Electrospun Poly(butylene-adipate-co-terephthalate)/Nano-hyDroxyapatite/Graphene Nanoribbon Scaffolds Improved the In Vivo Osteogenesis of the Neoformed Bone

Electrospun ultrathin fibrous scaffold filed with synthetic nanohydroxyapatite (nHAp) and graphene nanoribbons (GNR) has bioactive and osteoconductive properties and is a plausible strategy to improve bone regeneration. Poly(butylene-adipate-co-terephthalate) (PBAT) has been studied as fibrous scaffolds due to its low crystallinity, faster biodegradability, and good mechanical properties; however, its potential for in vivo applications remains underexplored. We proposed the application of electrospun PBAT with high contents of incorporated nHAp and nHAp/GNR nanoparticles as bone grafts. Ultrathin PBAT, PBAT/nHAp, and PBAT/nHAp/GNR fibers were produced using an electrospinning apparatus. The produced fibers were characterized morphologically and structurally using scanning electron (SEM) and high-resolution transmission electron (TEM) microscopies, respectively. Mechanical properties were analyzed using a texturometer. All scaffolds were implanted into critical tibia defects in rats and analyzed after two weeks using radiography, microcomputed tomography, histological, histomorphometric, and biomechanical analyses. The results showed through SEM and high-resolution TEM characterized the average diameters of the fibers (ranged from 0.208 µm ± 0.035 to 0.388 µm ± 0.087) and nHAp (crystallite around 0.28, 0.34, and 0.69 nm) and nHAp/GNR (200-300 nm) nanoparticles distribution into PBAT matrices. Ultrathin fibers were obtained, and the incorporated nHAp and nHAp/GNR nanoparticles were well distributed into PBAT matrices. The addition of nHAp and nHAp/GNR nanoparticles improved the elastic modulus of the ultrathin fibers compared to neat PBAT. High loads of nHAp/GNR (PBATnH5G group) improved the in vivo lamellar bone formation promoting greater radiographic density, trabecular number and stiffness in the defect area 2 weeks after implantation than control and PBAT groups.

Hydrothermal synthesis of perfectly shaped micro- and nanosized carbonated apatite

Herein we present a Ca[EDTA]-based synthesis and comparative study of perfectly shaped plate-like, rod–like, and prism-like carbonated apatites.

The role of the micro-pattern and nano-topography of hydroxyapatite bioceramics on stimulating osteogenic differentiation of mesenchymal stem cells

The micro/nano hybrid structure is considered to be a biomaterial characteristic to stimulate osteogenesis by mimicking the three-dimensional structure of the bone matrix. However, the mechanism of the hybrid structure induced osteogenic differentiation of stem cells is still unknown. For elucidating the mechanisms, one of the challenge is to directly fabricate micro/nano hybrid structure on bioceramics because of its brittleness. In this study, hydroxyapatite (HA) bioceramics with the micro/nano hybrid structure were firstly fabricated via a hydrothermal treatment and template method, and the effect of the different surface structures on the expression of integrins, BMP2 signaling pathways and cell-cell communication was investigated. Interestingly, the results suggested that the osteogenic differentiation induced by micro/nano structures was modulated first through activating integrins and then further activating BMP2 signaling pathway and cell-cell communication, while activated BMP2 could in turn activate integrins and Cx43-related cell-cell communication. Furthermore, differences in activation of integrins, BMP2 signaling pathway, and gap junction-mediated cell-cell communication were observed, in which nanorod and micropattern structures activated different integrin subunits, BMP downstream receptors and Cx43. This finding may explain the synergistic effect of the micro/nano hybrid structure on the activation of osteogenic differentiation of BMSCs. Based on our study, we concluded that the different activation mechanisms of micro- and nano-structures led to the synergistic stimulatory effect on integrin activation and osteogenesis, in which not only the direct contact of cells on micro/nano structure played an important role, but also other surface characteristics such as protein adsorption might contribute to the bioactive effect.

