Effect of ZrO2 addition on the mechanical properties of porous TiO2 bone scaffolds

This study aimed at the investigation of the effect of zirconium dioxide (ZrO₂) addition on the mechanical properties of titanium dioxide (TiO₂) bone scaffolds. The highly biocompatible TiO₂ has been identified as a promising material for bone scaffolds, whereas the more bioinert ZrO₂ is known for its excellent mechanical properties. Ultra-porous TiO₂ scaffolds (> 89% porosity) were produced using polymer sponge replication with 0–40 wt.% of the TiO₂ raw material substituted with ZrO₂. Microstructure, chemical composition, and pore architectural features of the prepared ceramic foams were characterised and related to their mechanical strength. Addition of 1 wt.% of ZrO₂ led to 16% increase in the mean compressive strength without significant changes in the pore architectural parameters of TiO₂ scaffolds. Further ZrO₂ additions resulted in reduction of compressive strength in comparison to containing no ZrO₂. The appearance of zirconium titanate (ZrTiO₄) phase was found to hinder the densification of the ceramic material during sintering resulting in poor intergranular connections and thus significantly reducing the compressive strength of the highly porous ceramic foam scaffolds.     

Ultra-porous titanium oxide scaffold with high compressive strength

Highly porous and well interconnected titanium dioxide (TiO₂) scaffolds with compressive strength above 2.5 MPa were fabricated without compromising the desired pore architectural characteristics, such as high porosity, appropriate pore size, surface-to-volume ratio, and interconnectivity. Processing parameters and pore architectural characteristics were investigated in order to identify the key processing steps and morphological properties that contributed to the enhanced strength of the scaffolds. Cleaning of the TiO₂ raw powder removed phosphates but introduced sodium into the powder, which was suggested to decrease the slurry stability. Strong correlation was found between compressive strength and both replication times and solid content in the ceramic slurry. Increase in the solid content resulted in more favourable sponge loading, which was achieved due to the more suitable rheological properties of the ceramic slurry. Repeated replication process induced only negligible changes in the pore architectural parameters indicating a reduced flaw size in the scaffold struts. The fabricated TiO₂ scaffolds show great promise as load-bearing bone scaffolds for applications where moderate mechanical support is required.     

Preparation and characterization of macroporous chitosan/wollastonite composite scaffolds for tissue engineering

Chitosan/wollastonite composite scaffolds were prepared by a thermally induced phase separation method. The microstructure, mechanical performance and in vitro bioactivity of the composite scaffolds were investigated. The composite scaffolds were macroporous and wollastonite particles were dispersed uniformly on the surface of the pore walls. Scanning electron microscope images of the composite scaffolds demonstrated that the scaffolds had interconnected pores with diameters from 60 to 200 microm. Both the pore size and structure were affected by freezing temperature. The mechanical performance of the composite scaffolds was improved compared to that of pure chitosan scaffolds. The in vitro bioactivity of the scaffolds was evaluated by soaking samples in simulated body fluid and the apatite layer was observed on the surface of the pore walls of the composite scaffolds. Our results suggest that the incorporation of wollastonite into chitosan could enhance both the mechanical strength and the in vitro bioactivity of the resultant composite. The macroporous chitosan/wollastonite scaffolds may be a potential candidate for application in tissue engineering.     

Thermal-crosslinked porous chitosan scaffolds for soft tissue engineering applications

The aim of this study was to demonstrate the feasibility of using a steam autoclave process for sterilization and simultaneously thermal-crosslinking of lyophilized chitosan scaffolds. This process is of great interest in biomaterial development due to its simplicity and low toxicity. The steam autoclave process had no significant effect on the average pore diameter (~ 70 μm) and overall porosity (> 80%) of the resultant chitosan scaffolds, while the sterilized scaffolds possessed more homogenous pore size distribution. The sterilized chitosan scaffolds exhibited an enhanced compressive modulus (109.8 kPa) and comparable equilibrium swelling ratio (23.3). The resultant chitosan scaffolds could be used directly for in vitro cell culture without extra sterilization. The data of in vitro studies demonstrated that the scaffolds facilitated cell attachment and proliferation, indicating great potential for soft tissue engineering applications.     

