qizhi chen
University of Pittsburgh, MSIS, Faculty Member
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The sol-gel process of producing SiO(2)-CaO bioactive glasses is well established, but problems remain with the poor mechanical properties of the amorphous form and the bioinertness of its crystalline counterpart. These properties may be... more
The sol-gel process of producing SiO(2)-CaO bioactive glasses is well established, but problems remain with the poor mechanical properties of the amorphous form and the bioinertness of its crystalline counterpart. These properties may be improved by incorporating Na(2)O into bioactive glasses, which can result in the formation of a hard yet biodegradable crystalline phase from bioactive glasses when sintered. However, production of Na(2)O-containing bioactive glasses by sol-gel methods has proved to be difficult. This work reports a new sol-gel process for the production of Na(2)O-containing bioactive glass ceramics, potentially enabling their use as medical implantation materials. Fine powders of 45S5 (a Na(2)O-containing composition) glass ceramic have for the first time been successfully synthesized using the sol-gel technique in aqueous solution under ambient conditions, with the mean particle size being approximately 5 microm. A comparative study of sol-gel derived S70C30 (a Na(2)O-free composition) and 45S5 glass ceramic materials revealed that the latter possesses a number of features desirable in biomaterials used for bone tissue engineering, including (i) the crystalline phase Na(2)Ca(2)Si(3)O(9) that couples good mechanical strength with satisfactory biodegradability, (ii) formation of hydroxyapatite, which may promote good bone bonding and (iii) cytocompatibility. In contrast, the sol-gel derived S70C30 glass ceramic consisted of a virtually inert crystalline phase CaSiO(3). Moreover, amorphous S70C30 largely transited to CaCO(3) with minor hydroxyapatite when immersed in simulated body fluid under standard tissue culture conditions. In conclusion, sol-gel derived Na(2)O-containing glass ceramics have significant advantages over related Na(2)O-free materials, having a greatly improved combination of mechanical capability and biological absorbability.
Research Interests: Biomaterials Engineering, Materials Science, Biomaterials, Hydroxyapatite, Glass, and 15 moreMaterials Science and Engineering, Biomaterials and Tissue Engineering, Cell line, Ceramics, Humans, Bone Tissue Engineering, Ceramic, Gels, Bioactive Glass, Materials Testing, Aqueous Solution, Biocompatible Materials, Body Fluids, Mechanical Property, and Mechanical strength
Biodegradable polymers and bioactive ceramics are being combined in a variety of composite materials for tissue engineering scaffolds. Materials and fabrication routes for three-dimensional (3D) scaffolds with interconnected high... more
Biodegradable polymers and bioactive ceramics are being combined in a variety of composite materials for tissue engineering scaffolds. Materials and fabrication routes for three-dimensional (3D) scaffolds with interconnected high porosities suitable for bone tissue engineering are reviewed. Different polymer and ceramic compositions applied and their impact on biodegradability and bioactivity of the scaffolds are discussed, including in vitro and in vivo assessments. The mechanical properties of today's available porous scaffolds are analyzed in detail, revealing insufficient elastic stiffness and compressive strength compared to human bone. Further challenges in scaffold fabrication for tissue engineering such as biomolecules incorporation, surface functionalization and 3D scaffold characterization are discussed, giving possible solution strategies. Stem cell incorporation into scaffolds as a future trend is addressed shortly, highlighting the immense potential for creating next-generation synthetic/living composite biomaterials that feature high adaptiveness to the biological environment.
