Abstract

Er³⁺/Yb³⁺ co-doped bioactive glasses were prepared via containerless processing in an aerodynamic levitation furnace. The as-prepared glasses were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) equipped with energy dispersive X-Ray spectroscopy (EDX). The up-conversion luminescence of as-prepared glasses was measured using an Omni- 3007 spectrometer. Furthermore, the in vitro bioactivity was evaluated by soaking the materials in simulated body fluid, and the biocompatibility was evaluated in MC3T3-E1 cell culture.

The results show that containerless processing is a unique method to prepare homogeneous rare earth doped bioactive glasses. The obtained Er³⁺/Yb³⁺ co-doped glasses show green and red up-conversion luminescence at the excitation of 980 nm laser. The XRD analysis confirmed that calcium silicate powders, as starting materials, were completely transformed from the original multi-crystalline phase (CS-P) into the amorphous-glassy phase (CS-G, EYS, LCS) via containerless processing. The SEM observation combined with EDX and FTIR analyses showed that the as-prepared glasses were bioactive. The cell proliferation assay also revealed that the as-prepared glasses were biocompatible and nontoxic to MC3T3-E1 cells. This study suggests that the luminescent bioactive glasses prepared by containerless processing could be used for studying biodegradation of bone implantation materials.

Abstract

Multifunctional bioactive materials with the ability to stimulate osteogenesis and angiogenesis of stem cells play an important role in the regeneration of bone defects. However, how to develop such biomaterials remains a significant challenge. In this study, we prepared mesoporous silica nanospheres (MSNs) with uniform sphere size (∼90 nm) and mesopores (∼2.7 nm), which could release silicon ions (Si) to stimulate the osteogenic differentiation of human bone marrow stromal cells (hBMSCs) via activating their ALP activity, bone-related gene and protein (OCN, RUNX2 and OPN) expression. Hypoxia-inducing therapeutic drug, dimethyloxaloylglycine (DMOG), was effectively loaded in the mesopores of MSNs (D-MSNs). The sustained release of DMOG from D-MSNs could stabilize HIF-1α and further stimulated the angiogenic differentiation of hBMSCs as indicated by the enhanced VEGF secretion and protein expression. Our study revealed that D-MSNs could combine the stimulatory effect on both osteogenic and angiogenic activity of hBMSCs. The potential mechanism of D-MSN-stimulated osteogenesis and angiogenesis was further elucidated by the supplementation of cell culture medium with pure Si ions and DMOG. Considering the easy handling characteristics of nanospheres, the prepared D-MSNs may be applied in the forms of injectable spheres for minimally invasive surgery, or MSNs/polymer composite scaffolds for bone defect repair. The concept of delivering both stimulatory ions and functional drugs may offer a new strategy to construct a multifunctional biomaterial system for bone tissue regeneration.

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Elastin, a main component of decellularized extracellular matrices and elastin-containing materials, has been used for tissue engineering applications due to their excellent biocompatibility. However, elastin is easily calcified, leading to the decrease of life span for elastin-based substitutes. How to inhibit the calcification of elastin-based scaffolds, but maintain their good biocompatibility, still remains significantly challenging. Procyanidins (PC) are a type of natural polyphenols with crosslinking ability. To investigate whether pure elastin could be crosslinked by PC with anti-calcification effect, PC was first used to crosslink aortic elastin. Results show that PC can crosslink elastin and effectively inhibit elastin-initiated calcification. Further experiments reveal the possible mechanisms for the anti-calcification of PC crosslinking including (1) inhibiting inflammation cell attachment, and secretion of inflammatory factors such as MMPs and TNF-α, (2) preventing elastin degradation by elastase, and (3) direct inhibition of mineral nucleation in elastin. Moreover, the PC-crosslinked aortic elastin maintains natural structure with high pore volume (1111 μL/g), large pore size (10–300 μm) and high porosity (75.1%) which facilitates recellularization of scaffolds in vivo, and displays excellent hemocompatibility, anti-thrombus and anti-inflammatory potential. The advantages of PC-crosslinked porous aortic elastin suggested that it can serve as a promising scaffold for tissue engineering.

Abstract

Although inorganic bone cements such as calcium phosphate cements have been widely applied in orthopaedic and dental fields because of their self-setting ability, development of high-strength bone cement with bioactivity and biodegradability remains a major challenge. Therefore, the purpose of this study is to prepare a tricalcium silicate/magnesium phosphate (C3S/MPC) composite bone cement, which is intended to combine the excellent bioactivity of C3S with remarkable self-setting properties and mechanical strength of MPC. The self-setting and mechanical properties, in vitro induction of apatite formation and degradation behaviour, and cytocompatibility of the composite cements were investigated. Our results showed that the C3S/MPC composite cement with an optimal composition had compressive strength up to 87 MPa, which was significantly higher than C3S (25 MPa) and MPC (64 MPa). The setting time could be adjusted between 3 min and 29 min with the variation of compositions. The hydraulic reaction products of the C3S/MPC composite cement were composed of calcium silicate hydrate (CSH) derived from the hydration of C3S and gel-like amorphous substance. The C3S/MPC composite cements could induce apatite mineralization on its surface in SBF solution and degraded gradually in Tris–HCl solution. Besides, the composite cements showed good cytocompatibility and stimulatory effect on the proliferation of MC3T3-E1 osteoblast cells. Our results indicated that the C3S/MPC composite bone cement might be a new promising high-strength inorganic bioactive material which may hold the potential for bone repair in load-bearing site.

