Biomineralization of stable and monodisperse vaterite microspheres using silk nanoparticles

A neurovascular unit-on-a-chip: culture and differentiation of human neural stem cells in a three-dimensional microfluidic environment

Biological studies typically rely on a simple monolayer cell culture, which does not reflect the complex functional characteristics of human tissues and organs, or their real response to external stimuli. Microfluidic technology has advantages of high-throughput screening, accurate control of the fluid velocity, low cell consumption, long-term culture, and high integration. By combining the multipotential differentiation of neural stem cells with high throughput and the integrated characteristics of microfluidic technology, an in vitro model of a functionalized neurovascular unit was established using human neural stem cell-derived neurons, astrocytes, oligodendrocytes, and a functional microvascular barrier. The model comprises a multi-layer vertical neural module and vascular module, both of which were connected with a syringe pump. This provides controllable conditions for cell inoculation and nutrient supply, and simultaneously simulates the process of ischemic/hypoxic injury and the process of inflammatory factors in the circulatory system passing through the blood-brain barrier and then acting on the nerve tissue in the brain. The in vitro functionalized neurovascular unit model will be conducive to central nervous system disease research, drug screening, and new drug development.

Conversion of soybean oil extraction wastes into high-performance wood adhesives based on mussel-inspired cation-π interactions

As a soybean oil extractive byproduct, high temperature defatted soy meal (HSM) presents great potential as a raw material for vegetable protein adhesives to replace aldehyde-based adhesives in the wood-based panel production. However, the application has been hindered by its poor cold-pressing adhesive performance. Herein, a novel HSM-based adhesive with excellent cold-pressing adhesion performance was developed based on mussel-inspired cation-π interactions. Highly reactive polyamidoamine-epichlorohydrin (PAE) and folic acid (FA) were added into an HSM-based adhesive to construct a dual-network system stabilized by strong cation-π interactions. The coacervate formed by PAE and FA served as an "internal adhesive" to bond HSM particles together, yielding high initial viscosity but easy sizing. As expected, the prepared adhesive exhibited an excellent cold-pressing bonding strength of 423 kPa, showing a 295% improvement compared to the soy protein (SP) adhesive. To improve the hot-pressing bonding strength of the adhesives, inorganic calcium carbonate (CaCO₃) particles were introduced into the adhesive system to build an organic-inorganic hybrid adhesive system. The wet shear strength of the SPAE-FA-CaCO₃ adhesive significantly improved from 0.63 MPa to 0.96 MPa, meeting the requirements for the practical application. This method provides a novel strategy to exploit high-performance vegetable protein-based wood adhesives.

Self-healing and easy-to-shape mineralized hydrogels for iontronics

Hydrogel-based multifunctional materials have attracted much attention. In this work, novel mineralized hydrogels were fabricated through physically cross-linked polyvinylpyrrolidone (PVP) and CaCO3. The mineralized hydrogels were prepared by simply mixing CaCl2, Na2CO3, and PVP in aqueous solutions. The CO32- induced the aggregation of the PVP chains and the CaCO3 particles in situ generated in the aqueous solution worked as fillers to strengthen the hydrogels. Based on this method, other kinds of mineralized hydrogels were prepared by replacing the Ca2+ with different metal ions. The mineralized hydrogels displayed shapeable, self-healing and thixotropic properties. Moreover, the mineralized hydrogel-based sensor showed good and stable sensitivity to compressive pressure, and could be used to monitor human actions. This work presents a facile method for preparing mineralized hydrogels, which are promising for various applications due to their outstanding properties.

Synthesis and characterization of porous CaCO3 microspheres templated by yeast cells and the application as pH value-sensitive anticancer drug carrier

Using yeast as organic template and PDDA/PSS with opposite charge as polyelectrolyte, CaCO₃ was deposited on yeast cells by Layer-by-Layer self-assembly method, and then porous calcium carbonate hybrid microspheres (CaCO₃-HMPs) were prepared by calcination. The CaCO₃-HMPs were characterized by FT-IR, XRD, SEM and TG. It was found that the prepared CaCO₃-HMPs were nearly spherical, with visible pores on the surface, small particle size uniformity (d = 3 μ m) and good dispersion. Doxorubicin hydrochloride (DOX) was used as the model drug to study drug loading and release properties of CaCO₃-HMPs. Then, the drug loading, DOX release under different pH conditions, and the degradation of CaCO₃-HMPs under different pH conditions were investigated. The drug release test results showed that the DOX-loaded microspheres released more drugs (99 %) at pH = 4.8 than pH = 7. It indicated that the CaCO₃-HMPs were pH sensitive. The cytotoxicity of DOX-loaded microspheres was also studied. It was found that CaCO₃-HMPs had good biocompatibility. In addition, compared with DOX group, cytotoxicity test results showed that the DOX-loaded microspheres had the same efficacy but sustained drug release for up to 120 h. Therefore, the CaCO₃-HMP microspheres have good application prospects as anticancer drug carriers.