Research Interests: Biomaterials Engineering, Biomaterials, Tissue Engineering, Stem Cell, Multidisciplinary, and 11 moreBiomaterials and Tissue Engineering, Ceramics, Porosity, Compressive Strength, Bone Tissue Engineering, Composite Material, Biodegradable Polymer, Next Generation, Three Dimensional, Bone Substitutes, and Mechanical Property
Research Interests: Materials Science, Glass, Medicine, Biomaterials and Tissue Engineering, Cell line, and 15 moreCeramics, Humans, Elements, Compressive Strength, Cell Death, Gels, Cell Shape, Bioactive Glass, Bone Formation, Cell Proliferation, Culture Media, Biocompatible Materials, Ions, Mechanical Property, and Mechanical strength
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ABSTRACT An investigation of the microstructure of the bonding region between hydroxyapatite (HA) and host bone in vivo has been undertaken using high-resolution transmission electron microscope (HRTEM). The TEM observation showed that... more
ABSTRACT An investigation of the microstructure of the bonding region between hydroxyapatite (HA) and host bone in vivo has been undertaken using high-resolution transmission electron microscope (HRTEM). The TEM observation showed that the bonding region is bone-like, but not identical to bone; and that it is nanostructured with crystallites smaller than 10 nm. A continuous structure had been established crossing the interface between HA and bone-like region at 3 months after implantation. EDX analysis showed that the bone-like zone had higher levels of calcium and phosphate than bone. In addition, there was an amorphous layer on the surface of HA particles at this stage. These findings indicate that the transformation from crystalline to amorphous HA had occurred prior to HA biodegradation, and that the mechanism of the formation of bonding zone might have involved the dissolution of amorphous HA in surrounding solution and precipitation of nanocrystalline HA in the over-saturated solution. The good mechanical properties of the bonding region can be attributable to its nanostructure, high levels of calcium and phosphate, and chemical bonding crossing the interface between the bonding-zone and HA particles.
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ABSTRACT Poly(glycerol sebacate) (PGS) is a soft elastomer suitable for tissue engineering of soft types. However, the rapid degradation kinetics of this polyester has become one of the major drawbacks in the application of tissue... more
ABSTRACT Poly(glycerol sebacate) (PGS) is a soft elastomer suitable for tissue engineering of soft types. However, the rapid degradation kinetics of this polyester has become one of the major drawbacks in the application of tissue engineering. In this work, a comparative study on in vitro enzymatic degradation of PGS- and poly(xylitol sebacate) (PXS)-based materials has been conducted, using a recently established in vitro experimental protocol. This protocol, which can simulate and predict in vivo enzymatic degradation kinetics of polymer implants, was further refined in this work. The comparative study was conducted in tissue culture medium and a buffer solution of pH optima, under static and cyclic mechanical loading conditions. It was found that in vitro enzymatic degradation rates of the PXS-based materials were significantly slower than those of PGS in both the tissue culture medium and buffered solution of pH optima (pH 8). The in vitro enzymatic degradation of PGS-based biomaterials tested was about 0.1–0.4 mm month−1 in tissue culture medium, while the rates were in the range of 0.05–0.2 mm month−1 for PXS-based materials. Enzymatic degradation was enhanced in relation to mechanical deformation, whereas PXS-based materials were influenced little. Hence, PXS, which is as soft as PGS but degrades significantly slower than PGS, is a better option for applications in tissue engineering of soft types.
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... 10, JL Whiteside, RB Asif and RJ Novello, Obstet. Gynecol., 2010, 115, 403404 . 11, F. Maisano, HK Kjaergard, R. Bauernschmitt, A. Pavie, G. Rabago, M. Laskar, JP Marstein and V. Falk, Eur. J. Cardio Thorac. Surg., 2009, 36, 708714... more
... 10, JL Whiteside, RB Asif and RJ Novello, Obstet. Gynecol., 2010, 115, 403404 . 11, F. Maisano, HK Kjaergard, R. Bauernschmitt, A. Pavie, G. Rabago, M. Laskar, JP Marstein and V. Falk, Eur. J. Cardio Thorac. Surg., 2009, 36, 708714 . 12, T. Erdogru, A. Sanli, O. Celik and M ...
