Synthesis of hydroxyapatite nanotubes for biomedical applications

The multifunctional role of hydroxyapatite nanoparticles as an emerging tool in tumor therapy

Hydroxyapatite nanoparticles (HANPs) are well-known nanomaterials for bone regeneration or repair. In recent years, HANPs have emerged as a potential tool in tumor therapy because of the numerous advantages the nanoparticles offer, including the diverse physicochemical properties, the selective anti-tumor effect, intrinsic immunomodulatory activity, ability to reverse of drug or immune tolerance, allowance of ion substation, good drug-loading capabilities, etc. Notably, the physicochemical properties of the particles, such as size and shape, significantly influence their anti-tumor efficacy. Therefore, to offer a comprehensive understanding of the key properties of HANPs and the involving molecular mechanisms, and provide crucial cues for rational design and development of novel HANPs-based anti-tumor platforms, this review summarizes various synthesis methods of HANPs with controlled physiochemical characteristics and highlights the multifaceted effects such as interactions with tumor cells and immune cells, regulation of the tumor microenvironment (TME), overcoming drug or immune resistance, and their potentials as effective drug carriers. This review also outlines the emerging strategies leveraging HANPs for tumor therapy and diagnostic imaging. At last, we discuss the challenges HANPs face when used for tumor treatment. STATEMENT OF SIGNIFICANCE: Hydroxyapatite nanoparticles (HANPs) have emerged as a promising tool in tumor therapy without compromising biocompatibility. This review highlights the unique and multifaceted features of HANPs in tumor therapy, including the selective induction of tumor cell apoptosis, engagement in immune regulation, reversal of drug or immune resistance, and the loading of diverse anti-tumor drugs or biomaterials. Additionally, this review emphasizes the influence of the intrinsic physicochemical properties of HANPs on their anti-tumor activity, and explores the emerging strategies that leverage HANPs for tumor therapy and diagnostic imaging. In summary, this work aims to provide a comprehensive and deep understanding of the role of HANPs in tumor therapy and is significant for the improved design of HANP-based platforms for tumor therapy.

Hydroxyapatite Chitosan Gradient Pore Scaffold Activates Oxidative Phosphorylation Pathway to Induce Bone Formation

BACKGROUND

In this study, we prepared a porous gradient scaffold with hydroxyapatite microtubules (HAMT) and chitosan (CHS) and investigated osteogenesis induced by these scaffolds.

METHODS

The arrangement of wax balls in the mold can control the size and distribution of the pores of the scaffold, and form an interconnected gradient pore structure. The scaffolds were systematically evaluated in vitro and in vivo for biocompatibility, biological activity, and regulatory mechanisms.

RESULTS

The porosity of the four scaffolds was more than 80%. The 50% and 70% HAMT-CHS scaffolds formed an excellent gradient pore structure, with interconnected pores. Furthermore, the 70% HAMT-CHS scaffold showed better anti-compressive deformation ability. In vitro experiments indicated that the scaffolds had good biocompatibility, promoted the expression of osteogenesis-related genes and proteins, and activated the oxidative phosphorylation pathway to promote bone regeneration. Eight weeks after implanting the HAMT-CHS scaffold in rat skull defects, new bone formation was observed in vivo by micro-computed tomographic (CT) staining. The obtained data were statistically analyzed, and the p-value < 0.05 was statistically significant.

CONCLUSION

HAMT-CHS scaffolds can accelerate osteogenesis in bone defects, potentially through the activation of the oxidative phosphorylation pathway. These results highlight the potential therapeutic application of HAMT-CHS scaffolds.