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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.

Abstract

Polymer biomaterials have been widely used for bone replacement/regeneration because of their unique mechanical properties and workability. Their inherent low bioactivity makes them lack osseointegration with host bone tissue. For this reason, bioactive inorganic particles have been always incorporated into the matrix of polymers to improve their bioactivity. However, mixing inorganic particles with polymers always results in inhomogeneity of particle distribution in polymer matrix with limited bioactivity. This study sets out to apply the pulsed laser deposition (PLD) technique to prepare uniform akermanite (Ca₂MgSi₂O₇, AKT) glass nanocoatings on the surface of two polymers (non-degradable polysulfone (PSU) and degradable polylactic acid (PDLLA)) in order to improve their surface osteogenic and angiogenic activity. The results show that a uniform nanolayer composed of amorphous AKT particles (∼30 nm) of thickness 130 nm forms on the surface of both PSU and PDLLA films with the PLD technique. The prepared AKT-PSU and AKT-PDLLA films significantly improved the surface roughness, hydrophilicity, hardness and apatite mineralization, compared with pure PSU and PDLLA, respectively. The prepared AKT nanocoatings distinctively enhance the alkaline phosphate (ALP) activity and bone-related gene expression (ALP, OCN, OPN and Col I) of bone-forming cells on both PSU and PDLLA films. Furthermore, AKT nanocoatings on two polymers improve the attachment, proliferation, VEGF secretion and expression of proangiogenic factors and their receptors of human umbilical vein endothelial cells (HUVEC). The results suggest that PLD-prepared bioceramic nanocoatings are very useful for enhancing the physicochemical, osteogenic and angiogenic properties of both degradable and non-degradable polymers for application in bone replacement/regeneration.

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It is known that porous scaffolds play an important role in bone/periodontal tissue engineering. A new nagelschmidtite (NAGEL, Ca₇Si₂P₂O₁₆) ceramic has recently been prepared which shows excellent apatite mineralization ability and osteo-/cementostimulation properties in vitro. However, up to now porous NAGEL scaffolds have not been developed yet. There has been no systematic study of the effect of macropore morphology of bioceramic scaffolds on their physico-chemical and biological properties. The aim of this study was to prepare NAGEL scaffolds for bone tissue engineering applications. We applied a modified three-dimensional (3-D) plotting method to prepare highly controllable NAGEL scaffolds and investigated the effect of macropore morphology on the physico-chemical and biological properties. The results showed that the macropore size and morphology of 3-D plotted NAGEL scaffolds could be effectively controlled. Compared with β-tricalcium phosphate (β-TCP) scaffolds NAGEL scaffolds possess a significantly enhanced compressive strength, a higher modulus and better degradability. Nagel scaffolds with a square pore morphology presented a higher compressive strength, a higher modulus and greater weight loss rate than those with triangular and parallelogram pore morphologies. In addition, all of the NAGEL scaffolds with the three macropore morphologies supported the attachment and proliferation of MC3T3 cells. The proliferation of MC3T3 cells on NAGEL scaffolds with triangular and parallelogram structures was higher than that on β-TCP scaffolds with the same pore structure. Cells on all three groups of NAGEL scaffolds revealed higher alkaline phosphatase (ALP) activity compared with cells on β-TCP scaffolds, and among the three NAGEL scaffolds groups those with a parallelogram pore structure showed the highest ALP activity. Furthermore, the angiogenic cell experiments showed that the ionic products from NAGEL scaffolds promoted tube formation, expression of pro-angiogenic factors and their receptors on human umbilical vein endothelial (HUVECs) compared with β-TCP scaffolds, indicating that NAGEL scaffolds possessed improved angiogenesis capacity. Our results suggest that 3-D plotted NAGEL scaffolds are a promising bioactive material for bone tissue engineering by virtue of their highly controllable macropore structure, excellent mechanical strength, degradability and in vitro biological response to osteogenic/angiogenic cells.

Abstract

The nanostructured surface of biomaterials plays an important role in improving their in vitro cellular bioactivity as well as stimulating in vivo tissue regeneration. Inspired by the mussel’s adhesive versatility, which is thought to be due to the plaque–substrate interface being rich in 3,4-dihydroxy-l-phenylalamine (DOPA) and lysine amino acids, in this study we developed a self-assembly method to prepare a uniform calcium phosphate (Ca-P)/polydopamine composite nanolayer on the surface of β-tricalcium phosphate (β-TCP) bioceramics by soaking β-TCP bioceramics in Tris–dopamine solution. It was found that the addition of dopamine, reaction temperature and reaction time are three key factors inducing the formation of a uniform Ca-P/polydopamine composite nanolayer. The formation mechanism of a Ca-P/polydopamine composite nanolayer involved two important steps: (i) the addition of dopamine to Tris–HCl solution decreases the pH value and accelerates Ca and P ionic dissolution from the crystal boundaries of β-TCP ceramics; (ii) dopamine is polymerized to form self-assembled polydopamine film and, at the same time, nanosized Ca-P particles are mineralized with the assistance of polydopamine, in which the formation of polydopamine occurs simultaneously with Ca-P mineralization (formation of nanosized microparticles composed of calcium phosphate-based materials), and finally a self-assembled Ca-P/polydopamine composite nanolayer forms on the surface of the β-TCP ceramics. Furthermore, the formed self-assembled Ca-P/polydopamine composite nanolayer significantly enhances the surface roughness and hydrophilicity of β-TCP ceramics, and stimulates the attachment, proliferation, alkaline phosphate (ALP) activity and bone-related gene expression (ALP, OCN, COL1 and Runx2) of human bone marrow stromal cells. Our results suggest that the preparation of self-assembled Ca-P/polydopamine composite nanolayers is a viable method to modify the surface of biomaterials by significantly improving their surface physicochemical properties and cellular bioactivity for bone regeneration application.