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ABSTRACT Recently there have been increasing research efforts in the development of elastomeric biomaterials with desirable biocompatibility, degradation profiles and mechanical properties for use in soft tissue engineering. This review... more
ABSTRACT Recently there have been increasing research efforts in the development of elastomeric biomaterials with desirable biocompatibility, degradation profiles and mechanical properties for use in soft tissue engineering. This review provides an update on the progresses of developing biodegradable, soft elastomeric biomaterials and their tissue engineering scaffolding techniques. Following a brief review on traditional thermoplastic elastomers, including polyurethane (PU), polyhydroxyalkanoates (PHA) and aliphatic copolyesters, detailed review is devoted to the synthesis, properties and scaffold fabrication of recently developed soft, biodegradable elastomers, including poly(polyol sebacate) (PPS), PPS-based elastomers, and citric-acid based elastomers. Although biodegradable, soft elastomeric biomaterials have advantages (compliant and biodegradable), this review also identified a number of issues associated with these elastomers, including cytotoxicity, rapid in vivo degradation rates, and poor reproducibility. Future research directions are discussed to address these issues.
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Fabrication of nonlinear elastic materials that resemble biological tissues remains a challenge in biomaterials research. Here, a new fabrication protocol to produce elastomeric fibrous scaffolds was established, using the core/shell... more
Fabrication of nonlinear elastic materials that resemble biological tissues remains a challenge in biomaterials research. Here, a new fabrication protocol to produce elastomeric fibrous scaffolds was established, using the core/shell electrospinning technique. A prepolymer of poly(xylitol sebacate) with a 2:5mol ratio of xylitol:sebacic acid (PXS2:5) was first formulated, then co-electrospun with polyvinyl alcohol (PVA - 95,000Mw). After cross-linking of core polymer PXS2:5, the PVA shells were rinsed off in water, leaving a porous elastomeric network of PXS2:5 fibres. Under aqueous conditions, the PXS2:5 fibrous scaffolds exhibited stable, nonlinear J-shaped stress-strain curves, with large average rupture elongation (76%) and Young׳s modulus (~1.0MPa), which were in the range of muscle tissue. Rupture elongation of PXS2:5 was also much higher when electrospun, compared to 2D solid sheets (45%). In direct contact with cell monolayers under physiological conditions, PXS2:5 scaffolds...
Research Interests: Materials Engineering, Mechanical Engineering, Biomaterials Engineering, Biomedical Engineering, Biomaterials, and 14 moreTissue Engineering, Polymers, Elastomers, Materials Science and Engineering, Biomaterials and Tissue Engineering, Elasticity, Xylitol, Biomaterials and tissue engineering scaffolds, Mechanical Stress, Mechniac Engineer, Materials Testing, Tensile Strength, Biocompatible Materials, and Tissue Scaffolds
Polyetheretherketone (PEEK)-Al2O3 composite coatings have been successfully deposited on 316L stainless steel substrates by electrophoretic deposition (EPD) from ethanolic suspensions containing nanosize alumina and micrometric PEEK... more
Polyetheretherketone (PEEK)-Al2O3 composite coatings have been successfully deposited on 316L stainless steel substrates by electrophoretic deposition (EPD) from ethanolic suspensions containing nanosize alumina and micrometric PEEK particles. Uniform composite coatings containing between 20 and 70 wt.% of PEEK have been obtained. An electrostatic interaction between the two kinds of particles has been confirmed by zeta potential and TEM analysis. The EPD yield increased with deposition time and difference ...