Chitosan-Based Nanocomposite Scaffolds for Tissue Engineering Applications

This article reports the fabrication of three-dimensional porous chitosan and hydroxyapatite (HA)/chitosan composite scaffolds by the thermally induced phase separation (TIPS) technique, for bone tissue engineering. Different amounts of HA nanoparticles (10%, 20%, and 30% g/g) were added to the chitosan solution to produce HA/chitosan composite scaffolds of varying compositions. The morphology and pore structure of the scaffolds vis-à-vis composition were characterized using scanning electron microscopy (SEM) and an energy dispersive X-ray (EDX). Both pure chitosan and HA/chitosan composite scaffolds were highly porous and had interconnected pores. The pore sizes ranged from several micrometers to a few hundred micrometers. The HA nanoparticles were well dispersed and physically coexisted with chitosan in the composite scaffolds. However, some agglomeration of HA nanoparticles was observed on the surface of pore walls when a relatively large amount of HA was used. The composite 3D scaffolds are very promising for use in bone tissue engineering application.     

Fabrication of porous titanium scaffolds with high compressive strength using camphene-based freeze casting

We herein report the fabrication of highly porous titanium (Ti) scaffolds with unusually high compressive strength by freezing a titanium hydride (TiH₂)/camphene slurries at 42 °C. As the freezing time was increased from 1 to 7 days, the pore size obtained was increased significantly from 143 to 271 μm due to the continual overgrowth of camphene dendrites. However, interestingly, the formation of the micro-pores inside the Ti walls was suppressed at longer freezing time. This resulted in a significant increase in compressive strength up to 110 ± 17 MPa with a porosity of 64%. It is believed that this unusually high compressive strength with large interconnected pores makes this material suitable for applications as load-bearing parts.     

Development of polycaprolactone/chitosan blend porous scaffolds

Polycaprolactone (PCL) and chitosan were blended to fabricate porous scaffolds for tissue-engineering applications by employing a concentrated acetic acid solution as solvent and salt particles as porogen. These scaffolds showed well-controlled and interconnected porous structures. The pore size and porosity of the scaffolds could be effectively modulated by selecting appropriate amounts and sizes of porogen. The results obtained from compressive mechanical measurements indicated that PCL/chitosan could basically retain their strength in their dry state compared to individual components. In a hydrated state, their compressive stress and modulus could be still well maintained even though the weight ratio of chitosan reached around 50 wt%.     

Effect of TiO2 nanoparticle loading on Poly(l-lactic acid) porous scaffolds fabricated by TIPS

Porous nanocomposite scaffolds of poly(l-lactic acid) (PLA), loaded with TiO₂ nanoparticles, were prepared by thermally induced phase-separation (TIPS). The preparation procedure induced crystalline polymer structures (with degree of crystallinity up to 51%) with no evidence of residual solvent, as confirmed by thermal analysis. Scaffold porosity, distribution of the nanofiller and shape of the pores were investigated by X-ray micro computed tomography (μ-CT) and scanning electron microscopy (SEM). The produced scaffolds with porosity of 86 ± 2% have interconnected open tubular pores with diameter and length in the ranges 40–80 μm and 200–400 μm respectively. The inorganic TiO₂ nano-additive is well dispersed in the scaffold walls, with only a small fraction of micrometric aggregates observable. All investigated polymer scaffolds display similar compressive moduli (between 2.1 and 2.8 MPa). Thermogravimetry (TGA), wide angle X-ray diffraction (XRD) and SEM analyses run on scaffolds subjected to in vitro mineralization tests showed that PLA scaffolds loaded with TiO₂ develop an amount of hydroxyapatite four times higher than that of plain PLA, thus assessing that titania nanoparticles confer improved bioactivity to the scaffolds.     