Abstract

The calcium silicate (CaSiO₃, CS) microspheres with diameter of 75–100 μm were fabricated by a spray-drying method. A new bone-like apatite layer fully covered the surface of the fabricated CS microspheres after soaking in simulated body fluid (SBF), suggesting the excellent activity of the material in inducing apatite deposition. The ionic extracts of CS microspheres promoted the proliferation of human osteoblast-like cells (MC3T3-E1). In addition, the porous structures of the CS microspheres resulted in favorable drug loading and sustained release property. Our study indicates that the fabricated multifunctional CS microspheres are a promising drug delivery system as an injectable bioactive filling material for bone-regeneration.

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Angiogenesis is critical in tissue engineering, and bioceramic-induced angiogenesis has been reported. However, the role of other types of cells such as fibroblasts in this bioceramic-induced angiogenesis process has not been reported, and is closer to the in vivo situation of tissue regeneration. In this study, the paracrine effect of silicate bioceramic-induced angiogenesis in the presence of fibroblasts was confirmed by investigating the effects of calcium silicate (CS), one of the simplest silicate bioactive ceramics, on angiogenesis in co-cultures of human dermal fibroblasts (HDF) and human umbilical vein endothelial cells (HUVEC). Results showed that CS extracts stimulated the expression of vascular endothelial growth factor (VEGF) from co-cultured HDF and subsequently enhanced the expression of VEGF receptor 2 on co-cultured HUVEC (co-HUVEC). The endothelial nitric oxide synthase and nitric oxide production in co-HUVEC was then increased to finally initiate the proangiogenesis. During this process, the expression of vascular endothelial cadherin from co-HUVEC was up-regulated, and cadherin proteins were concentrated at the cell junctions to facilitate tube formation. Silicon ions are confirmed to play an important role during silicate bioceramic-inducing angiogenesis, and effective silicon ion concentrations (0.7–1.8 μg ml⁻¹) are proposed.

Abstract

Ideal biomaterials for bone tissue engineering should have the capability to guide the osteogenic differentiation of mesenchymal stem cells and, at the same time, to stimulate angiogenesis of endothelia cells. In this study it was found that three Ca–Mg–Si-containing bioceramics (bredigite Ca₇MgSi₄O₁₆, akermanite Ca₂MgSi₂O₇ and diopside CaMgSi₂O₆) had osteogenic and angiogenic potential. The effects of three silicate ceramics on the osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs) and the angiogenesis of human aortic endothelial cells (HAECs) were explored in comparison with β-tricalcium phosphate (β-TCP) bioceramics. The proliferation, alkaline phosphatase (ALPase) activity and bone-related gene expression (COL1, ALPase, OP, BSP and OC) of hBMSCs were significantly enhanced upon stimulation with ionic extracts of these silicate bioceramics. In addition, the results showed that extracts from the three silicate bioceramics also stimulated HAEC proliferation and in vitro angiogenesis with improved NO synthesis and angiogenic gene expression (KDR, FGFR1, ACVRL1 and NOS3). Among the three silicate ceramics bredigite showed the highest osteogenic and angiogenic potential and with the highest extract Si (possibly Si(OH)₃O⁻) concentration, while diopside had the lowest osteogenic and angiogenic potential with the lowest extract Si concentration. Furthermore, it was found that the concentration of Si ions in extracts of the three silicate bioceramics was obviously higher than that of β-TCP ceramics, indicating an important role of Si ions in stimulating cell proliferation, osteogenic differentiation and angiogenesis. The results suggest that the silicate-based akermanite and bredigite ceramics might be good scaffold biomaterials for bone tissue engineering applications due to their distinctive dual functions of osteogenesis/angiogenesis stimulation.

Abstract

Angiogenesis is critical for bone tissue engineering. Stimulating proangiogenesis in an engineered bone construct using bioglass or bioceramic is now attracting much attention. However, the specific ion that plays important roles in the stimulation of proangiogenesis has not yet been elucidated. In this study, calcium silicate (CS), an osteogenic bioceramic containing only Ca and Si ions, significantly stimulated proangiogenesis of human umbilical vein endothelial cells (HUVECs). The determination of the ionic dissolution product indicates that Si ion concentrations of the CS extracts were significantly higher than that of the calcium phosphate ceramic extracts and control medium. However, the concentrations of Ca and P ions of both ceramic extracts and normal medium were at the same level. With the specific Si ion and its effective concentrations, CS extracts stimulated the proliferation of HUVECs, up-regulated the expression of vascular endothelial growth factor, basic fibroblast growth factor and their receptors, and finally stimulated the proangiogenesis. As the Si ion played an important role in osteogenesis stimulated by Si-containing bioceramics, confirmation of the Si ion’s specific role and its effective ion concentrations in CS-induced angiogenesis may be extremely useful in designing osteogenic and angiogenic bioactive materials for bone tissue engineering.