Research Interests: Materials Engineering, Condensed Matter Physics, Powder Metallurgy, Composite Materials, Transmission Electron Microscopy, and 9 moreHeat Treatment, Stainless Steel, Hardness, Electrophoretic Deposition, Surface and Coatings Technology, Zeta Potential, Corrosion Resistance, Mechanical Property, and Electrostatic interaction
The relationship between the deformation orientation distribution function (ODF) and the primary recrystallised ODF in cold and warm rolled metals, is not a simple mathematical transformation from one to the other, but is through... more
The relationship between the deformation orientation distribution function (ODF) and the primary recrystallised ODF in cold and warm rolled metals, is not a simple mathematical transformation from one to the other, but is through thermally activated processes occurring in the deformation microstructure. In BCC metals the mature rolling microstructure consists of cells, microbands and shear bands on a length scale of fraction of a micron, to deformation and transition bands at the grain scale, when this is of the order of 10 or more microns. There is evidence that grain boundary regions are sometimes distinct from grain interiors. Wherever there is a relatively sharp change in either orientation or microstructure such locations are potential sites of recrystallisation nuclei. In this paper the results of a systematic investigation of the development of microstructure in rolled interstitial free (IF) steel using both transmission and scanning electron microscopy are presented. It is s...
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The effect of minor additions of carbon and hafnium on the microporosity of single crystal superalloy RR2086 has been investigated. The results provided additional evidence that carbon has a positive effect on the alleviation of... more
The effect of minor additions of carbon and hafnium on the microporosity of single crystal superalloy RR2086 has been investigated. The results provided additional evidence that carbon has a positive effect on the alleviation of microshrinkage in this alloy system.
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The stress fields around the first butterfly martensite in an Fe-Ni based alloy were calculated. The calculation results inducate that there are tensile stress fields near the convexity and the two ends of a butterfly martensite. There is... more
The stress fields around the first butterfly martensite in an Fe-Ni based alloy were calculated. The calculation results inducate that there are tensile stress fields near the convexity and the two ends of a butterfly martensite. There is a compressive stress field near the concavity. New butterfly martensite is likely induced not only near the convexity but also probably near the concavity. The butterfly martensites induced in tensile stress fields are bigger than those in compressive stress fields. The second butterfly martensite is likely induced near the convexity within 2πm region. All these results agree with the experimental observation.
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ABSTRACT This work aims to find an efficient sintering technique and optimal sintering conditions of a novel sol–gel derived Bioglass®-ceramic powder so as to achieve much improved mechanical properties compared to conventional Bioglass®.... more
ABSTRACT This work aims to find an efficient sintering technique and optimal sintering conditions of a novel sol–gel derived Bioglass®-ceramic powder so as to achieve much improved mechanical properties compared to conventional Bioglass®. To this end, the spark plasma sintering (SPS) technique was for the first time used to densify the sol–gel derived Bioglass®-ceramic powder. It was found that the sol–gel derived Bioglass®-ceramics sintered with the SPS technique at 950 °C for 15 min had a high Young's modulus value of ~ 110 GPa, which was comparable to that of compact bone and significantly higher than the maximal value achieved by the conventional heat treatment. Moreover, the Bioglass®-ceramic compacts sintered with SPS released alkaline ions slowly and as a result, these highly densified Bioglass®-ceramics exhibited better cytocompatibility at the early stage of cell culture testing, compared to the conventional Bioglass®. Hence, the SPS technique is recommended to be used in the process of sol–gel derived Bioglass®-ceramics and its tissue engineering scaffolds.
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Research Interests: Materials Science, Biomedical Engineering, Tissue Engineering, Hydroxyapatite, Scanning Electron Microscopy, and 9 moreSurface Roughness, Titanium dioxide, Cell Viability, Energy Dispersive X-Ray Analysis, Biodegradable Polymer, X ray diffraction, Simulated Body Fluid, Lactic Acid, and Polymer Matrix Composite
... Much attention has been paid also to hydroxycarbonate apatite (HCA) as an interesting biomaterial. HCA is very similar to the apatite phase in living bone in its chemical composition and crystalline structure and has the ability to... more
... Much attention has been paid also to hydroxycarbonate apatite (HCA) as an interesting biomaterial. HCA is very similar to the apatite phase in living bone in its chemical composition and crystalline structure and has the ability to form a chemical bond directly with natural bone. ...
