Porous zirconia/hydroxyapatite scaffolds for bone reconstruction

Synthesis of cerium, zirconium, and copper doped zinc oxide nanoparticles as potential biomaterials for tissue engineering applications

A novel eco-friendly high throughput continuous hydrothermal flow system was used to synthesise phase pure ZnO and doped ZnO in order to explore their properties for tissue engineering applications. Cerium, zirconium, and copper were introduced as dopants during flow synthesis of ZnO nanoparticles, Zirconium doped ZnO were successfully synthesised, however secondary phases of CeO and CuO were detected in X-ray diffraction (XRD). The nanoparticles were characterised using X-ray diffraction, Brunauer-Emmett-Teller (BET), Dynamic Light scattering Measurements, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and RAMAN spectroscopy was used to evaluate physical, chemical, and structural properties. The change in BET surface area was also significant, the surface area increased from 11.35 (ZnO_2) to 26.18 (ZrZnO_5). However. In case of CeZnO_5 and CuZnO_5 was not significant 13.68 (CeZnO_5) and 12.16 (CuZnO_5) respectively. Cell metabolic activity analysis using osteoblast-like cells (MG63) and human embryonic derived mesenchymal stem cells (hES-MP) demonstrated that doped ZnO nanoparticles supported higher cell metabolic activity compared to cells grown in standard media with no nanoparticles added, or pure zinc oxide nanoparticles. The ZrZnO_5 demonstrated the highest cell metabolic activity and non-cytotoxicity over the duration of 28 days as compared to un doped or Ce or Cu incorporated nanoparticles. The current data suggests that Zirconium doping positively enhances the properties of ZnO nanoparticles by increasing the surface area and cell proliferation. Therefore, are potential additives within biomaterials or for tissue engineering applications.

Load, unload and repeat: Understanding the mechanical characteristics of zirconia in dentistry

OBJECTIVES

Zirconia-based dental restorations and implants are gaining attention due to their bioactivity, corrosion resistance and mechanical stability. Further, surface modification of zirconia implants has been performed at the macro-, micro- and nanoscale to augment bioactivity. While zirconia's physical and chemical characteristics have been documented, its relation to mechanical performance still needs to be explored. This extensive review aims to address this knowledge gap.

METHODS

This review critically compares and contrasts the findings from articles published in the domain of 'mechanical stability of zirconia\ in dentistry' based on a literature survey (Web of Science, Medline/PubMed and Scopus databases) and a review of the relevant publications in international peer-reviewed journals. Reviewing the published data, the mechanical properties of zirconia, such as fracture resistance, stress/tension, flexural strength, fatigue, and wear are detailed and discussed to understand the biomechanical compatibility of zirconia with the mechanical performance of modified zirconia in dentistry also explored.

RESULTS

A comprehensive insight into dental zirconia's critical fundamental mechanical characteristics and performance is presented. Further, research challenges and future directions in this domain are recommended.

SIGNIFICANCE

This review extends existing knowledge of zirconia's biomechanical performance and it they can be modulated to design the next generation of zirconia dental restorations and implants to withstand long-term constant loading.

Porous Zirconia Scaffolds Functionalized with Calcium Phosphate Layers and PLGA Nanoparticles Loaded with Hydrophobic Gentamicin

Implant-related infections are a worldwide issue that is considered very challenging. Conventional therapies commonly end up failing; thus, new solutions are being investigated to overcome this problem. The in situ delivery of the drug at the implant site appears to be more sufficient compared to systemic antibiotic therapy. In this study, we manufactured porous zirconia scaffolds using the foam replication method. To improve their overall bioactivity, they were coated with a calcium phosphate (CaP) layer containing antibiotic-loaded degradable polymer nanoparticles (NPs) obtained by the double emulsion method to achieve the antibacterial effect additionally. Encapsulation efficiency (EE) and drug loading (DL) were superior and were equal to 99.9 ± 0.1% and 9.1 ± 0.1%, respectively. Scaffolds were analyzed with scanning electron microscopy, and their porosity was evaluated. The porosity of investigated samples was over 90% and resembled the microstructure of spongy bone. Furthermore, we investigated the cytocompatibility with osteoblast-like MG-63 cells and antimicrobial properties with Staphylococcus aureus. Scaffolds coated with a CaP layer were found non-toxic for MG-63 cells. Moreover, the presence of antibiotic-loaded nanoparticles had no significant influence on cell viability, and the obtained scaffolds inhibited bacteria growth. Provided processes of fabrication of highly porous zirconia scaffolds and surface functionalization allow minimizing the risk of implant-related infection.

Effect of Pore Defects on Uniaxial Mechanical Properties of Bulk Hexagonal Hydroxyapatite: A Molecular Dynamics Study

Hydroxyapatite (HAP) is a calcium apatite bioceramic used in various naturally-derived and synthetic forms for bone repair and regeneration. While useful for the regrowth of osseus tissue, the poor load-bearing capacity of this material relative to other biomaterials is worsened by the propensity for pore formation during the synthetic processing of scaffolds, blocks, and granules. Here we use molecular dynamics (MD) simulations to improve the current understanding of the defect-altered uniaxial mechanical response in hexagonal HAP single crystals relative to defect-free structures. The inclusion of a central spherical pore within a repeated lattice was found to reduce both the failure stress and failure strain in uniaxial tension and compression, with up to a 30% reduction in maximum stress at the point of failure compared to a perfect crystalline structure observed when a 30 Å diameter pore was included. The Z axis ([0 0 0 1] crystalline direction) was found to be the least susceptible to pore defects in tension but the most sensitive to pore inclusion in compression. The deformation mechanisms are discussed to explain the observed mechanical responses, for which charge imbalances and geometric stress concentration factor effects caused by pore inclusion play a significant role.

