A feasible approach toward bioactive glass nanofibers with tunable protein release kinetics for bone scaffolds

Electrospinning of in situ synthesized silica-based and calcium phosphate bioceramics for applications in bone tissue engineering: A review

The field of bone tissue engineering (BTE) focuses on the repair of bone defects that are too large to be restored by the natural healing process. To that purpose, synthetic materials mimicking the natural bone extracellular matrix (ECM) are widely studied and many combinations of compositions and architectures are possible. In particular, the electrospinning process can reproduce the fibrillar structure of bone ECM by stretching a viscoelastic solution under an electrical field. With this method, nano/micrometer-sized fibres can be produced, with an adjustable chemical composition. Therefore, by shaping bioactive ceramics such as silica, bioactive glasses and calcium phosphates through electrospinning, promising properties for their use in BTE can be obtained. This review focuses on the in situ synthesis and simultaneous electrospinning of bioceramic-based fibres while the reasons for using each material are correlated with its bioactivity. Theoretical and practical considerations for the synthesis and electrospinning of these materials are developed. Finally, investigations into the in vitro and in vivo bioactivity of different systems using such inorganic fibres are exposed.

Enhanced cell uptake of fluorescent drug-loaded nanoparticles via an implantable photothermal fibrous patch for more effective cancer cell killing

Great efforts have been devoted to effective delivery of therapeutics into cells for cancer therapy. The exploration of nanoparticle based drug delivery systems (DDSs) faces daunting challenges in low efficacy of intracellular delivery. Herein, a localized drug delivery device consisting of photoluminescent mesoporous silica nanoparticles (PLMSNs) and photothermal fibrous matrix was investigated. Specifically, PLMSNs modified with a pH-sensitive polydopamine (PDA) 'gatekeeper' served as a doxorubicin (DOX) carrier and could release DOX once the PLMSNs were up-taken by the cancer cells. The PLMSNs were electrostatically assembled on the surface of electrospun biodegradable poly(ε-caprolactone)/gelatin fibrous mesh incorporated with photothermal carbon nanoparticles (CNPs), leading to an implantable patch used as localized delivery platform. Comparing to free particulate DDSs, this implantable composite patch device was found to significantly enable superior cell up-taking effect and consequently enhance in-vitro therapeutic efficacy against tumor cells. Namely, under near infrared irradiation, the photothermal effect of CNPs in the implantable patch weakens the electrostatic interaction between the PLMSNs and poly(ε-caprolactone)/gelatin/CNP fibrous mesh, resulting in the controlled release of the PLMSNs and subsequent internalization into the tumor cells for more effective cancer cell killing. This implantable therapeutic device may therefore inspire another way of developing localized cancer therapy.

Binary Doping of Strontium and Copper Enhancing Osteogenesis and Angiogenesis of Bioactive Glass Nanofibers while Suppressing Osteoclast Activity

Electrospun bioactive glass fibers show great potential as scaffolds for bone tissue engineering due to their architectural biomimicry of the bone extracellular matrix and their composition capable of providing soluble bioactive cues for bone regeneration and remodeling. Trace elements can be doped to further promote osteogenesis and angiogenesis during bone regeneration. Cationic substitution of strontium for calcium in bioactive glass positively enhances osteoblast phenotype, while suppressing osteoclast activity. Further, the addition of copper spontaneously improves the vascularization during neobone formation. The objective of this study was to fabricate and characterize electrospun bioactive glass fibers doped with strontium and copper and evaluate their potential for bone repair/regeneration in vitro. Different ratios of strontium and copper were doped in electrospun bioactive glass fibers. The released strontium and copper from doped fibers could reach effective concentrations within 40 h and last for 4 weeks. These bioactive glass fibers demonstrate their bioactivity by promoting osteoblastic and endothelial cell activity and inhibiting the formation of osteoclasts or bone resorbing cells. Additionally, in vitro cell culture of different cell types in the presence of extraction solutions of the electrospun bioactive glass fibers showed that the dopants achieved their individual goals without causing significant cytotoxicity. Altogether, this novel class of bioactive glass fibers holds great promise for bone regeneration.

A Multifunctional Nanocrystalline CaF2:Tm,Yb@mSiO2 System for Dual-Triggered and Optically Monitored Doxorubicin Delivery

Daunting challenges in investigating the controlled release of drugs in complicated intracellular microenvironments demand the development of stimuli-responsive drug delivery systems. Here, a nanoparticle system, CaF2:Tm,Yb@mSiO2, made of a mesoporous silica (mSiO2) nanosphere with CaF2:Tm,Yb upconversion nanoparticles (UCNPs) is developed, filling its mesopores and with its surface-modified with polyacrylic acid for binding the anticancer drug molecules (doxorubicin, DOX). The unique design of CaF2:Tm,Yb@mSiO2 enables us to trigger the drug release by two mechanisms. One is the pH-triggered mechanism, where drug molecules are preferentially released from the nanoparticles at acidic conditions unique for the intracellular environment of cancer cells compared to normal cells. Another is the 808 nm near infrared (NIR)-triggered mechanism, where 808 nm NIR induces the heating of the nanoparticles to weaken the electrostatic interaction between drug molecules and nanoparticles. In addition, luminescence resonance energy transfer occurs from the UCNPs (the energy donor) to the DOX drug (the energy acceptor) in the presence of 980 nm NIR irradiation, allowing us to monitor the drug release by detecting the vanishing blue emission from the UCNPs. This study demonstrates a new multifunctional nanosystem for dual-triggered and optically monitored drug delivery, which will facilitate the rational design of personalized cancer therapy.