Comparison of Aging Performances and Mechanisms: Super-Durable Fire-Resistant "Xuan Paper" Versus Chinese Traditional Xuan Paper

Paper is a thin nonwoven material made from cellulose fibers as the main raw material together with some additives. Paper is highly flammable, leading to the destruction of countless precious ancient books, documents, and art works in fire disasters. In recent years, researchers have made a lot of efforts in order to obtain more durable and fire-retardant paper. Owing to the successful synthesis of ultralong hydroxyapatite (HAP) nanowires as a new kind of inorganic nanofiber material, it becomes possible to develop a new kind of super-durable and fire-resistant paper. Recently, the authors' research group prepared a new kind of fire-resistant "Xuan paper" consisting of ultralong HAP nanowires. In this article, the super-durable fire-resistant "Xuan paper" based on ultralong HAP nanowires and the traditional Xuan paper based on cellulose fibers were evaluated by the accelerated aging method for 1200 days at 105 °C in air, which is the equivalent of 10,000 years of natural aging in the ambient environment. The aging mechanism of the traditional Xuan paper was further investigated by studying the fiber length/width and their distributions, morphology, infrared spectroscopy, thermogravimetric analysis, H-nuclear magnetic resonance spectra, and C-nuclear magnetic resonance spectra of cellulose fibers before and after the accelerated aging. The durability, properties, and mechanism of the fire-resistant "Xuan paper" based on ultralong HAP nanowires during the accelerated aging were studied. The experiments reveal the reasons for the deteriorated properties and reduced durability by aging of the traditional Xuan paper based on cellulose fibers, and the mechanism for the super-durability and excellent performances of the fire-resistant "Xuan paper" based on ultralong HAP nanowires during the accelerated aging process.

Tubular nanomaterials for bone tissue engineering

Nanomaterial composition, morphology, and mechanical performance are critical parameters for tissue engineering. Within this rapidly expanding space, tubular nanomaterials (TNs), including carbon nanotubes (CNTs), titanium oxide nanotubes (TNTs), halloysite nanotubes (HNTs), silica nanotubes (SiNTs), and hydroxyapatite nanotubes (HANTs) have shown significant potential across a broad range of applications due to their high surface area, versatile surface chemistry, well-defined mechanical properties, excellent biocompatibility, and monodispersity. These include drug delivery vectors, imaging contrast agents, and scaffolds for bone tissue engineering. This review is centered on the recent developments in TN-based biomaterials for structural tissue engineering, with a strong focus on bone tissue regeneration. It includes a detailed literature review on TN-based orthopedic coatings for metallic implants and composite scaffolds to enhance in vivo bone regeneration.

Comparison of the effect of argon, hydrogen, and nitrogen gases on the reduced graphene oxide-hydroxyapatite nanocomposites characteristics

In this study, the effect of the argon, nitrogen, and hydrogen gases on the final properties of the reduced graphene oxide- hydroxyapatite nanocomposites synthesized by gas injected hydrothermal method was investigated. Four samples were synthesized, which in the first sample the pressure was controlled by volume change at a constant concentration. In subsequent samples, the pressure inside the autoclave was adjusted by the injecting gases. The initial pressure of the injected gases was 10 bar and the final pressure considered was 25 bar. The synthesized powders were consolidated at 950 °C and 2 MPa by spark plasma sintering method. The final samples were subjected to Vickers indentation analysis. The findings of this study indicate that the injection of argon, hydrogen, and nitrogen gases improved the mechanical properties of the nanocomposites. Injection of gases increased the crystallinity and particle size of hydroxyapatite, and this increase was greater for nitrogen gas than for others. Injection of these gases increased the rate of graphene oxide reduction and in this case the effect of nitrogen gas was greater than the others.

Synthesis of Graphene Nanoribbons–Hydroxyapatite Nanocomposite Applicable in Biomedicine and Theranostics