Frontiers of Hydroxyapatite Composites in Bionic Bone Tissue Engineering

Bone defects caused by various factors may cause morphological and functional disorders that can seriously affect patient's quality of life. Autologous bone grafting is morbid, involves numerous complications, and provides limited volume at donor site. Hence, tissue-engineered bone is a better alternative for repair of bone defects and for promoting a patient's functional recovery. Besides good biocompatibility, scaffolding materials represented by hydroxyapatite (HA) composites in tissue-engineered bone also have strong ability to guide bone regeneration. The development of manufacturing technology and advances in material science have made HA composite scaffolding more closely related to the composition and mechanical properties of natural bone. The surface morphology and pore diameter of the scaffold material are more important for cell proliferation, differentiation, and nutrient exchange. The degradation rate of the composite scaffold should match the rate of osteogenesis, and the loading of cells/cytokine is beneficial to promote the formation of new bone. In conclusion, there is no doubt that a breakthrough has been made in composition, mechanical properties, and degradation of HA composites. Biomimetic tissue-engineered bone based on vascularization and innervation show a promising future.

Bioactive Surface of Zirconia Implant Prepared by Nano-Hydroxyapatite and Type I Collagen

Zirconia, with its excellent mechanical strength and esthetics, has a growing potential for applications in dentistry and orthopedics. However, in order for zirconia to have a high affinity with bone tissue, the bioactivity of the surface must be further increased. In order to increase the bioactivity of zirconia, research was conducted to make a porous support or to fill the porous structure with nano-hydroxyapatite (nHA). In this case, there is a risk that physically filled nHA could be released depending on the living environment. In this study, nHA and type I collagen were introduced to the zirconia surface by chemical covalent bonding to increase bioactivity and ensure safety in the body. The chemical reaction of the surface was confirmed by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FT-IR) spectroscopy. In addition, the biological activity was evaluated by examining the cytotoxicity and bone formation ability of the modified zirconia using osteoblasts. As a result, it was found that the bioactivity of the zirconia surface was greatly improved by immobilizing nHA and type I collagen.

Review on synthesis, properties and multifarious therapeutic applications of nanostructured zirconia in dentistry

Amongst dental ceramics, nano zirconia (ZrNp) has shown exceptional developments in the field of dentistry in recent years. Zirconia is an oxide that possess superior optical, mechanical, and biological properties. As a novel nanoparticle, it has been widely used in various fields of dentistry due to its improved mechanical properties, biocompatibility, and stable structure. Provision of metal free solutions is one of the prime requirements in dental materials. Many metal alloys used extensively possess unaesthetic colors and display chemical interactions in the oral cavity encouraging use of zirconia for dental use. Use of ZrNp based ceramics has increased due to its resistance to corrosion, superior color matching that enhances esthetics and improved strength compared to conventional biomaterials. This review discusses the recent scientific literature on the synthesis, properties and types, applications, and toxicity of ZrNp in the field of dentistry.

Characterization of 3D Printed Yttria-Stabilized Zirconia Parts for Use in Prostheses

The main aim of the present paper is to study and analyze surface roughness, shrinkage, porosity, and mechanical strength of dense yttria-stabilized zirconia (YSZ) samples obtained by means of the extrusion printing technique. In the experiments, both print speed and layer height were varied, according to a 2² factorial design. Cuboid samples were defined, and three replicates were obtained for each experiment. After sintering, the shrinkage percentage was calculated in width and in height. Areal surface roughness, S_a, was measured on the lateral walls of the cuboids, and total porosity was determined by means of weight measurement. The compressive strength of the samples was determined. The lowest S_a value of 9.4 μm was obtained with low layer height and high print speed. Shrinkage percentage values ranged between 19% and 28%, and porosity values between 12% and 24%, depending on the printing conditions. Lowest porosity values correspond to low layer height and low print speed. The same conditions allow obtaining the highest average compressive strength value of 176 MPa, although high variability was observed. For this reason, further research will be carried out about mechanical strength of ceramic 3D printed samples. The results of this work will help choose appropriate printing conditions extrusion processes for ceramics.

A flexible and biocompatible bombyx mori silk fibroin/wool keratin composite scaffold with interconnective porous structure

The paper describes the preparation of a porous bombyx mori silk fibroin (SF)/wool keratin (WK) composite scaffold with mimic structure and function for cartilage tissue engineering. A porous composite scaffold made from SF/WK in an appropriate concentration and mass ratio was prepared using a freeze-drying technique. Results showed that the composite scaffolds are water-insoluble; possess good mechanical properties, porosity above 80%, and pore size above 200 μm. Larger pore size and better connectivity of the composite scaffold than the pure SF scaffolds were contributed by the WK addition. The heat resistance and water-swelling of WK enhanced the thermal and mechanical properties of the composite scaffolds. In vitro cytotoxicity assessments showed cells with a good growth state, confirming no toxicity to the cells. The results of in vivo biocompatibility assessments exhibited that there is almost no inflammatory response in the implantation site tissue of the rats. The development of porous SF/WK composite scaffold has the potential in cartilage tissue engineering.

Three-Dimensional Zirconia-Based Scaffolds for Load-Bearing Bone-Regeneration Applications: Prospects and Challenges

The design of zirconia-based scaffolds using conventional techniques for bone-regeneration applications has been studied extensively. Similar to dental applications, the use of three-dimensional (3D) zirconia-based ceramics for bone tissue engineering (BTE) has recently attracted considerable attention because of their high mechanical strength and biocompatibility. However, techniques to fabricate zirconia-based scaffolds for bone regeneration are in a stage of infancy. Hence, the biological activities of zirconia-based ceramics for bone-regeneration applications have not been fully investigated, in contrast to the well-established calcium phosphate-based ceramics for bone-regeneration applications. This paper outlines recent research developments and challenges concerning numerous three-dimensional (3D) zirconia-based scaffolds and reviews the associated fundamental fabrication techniques, key 3D fabrication developments and practical encounters to identify the optimal 3D fabrication technique for obtaining 3D zirconia-based scaffolds suitable for real-world applications. This review mainly summarized the articles that focused on in vitro and in vivo studies along with the fundamental mechanical characterizations on the 3D zirconia-based scaffolds.