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In this study, an injectable calcium silicate (CS)/sodium alginate (SA) hybrid hydrogel was prepared using a novel material composition design. CS was incorporated into an alginate solution and internal in situ gelling was induced by the calcium ions directly released from CS with the addition of d-gluconic acid δ-lactone (GDL). The gelling time could be controlled, from about 30 s to 10 min, by varying the amounts of CS and GDL added. The mechanical properties of the hydrogels with different amounts of CS and GDL were systematically analyzed. The compressive strength of 5% CS/SA hydrogels was higher than that of 10% CS/SA for the same amount of GDL. The swelling behaviors of 5% CS/SA hydrogels with different contents of GDL were therefore investigated. The swelling ratios of the hydrogels decreased with increasing GDL, and 5% CS/SA hydrogel with 1% GDL swelled by only less than 5%. Scanning electron microscopy (SEM) observation of the scaffolds showed an optimal interconnected porous structure, with the pore size ranging between 50 and 200 μm. Fourier transform infrared spectroscopy and SEM showed that the CS/SA composite hydrogel induced the formation of hydroxyapatite on the surface of the materials in simulated body fluid. In addition, rat bone mesenchymal stem cells (rtBMSCs) cultured in the presence of hydrogels and their ionic extracts were able to maintain the viability and proliferation. Furthermore, the CS/SA composite hydrogel and its ionic extracts stimulated rtBMSCs to produce alkaline phosphatase, and its ionic extracts could also promote angiogenesis of human umbilical vein endothelial cells. Overall, all these results indicate that the CS/SA composite hydrogel efficiently supported the adhesion, proliferation and differentiation of osteogenic and angiogenic cells. Together with its porous three-dimensional structure and injectable properties, CS/SA composite hydrogel possesses great potential for bone regeneration and tissue engineering applications.

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Development of hypoxia-mimicking bone tissue engineering scaffolds is of great importance in stimulating angiogenesis for bone regeneration. Dimethyloxallyl glycine (DMOG) is a cell-permeable, competitive inhibitor of hypoxia-inducible factor prolyl hydroxylase (HIF-PH), which can stabilize hypoxia-inducible factor 1α (HIF-1α) expression. The aim of this study was to develop hypoxia-mimicking scaffolds by delivering DMOG in mesoporous bioactive glass (MBG) scaffolds and to investigate whether the delivery of DMOG could induce a hypoxic microenvironment for human bone marrow stromal cells (hBMSC). MBG scaffolds with varied mesoporous structures (e.g. surface area and mesopore volume) were prepared by controlling the contents of mesopore-template agent. The composition, large-pore microstructure and mesoporous properties of MBG scaffolds were characterized. The effect of mesoporous properties on the loading and release of DMOG in MBG scaffolds was investigated. The effects of DMOG delivery on the cell morphology, cell viability, HIF-1α stabilization, vascular endothelial growth factor (VEGF) secretion and bone-related gene expression (alkaline phosphatase, ALP; osteocalcin, OCN; and osteopontin, OPN) of hBMSC in MBG scaffolds were systematically investigated. The results showed that the loading and release of DMOG in MBG scaffolds can be efficiently controlled by regulating their mesoporous properties via the addition of different contents of mesopore-template agent. DMOG delivery in MBG scaffolds had no cytotoxic effect on the viability of hBMSC. DMOG delivery significantly induced HIF-1α stabilization, VEGF secretion and bone-related gene expression of hBMSC in MBG scaffolds in which DMOG counteracted the effect of HIF-PH and stabilized HIF-1α expression under normoxic condition. Furthermore, it was found that MBG scaffolds with slow DMOG release significantly enhanced the expression of bone-related genes more than those with instant DMOG release. The results suggest that the controllable delivery of DMOG in MBG scaffolds can mimic a hypoxic microenvironment, which not only improves the angiogenic capacity of hBMSC, but also enhances their osteogenic differentiation.

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β-Tricalcium phosphate (β-TCP) is osteoconductive, while β-calcium silicate (β-CS) is bioactive with osteostimulative properties. Porous β-CaSiO₃/β-Ca₃(PO₄)₂ composite bioceramic scaffolds with various β-TCP:β-CS ratios were designed to combine both osteoconductivity and osteostimulation in order to enhance bone regeneration. The composite scaffolds were implanted in critical sized femur defects (6 × 12 mm) for 4, 12 and 26 weeks with pure β-TCP and β-CS scaffolds as the controls. The in vivo biodegradation and bone regeneration of the specimens were investigated using sequential histological evaluations, immunohistochemical examination and micro-computed tomography technology. The results showed that the scaffolds with 50 and 80 wt.% β-CS dramatically enhanced the amount of newly formed bone and reduced the degradation rate. In contrast, porous β-CS displayed poor new bone formation due to its rapid degradation, while porous β-TCP showed moderate bone regeneration starting on the surface of the implants, due to a lack of osteostimulation. More importantly, the scaffolds with 50 and 80 wt.% β-CS not only had excellent osteoconductivity, but also stimulated rapid bone formation, and they could degrade progressively at a rate matching the regeneration of new bone. In summary, our findings indicated that the degradation rate and bioactivity of β-CS/β-TCP composite bioceramic scaffolds could be adjusted by controlling the ratio of β-CS to β-TCP, suggesting the potential application of β-CS/β-TCP composite bioceramic scaffolds with 50 and 80 wt.% β-CS component in hard tissue regeneration and bone tissue engineering.