In order to investigate the effect of graphene nanoribbons on the final properties of hydroxyapatite-based nanocomposites, a solvothermal method was used at 180 °C and 5 h for the synthesis of graphene nanoribbons–hydroxyapatite nanopowders by employing hydrogen gas injection. Calcium nitrate tetrahydrate and diammonium hydrogenphosphate were used as calcium and phosphate precursors, respectively. To synthesize the powders, a solvent containing diethylene glycol, anhydrous ethanol, dimethylformamide, and water was used. Graphene oxide nanoribbons were synthesized by chemical unzipping of carbon nanotubes under oxidative conditions. The synthesized powders were consolidated by spark plasma sintering methodat 950 °C and a pressure of 50 MPa. The powders and sintered samples were then evaluated using X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, Vickers microindentation techniques, and biocompatibility assay. The findings of this study showed that the final powders synthesized by the solvothermal method had calcium to phosphate ratio of about 1.67. By adding a small amount of graphene nanoribbon (0.5%W), elastic modulus and hardness of hydroxyapatite increased dramatically. In biological experiments, the difference of hydroxyapatite effect in comparison with the nanocomposite was not significant. The findings of this study showed that graphene nanoribbons have a positive effect on the properties of hydroxyapatite, and these findings would be useful for the medical and theranostic application of this type of nanocomposites.

Comprehensive In Vitro Testing of Calcium Phosphate-Based Bioceramics with Orthopedic and Dentistry Applications

Recently, a large spectrum of biomaterials emerged, with emphasis on various pure, blended, or doped calcium phosphates (CaPs). Although basic cytocompatibility testing protocols are referred by International Organization for Standardization (ISO) 10993 (parts 1-22), rigorous in vitro testing using cutting-edge technologies should be carried out in order to fully understand the behavior of various biomaterials (whether in bulk or low-dimensional object form) and to better gauge their outcome when implanted. In this review, current molecular techniques are assessed for the in-depth characterization of angiogenic potential, osteogenic capability, and the modulation of oxidative stress and inflammation properties of CaPs and their cation- and/or anion-substituted derivatives. Using such techniques, mechanisms of action of these compounds can be deciphered, highlighting the signaling pathway activation, cross-talk, and modulation by microRNA expression, which in turn can safely pave the road toward a better filtering of the truly functional, application-ready innovative therapeutic bioceramic-based solutions.

Manufacturing and Characterization of Functionalized Aliphatic Polyester from Poly(lactic acid) with Halloysite Nanotubes

This work reports the potential of poly(lactic acid)-PLA composites with different halloysite nanotube (HNTs) loading (3, 6 and 9 wt%) for further uses in advanced applications as HNTs could be used as carriers for active compounds for medicine, packaging and other sectors. This work focuses on the effect of HNTs on mechanical, thermal, thermomechanical and degradation of PLA composites with HNTs. These composites can be manufactured by conventional extrusion-compounding followed by injection molding. The obtained results indicate a slight decrease in tensile and flexural strength as well as in elongation at break, both properties related to material cohesion. On the contrary, the stiffness increases with the HNTs content. The tensile strength and modulus change from 64.6 MPa/2.1 GPa (neat PLA) to 57.7/2.3 GPa MPa for the composite with 9 wt% HNTs. The elongation at break decreases from 6.1% (neat PLA) down to a half for composites with 9 wt% HNTs. Regarding flexural properties, the flexural strength and modulus change from 116.1 MPa and 3.6 GPa respectively for neat PLA to values of 107.6 MPa and 3.9 GPa for the composite with 9 wt% HNTs. HNTs do not affect the glass transition temperature with invariable values of about 64 °C, or the melt peak temperature, while they move the cold crystallization process towards lower values, from 112.4 °C for neat PLA down to 105.4 °C for the composite containing 9 wt% HNTs. The water uptake has been assessed to study the influence of HNTs on the water saturation. HNTs contribute to increased hydrophilicity with a change in the asymptotic water uptake from 0.95% (neat PLA) up to 1.67% (PLA with 9 wt % HNTs) and the effect of HNTs on disintegration in controlled compost soil has been carried out to see the influence of HNTs on this process, which is a slight delay on it. These PLA-HNT composites show good balanced properties and could represent an interesting solution to develop active materials.

Biomimetic Hydroxyapatite a Potential Universal Nanocarrier for Cellular Internalization & Drug Delivery

PURPOSE

Functional biomaterials can be used as drug loading devices, components for tissue engineering or as biological probes. As such, the design, synthesis and evaluation of a variety of local-drug delivery structures has been undertaken over the past few decades with the ultimate aim of providing materials that can encapsulate a diverse array of drugs (in terms of their sizes, chemical compositions and chemical natures (i.e. hydrophilic/hydrophobic).