Characterization of Titanium Surface Modification Strategies for Osseointegration Enhancement

As biocompatible metallic materials, titanium and its alloys have been widely used in the orthopedic field due to their superior strength, low density, and ease of processing. However, further improvement in biological response is still required for rapid osseointegration. Here, various Ti surface-treatment technologies were applied: hydroxyapatite blasting, sand blasting and acid etching, anodic oxidation, and micro-arc oxidation. The surface characteristics of specimens subjected to these techniques were analyzed in terms of structure, elemental composition, and wettability. The adhesion strength of the coating layer was also assessed for the coated specimens. Biocompatibility was compared via tests of in vitro attachment and proliferation of pre-osteoblast cells.

Biological response, antibacterial properties of ZrO2/hydroxyapatite/graphene oxide encapsulated into nanofibrous scaffolds of polylactic acid for wound healing applications

Designing proper nanofibrous scaffolds for wound healing applications is a necessity for improving the health care system. Hydroxyapatite (HAP), zirconia (ZrO₂), and graphene oxide (GO) nanosheets have been encapsulated in mono, di, or tri phases into nanofibrous scaffolds of polylactic acid (PLA). The structure of nanofibrous scaffolds is confirmed using XRD, XPS, while FESEM inspected the surface morphology. The surface morphology detection exhibited that the scaffolds have been formed in networked nanofibers with diameters from 1.19 to 2.38 to 0.59-1.42 µm, while the maximum height of the roughness increased from 610.4 to 809 nm for HAP@PLA and HAP/ZrO₂/GO@PLA, respectively. The contact angle was measured and showed a decreasing trend from 101.2 ± 4.1° and 89.1 ± 5.4° for HAP@PLA and HAP/ZrO₂/GO@PLA nanofibrous scaffolds. Moreover, the mechanical properties were examined and revealed that ZrO₂ dopant induced a significant enhancement into the tensile strength, which increased from 3.49 ± 0.3 to 8.45 ± 1.1 MPa for the nanofibrous scaffolds of HAP@PLA and HAP/ZrO₂/GO@PLA, respectively. The incorporation of ternary phases into PLA nanofibers promoted the cell viability to be around 98.2 ± 5%. The antibacterial potency has been investigated and showed that the activity increased to 69.2 ± 3.6 and 78.1 ± 4.5% against E. coli and S. aureus, respectively. Additionally, human fibroblasts proliferated on the surface and pores of nanofibrous scaffolds and significantly grown upon the compositional variation.

Titanium-based composite scaffolds reinforced with hydroxyapatite-zirconia: Production, mechanical and in-vitro characterization

In this study, titanium (Ti)-based composite scaffolds reinforced with hydroxyapatite-zirconia (HA-ZrO₂) were successfully produced with powder metallurgy and atmosphere-controlled sintering processes. The scaffolds structures were theoretically selected as 40% and 60% porosity, and fabricated with approximately 1.47 and 4.02 std dev values, respectively. The porosity of the scaffolds was verified by Archimedes' measurements. The scaffolds were characterized by DTA, SEM/EDS, XRD analyses. The mechanical behaviors of the scaffolds were evaluated by compression and hardness tests. Besides, the electrochemical corrosion behaviors of the structures were compared with potentiodynamic scanning (PDS) measurements in simulated body fluids (SBF) at 37 ± 1 °C. It has been observed that all scaffolds have a bimodal porous structure as they contain varying proportions of micropores as well as macropores in desired dimensions. Biocompatible phases such as Ti_xP_y, Ca₃(PO₄)₂ and CaTiO₃, respectively, were found in the microstructure after sintering. In compression tests, 40% porous Ti had the highest strength with 37.98 MPa, interestingly, the lowest strength was seen in Ti/HA-ZrO₂ scaffold with 60% porosity with 3.80 MPa. Young's modulus values of all scaffolds vary between 1.67 - 7.20 GPa, due to the bimodal pore structure and composition effect. However, in-vitro corrosion resistance of scaffolds decreased with HA reinforcement, while increased with ZrO₂ additive to HA.

Materials and Manufacturing Techniques for Polymeric and Ceramic Scaffolds Used in Implant Dentistry

Preventive and regenerative techniques have been suggested to minimize the aesthetic and functional effects caused by intraoral bone defects, enabling the installation of dental implants. Among them, porous three-dimensional structures (scaffolds) composed mainly of bioabsorbable ceramics, such as hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) stand out for reducing the use of autogenous, homogeneous, and xenogenous bone grafts and their unwanted effects. In order to stimulate bone formation, biodegradable polymers such as cellulose, collagen, glycosaminoglycans, polylactic acid (PLA), polyvinyl alcohol (PVA), poly-ε-caprolactone (PCL), polyglycolic acid (PGA), polyhydroxylbutyrate (PHB), polypropylenofumarate (PPF), polylactic-co-glycolic acid (PLGA), and poly L-co-D, L lactic acid (PLDLA) have also been studied. More recently, hybrid scaffolds can combine the tunable macro/microporosity and osteoinductive properties of ceramic materials with the chemical/physical properties of biodegradable polymers. Various methods are suggested for the manufacture of scaffolds with adequate porosity, such as conventional and additive manufacturing techniques and, more recently, 3D and 4D printing. The purpose of this manuscript is to review features concerning biomaterials, scaffolds macro and microstructure, fabrication techniques, as well as the potential interaction of the scaffolds with the human body.