Abstract

The capacity to induce rapid vascular ingrowth during new bone formation is an important feature of biomaterials that are to be used for bone regeneration. Akermanite, a Ca-, Mg- and Si-containing bioceramic, has been demonstrated to be osteoinductive and to promote bone repair. This study further demonstrates the ability of akermanite to promote angiogenesis and investigates the mechanism of this behavior. The akermanite ion extract predominantly caused Si-ion-stimulated proliferation of human aortic endothelial cells. The Si ion in the extract was the most important component for the effect and the most effective concentration was found to be 0.6–2 μg ml⁻¹. In this range of Si ion concentration, the stimulating effect of the ceramic ion extract was demonstrated by the morphology of cells at the primary, interim and late stages during in vitro angiogenesis using ECMatrix™. The akermanite ion extract up-regulated the expression of genes encoding the receptors of proangiogenic cytokines and also increased the expression level of genes encoding the proangiogenic downstream cytokines, such as nitric oxide synthase and nitric oxide synthesis. Akermanite implanted in rabbit femoral condyle model promoted neovascularization after 8 and 16 weeks of implantation, which further confirmed its stimulation effect on angiogenesis in vivo. These results indicate that akermanite ceramic, an appropriate Si ion concentration source, could induce angiogenesis through increasing gene expression of proangiogenic cytokine receptors and up-regulated downstream signaling. To our knowledge, akermanite ceramic is the first Si-containing ceramic demonstrated to be capable of inducing angiogenesis during bone regeneration.

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The aim of this study was to fabricate dual drug-loaded poly(lactic-co-glycolic acid) (PLGA)/mesoporous silica nanoparticles (MSNs) electrospun composite mat, with the two model drugs (fluorescein (FLU) and rhodamine B (RHB)) releasing in separate and distinct release kinetics. The PLGA-based electrospun mat loading with the same amount of FLU (5%, with respect to the weight of PLGA) and different amounts of RHB-loaded MSNs (5, 15 and 25%, with respect to the weight of PLGA) were prepared and studied for their releasing properties. The morphology of the composite mats was characterized by scanning electron microscopy and transmission electron microscopy. Finally, the release profiles of the dual drug-loaded electrospun mats were measured, and the results indicated that the FLU and RHB released from the PLGA/FLU/RHB-loaded MSNs electrospun mats showed separate and distinct profiles. Most of the FLU was released rapidly during the 324 h of the trial; however, RHB showed a sustained release behavior, and the release rate could be controlled by the content of the RHB-loaded MSNs in the electrospun mat.

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How to accurately control the microstructure of bioactive inorganic/organic nanocomposites still remains a significant challenge, which is of great importance in influencing their mechanical strength and biological properties. In this study, using a combined method of electrospinning and hot press processing, calcium silicate hydrate (CSH) nanowire/poly(l-lactide) (PLLA) nanocomposites with controllable microstructures and tailored mechanical properties were successfully prepared as potential bone graft substitutes. The electrospun hybrid nanofibers with various degrees of alignment were stacked together in a predetermined manner and hot pressed into hierarchically structured nanocomposites. The relationship between the microstructure and mechanical properties of the as-prepared nanocomposites were systematically evaluated. The results showed that CSH nanowires in a PLLA matrix were able to be controlled from completely randomly oriented to uniaxially aligned, and then hierarchically organized with different interlayer angles, leading to corresponding nanocomposites with improved mechanical properties and varied anisotropies. It was also found that the bending strength of nanocomposites with 5 wt.% CSH nanowires (130 MPa) was significantly higher than that of pure PLLA (86 MPa) and other composites. The addition of CSH nanowires greatly enhanced the hydrophilicity and apatite-forming ability of PLLA films, as well as the attachment and proliferation of bone marrow stromal cells. The study suggested that a combination of electrospinning and hot pressing is a viable means to control the microstructure and mechanical properties, and improve the mineralization ability and cellular responses, of CSH/PLLA nanocomposites for potential bone repair applications.

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Bioprosthetic heart valves, prepared by glutaraldehyde (GA) crosslinking, have some limitations due to poor durability, calcification and immunogenic reactions. The aim of this study was to evaluate the crosslinking effect of a natural product, quercetin, on decellularized porcine heart valve extracellular matrix (ECM). After crosslinking, the mechanical properties, stability, anticalcification and cytocompatibility were examined. The results showed that the tensile strength of quercetin-crosslinked ECM was higher than that of GA-crosslinked ECM. After crosslinking with quercetin, the thermal denaturation temperature of ECM was clearly increased. Quercetin-crosslinked ECM could be stored in D-Hanks solution for at least 30 days without any loss of ultimate tensile strength and elasticity. After soaking in D-Hanks solution for 36 days, there was only 11.55% non-crosslinked excess quercetin released and no further release thereafter. Cell culture study shows that no inhibition on proliferation of vascular endothelial cells occurred when the quercetin concentration was lower than 1 μg ml⁻¹. This non-cytotoxic concentration was 100 times higher than that of GA. The resistibility of quercetin-crosslinked ECM to in vitro enzymatic hydrolysis was comparable to that of GA-crosslinked ECM. An in vitro anticalcification experiment showed that quercetin crosslinking could protect ECM from deposition of minerals in simulated body fluid. The present study demonstrated that quercetin can crosslink porcine heart valve ECM effectively, which suggests that quercetin might be a new crosslinking reagent for the preparation of bioprosthetic heart valve xenografts and scaffolds for heart valve tissue engineering.