Fabrication of chitosan/poly(ε-caprolactone) composite hydrogels for tissue engineering applications

The aim of this study was to fabricate three-dimensional (3D) porous chitosan/poly(ε-caprolactone) (PCL) hydrogels with improved mechanical properties for tissue engineering applications. A modified emulsion lyophilisation technique was developed to produce 3D chitosan/PCL hydrogels. The addition of 25 and 50 wt% of PCL into chitosan substantially enhanced the compressive strength of composite hydrogel 160 and 290%, respectively, compared to pure chitosan hydrogel. The result of ATR–FTIR imaging corroborated that PCL and chitosan were well mixed and physically co-existed in the composite structures. The composite hydrogels were constructed of homogenous structure with average pore size of 59.7 ± 14 μm and finer pores with average size of 4.4 ± 2 μm on the wall of these larger pores. The SEM and confocal laser scanning microscopy images confirmed that fibroblast cells were attached and proliferated on the 3D structure of these composite hydrogels. The composite hydrogels acquired in this study possessed homogeneous porous structure with improved mechanical strength and integrity. They may have a high potential for the production of 3D hydrogels for tissue engineering applications.     

A novel bioactive three-dimensional β-tricalcium phosphate/chitosan scaffold for periodontal tissue engineering

The development of suitable bioactive three-dimensional scaffold for the promotion of cellular proliferation and differentiation is critical in periodontal tissue engineering. In this study,porous β-tricalcium phosphate/chitosan composite scaffolds were prepared through a freeze-drying method. These scaffolds were evaluated by analysis of microscopic structure, porosity, and cytocompatibility. The gene expression of bone sialoprotein (BSP) and cementum attachment protein (CAP) was detected with RT-PCR after human periodontal ligament cells (HPLCs) were seeded in these scaffolds. Then cell–scaffold complexes were implanted subcutaneously into athymic mice. The protein expression of alkaline phosphatase (ALP) and osteopontin (OPN) was detected in vivo. Results indicated that composite scaffolds displayed a homogeneous three-dimensional microstructure; suitable pore size (120 μm) and high porosity (91.07%). The composite scaffold showed higher proliferation rate than the pure chitosan scaffold, and up-regulated the gene expression of BSP and CAP. In vivo, HPLCs in the composite scaffold not only proliferated but also recruited vascular tissue ingrowth. The protein expression of ALP and OPN was up-regulated in the composite scaffold. Therefore, it was suggested that the composite scaffold could promote the differentiation of HPLCs towards osteoblast and cementoblast phenotypes.     

Improving the strength and biocompatibility of porous titanium scaffolds by creating elongated pores coated with a bioactive, nanoporous TiO2 layer

This paper reports a novel way of improving the mechanical properties and biocompatibility of porous Ti scaffolds using a combination of the modified sponge replication method and anodization process. The use of a stretched polymeric sponge as a novel template allowed the creation of elongated pores in a porous Ti scaffold, which, accordingly, led to a high compressive strength of 24.2 ± 2.08 MPa at a porosity of approximately 70 vol%. Furthermore, the surfaces of the Ti walls were coated successfully with a bioactive nanoporous TiO₂ layer using the anodization process, which enhanced the biocompatibility remarkably, as assessed by the attachment of MC3T3-E1 cells.     

Preparation of high strength macroporous hydroxyapatite scaffold

Hydroxyapatite (HAp) powder was prepared from CaNO₃·4H₂O and (NH₄)₂HPO₄ by wet-chemical method and has phase stable up to 1250 °C. High strength macroporous HAp–naphthalene (HN) and HAp–naphthalene–benzene (HNB) scaffolds were fabricated by adapting sintering method. The resulting HAp scaffolds have porosity about 60 vol.% with compressive strength of ~ 11 MPa and average pore diameter in the range of ~ 125 μm. The incorporation of benzene in HN scaffold reduces the strength whereas enhanced both the porosity and pore size distribution. XRD, FTIR, SEM and mercury porosimeter techniques were used to study the phase purity, morphology, pore size and pore size distribution of scaffold. The study compared the effect of concentration of naphthalene on strength, porosity and pore size distribution on both HN and HNB scaffold. In-vitro bioactivity studies on HN and HNB scaffolds show the nucleation of spherical carbonated apatite particles on the surface in SBF solution.     