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Polyamidoamine (PAMAM) dendrimer-coated magnetic nanoparticles are a promising drug-delivery system that can enhance the therapeutic effects of chemotherapy drugs, such as doxorubicin (DOX), with minimized side effects. This work explores... more
Polyamidoamine (PAMAM) dendrimer-coated magnetic nanoparticles are a promising drug-delivery system that can enhance the therapeutic effects of chemotherapy drugs, such as doxorubicin (DOX), with minimized side effects. This work explores the optimization of the potential therapeutic efficiency of PAMAM-Fe3O4-DOX triads. Different generations (G3, G5, and G6) of PAMAMs were synthesized and modified with poly(ethylene glycol) (PEG) and then used to encapsulate glutamic acid-modified Fe3O4 nanoparticles. The Fe3O4-dendrimer carriers (Fe3O4-DGx where x = the generation 3, 5, or 6 of dendrimers) were electrostatically conjugated with drug DOX. The loading and releasing efficiencies of DOX increased with the PAMAM generation from 3 to 6. The loading efficiencies of DOX molecules were 87, 93, and 96% for generations 3, 5, and 6, respectively. At pH 5, the DOX release efficiencies within 24 h were approximately 60, 68, and 80% for generations 3, 5, and 6, respectively. At pH 7.4, the DOX releasing efficiency was as low as ∼ 15%. Compared to the negative control, the PAMAM-Fe3O4-DOX triads showed only mild toxicity against human cervical adenocarcinoma cell line HeLa at pH 7.4, which indicated that DOX can be fairly benignly carried and sparingly released until PAMAM-Fe3O4-DOX is taken up into the cell.
Research Interests: Biomedical Engineering, Fluorescence Microscopy, Drug delivery, Drug Delivery System, Dendrimers, and 15 moreMultidisciplinary, Controlled Drug Release, Drugs, Humans, Novel drug delivery systems, Drug Design, Doxorubicin, HeLa cells, Langmuir, Nanoparticulate Drug Delivery System, Drug Carriers, Drug Compounding, Cell Survival, Glutamic Acid, and Magnetite Nanoparticles
Research Interests: Biomedical Engineering, Tissue Engineering, Polymers, Regenerative Medicine, Stem Cell Transplantation, and 13 moreBiomaterials and Tissue Engineering, Heart Failure, Cell therapy, Humans, Medical Physiology, Left Ventricular Dysfunction, Tissue engineering and regenerative medicine, Clinical Sciences, Myocardial Infarction, Myocardium, Biocompatible Materials, Clinical Trials as Topic, and Tissue Scaffolds
ABSTRACT The production of mechanically reliable scaffolds from bioceramics for use in bone tissue engineering remains challenging. This paper describes the establishment of optimal processing parameters of Bioglass® scaffolds using the... more
ABSTRACT The production of mechanically reliable scaffolds from bioceramics for use in bone tissue engineering remains challenging. This paper describes the establishment of optimal processing parameters of Bioglass® scaffolds using the replication/slurry‐dip‐coating technique, based on theoretical design and experimental investigation. The foams fabricated under the optimized conditions, i.e., 5–20 μm particles and sintering at 1000°C–1100°C for 1–2 h, showed reproducible mechanical properties that could be predicted by Gibson and Ashby's theory. Excessively small (nano‐sized) or overly large (>30 μm) particles both resulted in poor quality scaffolds with unsatisfactory mechanical performance, due to a high population of microcracks in struts and poor fusion between particles during sintering, respectively. In conclusion, a mechanically reliable scaffold can be achieved using Bioglass® and the replication/slurry‐dip‐coating technique, provided that the particle size of the Bioglass powder is within the range of 5–20 μm and an appropriate sintering program (1000°C–1100°C, 1–2 h) is used.