STATEMENT OF SIGNIFICANCE

The micro/nano hybrid structure has been found to have synergistic bioactivity on osteogenesis. However, it is still a challenge to fabricate the hybrid structure directly on the bioceramics, and the role of micro- and nano-structure, in particular the mechanism of the micro/nano-hybrid structure induced stem cell differentiation is still unknown. In this study, we firstly fabricated hydroxyapatite bioceramics with the micro/nano hybrid structure, and then investigated the effect of different surface structure on expression of integrins, BMP2 signaling pathways and cell-cell communication. Interestingly, we found that the osteogenic differentiation induced by structure was modulated first through activating integrins and then further activating BMP2 signaling pathway and cell-cell communication, and activated BMP2 could in turn activate some integrin subunits and Cx43-related cell-cell communication. Furthermore, differences in activation of integrins, BMP2 signaling pathway, and gap junction-mediated cell-cell communication were observed, in which nanorod and micropattern structures activated different integrin subunits, BMP downstream receptors and Cx43. This finding may explain the synergistic effect of the micro/nano hybrid structure on the activation of osteogenic differentiation of BMSCs. Based on our study, we concluded that the different activation mechanisms of micro- and nano-structures led to the synergistic stimulatory effect on integrin activation and osteogenesis, in which not only the direct contact of cells on micro/nano structure played an important role, but also other surface characteristics such as protein adsorption might contribute to the bioactive effect.

Excavating the Role of Aloe Vera Wrapped Mesoporous Hydroxyapatite Frame Ornamentation in Newly Architectured Polyurethane Scaffolds for Osteogenesis and Guided Bone Regeneration with Microbial Protection

Guided bone regeneration (GBR) scaffolds are unsuccessful in many clinical applications due to a high incidence of postoperative infection. The objective of this work is to fabricate GBR with an anti-infective electrospun scaffold by ornamenting segmented polyurethane (SPU) with two-dimensional Aloe vera wrapped mesoporous hydroxyapatite (Al-mHA) nanorods. The antimicrobial characteristic of the scaffold has been retrieved from the prepared Al-mHA frame with high aspect ratio (∼14.2) via biosynthesis route using Aloe vera (Aloe barbadensis miller) extract. The Al-mHA frame was introduced into an unprecedented SPU matrix (solution polymerized) based on combinatorial soft segments of poly(ε-caprolactone) (PCL), poly(ethylene carbonate) (PEC), and poly(dimethylsiloxane) (PDMS), by an in situ technique followed by electrospinning to fabricate scaffolds. For comparison, pristine mHA nanorods are also ornamented into it. An enzymatic ring-opening polymerization technique was adapted to synthesize soft segment of (PCL-PEC-b-PDMS). Structure elucidation of the synthesized polymers is established by nuclear magnetic resonance spectroscopy. Sparingly, Al-mHA ornamented scaffolds exhibit tremendous improvement (175%) in the mechanical properties with promising antimicrobial activity against various human pathogens. After confirmation of high osteoconductivity, improved biodegradation, and excellent biocompatibility against osteoblast-like MG63 cells (in vitro), the scaffolds were implanted in rabbits as an animal model by subcutaneous and intraosseous (tibial) sites. Improved in vivo biocompatibilities, biodegradation, osteoconductivity, and the ability to provide an adequate biomimetic environment for biomineralization for GBR of the scaffolds (SPU and ornamented SPUs) have been found from the various histological sections. Early cartilage formation, endochondral ossification, and rapid bone healing at 4 weeks were found in the defects filled with Al-mHA ornamented scaffold compared to pristine SPU scaffold. Organ toxicity studies further confirm the absence of appreciable tissue architecture abnormalities in the renal hepatic and cardiac tissue sections. The entire results of this study manifest the feasibility of fabricating a mechanically adequate tailored nanofibrous SPU scaffold based on combinatorial soft segments of PCL, PEC, and PDMS by a biomimetic approach and the advantages of an Aloe vera wrapped mHA frame in promoting osteoblast phenotype progression with microbial protection for potential GBR applications.

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.

Highly porous ceramics based on ultralong hydroxyapatite nanowires

Highly porous ceramics with high biocompatibility are prepared using ultralong hydroxyapatite nanowires and palmitic acid spheres.

Silk sericin microcapsules with hydroxyapatite shells: protection and modification of organic microcapsules by biomimetic mineralization

Silk protein sericin based organic–inorganic hybrid microcapsules are fabricated by incubating sericin microcapsules with a supersaturated calcium phosphate solution containing citric acid.

Enhancing orthopedic implant bioactivity: refining the nanotopography

Advances in nanotechnology open up new possibilities to produce biomimetic surfaces that resemble the cell in vivo growth environment at a nanoscale level. Nanotopographical changes of biomaterials surfaces can positively impact the bioactivity and ossointegration properties of orthopedic and dental implants. This review introduces nanofabrication techniques currently used or those with high potential for use as surface modification of biomedical implants. The interactions of nanotopography with water, proteins and cells are also discussed, as they largely determine the final success of the implants. Due to the well-documented effects of surface chemistry and microtopography on the bioactivity of the implant, we here elaborate on the ability of the nanofabrication techniques to combine the dual (multi) modification of surface chemistry and/or microtopography.

Nb-C nanocomposite films with enhanced biocompatibility and mechanical properties for hard-tissue implant applications

One of the key challenges in engineering of orthopedic implants is to "bioactivate" their surface by using different surface techniques and materials. Carbon, especially amorphous (a-C) and diamond-like carbon down (DLC) films have attracted much attention in biomedical fields due to their biocompatibility and low coefficient of friction. However, they are unsuitable for uses as a "bioactivity enhancer" of orthopedic implants due to their bioinertness. In this work, we use the nonreactive magnetron sputtering technique to produce a-C films including the biocompatible niobium (Nb) element to alter the surface chemistry and nanotopography of the a-C films with the purpose of bioactivating the a-C film coated implants. Results show that the nanocomposite films (Nb-C) formed by the addition of Nb into the a-C films not only have improved corrosion resistance, but also possess enhanced mechanical properties (nanohardness, Young's modulus and superelastic recovery). Preosteoblasts (MC3T3-E1) cultured on the Nb-C films have enhanced adhesion and upregulated alkaline phosphatase (ALP) activity, compared to those cultured on the a-C film and TiO2 films used as a control, which are thought to be ascribed to the combined effects of the changes in surface chemistry and the refinement of the nanotopography caused by the addition of Nb.

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.

Refining nanotopographical features on bone implant surfaces by altering surface chemical compositions

Nb₂O₅/TiO₂ composite coatings with controllable nanostructures were achieved by adjusting the amount of Nb₂O₅ in one simple and single plasma spraying process and Nb₂O₅ doping showed its potential use in enhancing the biological properties of biomedical TiO₂ coatings.

Delicate refinement of surface nanotopography by adjusting TiO2 coating chemical composition for enhanced interfacial biocompatibility

Surface topography and chemistry have significant influences on the biological performance of biomedical implants. Our aim is to produce an implant surface with favorable biological properties by dual modification of surface chemistry and topography in one single simple process. In this study, because of its chemical stability, excellent corrosion resistance, and biocompatibility, titanium oxide (TiO2) was chosen to coat the biomedical Ti alloy implants. Biocompatible elements (niobium (Nb) and silicon (Si)) were introduced into TiO2 matrix to change the surface chemical composition and tailor the thermophysical properties, which in turn leads to the generation of topographical features under specific thermal history of plasma spraying. Results demonstrated that introduction of Nb2O5 resulted in the formation of Ti0.95Nb0.95O4 solid solution and led to the generation of nanoplate network structures on the composite coating surface. By contrast, the addition of SiO2 resulted in a hairy nanostructure and coexistence of rutile and quartz phases in the coating. Additionally, the introduction of Nb2O5 enhanced the corrosion resistance of TiO2 coating, whereas SiO2 did not exert much effect on the corrosion behaviors. Compared to the TiO2 coating, TiO2 coating doped with Nb2O5 enhanced primary human osteoblast adhesion and promoted cell proliferation, whereas TiO2 coatings with SiO2 were inferior in their bioactivity, compared to TiO2 coatings. Our results suggest that the incorporation of Nb2O5 can enhance the biological performance of TiO2 coatings by changing the surface chemical composition and nanotopgraphy, suggesting its potential use in modification of biomedical TiO2 coatings in orthopedic applications.