Clinoptilolite/PCL–PEG–PCL composite scaffolds for bone tissue engineering applications

The aim of this study was to prepare and characterize highly porous clinoptilolite/poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) composite scaffolds. Scaffolds with different clinoptilolite contents (10% and 20%) were fabricated with reproducible solvent-free powder compression/particulate leaching technique. The scaffolds had interconnective porosity in the range of 55–76%. Clinoptilolite/poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) scaffolds showed negligible degradation within eight weeks and displayed less water uptake and higher bioactivity than poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) scaffolds. The presence of clinoptilolite improved the mechanical properties. Highest compressive strength (5.6 MPa) and modulus (114.84 MPa) were reached with scaffold group containing 20% clinoptilolite. In vitro protein adsorption capacity of the scaffolds was also higher for clinoptilolite/poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) scaffolds. These scaffolds had 0.95 mg protein/g scaffold adsorption capacity and also higher osteoinductivity in terms of enhanced ALP, OSP activities and intracellular calcium deposition. Stoichiometric apatite deposition (Ca/P=1.686) was observed during cellular proliferation analysis with human fetal osteoblasts cells. Thus, it can be suggested that clinoptilolite/poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) composite scaffolds could be promising carriers for enhancement of bone regeneration in bone tissue engineering applications.

A Facile Approach to Upconversion Crystalline CaF2:Yb3+,Tm3+@mSiO2 Nanospheres for Tumor Therapy

A new facile approach, namely chemical-assisted sol-gel growth (CASGG), was successfully developed to induce the formation of fine CaF2:Yb3+, Tm3+ nanocrytals within the pore channels of mesoporous silica (mSiO2) nanoparticles. A series of upconversion photoluminescent crystalline CaF2:Yb3+,Tm3+@mSiO2 nanospheres with controlled diameters from ~65 nm to ~290 nm were fabricated. All nanospheres presented sound cyto-compatibility and unique ratiometric spectral monitoring functionalities for drug release kinetics. The nanospheres with smallest dimension (UCNP-2.5, ~65nm) induced the most sustained DOX release kinetics. More importantly, the in-vitro study demonstrated that the DOX loaded UCNP-2.5 nanopheres presented the strongest anti-cancer efficacy to MCF-7 human breast cancer cells due to its stronger penetration ability to cell nuclei due to the size effect.

Optically Monitoring Mineralization and Demineralization on Photoluminescent Bioactive Nanofibers

Bone regeneration and scaffold degradation do not usually follow the same rate, representing a daunting challenge in bone repair. Toward this end, we propose to use an external field such as light (in particular, a tissue-penetrating near-infrared light) to precisely monitor the degradation of the mineralized scaffold (demineralization) and the formation of apatite mineral (mineralization). Herein, CaTiO3:Yb(3+),Er(3+)@bioactive glass (CaTiO3:Yb(3+),Er(3+)@BG) nanofibers with upconversion (UC) photoluminescence (PL) were synthesized. Such nanofibers are biocompatible and can emit green and red light under 980 nm excitation. The UC PL intensity is quenched during the bone-like apatite formation on the surface of the nanofibers in simulated body fluid; more mineral formation on the nanofibers induces more rapid optical quenching of the UC PL. Furthermore, the quenched UC PL can recover back to its original magnitude when the apatite on the nanofibers is degraded. Our work suggests that it is possible to optically monitor the apatite mineralization and demineralization on the surface of nanofibers used in bone repair.

Regulating micro-structure and biomineralization of electrospun PVP-based hybridized carbon nanofibers containing bioglass nanoparticles via aging time

Morphological and micro-structural evolution of BG components in PVP-based CNF/BG composite with aging time.

Synthesis of CaTiO3 Nanofibers with Controllable Drug-Release Kinetics

Calcium titanate (CaTiO3) nanofibers with controlled microstructure were fabricated by a combination of sol-gel and electrospinning approaches. The fiber morphology has been found to rely significantly on the precursor composition. Altering the volume ratio of ethanol to acetic acid from 3.5 to 1.25 enables the morphology of the CaTiO3 nanofibers to be transformed from fibers with a circular cross section to curved ribbon-like structures. Ibuprofen (IBU) was used as a model drug to investigate the drug-loading capacity and drug-release profile of the nanofibers. It was found that the BET surface area and the pore volume decrease markedly with the utilization of F127 surfactant. The nanofibers synthesized without F127 surfactant present the highest drug-loading capacity and the most sustained release kinetics. This study suggests that calcium titanate nanofibers can offer a promising platform for localized drug delivery.