纳米羟基磷灰石/聚己内酯复合生物活性多孔支架研究

采用水热法制备了纳米羟基磷灰石（n-HA）及其与聚己内酯（PCL）的复合材料. 用熔融浇铸/食盐微粒浸出法制备了孔径在200～400μｍ、大孔互相贯通的复合材料支架. 通过细胞培养和体内动物实验研究了该支架的生物学性能. 结果表明,复合支架的孔隙率随致孔剂用量的增加而增加,而抗压强度随之而减小;支架的最大孔隙率可达86%,相应的抗压强度为2.4MPa. 成骨细胞在支架上的细胞粘附率和增殖随磷灰石含量增加而提高,复合材料明显高于单纯的PCL支架. 组织学观察显示,新生骨长入多孔支架和复合材料形成了直接的骨性结合. n-HA/PCL复合材料支架有很好的生物相容性和生物活性.     

Silk fibroin/chitosan scaffold: preparation,characterization, and culture with HepG2 cell

Tissue engineering requires the development of three-dimensional water-stable scaffolds. In this study, silk fibroin/chitosan (SFCS) scaffold was successfully prepared by freeze-drying method. The scaffold is water-stable, only swelling to a limited extent depending on its composition. Fourier Transform Infrared (FTIR) spectra and X-Ray diffraction curves confirmed the different structure of SFCS scaffolds from both chitosan and silk fibroin. The homogeneous porous structure, together with nano-scale compatibility of the two naturally derived polymers, gives rise to the controllable mechanical properties of SFCS scaffolds. By varying the composition, both the compressive modulus and compressive strength of SFCS scaffolds can be controlled. The porosity of SFCS scaffolds is above 95% when the total concentration of silk fibroin and chitosan is below 6 wt%. The pore sizes of the SFCS scaffolds range from 100 μm to 150 μm, which can be regulated by changing the total concentration. MTT assay showed that SFCS scaffolds can promote the proliferation of HepG2 cells (human hepatoma cell line) significantly. All these results make SFCS scaffold a suitable candidate for tissue engineering.     

In vitro characterization of chitosan scaffolds: influence of composition and deacetylation degree

In this study, the influence of degree of deacetylation (DD) and composition on some structural and biological properties of chitosan scaffolds were examined in vitro. 3D chitosan scaffolds of 2% (w/v) and 3% (w/v) composition in different DDs i.e. 75–85% and >85% were prepared by freeze-drying method at −80 °C. We noticed that >85% deacetylated chitosan scaffolds of 2% (w/v) composition has a highly interconnected morphological structure having ∼100 μm pore size with 0.0917 N/mm² compression modulus. L929 fibroblastic cells were cultured on chitosan scaffolds in order to evaluate their biocompatibilities. Cell culture studies demonstrated that fibroblastic cell attachment and proliferation is affected by DD. The higher deacetylated chitosan scaffolds strongly supported the attachment and proliferation when compared with the lower deacetylated scaffolds. MTT assay indicated that >85% deacetylated chitosan scaffolds of 2% (w/v) composition, having the highest specific growth rate 0.017 h⁻¹ of all, was found to be the most suitable for cell culture studies and a potential candidate for tissue engineering with enhanced biostability and good biocompatibility.     

Attachment of stem cells on porous chitosan scaffold crosslinked by Na5P3O10

In this study, porous chitosan scaffolds were prepared by freeze-dried method using Na₅P₃O₁₀ as a crosslinking agent. The three-dimensional pore structure of the scaffold was interconnected with a mean pore size about 40 to 100 μm. The remained weight of crosslinked scaffold was about 76% after being exposed to PBS for 30 days. Mouse embryonic stem (E. S.) cells could grow on these crosslinked scaffolds. E. S. cells differentiated to other cells after 21 days of culturing on the scaffolds. The growth rate of E. S. cells was improved by post surface treatment of the scaffolds with collagen. However, there was no significant increase in growth rate of E. S. cells when scaffolds were surface treated with argon plasma. These porous chitosan scaffolds present a promising approach for tissue engineering applications.     

Fabrication of biocompatible titanium scaffolds using space holder technique

Open-pore titanium scaffolds were fabricated by sintering of compressed mixtures of TiH_1.924 and urea. Spherical and irregular shaped space holders were used to investigate the effect of pore shape on cellular behavior. After removal of the space holder, the shape of the spacers was replicated to the pores. Average diameter of the pores was in the range of 300–600?μm. SEM images showed that titanium hydride resulted in higher surface roughness and larger micro porosities than pure titanium. In vitro evaluations were carried out by using MTT assay, measuring alkaline phosphatase activity and alizarin red staining in flow perfusion bioreactor for cell culture. Observations revealed excellent attachment and proliferation of G-292 cells to the highly porous scaffolds fabricated with titanium hydride and urea of this research.     