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Bioactive and inductive silicate-based bioceramics play an important role in hard tissue prosthetics such as bone and teeth. In the present study, a model was established to study the acid-etched enamel remineralization with tricalcium silicate (Ca₃SiO₅, C₃S) paste in vitro. After soaking in simulated oral fluid (SOF), Ca–P precipitation layer was formed on the enamel surface, with the prolonged soaking time, apatite layer turned into density and uniformity and thickness increasingly from 250 to 350 nm for 1 day to 1.7–1.9 μm for 7 days. Structure of apatite crystals was similar to that of hydroxyapatite (HAp). At the same time, surface smoothness of the remineralized layer is favorable for the oral hygiene. These results suggested that C₃S treated the acid-etched enamel can induce apatite formation, indicating the biomimic mineralization ability, and C₃S could be used as an agent of inductive biomineralization for the enamel prosthesis and protection.

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Bioactive composite bone cements were obtained by incorporation of tricalcium silicate (Ca₃SiO₅, C₃S) into a brushite bone cement composed of β-tricalcium phosphate [β-Ca₃(PO₄)₂, β-TCP] and monocalcium phosphate monohydrate [Ca(H₂PO₄)₂·H₂O, MCPM], and the properties of the new cements were studied and compared with pure brushite cement. The results indicated that the injectability, setting time and short- and long-term mechanical strength of the material are higher than those of pure brushite cement, and the compressive strength of the TCP/MCPM/C₃S composite paste increased with increasing aging time. Moreover, the TCP/MCPM/C₃S specimens showed significantly improved in vitro bioactivity in simulated body fluid and similar degradability in phosphate-buffered saline as compared with brushite cement. Additionally, the reacted TCP/MCPM/C₃S paste possesses the ability to stimulate osteoblast proliferation and promote osteoblastic differentiation of the bone marrow stromal cells. The results indicated that the TCP/MCPM/C₃S cements may be used as a bioactive material for bone regeneration, and might have significant clinical advantage over the traditional β-TCP/MCPM brushite cement.

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Electrospun mats with complex ordered architectures are fabricated by using patterned conductive collectors. The effect of the diameter of the web wires and the protrusions on the formation of the patterns of the fibrous materials are elaborated and woven structures that have been generated by a time-dependent control of the arrangement of the protrusions in the collector are shown (see figure).

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The major problem with the use of porous bioceramics as bone regeneration grafts is their weak mechanical strength, which has not been overcome to date. Here we described a novel way to solve this problem. Beta-tricalcium phosphate (β-TCP) bioceramics with a bioinspired structure were designed and prepared with a porous cancellous core (porosity: 70–90%) inside and a dense compact shell (porosity: 5–10%) outside that mimics the characteristics of natural bone. They showed excellent mechanical properties, with a compressive strength of 10–80 MPa and an elastic modulus of 180 MPa–1.0 GPa, which could be tailored by the dense/porous cross-sectional area ratio obeying the rule of exponential growth. The in vitro degradation of the bioinspired bioceramics was faster than that of dense bioceramics but slower than that of porous counterparts. The changes in mechanical properties of the bioinspired ceramics during in vitro degradation were also investigated. A concept of the bioinspired macrostructure design of natural bone was proposed which provided a simple but effective way to increase the mechanical properties of porous bioceramics for load-bearing bone regeneration applications. It should be readily applicable to other porous materials.

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Self-setting biomaterials are widely used for tissue repair and regeneration. Calcium sulfate hemihydrate has been used for many years as a self-setting biomaterial due to its good setting properties. However, too fast a degradation rate and lack of bioactivity have limited its application in orthopaedic field. Herein, tricalcium silicate was introduced into calcium sulfate hemihydrate (CaSO₄ · 1/2H₂O) to form a calcium sulfate hemihydrate-based composite, and its behavior as a cement was studied in comparison with pure calcium sulfate hemihydrate. The results indicated that the workability and setting time of the composite pastes are higher than those of pure CaSO₄ · 1/2H₂O, and the composite pastes showed much better short- and long-term mechanical properties than those of pure CaSO₄ · 1/2H₂O. Moreover, the biphasic specimens showed significantly improved bioactivity and degradability compared with those of pure CaSO₄ · 1/2H₂O, indicating that the composite cements might have a significant clinical advantage over the traditional CaSO₄ · 1/2H₂O cement.

Abstract

Forsterite (Mg₂SiO₄) ceramics were prepared by sintering the Mg₂SiO₄ green compacts at 1350–1550 °C and the sintering behavior and mechanical properties were examined. The results showed that the optimal bending strength (203 MPa) and fracture toughness (2.4 MPa m^1/2) of forsterite ceramics were obtained after hot treatment at 1450 °C for 8 h, which were higher than those of the currently available hydroxyapatite ceramics. In order to clarify the biocompatibility of the forsterite ceramics, osteoblast adhesion and proliferation experiments were carried out. Well-spread cells were observed on the surface of forsterite ceramics. In addition, MTT tests confirmed that the osteoblast proliferation rate was significantly higher on the surface of the sintered ceramics than on the controls at 7 days (p < 0.05). These findings suggest that forsterite ceramics possess good biocompatibility and mechanical properties and might be suitable for potential application like bone implant material.