Engineered bioactive nanoparticles incorporated biofunctionalized ECM/silk proteins based cardiac patches combined with MSCs for the repair of myocardial infarction: In vitro and in vivo evaluations

The development of cardiac patches by the combination of bioactive nano- and bio-materials with mesenchymal stem cells signifies an auspicious approach for the treatment of cardiac repair in myocardial infarction. In the present investigation, we study about the cardiac function of morphology improved gold nanoparticles combined with extracellular matrix/silk proteins for the cell proliferation and expansion of cardiomyocytes. The physico-chemical and morphological characteristics demonstrated that spherical and homogeneous Au particles are distributed on the matrix porous surface for providing favorable conductivity and biological influences in cardiac repair. The in vitro cell studies of prepared patches have established enhanced cell compatibility and retention of cardiomyocytes survival. The in vivo determinations imply that Au-ESF group decreases infarct size to 65% from 89% in control group. These developed cardiac patches can be highly suitable in the cardiac regeneration and offer new platform in cardiac tissue engineering.

Injectable Silk-Vaterite Composite Hydrogels with Tunable Sustained Drug Release Capacity

Improving the efficiency of chemotherapy remains a key challenge in drug delivery. Many drug carriers have been designed to achieve multifunctional factors as part of their performance, including controlled release, dispersibility in aqueous environments, and targeting to cancer sites. However, it is difficult to optimize multiple properties simultaneously for a single carrier system. Here, synergistic carriers composed of vaterite microspheres and silk nanofiber hydrogels were developed to improve the dispersibility of vaterite spheres and the control of drug delivery without compromising the injectability or sensitivity to pH. The vaterite microspheres were dispersed homogeneously and remained stable in the silk nanofiber hydrogels. Doxorubicin (DOX) was effectively loaded on the vaterite spheres and silk nanofibers, forming synergistic silk-vaterite hydrogel delivery systems. The sustained delivery of DOX was tuned and controlled by vaterite stability and the DOX content loaded on the spheres and nanofibers. The cytotoxicity was regulated via the controlled delivery of DOX, suggesting the possibility of optimizing chemotherapeutic strategies. These silk-vaterite delivery hydrogels suggest a useful strategy for designing novel delivery systems for improved delivery and therapeutic benefits.

ECM-Mimetic Multiresponsive Nanobullets Targeted Against Metastasizing Circulating Tumor Clusters in Breast Cancer

Targeting smaller populations of circulating tumor clusters (CTC) with tumor-initiating and colonization potentials at distant sites in circulation remains a challenge as clusters possess both epithelial and mesenchymal characteristics. Bullet shaped ellipsoidal nanostructures of size 600 ± 11.3 nm (major axis) and 281.9 ± 5.3 nm (minor axis) with 2.2 aspect ratio were self-assembled using inorganic and organic GRAS biomaterials to preferentially target tumor-causing CTCs. Negatively-charged chondroitin sulfate in presence of gelatin guides unidirectional growth of calcium carbonate mesocrystals to form nanobullets, mediates CD44 targeting of CTCs. Switchable multi-responsive drug release profiles (temperature and pH) were recorded for nanobullets promoting spontaneous and efficient cell-killing. CD44 and E-cadherin overexpressing 'seeding' cell clusters of 170 ± 22 µm were developed as in vitro CTC model. pH responsive release of Dox into lysosome stimulates calcium influx resulting in cell death. CD44-blocked CTCs showed significantly reduced internalization when compared to CD44-expressing CTCs thereby confirming CD44 specific internalization of nanobullets. Significantly retarded expansion of clusters when shifted to cell adhesive surfaces depicts the potential of nanobullets against colonization of CTCs. Hence, newer insights on developed anisotropic ECM-mimetic nanohybrids would enhance targeted capture of tumor-initiating clusters in systemic circulation that would potentially reduce the progression of tumor in breast cancer patients.