METHODS

Presented here is the evaluation of specifically hollow 1D structures consisting of nanotubes (NTs) of HAp and their efficacy for cellular internalization using two distinguished anti-cancer model drugs: Paclitaxel (hydrophobic) and Doxorubicin hydrochloride (hydrophilic).

RESULTS

Importantly, it has been observed through this work that HAp NTs consistently showed not only higher drug loading capacity as compared to HAp nanospheres (NSs) but also had better efficacy with respect to cell internalization/encapsulation. The highly porous structure, with large surface area of nanotube morphology, gave the advantage of targeted delivery due to its high drug loading and retention capacity. This was done using the very simple techniques of physical adsorption to load the drug/dye molecules and therefore this can be universally applied to a diverse array of molecules.

CONCLUSIONS

Our synthesized nanocarrier can be widely employed in biomedical applications due to its bio-compatible, bio-active and biodegradable properties and as such can be considered to be a universal carrier. Graphical Abstract Schematic representation for a comparative study of hydroxyapatite (hollow nanotubes vs solid nanospheres) with variety of drug/ dye molecules.

Novel Hierarchical Nitrogen-Doped Multiwalled Carbon Nanotubes/Cellulose/Nanohydroxyapatite Nanocomposite As an Osteoinductive Scaffold for Enhancing Bone Regeneration

Nanomaterials based on hybrid scaffolds have shown a high potential to promote osteointegration and bone regeneration. In this study, a novel nanocomposite scaffold was synthesized via a cross-linking/hydrothermal/freeze-drying method, resulting in layer-by-layer structures with functional and structural properties mimicking the natural bone. The hierarchical structures of the scaffold were reinforced with nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs), cellulose, and nanohydroxyapatite. The N-MWCNT/Cel/nHA scaffolds were characterized and evaluated in terms of structure, morphology, biocompatibility, cellular responses, and bone repair efficiency in vivo. The resulting scaffolds showed that incorporation of 1 wt % N-MWCNTs into the hybrid scaffold with micropores (∼5 μm) significantly improved its mechanical properties, although the surface morphology of the scaffold tended to be rough and porous. Importantly, the resulting scaffolds supported in vitro cellular attachment, proliferation, viability, and mineralization of bone mesenchymal stem cells (BMSCs). On the other hand, incorporation of N-MWCNTs into the scaffold induced preferential differentiation of BMSCs to osteogenic lineage accompanied by increased alkaline phosphatase activity and expression of key osteogenic genes. Furthermore, 12 weeks after implantation, the 1%N-MWCNT/Cel/nHA porous scaffolds successfully cicatrized a distal femoral condyle critical size defect in rabbit without obvious inflammatory responses, as indicated by the results of the Micro-CT and histological analyses. In vitro and in vivo experiments confirmed that the scaffolds not only improved the interface bonding with bone tissue but also accelerated the new bone formation and regeneration by up-regulating signaling molecules that are involved in cell proliferation and differentiation. These results indicated that the novel N-MWCNT/Cel/nHA scaffold is an efficient platform for osteogenesis research and bone regeneration medicine.

3D porous collagen/functionalized multiwalled carbon nanotube/chitosan/hydroxyapatite composite scaffolds for bone tissue engineering