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The first and foremost function of a tissue engineering scaffold is its role as a substrate for cell attachment, and their subsequent growth and proliferation. However, cells do not attach directly to the culture substrate; rather they... more
The first and foremost function of a tissue engineering scaffold is its role as a substrate for cell attachment, and their subsequent growth and proliferation. However, cells do not attach directly to the culture substrate; rather they bind to proteins that are adsorbed to the scaffold's surface. Like standard tissue culture plates, tissue engineering scaffolds can be chemically treated to couple proteins without losing the conformational functionality; a process called surface functionalization. In this work, novel highly porous 45S5 Bioglass-based scaffolds have been functionalized applying 3-AminoPropyl-TriethoxySilane (APTS) and glutaraldehyde (GA) without the use of organic solvents. The efficiency and stability of the surface modification was assessed by X-ray photoemission spectroscopy (XPS). The bioactivity of the functionalized scaffolds was investigated using simulated body fluid (SBF) and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). It was found that the aqueous heat-treatment applied at 80 degrees C for 4 hrs during the surface functionalization procedure accelerated the structural transition of the crystalline Na2Ca2Si3O9 phase, present in the original scaffold structure as a result of the sintering process used for fabrication, to an amorphous phase during SBF immersion. The surface functionalized scaffolds exhibited an accelerated crystalline hydroxyapatite layer formation upon immersion in SBF caused by ion leaching and the increased surface roughness induced during the heat treatment step. The possible mechanisms behind this phenomenon are discussed.
Research Interests: Materials Engineering, Biomedical Engineering, Tissue Engineering, Hydroxyapatite, Glass, and 12 moreScanning Electron Microscopy, Scanning Transmission Electron Microscopy, Heat Treatment, Surface Roughness, Ceramics, Tissue culture, Surface modification, X ray diffraction, Materials Testing, Energy Dispersive Spectroscopy, Biocompatible Materials, and Simulated Body Fluid
TiO2 foam-like scaffolds with pore size ~300 μm and >95% porosity were fabricated by the foam replication method. A new approach to improve the structural integrity of the as-sintered foams, which exhibit extremely low... more
TiO2 foam-like scaffolds with pore size ~300 μm and >95% porosity were fabricated by the foam replication method. A new approach to improve the structural integrity of the as-sintered foams, which exhibit extremely low compression strength, was explored by coating them with poly-(d,l-lactic acid) (PDLLA) or PDLLA/Bioglass® layers. The PDLLA coating was shown to improve the mechanical properties of the
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New coating processes have been investigated for degradable (Vicryl) and nondegradable (Mersilk) sutures with the aim to develop Bioglass coated polymer fibers for wound healing and tissue engineering scaffold applications. First, the... more
New coating processes have been investigated for degradable (Vicryl) and nondegradable (Mersilk) sutures with the aim to develop Bioglass coated polymer fibers for wound healing and tissue engineering scaffold applications. First, the aqueous phase of a Bioglass particle slurry was replaced with a poly(D,L-lactic acid) (PDLLA) polymer dissolved in solvent dimethyle carbonate (DMC) to act as third phase. SEM observations indicated that this alteration significantly improved the homogeneity of the coatings. Second, a new coating strategy involving two steps was developed: the sutures were first coated with a Bioglass-PDLLA composite film followed by a second PDLLA coating. This two-step process of coating has addressed the problem of poor adherence of Bioglass particles on suture surfaces. The coated sutures were knotted to determine qualitatively the mechanical integrity of the coatings. The results indicated that adhesion strength of coatings obtained by the two-step method was remarkably enhanced. A comparative assessment of the bioactivity of one-step and two-step produced coatings was carried out in vitro using acellular simulated body fluid (SBF) for up to 28 days. Coatings produced by the two-step process were found to have similar bioactivity as the one-step produced coatings. The novel Bioglass/PDLLA/Vicryl and Bioglass/PDLLA/Mersilk composite sutures are promising bioactive materials for wound healing and tissue engineering applications.