Hydroxyapatite Formation on Self-Assembling Peptides with Differing Secondary Structures and Their Selective Adsorption for Proteins

Self-assembling peptides have been employed as biotemplates for biomineralization, as the morphologies and sizes of the inorganic materials can be easily controlled. We synthesized two types of highly ordered self-assembling peptides with different secondary structures and investigated the effects of secondary structures on hydroxyapatite (HAp) biomineralization of peptide templates. All as-synthesized HAp-peptides have a selective protein adsorption capacity for basic protein (e.g., cytochrome c and lysozyme). Moreover, the selectivity was improved as peptide amounts increased. In particular, peptide-HAp templated on β-sheet peptides adsorbed more cytochrome c than peptide-HAp with α-helix structures, due to the greater than 2-times carboxyl group density at their surfaces. It can be expected that self-assembled peptide-templated HAp may be used as carriers for protein immobilization in biosensing and bioseparation applications and as enzyme-stabilizing agents.

Design, Fabrication, and Function of Silk-Based Nanomaterials

Animal silks are built from pure protein components and their mechanical performance, such as strength and toughness, often exceed most engineered materials. The secret to this success is their unique nanoarchitectures that are formed through the hierarchical self-assembly of silk proteins. This natural material fabrication process in sharp contrast to the production of artificial silk materials, which usually are directly constructed as bulk structures from silk fibroin (SF) molecular. In recent years, with the aim of understanding and building better silk materials, a variety of fabrication strategies have been designed to control nanostructures of silks or to create functional materials from silk nanoscale building blocks. These emerging fabrication strategies offer an opportunity to tailor the structure of SF at the nanoscale and provide a promising route to produce structurally and functionally optimized silk nanomaterials. Here, we review the critical roles of silk nanoarchitectures on property and function of natural silk fibers, outline the strategies of utilization of these silk nanobuilding blocks, and we provide a critical summary of state of the art in the field to create silk nanoarchitectures and to generate silk-based nanocomponents. Further, such insights suggest templates to consider for other materials systems.

Enhanced activity and stability of papain by covalent immobilization on porous magnetic nanoparticles

Papain enzyme was successfully immobilized by covalent bonding onto biocompatible Fe₃O₄/SF nanoparticles, which were prepared with the soft template of silk fibroin (SF). The optimized immobilization condition is pH6.0, hydrolysis time of 60min, and an enzyme/support ratio of 10.0mg/g. Compared with free papain, the immobilized papain exhibits a high effective activity, broader working pH and temperature. This immobilized papain can be separated from the solution by the external magnetic field for cyclic utilization, and 70% of initial activity was retained after eight consecutive operations while completely loss of proteolytic activity for the free papain. Furthermore, the immobilized papain maintained 85% of their initial activity after being stored for 28days. Kinetic parameters, maximum reaction rate (V_max) and Michaelis constant (K_m) of immobilized papain, were determined as 4.95mg/l·min and 0.23mg/ml, larger than its free counterpart. All the results above indicated that the immobilized papain onto magnetic Fe₃O₄/SF nanoparticles would have potential industrial and medical applications.

Biomineralization of varied calcium carbonate crystals by the synergistic effect of silk fibroin/magnesium ions in a microbial system

The influence of silk fibroin (SF) and magnesium ions (Mg²⁺) on calcium carbonate (CaCO₃) bio-mineralization has been investigated.

Calcium-based biomaterials for diagnosis, treatment, and theranostics

Calcium-based biomaterials with good biosafety and bio-absorbability are promising for biomedical applications such as diagnosis, treatment, and theranostics.

Single Enzyme Direct Biomineralization of CdSe and CdSe-CdS Core-Shell Quantum Dots

Biomineralization is the process by which biological systems synthesize inorganic materials. Herein, we demonstrate an engineered cystathionine γ-lyase enzyme, smCSE that is active for the direct aqueous phase biomineralization of CdSe and CdSe-CdS core-shell nanocrystals. The nanocrystals are formed in an otherwise unreactive buffered solution of Cd acetate and selenocystine through enzymatic turnover of the selenocystine to form a reactive precursor, likely H₂Se. The particle size of the CdSe core nanocrystals can be tuned by varying the incubation time to generated particle sizes between 2.74 ± 0.63 nm and 4.78 ± 1.16 nm formed after 20 min and 24 h of incubation, respectively. Subsequent purification and introduction of l-cysteine as a sulfur source facilitates the biomineralization of a CdS shell onto the CdSe cores. The quantum yield of the resulting CdSe-CdS core-shell particles is up to 12% in the aqueous phase; comparable to that reported for more traditional chemical synthesis routes for core-shell particles of similar size with similar shell coverage. This single-enzyme route to functional nanocrystals synthesis reveals the powerful potential of biomineralization processes.

