Branched polymer grafted graphene oxide (GO) as a 2D template for calcium phosphate growth

HYPOTHESIS

Graphene Oxide (GO)-templated deposition of inorganic materials through synthesis on dispersed single sheets of GO is often complicated by the loss of the desired 2D morphology owing to the coagulation of GO sheets at high salt concentrations and non-templated homogenous nucleation. Modifying GO with anionic polymer is expected to solve both problems by i) enhancing electrostatic(steric) stabilization upon exposure to high concentrations of the ionic precursors, and ii) offering additional nucleation sites at the grafted anionic moieties to avoid homogeneous secondary nucleation.

EXPERIMENTS

GO was grafted with branched copolymers of poly(ethylene glycol) methacrylate (PEGMA 500) and diethylene glycol dimethacrylate (DEGDMA) and ω-vinyl terminated methacrylic acid macromonomer (P(MAA)), the latter serving as an addition-fragmentation chain transfer agent. The colloidal stability of GO dispersions in water toward salt was evaluated before and after modification. Precipitation of calcium phosphate (CaP) was performed by incubating modified GO in the precursor solutions. The conditions were optimized to maximize the nucleation selectively onto GO without homogeneous CaP nucleation and coagulation of the GO-sheets.

FINDINGS

The copolymer grafted GO-sheets shows superior colloidal stability when dispersed in water. No aggregation occurs in the incubating ionic CaP precursor solutions. The optimum templated deposition of CaP onto the GO sheets by precipitation is to add a second shot of precursors after the nucleation stage to obtain GO sheets fully decorated with calcium phosphate nanorods without self-nucleation. Via the careful design on the GO modification and incubation process, the growth of calcium phosphate nanorods were confined in the desired 2D order exclusively, hereby achieving the goal of an efficient GO-templated synthesis.

New Progress in Improving the Delivery Methods of Bisphosphonates in the Treatment of Bone Tumors

Bone tumors are tumors that occur in the bone or its accessory tissues, including primary tumors and metastatic tumors. The main mechanism of bisphosphonate is to inhibit the resorption of destructive bone, inhibit the activity of osteoclasts and reduce the concentration of blood calcium. Therefore, bisphosphonates can be used for malignant hypercalcaemia, pain caused by osteolytic bone metastasis, prevention of osteolytic bone metastasis, multiple myeloma osteopathy, improving radiosensitivity and so on. However, the traditional administration of bisphosphonates can cause a series of adverse reactions. To overcome this disadvantage, it is necessary to develop novel methods to improve the delivery of bisphosphonates. In this paper, the latest research progress of new and improved bisphosphonate drug delivery methods in the treatment of bone tumors is reviewed. At present, the main design idea is to connect bisphosphonate nanoparticles, liposomes, microspheres, microcapsules, couplings, prodrugs and bone tissue engineering to targeted anti-tumors systems, and positive progress has been made in in vitro and animal experiments. However, its safety and effectiveness in human body still need to be verified by more studies.

Deposition of non-porous calcium phosphate shells onto liquid filled microcapsules

The efficient encapsulation of small molecule active ingredients has been a challenge for many decades across many commercial applications. Recently, successful attempts to address this issue have included deposition of thin metal shells onto liquid filled polymer microcapsules or emulsion droplets to provide an impermeable barrier to diffusion. In this work we have developed a novel method to protect small molecule active ingredients by deposition of thin mineral shells. Platinum nanoparticles are used to catalyse and direct growth of a calcium phosphate shell onto liquid filled polymer microcapsules under various reaction conditions. Findings indicate that a non-porous protective shell is formed on the majority of the microcapsule population, with small concentrations of the core material being released only from those microcapsules with defects, over a 7 days period, when conducting forced release studies into a solvent for the core oil. The resulting microcapsules show no significant cell toxicity when exposed to HEK 293 cells for 72 h.

Potentiating bisphosphonate-based coordination complexes to treat osteolytic metastases