New insights into bioactivity of ceria-stabilized zirconia: Direct bonding to bone-like hydroxyapatite at nanoscale

Osseointegration resulting from biomineralization means tight bone-implant attachment, which is clinically essential for successful dental implant treatment. The osseointegration ability of ceria-stabilized zirconia, a promising implant material, has been questionable and is unclear despite its clinical use due to zirconia's bioinert nature. The purpose of this research was to investigate the osseointegration ability of ceria-stabilized zirconia by clarifying its bioactivity. Here we show that ceria-stabilized zirconia is highly bioactive, contrary to the general consensus. Transmission electron microscopy observation revealed that the zirconia nanocrystals of a ceria-stabilized zirconia substrate directly bonded to osteoblastic cell-precipitated hydroxyapatite crystals at lattice fringe scale. This bonding was achieved without chemical treatment of the substrate surface before use. Hydroxyapatite crystals exhibited a morphology of flexible nanofibers less than 10 nm wide with nanometer-thick plates filling the spaces between nanofibers. Elemental analysis of the hydroxyapatites showed that they contained alkaline metal cations (Na, Mg, and K) as minor elements and that their average Ca/P atomic % ratio was ~1.40, similar to those of bone apatite. High bioactivity of ceria-stabilized zirconia resulted in direct bonding to bone-like hydroxyapatite, suggesting nanoscale direct osseointegration with bone in vivo that contributes to improving the success rate of dental implant treatment.

Hybrid porous zirconia scaffolds fabricated using additive manufacturing for bone tissue engineering applications

For the formation of new bone in critical-sized bone defects, bioactive scaffolds with an interconnected porous network are necessary. Herein, we fabricated three-dimensional (3D) porous hybrid zirconia scaffolds to promote hybrid functionality, i.e., excellent mechanical properties and bioactive performance. Specifically, the 3D printed scaffolds were subjected to Zn-HA/glass composite coating on glass-infiltrated zirconia (ZC). In addition, to pertain the extracellular matrix of bone, biopolymer (alginate/gelatine) was embedded in a developed 3D construct (ZB and ZCB). A zirconia-printed scaffold (Z) group served as a control. The structural and mechanical properties of the constructed scaffolds were studied using essential characterization techniques. Furthermore, the biological performance of the designed scaffolds was tested by a sequence of in vitro cell tests, including the attachment, proliferation, and osteogenic differentiation of dental pulp cells (DPCs). The ZC and ZCB scaffolds exhibited 20% higher compression strength than the zirconia (Z) scaffolds. More importantly, the ZC constructs exhibited superior cell-adhesion, distribution, and osteogenic differentiation ability due to the synergistic effects of the composite coating. In addition, the biopolymer-embedded scaffolds (ZB, ZCB) showed an excellent biological and mechanical performance. Thus, our results suggest that the Zn-HA/glass composite-coated glass-infiltrated zirconia (ZC, ZCB) scaffolds are a dynamic approach to designing bioactive 3D scaffolds for the load-bearing bone regeneration applications.

Exosomes from 3D culture of marrow stem cells enhances endothelial cell proliferation, migration, and angiogenesis via activation of the HMGB1/AKT pathway

BACKGROUND

Angiogenesis is an essential step in tissue engineering. MSC exosomes play an important role in angiogenesis. Functional biomolecules in exosomes vested by the culture microenvironment can be transferred to recipient cells and affects their effect. 3D culture can improve the proliferation and activity of MSCs. However, whether exosomes derived from 3D culture of MSCs have an enhanced effect on angiogenesis is unclear.

METHODS

Herein, we compared the bioactivity of exosomes produced by conventional 2D culture (2D-exos) and 3D culture (3D-exos) of bone marrow stem cells (BMSCs) in angiogenesis.

RESULTS

A series of in vitro and in vivo experiments indicated that 3D-exos exhibited stronger effects on HUVEC cell proliferation, migration, tube formation, and in vivo angiogenesis compared with 2D-exos. Moreover, the superiority of 3D-exos might be attributed to the activation of HMGB1/AKT signaling.

CONCLUSIONS

These results indicate that exosomes from 3D culture of MSCs may serve as a potential therapeutic approach for pro-angiogenesis.

Mesenchymal Stem Cells Coated with Synthetic Bone-Targeting Polymers Enhance Osteoporotic Bone Fracture Regeneration

Osteoporosis is a progressive skeletal disease characterized by reduced bone density leading to bone fragility and an elevated risk of bone fractures. In osteoporotic conditions, decrease in bone density happens due to the augmented osteoclastic activity and the reduced number of osteoblast progenitor cells (mesenchymal stem cells, MSCs). We investigated a new method of cell therapy with membrane-engineered MSCs to restore the osteoblast progenitor pool and to inhibit osteoclastic activity in the fractured osteoporotic bones. The primary active sites of the polymer are the N-hydroxysuccinimide and bisphosphonate groups that allow the polymer to covalently bind to the MSCs' plasma membrane, target hydroxyapatite molecules on the bone surface and inhibit osteolysis. The therapeutic utility of the membrane-engineered MSCs was investigated in female rats with induced estrogen-dependent osteoporosis and ulnar fractures. The analysis of the bone density dynamics showed a 27.4% and 21.5% increase in bone density at 4 and 24 weeks after the osteotomy of the ulna in animals that received four transplantations of polymer-modified MSCs. The results of the intravital observations were confirmed by the post-mortem analysis of histological slices of the fracture zones. Therefore, this combined approach that involves polymer and cell transplantation shows promise and warrants further bio-safety and clinical exploration.