Nano-antacids enhance pH neutralization beyond their bulk counterparts: synthesis and characterization

Antacids are crucial in the treatment of gastro-esophageal reflux disease and peptic ulcers. Antacids based on the calcite phase of bulk calcium carbonate have been the standard for over fifty years. More recent research has shown that nanomaterial forms of such bulk materials often have improved properties. However, the metastable vaterite form of calcium carbonate is particularly difficult to synthesize as a nanomaterial, and thus has not been extensively studied. Here, we describe the synthesis of these particles and investigate them for antacid applications. Experimental and computational approaches show that nanoscale vaterite particles maintain neutral gastric pH values three times longer than commercial antacids.

Carbonate Mineral Formation under the Influence of Limestone-Colonizing Actinobacteria: Morphology and Polymorphism

Microorganisms and their biomineralization processes are widespread in almost every environment on earth. In this work, Streptomyces luteogriseus DHS C014, a dominant lithophilous actinobacteria isolated from microbial mats on limestone rocks, was used to investigate its potential biomineralization to allow a better understanding of bacterial contributions to carbonate mineralization in nature. The ammonium carbonate free-drift method was used with mycelium pellets, culture supernatant, and spent culture of the strain. Mineralogical analyses showed that hexagonal prism calcite was only observed in the sub-surfaces of the mycelium pellets, which is a novel morphology mediated by microbes. Hemispheroidal vaterite appeared in the presence of spent culture, mainly because of the effects of soluble microbial products (SMP) during mineralization. When using the culture supernatant, doughnut-like vaterite was favored by actinobacterial mycelia, which has not yet been captured in previous studies. Our analyses suggested that the effects of mycelium pellets as a molecular template almost gained an advantage over SMP both in crystal nucleation and growth, having nothing to do with biological activity. It is thereby convinced that lithophilous actinobacteria, S. luteogriseus DHS C014, owing to its advantageous genetic metabolism and filamentous structure, showed good biomineralization abilities, maybe it would have geoactive potential for biogenic carbonate in local microenvironments.

Organic Nanomaterials and Their Applications in the Treatment of Oral Diseases

There is a growing interest in the development of organic nanomaterials for biomedical applications. An increasing number of studies focus on the uses of nanomaterials with organic structure for regeneration of bone, cartilage, skin or dental tissues. Solid evidence has been found for several advantages of using natural or synthetic organic nanostructures in a wide variety of dental fields, from implantology, endodontics, and periodontics, to regenerative dentistry and wound healing. Most of the research is concentrated on nanoforms of chitosan, silk fibroin, synthetic polymers or their combinations, but new nanocomposites are constantly being developed. The present work reviews in detail current research on organic nanoparticles and their potential applications in the dental field.

Preparation of silk fibroin carriers for controlled release

Silk fibroin provides a new option for controlled release systems as a result of its excellent biodegradability, biocompatibility, and mechanical properties. As the core material, silk fibroin can be designed and widely used in drug/gene delivery, regenerative medicine, and other biomedical fields. This review focuses on the preparation methods, loading molecules, and applications of silk fibroin-based controlled release systems including microspheres, microcapsules, films, microparticles, microneedles, liposomes, and hydrogels. These systems provide numerous advantages such as high encapsulation efficiency, avoiding loss of bioactivity and maintaining desirable range without peaks and valleys in comparison to the traditional administration approaches. Microsc. Res. Tech. 80:312-320, 2017. © 2015 Wiley Periodicals, Inc.

Design of Silk-Vaterite Microsphere Systems as Drug Carriers with pH-responsive Release Behavior

Improving the therapeutic efficacy of chemotherapy remains a key goal for cancer therapy. Various passive and active targeting strategies have been developed to facilitate drug release targeted to cancer lesions, but actively designing tunable drug release behavior for these needs remains a challenge. As a step towards this need, silk-vaterite microspheres were fabricated and utilized as carriers to tune drug release. Doxorubicin (DOX) was loaded on the microspheres with high efficiency and the release behavior was regulated by tuning the microspheres via thermal processing. In vitro cell inhibition results showed that the drug-loaded microspheres had different cytotoxic efficiencies depending on the DOX release rates. Better efficacy at lower drug doses suggests options to optimize anticancer effects while minimizing toxic side effects. The tunable drug release capacity combined with the inherent passive targeting property of vaterite-based carriers based on pH sensitivity suggests a promising system for enhanced efficacy of chemotherapy.