In this study, we describe new collagen/functionalized multiwalled carbon nanotube/chitosan/hydroxyapatite (Col/f-MWCNT/CS/HA) composite scaffolds which were fabricated by freezing (-40 °C at 0.9 °C/min) and lyophilization (48 h, 0 °C and 200 mtorr). The compressive stresses (from 523 to 1112 kPa), swelling (from 513.9 ± 27 to 481.05 ± 25%), porosity (from 98 ± 0.15 to 95.7 ± 0.1%), contact angle (from 87.8 to 76.7°) properties examined before and after biomineralization for comparison 3D porous Col, CS, Col/f-MWCNT and Col/f-MWCNT/CS scaffolds. Biomineralization was performed by biomimetic method in concentrated SBF (10 × SBF, at 37 °C and 6.5 pH). XRD, SEM, EDS, FTIR, TGA, Optical microscopy and BET results showed that compared to Col, CS and Col/f-MWCNT scaffolds, Col/f-MWCNT/CS scaffolds had higher in vitro bioactivity, large surface area (11.746 m²/g) and a good pore volume (0.026 cc/g), interconnected porous microstructure (with 20-350 μm pore size) and incorporates the advantageous properties of both Col, f-MWCNT, CS and HA. Finally, the methyl thiazolyl tetrazolium (MTT) assay was performed to evaluate scaffolds cytotoxicity which showed that Col/f-MWCNT/CS scaffolds have the best biocompatibility.

Hydrothermally processed 1D hydroxyapatite: Mechanism of formation and biocompatibility studies

Recent developments in bone tissue engineering have led to an increased interest in one-dimensional (1D) hydroxyapatite (HA) nano- and micro-structures such as wires, ribbons and tubes. They have been proposed for use as cell substrates, reinforcing phases in composites and carriers for biologically active substances. Here we demonstrate the synthesis of 1D HA structures using an optimized, urea-assisted, high-yield hydrothermal batch process. The one-pot process, yielding HA structures composed of bundles of ribbons and wires, was typified by the simultaneous occurrence of a multitude of intermediate reactions, failing to meet the uniformity criteria over particle morphology and size. To overcome these issues, the preparation procedure was divided to two stages: dicalcium phosphate platelets synthesized in the first step were used as a precursor for the synthesis of 1D HA in the second stage. Despite the elongated particle morphologies, both the precursor and the final product exhibited excellent biocompatibility and caused no reduction of viability when tested against osteoblastic MC3T3-E1 cells in 2D culture up to the concentration of 2.6mg/cm(2). X-ray powder diffraction combined with a range of electron microscopies and laser diffraction analyses was used to elucidate the formation mechanism and the microstructure of the final particles. The two-step synthesis involved a more direct transformation of DCP to 1D HA with the average diameter of 37nm and the aspect ratio exceeding 100:1. The comparison of crystalline domain sizes along different crystallographic directions showed no signs of significant anisotropy, while indicating that individual nanowires are ordered in bundles in the b crystallographic direction of the P63/m space group of HA. Intermediate processes, e.g., dehydration of dicalcium phosphate, are critical for the formation of 1D HA alongside other key aspects of this phase transformation, it must be investigated in more detail in the continuous design of smart HA micro- and nano-structures with advanced therapeutic potentials.

Template-based syntheses for shape controlled nanostructures

A variety of nanostructured materials are produced through template-based synthesis methods, including zero-dimensional, one-dimensional, and two-dimensional structures. These span different forms such as nanoparticles, nanowires, nanotubes, nanoflakes, and nanosheets. Many physical characteristics of these materials such as the shape and size can be finely controlled through template selection and as a result, their properties as well. Reviewed here are several examples of these nanomaterials, with emphasis specifically on the templates and synthesis routes used to produce the final nanostructures. In the first section, the templates have been discussed while in the second section, their corresponding synthesis methods have been briefly reviewed, and lastly in the third section, applications of the materials themselves are highlighted. Some examples of the templates frequently encountered are organic structure directing agents, surfactants, polymers, carbon frameworks, colloidal sol-gels, inorganic frameworks, and nanoporous membranes. Synthesis methods that adopt these templates include emulsion-based routes and template-filling approaches, such as self-assembly, electrodeposition, electroless deposition, vapor deposition, and other methods including layer-by-layer and lithography. Template-based synthesized nanomaterials are frequently encountered in select fields such as solar energy, thermoelectric materials, catalysis, biomedical applications, and magnetowetting of surfaces.

Hydroxyapatite-coated sillicone rubber enhanced cell adhesion and it may be through the interaction of EF1β and γ-actin

Silicone rubber (SR) is a common soft tissue filler material used in plastic surgery. However, it presents a poor surface for cellular adhesion and suffers from poor biocompatibility. In contrast, hydroxyapatite (HA), a prominent component of animal bone and teeth, can promote improved cell compatibility, but HA is an unsuitable filler material because of the brittleness in mechanism. In this study, using a simple and economical method, two sizes of HA was applied to coat on SR to counteract the poor biocompatibility of SR. Surface and mechanical properties of SR and HA/SRs confirmed that coating with HA changes the surface topology and material properties. Analysis of cell proliferation and adhesion as well as measurement of the expression levels of adhesion related molecules indicated that HA-coated SR significantly increased cell compatibility. Furthermore, mass spectrometry proved that the biocompatibility improvement may be related to elongation factor 1-beta (EF1β)/γ-actin adjusted cytoskeletal rearrangement.

Advances in synthesis of calcium phosphate crystals with controlled size and shape

Calcium phosphate (CaP) materials have a wide range of applications, including biomaterials, adsorbents, chemical engineering materials, catalysts and catalyst supports and mechanical reinforcements. The size and shape of CaP crystals and aggregates play critical roles in their applications. The main inorganic building blocks of human bones and teeth are nanocrystalline CaPs; recently, much progress has been made in the application of CaP nanocrystals and their composites for clinical repair of damaged bone and tooth. For example, CaPs with special micro- and nanostructures can better imitate the biomimetic features of human bone and tooth, and this offers significantly enhanced biological performances. Therefore, the design of CaP nano-/microcrystals, and the shape and hierarchical structures of CaPs, have great potential to revolutionize the field of hard tissue engineering, starting from bone/tooth repair and augmentation to controlled drug delivery devices. Previously, a number of reviews have reported the synthesis and properties of CaP materials, especially for hydroxyapatite (HAp). However, most of them mainly focused on the characterizations and physicochemical and biological properties of HAp particles. There are few reviews about the control of particle size and size distribution of CaPs, and in particular the control of nano-/microstructures on bulk CaP ceramic surfaces, which is a big challenge technically and may have great potential in tissue engineering applications. This review summarizes the current state of the art for the synthesis of CaP crystals with controlled sizes from the nano- to the macroscale, and the diverse shapes including the zero-dimensional shapes of particles and spheres, the one-dimensional shapes of rods, fibers, wires and whiskers, the two-dimensional shapes of sheets, disks, plates, belts, ribbons and flakes and the three-dimensional (3-D) shapes of porous, hollow, and biomimetic structures similar to biological bone and tooth. In addition, this review will also summarize studies on the controlled formation of nano-/microstructures on the surface of bulk ceramics, and the preparation of macroscopical bone grafts with 3-D architecture nano-/microstructured surfaces. Moreover, the possible directions of future research and development in this field, such as the detailed mechanisms behind the size and shape control in various strategies, the importance of theoretical simulation, self-assembly, biomineralization and sacrificial precursor strategies in the fabrication of biomimetic bone-like and enamel-like CaP materials are proposed.

Structure, properties and animal study of a calcium phosphate/calcium sulfate composite cement

In-vitro and in-vivo studies have been conducted on an in-house-developed tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)/calcium sulfate hemihydrate (CSH)-derived composite cement. Unlike most commercial calcium-based cement pastes, the investigated cement paste can be directly injected into water and harden without dispersion. The viability value of cells incubated with a conditioned medium of cement extraction is >90% that of Al2O3 control and >80% that of blank medium. Histological examination reveals excellent bonding between host bone and cement without interposition of fibrous tissues. At 12 weeks-post implantation, significant remodeling activities are found and a new bone network is developed within the femoral defect. The 26-week samples show that the newly formed bone becomes more mature, while the interface between residual cement and the new bone appears less identifiable. Image analysis indicates that the resorption rate of the present cement is much higher than that of TTCP or TTCP/DCPA-derived cement under similar implantation conditions.