GLC-TEM. Our findings with this technology open new realms for the development of novel drugs on pathological pancreatic β-cells, because this approach facilitates observing the effects of the stimuli on the live cells and insulin granules. Keywords: transmission electron microscopy, graphene liquid cell, insulin secretion, exocytosis

Modifications of Ti–6Al–4V surface roughness, wettability and composition are increasingly studied to improve cellular viability on biomedical implants involving Ti–6Al–4V. In this study, it is shown that modification of Ti–6Al–4V samples using anodization (for the formation of titania nanotubes) combined with thermal oxidation (TO) results in superior surface characteristics to those of a smooth, rough, anodized-smooth or anodized-rough surface alone. Surface characterization is performed using water contact angle (WCA) measurements, white-light interferometry, Fourier transform infrared spectroscopy (FTIRS), field emission scanning electron microscopy and grazing incidence X-ray diffraction (GIXRD). WCA measurements before TO indicate that anodized-smooth and anodized-rough samples are super-hydrophilic (WCA less than 5°); WCA of non-anodized smooth and rough surfaces are 57 ± 6° and 86 ± 7°, respectively. After TO at 450 °C for 3 hours, all samples become super-hydrophilic; however, three weeks after TO, smooth and rough surfaces become hydrophobic, while anodized-smooth and anodized-rough surfaces remain hydrophilic. FTIRS and GIXRD data show that the TO of anodized and non-anodized smooth samples results in anatase and rutile TiO2, of which anatase is favorable for cellular attachment. Micro-/nano-scale roughness and TO are discussed in the context of enhanced Ti–6Al–4V surface characteristics for improved cellular response.

Corneal injuries are a major cause of blindness worldwide. To restore corneal integrity and clarity, there is a need for regenerative bio-integrating materials for in-situ repair and replacement of corneal tissue. Here, we introduce Light-curable COrnea Matrix (LC-COMatrix), a tunable material derived from decellularized porcine cornea extracellular matrix containing un-denatured collagen and sulfated glycosaminoglycans. It is a functionalized hydrogel with proper swelling behavior, biodegradation, and viscosity that can be cross-linked in situ with visible light, providing significantly enhanced biomechanical strength, stability, and adhesiveness. Cross-linked LC-COMatrix strongly adheres to human corneas ex vivo and effectively closes full-thickness corneal perforations with tissue loss. Likewise, in vivo, LC-COMatrix seals large corneal perforations, replaces partial-corneal stromal defects and bio-integrates into the tissue in rabbit models. LC-COMatrix is a natural ready-to-apply bio-integrating adhesive that is representative of native corneal matrix with potential applications in corneal and ocular surgeries.

One of the biggest bottlenecks for structural analysis of proteins remains the creation of high-yield and high-purity samples of the target protein. Cell-free protein synthesis technologies are powerful and customizable platforms for obtaining functional proteins of interest in short timeframes, while avoiding potential toxicity issues and permitting high-throughput screening. These methods have benefited many areas of genomic and proteomics research, therapeutics, vaccine development and protein chip constructions. In this work, we demonstrate a versatile and multiscale eukaryotic wheat germ cell-free protein expression pipeline to generate functional proteins of different sizes from multiple host organism and DNA source origins. We also report on a robust purification procedure, which can produce highly pure (> 98%) proteins with no specialized equipment required and minimal time invested. This pipeline successfully produced and analyzed proteins in all three major geometry formats used for structural biology including single particle analysis with electron microscopy, and both two-dimensional and three-dimensional protein crystallography. The flexibility of the wheat germ system in combination with the multiscale pipeline described here provides a new workflow for rapid production and purification of samples that may not be amenable to other recombinant approaches for structural characterization. Electronic supplementary material The online version of this article (10.1186/s40679-018-0062-9) contains supplementary material, which is available to authorized users.

In the modern construction industry, large gypsum (CaSO4·2H2O) boards are manufactured through a two-step procedure, which features the heating of fine gypsum powders to form the intermediate plast...

In search for bone and dentin extracellular matrix (ECM) proteins, transforming growth factor beta receptor II interacting protein 1 (TRIP-1) was identified as a novel protein synthesized by osteoblasts and odontoblasts and exported to the ECM. TRIP-1 is a WD-40 (WD is Tryptophan-Aspartic acid dipeptide) protein that has been well recognized for its physiological role in the endoplasmic reticulum (ER). In the ER, TRIP-1 functions as an essential subunit of eukaryotic elongation initiation factor 3 and is involved in the protein translational machinery. Recently, we reported that TRIP-1 is localized in the ECM of bone and dentin. In this study, we demonstrate that varying concentrations of TRIP-1 can participate in the nucleation of calcium phosphate polymorphs. Nucleation studies performed with high calcium and phosphate concentration demonstrated that recombinant TRIP-1 could orchestrate the formation of hydroxyapatite crystals. Nucleation experiments performed on demineralized and deproteinized dentin wafer under physiological conditions and subsequent transmission electron microscope analysis of the deposits at the end of 7 and 14 days showed that TRIP-1 promoted the deposition of calcium phosphate mineral aggregates in the gap-overlap region of type I collagen. Taken together, we provide mechanistic insight into the role of this intracellular protein in matrix mineralization.