In vitro evaluation of borate-based bioactive glass scaffolds prepared by a polymer foam replication method

Borate-based bioactive glass scaffolds with a microstructure similar to that of human trabecular bone were prepared using a polymer foam replication method, and evaluated in vitro for potential bone repair applications. The scaffolds (porosity = 72 ± 3%; pore size = 250–500 μm) had a compressive strength of 6.4 ± 1.0 MPa. The bioactivity of the scaffolds was confirmed by the formation of a hydroxyapatite (HA) layer on the surface of the glass within 7 days in 0.02 M K₂HPO₄ solution at 37 °C. The biocompatibility of the scaffolds was assessed from the response of cells to extracts of the dissolution products of the scaffolds, using assays of MTT hydrolysis, cell viability, and alkaline phosphatase activity. For boron concentrations below a threshold value (0.65 mM), extracts of the glass dissolution products supported the proliferation of bone marrow stromal cells, as well as the proliferation and function of murine MLO-A5 cells, an osteogenic cell line. Scanning electron microscopy showed attachment and continuous increase in the density of MLO-A5 cells cultured on the surface of the glass scaffolds. The results indicate that borate-based bioactive glass could be a potential scaffold material for bone tissue engineering provided that the boron released from the glass could be controlled below a threshold value.     

Biomorphous porous hydroxyapatite-ceramics from rattan (<Emphasis Type="Italic">Calamus Rotang</Emphasis>)

The three-dimensional, highly oriented pore channel anatomy of native rattan (Calamus rotang) was used as a template to fabricate biomorphous hydroxyapatite (Ca₅(PO₄)₃OH) ceramics designed for bone regeneration scaffolds. A low viscous hydroxyapatite-sol was prepared from triethyl phosphite and calcium nitrate tetrahydrate and repeatedly vacuum infiltrated into the native template. The template was subsequently pyrolysed at 800°C to form a biocarbon replica of the native tissue. Heat treatment at 1,300°C in air atmosphere caused oxidation of the carbon skeleton and sintering of the hydroxyapatite. SEM analysis confirmed detailed replication of rattan anatomy. Porosity of the samples measured by mercury porosimetry showed a multimodal pore size distribution in the range of 300 nm to 300 μm. Phase composition was determined by XRD and FT-IR revealing hydroxyapatite as the dominant phase with minimum fractions of CaO and Ca₃(PO₄)₂. The biomorphous scaffolds with a total porosity of 70–80% obtained a compressive strength of 3–5 MPa in axial direction and 1–2 MPa in radial direction of the pore channel orientation. Bending strength was determined in a coaxial double ring test resulting in a maximum bending strength of ~2 MPa.     

Hydrothermal synthesis of zirconia-based nanocomposite powder reinforced by graphene and its application for bone scaffold with 3D printing

Hydrothermal method is a cheap and green approach for the synthesis of composite powders. In this study, the zirconia (ZrO₂)-based nanocomposite powder was reinforced with reduced graphene oxide (ZrO₂/RGO) and was synthesized in a one-pot as a precursor for bone scaffold applications. Moreover, for the stimulation of osseointegration in bone scaffolds, Hydroxyapatite (HA) was used in 10 wt%. In this regard, the two types of ZrO₂/RGO and ZrO₂/RGO/HA precursors were applied for the fabrication of bone scaffolds via 3D printing and finally, the mechanical and biological properties of scaffolds were evaluated. For characterization, the X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), compress strength, and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide as MTT assay protocol were performed. The results demonstrated that the ZrO₂/RGO scaffolds with a tolerance of compressive stress of 240.11 MPa depicted better mechanical properties compared with ZrO₂/RGO/HA with the compress strength of 141.66 MPa. Moreover, after 7 days of bone scaffolds immersion in simulated body fluid (SBF) the growth of compressive strength began while after 28 days reached 260.15 MPa for ZrO₂/RGO and 192.31 for ZrO₂/RGO/HA. Finally, the cellular response of the scaffolds indicated the lack of cellular toxicity of the scaffolds during MTT assay.