The hydrothermal reaction between bioactive metal (Ca2+, Zn2+, and Mg2+) salts and a clinically utilized bisphosphonate, alendronate (ALEN), promotes the formation of several materials denominated as bisphosphonate-based coordination complexes (BPCCs). The systematic exploration of the effect of three variables, M2+/ALEN molar ratio, temperature, and pH, on the reaction yielded an unprecedented number of materials of enough crystal quality for structural elucidation. Five crystal structures were unveiled by single crystal X-ray diffraction (ALEN-Ca forms I and II, ALEN-Zn forms I and II, and ALEN-Mg) and their solid-state properties revealed in tandem with other techniques. The dissolution of these BPCCs was tested and contrasted to that of the commercially employed generic form of Fosamax® Alendronate Sodium, using fasted-state simulated gastric fluid and phosphate-buffered saline solution. Quantification of ALEN content was performed by derivatization with Cu2+, which produced a soluble complex suitable for quantification. The results show that these materials present a pH-dependent degradation. Moreover, a phase inversion temperature (PIT) nano-emulsion method was applied to the synthesis of ALEN-Ca form II. Size distribution analysis demonstrated the efficiency of the PIT-nano-emulsion method to decrease the particle size of this BPCC from ∼60 μm to ∼438 d nm. The cytotoxicity of ALEN, ALEN-Ca form II (bulk crystals), and nano-Ca@ALEN (nanocrystals) against the MDA-MB-231 cell line was investigated. Nano-Ca@ALEN form II presents higher cytotoxicity effects than ALEN and ALEN-Ca form II (bulk crystals), showing inhibition of cell proliferation at 7.5 μM. These results provide evidence of the structure, stability, dissolution and cytotoxicity properties of ALEN-based BPCCs and pave the way for better formulation strategies for this drug through the design of nano-sized BPCCs for the treatment of bone-related diseases.

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.

Formulating Polyethylene Glycol as Supramolecular Emulsifiers for One-Step Double Emulsions

One-step double emulsions via only one-step emulsification are leading to an attractive branch of emulsion research studies owing to the ease of preparation and reduced surfactant numbers. In addition to controlling the oil/water ratio, exploiting emulsifiers with desirable amphiphilicity that can stabilize both the inner and outer water/oil interfaces is crucial to the formation of one-step double emulsions. In particular, new emulsifiers with saving laborious efforts are highly preferred in consideration of low cost and practical applications. In this work, a commonly used homopolymer, polyethylene glycol (PEG), was attempted as emulsifiers to prepare emulsions via one-step emulsification. PEG is generally considered as a hydrophilic polymer and always anchored with a hydrophobic polymer to make the copolymer amphiphilic. In the water-chloroform binary system, PEG itself exhibits amphiphilic performance and tailors the formation of single emulsions or double W/O/W emulsions on the dependence of the oil/water ratio and the PEG concentration. A possible mechanism as explained by dissipative particle dynamics simulation was proposed to demonstrate the amphiphilic feature and emulsification capability of PEG. The amphiphilicity of PEG was further tuned by interacting with iodine as a result of the formation of a supramolecular complex, which, in turn, led to the conversion from single emulsions to O/W/O double emulsions. It is believed that this line of research provides inspiration for the preparation of controllable emulsions through supramolecular routes.

On-Demand Guided Bone Regeneration with Microbial Protection of Ornamented SPU Scaffold with Bismuth-Doped Single Crystalline Hydroxyapatite: Augmentation and Cartilage Formation

Guided bone regeneration (GBR) scaffolds are futile in many clinical applications due to infection problems. In this work, we fabricated GBR with an anti-infective scaffold by ornamenting 2D single crystalline bismuth-doped nanohydroxyapatite (Bi-nHA) rods onto segmented polyurethane (SPU). Bi-nHA with high aspect ratio was prepared without any templates. Subsequently, it was introduced into an unprecedented synthesized SPU matrix based on dual soft segments (PCL-b-PDMS) of poly(ε-caprolactone) (PCL) and poly(dimethylsiloxane) (PDMS), by an in situ technique followed by electrospinning to fabricate scaffolds. For comparison, undoped pristine nHA rods were also ornamented into it. The enzymatic ring-opening polymerization technique was adapted to synthesize soft segments of PCL-b-PDMS copolymers of SPU. Structure elucidation of the synthesized polymers is done by nuclear magnetic resonance spectroscopy. Sparingly, Bi-nHA ornamented scaffolds exhibit tremendous improvement (155%) in the mechanical properties with excellent antimicrobial activity against various human pathogens. After confirmation of high osteoconductivity, improved biodegradation, and excellent biocompatibility against osteoblast cells (in vitro), the scaffolds were implanted in rabbits by subcutaneous and intraosseous (tibial) sites. Various histological sections reveal the signatures of early cartilage formation, endochondral ossification, and rapid bone healing at 4 weeks of the critical defects filled with ornamented scaffold compared to SPU scaffold. This implies osteogenic potential and ability to provide an adequate biomimetic microenvironment for mineralization for GBR of the scaffolds. Organ toxicity studies further confirm that no tissue architecture abnormalities were observed in hepatic, cardiac, and renal tissue sections. This finding manifests the feasibility of fabricating a mechanically adequate nanofibrous SPU scaffold by a biomimetic strategy and the advantages of Bi-nHA ornamentation in promoting osteoblast phenotype progression with microbial protection (on-demand) for GBR applications.