The area of cellular interactions of nanomaterials is an important research interest. The sensitivity of cells toward their extracellular matrix allows researchers to create microenvironments for guided stem cell differentiation. Among nanomaterials, graphene, often called the “wonder material,” and its derivatives are at the forefront of such endeavors. Graphene’s carbon backbone, paired with its biocompatibility and ease of functionalization, has been used as an enhanced method of controlled cell proliferation. Graphene’s honeycomb nature allows for compatibility with polymers and biological material for the creation of nanocomposite scaffolds that help differentiation into cell types that have otherwise been proven difficult. Such materials and their role in guiding cell growth can aid the construction of tissue grafts where shortages and patient compatibility create a low success rate. This review will bring together novel studies and techniques used to understand and optimizes graphene’s role in cell growth mechanisms.

Zirconia atomic layer deposition (ALD) using zirconium 2-methyl 2-butoxide (ZMB) and ethanol is reported for the first time. The process selectively deposits a uniform ZrO2 film on silicon with a high deposition rate (∼2 A/cycle), without any deposition on copper at a relatively low temperature (200 °C) and up to at least 200 cycles. This is the largest thickness of inherently surface selective ZrO2 ALD ever reported (∼400 A) and is at least 10 times more selective than that achieved using a similar deposition process but with a different precursor, tris(dimethylamino)cyclopentadienyl Zirconium (ZyALD™). The selectively deposited ZrO2 films were characterized using spectral ellipsometry, X-ray photoelectron spectroscopy, extended X-ray absorption fine structure spectroscopy (EXAFS), atomic force microscopy and energy dispersive spectroscopy obtained during scanning electron microscopy and scanning transmission electron microscopy. Surface characterization techniques employed here confirmed the chemical nature and topography of the deposited ZrO2, whereas EXAFS showed the ZrO2 to be amorphous on silicon having local bonding structure similar to that of ZrO2 deposited with ZyALD™ precursor.

The synthesis of silver-doped hydroxyapatite (Ag-HA) nanobelts as a HA-based antibacterial bioactive material is of great importance due to their being a potential candidate to curb the infections associated with HA implants along with their advantage as a reinforcement in biomaterials. Here, a facile one-step method for synthesizing Ag-doped hydroxyapatite (AgxHA) [Ca10−xAgx(PO4)6(OH)2] (x = 0, 0.2, 0.5) nanobelts using hydrothermal homogeneous precipitation is demonstrated. The samples were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Their antibacterial properties against Escherichia coli (E. coli) bacteria and cytotoxicity to Swiss embryonic mouse fibroblast (3T3-J2) cells were evaluated with the help of the disc diffusion method and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cell viability assay, respectively. Our study indicates that the increased optimum Ag amount in the HA nanobelt has enhanced its antibacterial properties and bioactivity. The flexibility behavior of an individual multi-layered Ag0.2HA nanobelt was observed by in situ TEM. The novel TEM cyclic compression–bending test results indicate that the Ag0.2HA nanobelt can retain its original shape after eight continuous deformation cycles at an extreme angle, revealing its high flexibility. This study provides new insights into the design of bioactive HA nanobelts with antibacterial properties and opens new opportunities for their load-bearing applications.

Highly flexible multi-layered hydroxyapatite (HA) nanobelts were successfully grown and compared to nanorods. The nanomechanical behaviour of individual HA nanostructures was visualized using in situ TEM. Compression-induced deformation in HA nanobelts can spontaneously recover at a maximal strain of 99.2%, much larger than the 2.63% failure strain observed for traditional HA nanorods.

Hydroxyapatite (HA) exhibits excellent biocompatibility, bioactivity, osteoconductivity, non-toxicity and so on, making it a perfect candidate for biomedical applications. However, HA is not qualified to be used in load-bearing sites due to its poor flexural strength and fracture toughness. Design, synthesis and application of fibrous HA is a promising strategy to overcome the inherent brittleness. This review provides a brief description of HA and hydroxyapatite fiber (HAF), then introduces different synthesis methods of HAF and highlights the inherent merits and drawbacks involved in each method. Finally, the future perspectives in this active research area are given. The purpose of this review is to acquaint the reader with this promising new field of biomaterials research and with emphasis on recent techniques to obtain continuous, uniform and long HAF.

Stem cells are recognized by their self-renewal ability and can give rise to specialized progeny. Hydrogels are an established class of biomaterials with the ability to control stem cell fate via mechanotransduction. They can mimic various physiological conditions to influence the fate of stem cells and are an ideal platform to support stem cell regulation. This review article provides a summary of recent advances in the application of different classes of hydrogels based on their source (e.g., natural, synthetic, or hybrid). This classification is important because the chemistry of substrate affects stem cell differentiation and proliferation. Natural and synthetic hydrogels have been widely used in stem cell regulation. Nevertheless, they have limitations that necessitate a new class of material. Hybrid hydrogels obtained by manipulation of the natural and synthetic ones can potentially overcome these limitations and shape the future of research in application of hydrogels in stem cell regulation.