Calcium silicate ceramics have been proposed as new bone repair biomaterials, since they have proved to be bioactive, degradable, and biocompatible. β-tricalcium phosphate ceramic is a well-known degradable material for bone repair. This study compared the effects of CaSiO₃ (α-, and β-CaSiO₃) and β-Ca₃(PO₄)₂ (β-TCP) ceramics on the early stages of rat osteoblast-like cell attachment, proliferation, and differentiation. Osteoblast-like cells were cultured directly on CaSiO₃ (α-, and β-CaSiO₃) and β-TCP ceramics. Attachment of a greater number of cells was observed on CaSiO₃ (α-, and β-CaSiO₃) ceramics compared with β-TCP ceramics after incubation for 6 h. SEM observations showed an intimate contact between cells and the substrates, significant cells adhesion, and that the cells spread and grew on the surfaces of all the materials. In addition, the proliferation rate and alkaline phosphatase (ALP) activity of the cells on the CaSiO₃ (α-, and β-CaSiO₃) ceramics were improved when compared with the β-TCP ceramics. In the presence of CaSiO₃, elevated levels of calcium and silicon in the culture medium were observed throughout the 7-day culture period. In conclusion, the results of the present study revealed that CaSiO₃ ceramics showed greater ability to support cell attachment, proliferation, and differentiation than β-TCP ceramic. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007

The aim of this study was to investigate the effect of three bioceramics in the CaO-SiO₂-MgO systems with different composition on the in vitro degradation, bioactivity, and cytocompatibility. The degradation was evaluated through the activation energy of Si ion release from ceramics and the weight loss of the ceramics in Tris-HCl buffers. The in vitro bioactivity of the ceramics was investigated by analysis of apatite-formation ability in the simulated body fluid (SBF). The cytocompatibility was evaluated through osteoblast morphology and proliferation. The results showed that the activation energy of Si ion release increased and the degradation decreased from bredigite to diopside ceramics with the increase of Mg content, and the apatite-formation ability in SBF decreased. The Ca, Si, and Mg containing ionic products from three ceramics could stimulate cell proliferation at lower concentration, and inhibit cell proliferation with the increase of ion concentrations. Furthermore, osteoblasts could adhere, spread, and proliferate on three ceramic disks, and cell proliferation on diopside was more obvious than that on other two ceramic disks. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007

In this paper, we obtained a novel bone cement composed of tricalcium silicate (Ca₃SiO₅; C₃S) and monocalcium phosphate monohydrate (MCPM). The weight ratio of MCPM in the cement is 0, 10, 20, and 30%. The initial setting time was dramatically reduced from 90 min to 30 min as the content of MCPM reached 20%. The workable paste with a liquid/powder (L/P) ratio of 0.8 mL/g could be injected for 2–20 min (nozzle diameter 2.0 mm). The pH variation of the composite cement in simulated body environment was obviously lowered. The compressive strength of the composite cement after setting for 4–28 days was slightly lower than that of the tricalcium silicate paste. The in vitro bioactivity was investigated by soaking in simulated body fluid for 7 days. The result showed that the novel bone cement had good bioactivity and could degrade in tris-(hydroxymethyl)-aminomethane-hydrochloric-acid (Tris-HCl) solution. Our result indicated that the Ca₃SiO₅/MCPM paste had good hydraulic properties, bioactivity, and degradability. The novel bone cement could be a potential candidate as bone substitute. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007

In this study, the bone-like apatite-formation ability of akermanite ceramics (Ca₂MgSi₂O₇) in simulated body fluid (SBF) and the effects of ionic products from akermanite dissolution on osteoblasts and mouse fibroblasts (cell line L929) were investigated. In addition, osteoblast morphology and proliferation on the ceramics were evaluated. The results showed that akermanite ceramics possessed bone-like apatite-formation ability comparable with bioactive wollastonite ceramics (CaSiO₃) after 20 days of soaking in SBF and the mechanism of bone-like apatite formation on akermanite ceramics is similar to that of wollastonite ceramics. The Ca, Si, and Mg ions from akermanite dissolution at certain ranges of concentration significantly stimulated osteoblast and L929 cell proliferation. Furthermore, osteoblasts spread well on the surface of akermanite ceramics, and proliferated with increasing the culture time. The results showed that akermanite ceramics possess bone-like apatite-formation ability and can release soluble ionic products to stimulate cell proliferation, which indicated good bioactivity. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2006