Study of nanoscale deformation mechanisms in bulk hexagonal hydroxyapatite under uniaxial loading using molecular dynamics

Hydroxyapatite (HAP) is a natural bioceramic which is currently used in scaffolds and coatings for the regrowth of osseous tissue but offers poor load-bearing capacity compared to other biomaterials. The deformation mechanisms responsible for the mechanical behavior of HAP are not well understood, although the advent of multiscale modeling offers the promise of improvements in many materials through computational materials science. This work utilizes molecular dynamics to study the nanoscale deformation mechanisms of HAP in uniaxial tension and compression. It was found that deformation mechanisms vary with loading direction in tension and compression leading to significant compression/tension asymmetry and crystal anisotropy. Bond orientation and geometry relative to the loading direction was found to be an indicator of whether a specific bond was involved in the deformation of HAP in each loading case. Tensile failure mechanisms were attributed to stretching and failure in loading case-specific ionic bond groups. The compressive failure mechanisms were attributed to coulombic repulsion in each case, although loading case-specific bond group rotation and displacement were found to affect specific failure modes. The elastic modulus was the highest for both tension and compression along the Z direction (i.e. normal to the basal plane), followed by Y and X.

Biocompatibility of α-Al2O3 Ceramic Substrates with Human Neural Precursor Cells

BACKGROUND

Biocompatible materials-topography could be used for the construction of scaffolds allowing the three-dimensional (3D) organization of human stem cells into functional tissue-like structures with a defined architecture.

METHODS

Structural characterization of an alumina-based substrate was performed through XRD, Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), and wettability measurements. Biocompatibility of the substrate was assessed by measuring the proliferation and differentiation of human neural precursor stem cells (NPCs).

RESULTS

α-Al₂O₃ is a ceramic material with crystallite size of 40 nm; its surface consists of aggregates in the range of 8-22 μm which forms a rough surface in the microscale with 1-8 μm cavities. The non-calcined material has a surface area of 5.5 m²/gr and pore size distribution of 20 nm, which is eliminated in the calcined structure. Thus, the pore network on the surface and the body of the ceramic becomes more water proof, as indicated by wettability measurements. The alumina-based substrate supported the proliferation of human NPCs and their differentiation into functional neurons.

CONCLUSIONS

Our work indicates the potential use of alumina for the construction of 3D engineered biosystems utilizing human neurons. Such systems may be useful for diagnostic purposes, drug testing, or biotechnological applications.

Fabrication and characterization of ZrO2 incorporated SiO2-CaO-P2O5 bioactive glass scaffolds

Sol-gel chemistry offers a flexible, widely accepted methodology that enables the creation of a new generation of bioactive glass (BG). In the current study, a sol-gel method was used to synthesize ZrO₂ incorporated 56SiO₂-34CaO-10P₂O₅ mol% bioactive glass. The highly crystalline structure was composed of small zirconium oxide nanoparticles (ZrO₂) of less than 200 nm in size. It was successfully fabricated using a hydrothermal method. Polyurethane foam (PU) was selected to fabricate a highly porous BG-ZrO₂ scaffold using a foam replica technique. The physicochemical, morphological properties of the BG-ZrO₂ compositions were evaluated using X-ray diffraction (XRD), Fourier transforms infrared (FTIR), thermo-gravimetric analysis (TGA), transmission electron microscope (TEM) and scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). In-vitro degradation analysis of the BG-ZrO₂ scaffolds was performed after immersion of the samples in simulated body fluid (SBF). The incorporation of ZrO₂ nanoparticles into the bioactive glass matrix enhances both the mechanical strength and thermal stability. Since the novel formed BG-ZrO₂ scaffolds possesses respectable antibacterial properties against some bacterial strains, this renders it an ideal tissue engineering substitute, capable of reducing failure rates in implants.

The role of apoptosis associated speck-like protein containing a caspase-1 recruitment domain (ASC) in response to bone substitutes

The apoptosis-associated Speck-like protein containing a caspase-1 recruitment domain (ASC), present in inflammasomes, regulates inflammation events and is involved in osteogenic phenotype. Nevertheless, its function in bone repair induced by bone substitute biomaterials is unclear. This study aimed to unveil the role of ASC on osteoprogenitor and tissue response to stoichiometric-hydroxyapatite (HA), nanostructured carbonated-hydroxyapatite (CHA), and CHA containing 5% Strontium (SrCHA), characterized previously by XRD, uXRF-SR, and FTIR spectroscopy implants. Thereafter, conditioned media by the biomaterials were used later to treat pre-osteoblasts and an osteogenic stimulus was shown in response to the materials, with higher expression of Runx2, Osterix, ALP, and Collagen 1a1 genes, with significant involvement of inflammatory-related genes. Thus, to better address the involvement of inflammasome, primary cells obtained from both genotypes [Wild-Type (WT) and ASC Knockout (ASC-KO) mice] were subjected to conditioned media up to 7 days, and our data reinforces both HA and CHA induces lower levels of alkaline phosphatase (ALP) than SrCHA, considering both genotypes (p < 0.01), and ASC seems contribute with osteogenic stimulus promoted by SrCHA. Complimentarily, the biomaterials were implanted into both subcutaneous and bone defects in tibia. Histological analysis on 28 days after implantation of biomaterials into mice's subcutaneous tissue revealed moderate inflammatory response to them. Both histomorphometry and μCT analysis of tibias indicated that the biomaterials did not reverse the delay in bone repair of ASC KO, reinforcing the involvement of ASC on bone regeneration and bone de novo deposition. Also, the bone density in CHA was >2-fold higher in WT than ASC-KO samples. HA was virtually not resorbed throughout the experimental periods, in opposition to CHA in the WT group. CHA reduced to half-area after 28 days, and the bone deposition was higher in CHA for WT mice than HA. Taken together, our results show that biomaterials did not interfere with the healing pattern of the ASC KO, but CHA promoted higher bone deposition in the WT group, probably due to its greater biodegradability. These results reinforce the importance of ASC during bone de novo deposition and healing.

Production and characterization of zirconia structures with a porous surface

The aim of this study was to produce zirconia structures with a porous surface by the dip coating technique and assess the mechanical properties of the structures as well as the integrity of the porous layers. Surface porous layers with homogenous and graded porosity were produced over zirconia substrate discs using zirconia powders with different average sizes (d₅₀ = 40 μm; d₅₀ = 70 μm and d₅₀ = 100 μm) and without pore forming fugitive phases. Specimens were inspected using Scanning Electron Microscopy. Bending strength of specimens was obtained from biaxial flexural tests (B3B). Porous layers were successfully produced on zirconia discs substrates and the bending strength of these specimens were ~35% lower than uncoated specimens. Delamination occurred especially in layers with higher thickness and made of bigger particles. Practical application examples were provided in this paper showing the versatility of these porous surfaces in the production of multifunctional surfaces for stronger interfaces.

Evaluation of the Possible Synergic Regenerative Effects of Platelet-Rich Plasma and Hydroxyapatite/Zirconia in the Rabbit Mandible Defect Model

BACKGROUND

Platelet-rich plasma (PRP) and bioceramics such as hydroxyapatite (HA) and zirconium oxide (ZrO₂) are used to reconstruct mandibular defects. We sought to determine the synergistic effects of HA/ZrO₂ and PRP and compare their osteogenic activity.

METHODS

ZrO₂ scaffolds were constructed by the slurry method and were then coated with HA and impregnated by PRP/heparan sulfate (HS). Bilateral mandibular defects were created in 26 male rabbits. In 20 rabbits, the left defects were treated with HA/ZrO₂/PRP (Group 1) and the corresponding right defects were filled with HA/ZrO₂ (Group 2). The 6 remaining models were treated with PRP gels at both sides (Group 3). The osteoconductivity of HA/ZrO₂/PRP was compared with that of HA/ZrO₂ or PRP by radiological and histological methods after the follow-up period, at weeks 2, 6 and 8. The statistical analyses were performed by ANOVA and LSD using SPSS, version 16.0, for Windows (P<0.05).

RESULTS

After 2 weeks, the percentage of the surface occupied by bone was significantly higher in the HA/ZrO₂/PRP-treated defects than in the PRP-treated defects (P=0.007). Osteoblast and osteocyte counts were higher significantly in the PRP-treated group (P=0.032); however, the cells had not started matrix formation on a large scale and just small islands of osteoid with trapped osteocytes were observed. In the long term, the regenerative potential of all the scaffolds was the same.

CONCLUSION

HA/ZrO₂ showed a superior osteoconductive capacity over PRP in the short term; however, they showed no long-term synergic effects.

Comparative investigation of porous nano-hydroxyapaptite/chitosan, nano-zirconia/chitosan and novel nano-calcium zirconate/chitosan composite scaffolds for their potential applications in bone regeneration

Zirconium (Zr) based bioceramic nanoparticles, as the filler material to chitosan (CS), for the development of composite scaffolds are less studied compared to hydroxyapatite nanoparticles. This is predominantly due to the biological similarity of nano-hydroxyapatite (nHA; Ca10(PO4)6(OH)2) with bone inorganic component. In this study, we compared the physical and biological properties of CS composite scaffolds hybridized with nHA, nano-zirconia (nZrO; ZrO2), and nano-calcium zirconate (nCZ; CaZrO3). For the first time in this study, the properties of CS-nCZ composite scaffolds have been reported. The porous composite scaffolds were developed using the freeze-drying technique. The compressive strength and modulus were in the range of 50-55 KPa and 0.75-0.95 MPa for composite scaffolds, significantly higher (p < 0.05), compared to CS alone scaffolds (28 KPa and 0.25 MPa) and were comparable among CS-nHA, CS-nZrO, and CS-nCZ scaffolds. Peak force quantitative nanomechanical mapping (PFQNM) using an atomic force microscope (AFM) showed that the Young's modulus of composite material was higher compared to only CS (p < 0.001), and the values were similar among the composite materials. One of the major issues in the use of Zr based bioceramic materials in bone tissue regeneration applications is their lower osteoblasts response. This study has shown that CS-nCZ supported higher proliferation of pre-osteoblasts compared to CS-nZrO and the spreading was more similar to that observed in CS-nHA scaffolds. Taken together, results show that the physical and biological properties, studied here, of CS composite with Zr based bio-ceramic was comparable with CS-nHA composite scaffolds and hence show the prospective of CS-nCZ for future bone tissue engineering applications.

Zirconia-Based Biomaterials for Hard Tissue Reconstruction

Implantable biomaterials are increasingly important in the practice of modern medicine, including fixative, replacement, and regeneration therapies, for reconstruction of hard tissues in patients with pathologic osseous and dental conditions. A number of newly developed advanced biomaterials have been introduced as promising candidates for tissue reconstruction. Among these, zirconia-based biomaterials have gained attention as a biomaterial for hard tissue reconstruction due to superior mechanical properties and good chemical and biological compatibilities. This review summarizes the types of zirconia, advantages of zirconia-based biomaterials for hard tissue reconstruction including bone and dental tissues, responses of tissue and cells to zirconia, and surface modifications for enhanced bioactivity of zirconia. Current and future applications of zirconia-based biomaterials for bone and dental reconstruction, ie, medical implanted devices, dental prostheses, and biocompatible osteogenic scaffolds, are also discussed.

Fabrication and evaluation of 3D printed BCP scaffolds reinforced with ZrO2 for bone tissue applications

Fused deposition modeling (FDM) is a promising 3D printing and manufacturing step to create well interconnected porous scaffold designs from the computer-aided design (CAD) models for the next generation of bone scaffolds. The purpose of this study was to fabricate and evaluate a new biphasic calcium phosphate (BCP) scaffold reinforced with zirconia (ZrO₂ ) by a FDM system for bone tissue engineering. The 3D slurry foams with blending agents were successfully fabricated by a FDM system. Blending materials were then removed after the sintering process at high temperature to obtain a targeted BCP/ZrO₂ scaffold with the desired pore characteristics, porosity, and dimension. Morphology of the sintered scaffold was investigated with SEM/EDS mapping. A cell proliferation test was carried out and evaluated with osteosarcoma MG-63 cells. Mechanical testing and cell proliferation evaluation demonstrated that 90% BCP and 10% ZrO₂ scaffold had a significant effect on the mechanical properties maintaining a structure compared that of only 100% BCP with no ZrO₂ . Additionally, differentiation studies of human mesenchymal stem cells (hMSCs) on BCP/ZrO₂ scaffolds in static and dynamic culture conditions showed increased expression of bone morphogenic protein-2 (BMP-2) when cultured on BCP/ZrO₂ scaffolds under dynamic conditions compared to on BCP control scaffolds. The manufacturing of BCP/ZrO₂ scaffolds through this innovative technique of a FDM may provide applications for various types of tissue regeneration, including bone and cartilage.

Osteogenesis ability of CAD/CAM porous zirconia scaffolds enriched with nano-hydroxyapatite particles

Background

The aim of this study was to evaluate osteogenesis ability of CAD/CAM porous zirconia scaffolds enriched with hydroxy apatite used to augment large boney defects in a dog model.

Methods

Surgical defects were made bilaterally on the lower jaw of 12 Beagle dogs. Cone beam CT images were used to create three dimensional images of the healed defects. Porous zirconia scaffolds were fabricated by milling custom made CAD/CAM blocks into the desired shape. After sintering, the pores of half of the scaffolds were filled with a nano-hydroxy apatite (HA) powder while the other half served as control. The scaffolds were inserted bilaterally in the healed mandibular jaw defects and were secured in position by resorbable fixation screws. After a healing time of 6 weeks, bone-scaffold interface was subjected to histomorphometric analysis to detect the amount of new bone formation. Stained histological sections were analyzed using a computer software (n=12, α=0.05). Mercury porosimetery was used to measure pore sizes, chemical composition was analyzed using energy dispersive x-ray analysis (EDX), and the crystal structure was identified using x-ray diffraction micro-analysis (XRD).

Results

HA enriched zirconia scaffolds revealed significantly higher volume of new bone formation (33% ± 14) compared to the controls (21% ± 11). New bone deposition started by coating the pore cavity walls and proceeded by filling the entire pore volume. Bone in-growth started from the surface of the scaffold and propagated towards the scaffold core. Islands of entrapped hydroxy apatite particles were observed in mineralized bone matrix.

Conclusions

Within the limitations of this study, hydroxy apatite enhanced osteogenesis ability of porous zirconia scaffolds.

Zein-based composites in biomedical applications

Considerable research efforts have been devoted to zein-based biomaterials for tissue engineering and other biomedical applications over the past decade. The attention given to zein-based polymers is primarily attributed to their biocompatibility and biodegradability. However, due to the relatively low mechanical properties of these polymers, numerous inorganic compounds (e.g., hydroxyapatite, calcium phosphate, bioactive glasses, natural clays) have been considered in combination with zein to create composite materials in an attempt to enhance zein mechanical properties. Inorganic phases also positively impact on the hydrophilic properties of zein matrices inducing a suitable environment for cell attachment, spreading, and proliferation. This review covers available literature on zein and zein-based composite materials, with focus on the combination of zein with commonly used inorganic fillers for tissue engineering and drug delivery applications. An overview of the most recent advances in fabrication techniques for zein-based composites is presented and key applications areas and future developments in the field are highlighted. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1656-1665, 2017.

Physico-mechanical and morphological features of zirconia substituted hydroxyapatite nano crystals

Zirconia doped Hydroxyapatite (HAP) nanocrystals [Ca₁₀(PO₄)_6−x(ZrO₂)_x(OH)₂]; (0 ≤ x ≤ 1 step 0.2) were synthesized using simple low cost facile method. The crystalline phases were examined by X-ray diffraction (XRD). The crystallinity percentage decreased with increasing zirconia content for the as-synthesized samples. The existence of zirconia as secondary phase on the grain boundaries; as observed from scanning electron micrographs (FESEM); resulted in negative values of microstrain. The crystallite size was computed and the results showed that it increased with increasing annealing temperature. Thermo-gravimetric analysis (TGA) assured the thermal stability of the nano crystals over the temperature from room up to 1200 °C depending on the zirconia content. The corrosion rate was found to decrease around 25 times with increasing zirconia content from x = 0.0 to 1.0. Microhardness displayed both compositional and temperature dependence. For the sample (x = 0.6), annealed at 1200 °C, the former increased up to 1.2 times its original value (x = 0.0).

Using mesenchymal stem cells as a therapy for bone regeneration and repairing

Bone is a unique tissue which could regenerate completely after injury rather than heal itself with a scar. Compared with other tissues the difference is that, during bone repairing and regeneration, after the inflammatory phase the mesenchymal stem cells (MSCs) are recruited to the injury site and differentiate into either chondroblasts or osteoblasts precursors, leading to bone repairing and regeneration. Besides these two precursors, the MSCs can also differentiate into adipocyte precursors, skeletal muscle precursors and some other mesodermal cells. With this multilineage potentiality, the MSCs are probably used to cure bone injury and other woundings in the near future. Here we will introduce the recent developments in understanding the mechanism of MSCs action in bone regeneration and repairing.

Application of dental nanomaterials: potential toxicity to the central nervous system

Nanomaterials are defined as materials with one or more external dimensions with a size of 1-100 nm. Such materials possess typical nanostructure-dependent properties (eg, chemical, biological, optical, mechanical, and magnetic), which may differ greatly from the properties of their bulk counterparts. In recent years, nanomaterials have been widely used in the production of dental materials, particularly in light polymerization composite resins and bonding systems, coating materials for dental implants, bioceramics, endodontic sealers, and mouthwashes. However, the dental applications of nanomaterials yield not only a significant improvement in clinical treatments but also growing concerns regarding their biosecurity. The brain is well protected by the blood-brain barrier (BBB), which separates the blood from the cerebral parenchyma. However, in recent years, many studies have found that nanoparticles (NPs), including nanocarriers, can transport through the BBB and locate in the central nervous system (CNS). Because the CNS may be a potential target organ of the nanomaterials, it is essential to determine the neurotoxic effects of NPs. In this review, possible dental nanomaterials and their pathways into the CNS are discussed, as well as related neurotoxicity effects underlying the in vitro and in vivo studies. Finally, we analyze the limitations of the current testing methods on the toxicological effects of nanomaterials. This review contributes to a better understanding of the nano-related risks to the CNS as well as the further development of safety assessment systems.

Fitting accuracy and fracture resistance of crowns using a hybrid zirconia frame made of both porous and dense zirconia

The purpose of this study is to evaluate the fitting accuracy and fracture resistance of crowns using a hybrid zirconia frame made of both porous and dense zirconia. Commercial semi-sintered zirconia, sintered dense zirconia and sintered hybrid zirconia were used. Sintered zirconia was milled using the CAD/CAM system, and semi-sintered zirconia was milled and sintered to fabricate molar crown frames. Completed frames were veneered with tooth-colored porcelain. The marginal and internal gaps between frames/crowns and abutments were measured. Each crown specimen was subjected to a fracture test. There were no significant differences in marginal and internal gap among all the frames and crowns. The crown with the hybrid zirconia frame had a 31-35% greater fracture load than that with the commercial or dense zirconia frame (p<0.01). This suggests that the all-ceramic crowns with a hybrid zirconia frame have a high fracture resistance.

Shear bond strength of veneering porcelain to porous zirconia

In this study, two types of porous zirconia and dense zirconia were used. The flexural strength of non-layered zirconia specimens and those of the layered zirconia specimens with veneering porcelain were examined. Furthermore, the shear bond strength of veneering porcelain to zirconia was examined. The flexural strength of the non-layered specimens was 1,220 MPa for dense zirconia and 220 to 306 MPa for porous zirconia. The flexural strength of the layered specimens was 360 MPa for dense zirconia and 132 to 156 MPa for porous zirconia, when a load was applied to the porcelain side. The shear bond strength of porcelain veneered to dense zirconia was 27.4 MPa and that of porcelain veneered to porous zirconia was 33.6 to 35.1 MPa. This suggests that the veneering porcelain bonded strongly to porous zirconia although porous zirconia has a lower flexural strength than dense zirconia.

Biomaterials in tooth tissue engineering: a review

Biomaterials play a crucial role in the field of tissue engineering. They are utilized for fabricating frameworks known as scaffolds, matrices or constructs which are interconnected porous structures that establish a cellular microenvironment required for optimal tissue regeneration. Several natural and synthetic biomaterials have been utilized for fabrication of tissue engineering scaffolds. Amongst different biomaterials, polymers are the most extensively experimented and employed materials. They can be tailored to provide good interconnected porosity, large surface area, adequate mechanical strengths, varying surface characterization and different geometries required for tissue regeneration. A single type of material may however not meet all the requirements. Selection of two or more biomaterials, optimization of their physical, chemical and mechanical properties and advanced fabrication techniques are required to obtain scaffold designs intended for their final application. Current focus is aimed at designing biomaterials such that they will replicate the local extra cellular environment of the native organ and enable cell-cell and cell-scaffold interactions at micro level required for functional tissue regeneration. This article provides an insight into the different biomaterials available and the emerging use of nano engineering principles for the construction of bioactive scaffolds in tooth regeneration.

The application of induced pluripotent stem cells for bone regeneration: current progress and prospects

Loss of healthy bone tissue and dysosteogenesis are still common and significant problems in clinics. Cell-based therapy using mesenchymal stem cells (MSCs) has been performed in patients for quite some time, but the inherent drawbacks of these cells, such as the reductions in proliferation rate and osteogenic differentiation potential that occur with aging, greatly limit their further application. Moreover, embryonic stem cells (ESCs) have brought new hope to osteoregenerative medicine because of their full pluripotent differentiation potential and excellent performance in bone regeneration. However, the ethical issues involved in destroying human embryos and the immune reactions that occur after transplantation are two major stumbling blocks impeding the clinical application of ESCs. Instead, induced pluripotent stem cells (iPSCs), which are ESC-like pluripotent cells that are reprogrammed from adult somatic cells using defined transcription factors, are considered a more promising source of cells for regenerative medicine because they present no ethical or immunological issues. Here, we summarize the primary technologies for generating iPSCs and the biological properties of these cells, review the current advances in iPSC-based bone regeneration and, finally, discuss the remaining challenges associated with these cells, particularly safety issues and their potential application for osteoregenerative medicine.