The aim of this study was to fabricate bioactive porous CaSiO₃ scaffolds and examine their effects on proliferation and differentiation of osteoblast-like cells. In this study, porous CaSiO₃ scaffolds were obtained by sintering a ceramic slip-coated polymer foam at 1350°C. X-ray diffraction (XRD) of the scaffolds indicated that the products were essentially pure α-CaSiO₃. The obtained scaffolds had a well-interconnected porous structure with pore sizes ranging from several micrometers to more than 100 μm and porosities of 88.5 ± 2.8%. The in vitro bioactivity of the scaffolds was investigated by soaking them in simulated body fluid (SBF) for 7 days and then characterizing them by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analysis. The results indicated that hydroxyapatite (HAp) was formed on the surface of the scaffolds. In addition, the scaffolds were incubated in Ringer's solution at 37°C to study the in vitro degradation by measurement of weight loss after incubation, which showed that the CaSiO₃ scaffolds were degradable. The cellular responses to the scaffolds were assessed in terms of cell proliferation and differentiation. Osteoblast-like cells were seeded into the CaSiO₃ scaffolds. SEM observations showed that there was significant cell adhesion, as the cells spread and grew in the scaffolds. In addition, the proliferation rate and alkaline phosphatase (ALP) activity of the cells in the scaffolds were improved as compared to the controls. These studies demonstrate initial in vitro cell compatibility and their potential application to bone tissue engineering. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2006

The aim of this study was to develop a bioactive, degradable, and cytocompatible akermanite (Ca₂MgSi₂O₇) scaffold with high porosity and pore interconnectivity. In brief, porous akermanite scaffolds were prepared using polymer sponge method. The porosity and corresponding compressive strength were evaluated. The in vitro degradability was investigated by soaking the scaffolds in Ringer's solution. Hydroxyapatite (HAp)-formation ability of akermantite scaffolds in simulated body fluid (SBF) and the effect of ionic products from the scaffolds dissolution on osteoblasts were investigated. In addition, bone marrow stromal cells (BMSC) adhesion and proliferation on the scaffolds were evaluated. Differentiation of the cells was assessed by measuring alkaline phosphatase (ALP) activity. The results showed that akermanite scaffolds possessed 63.5–90.3% of porosity, with a corresponding compressive strength between 1130 and 530 kPa. The weight loss of the scaffolds and ionic content of the Ringer's solution increased with the increase in soaking time, indicating the degradability of scaffolds. HAp was formed on the scaffolds in SBF and the ionic products from akermanite scaffolds dissolution stimulated osteoblasts proliferation, indicating good in vitro bioactivity. Furthermore, BMSC adhered and spread well on akermanite scaffolds and proliferated with the increase in the culture time, and the differentiation rate of osteoblasts on scaffolds was comparable to that on blank culture plate control. Our results suggested that akermanite scaffolds were bioactive, degradable, and cytocompatible, and might be used as bone tissue 1engineering materials. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006

Summary: Poly(butylene succinate) (PBSU) can be easily synthesized by condensation polymerization of the starting materials of succinic acid and butan-1,4-diol. It has good degradability and possesses excellent processability. Due to these advantages, PBSU was first evaluated in the present study for its potential application as a novel biomaterial. The in vitro biocompatibility of the PBSU was evaluated by monitoring proliferation and differentiation of osteoblasts cultured on the PBSU film substrates for different periods. The results showed that the PBSU was biocompatible as the osteoblasts could proliferate and differentiate on the PBSU plates. In addition, the hydrolytic degradation behavior of the PBSU films in the phosphate-buffered saline (PBS) was also investigated and the results suggested that the PBSU degraded in the PBS solution with the same behavior as that of the degradable poly(α-hydroxyesters). In addition to the biocompatibility and hydrolytic degradation, some physical properties, including hydrophilicity, and mechanical and thermal properties of the PBSU substrates, were also determined and the results revealed that the PBSU was hydrophilic and ductile with excellent processability. The biocompatibility of the PBSU, together with the advantages of hydrolytic degradability, hydrophilicity, and excellent processability, indicated that PBSU has the potential to be used as a biomaterial for tissue repair.

Novel tricalcium silicate (Ca₃SiO₅) ceramics were successfully fabricated. The mechanical properties of the ceramics were dependent remarkably on sintering temperature. The fracture toughness, Young's modules, and bending strength of Ca₃SiO₅ ceramics sintered at 1500°C were 1.93 MPa · m^1/2, 36.7 GPa, and 93.4 MPa, respectively. These findings suggest that the Ca₃SiO₅ ceramics possess good mechanical properties, and might be a potential bone implant material. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res 73A: 86–89, 2005

This study sought to investigate the physical and chemical properties of β-dicalcium silicate (β-Ca₂SiO₄) in order to evaluate its use as an injectable bioactive cement filler. Workable β-Ca₂SiO₄ pastes with a liquid-to-powder (L/P) ratio of 1.0–1.2 could be injected for 10–30 min (nozzle diameter 2.0 mm) and enabled initial setting times of 60–180 min. The setting process yielded cellular structures with compressive strengths of 4.8–28.8 MPa after 2–28 days. The paste was soaked in simulated body fluid (SBF), and the results demonstrated that it exhibited a moderate degradation and could induce carbonated hydroxyapatite formation. The ionic products of the paste dissolution enhanced a proliferative response of fibroblasts compared with the cells cultured alone, and this cement could also support adhesion and spreading of the mesenchymal stem cells. Finally, with the use of gentamicin as a model drug, it was found that a high dose of drug release from the paste was maintained for 14 days, and there was a sustained release over 4 weeks. This combination of properties indicates that the novel β-Ca₂SiO₄ cement might be suitable for potential applications in the biomedical field, preferentially as materials for bone/dental repair and controlled drug-delivery systems. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater