Yunzhi Yang

Publications of Yunzhi Yang

• Sequential delivery of BMP-2 and IGF-1 using a chitosan gel with gelatin microspheres enhances early osteoblastic differentiation.

  Authors: Sungwoo Kim, Yunqing Kang, Chad A Krueger, Milan Sen, John B Holcomb, Di Chen, Joseph C Wenke, Yunzhi Yang

  Acta biomaterialia. 01/2012;

  The purpose of this study was to develop and characterize a chitosan gel/gelatin microsphere (MSs) dual delivery system for sequential release of bone morphogenetic protein-2 (BMP-2) and insulin-likeThe purpose of this study was to develop and characterize a chitosan gel/gelatin microsphere (MSs) dual delivery system for sequential release of bone morphogenetic protein-2 (BMP-2) and insulin-like growth factor-1 (IGF-1) to enhance osteoblast differentiation in vitro. We made and characterized the delivery system based on its degree of cross-linking, degradation, and release kinetics. We also evaluated the cytotoxicity of the delivery system and the effect of growth factors on cell response using pre-osteoblast W-20-17 mouse bone marrow stromal cells. IGF-1 was first loaded into MSs, and then the IGF-1-containing MSs were encapsulated into the chitosan gel which contained BMP-2. Cross-linking of gelatin with glyoxal via Schiff bases significantly increased thermal stability and decreased the solubility of the MSs, leading to a significant decrease in the initial release of IGF-1. Encapsulation of the MSs into the chitosan gel generated polyelectrolyte complexes by intermolecular interactions, which further affected the release kinetics of IGF-1. This combinational delivery system provided an initial release of BMP-2 followed by a slow and sustained release of IGF-1. Significantly greater alkaline phosphatase activity was found in W-20-17 cells treated with the sequential delivery system compared with other treatments (P<0.05) after a week of culture.

• SAM-based cell transfer to photopatterned hydrogels for microengineering vascular-like structures.

  Authors: Nasser Sadr, Mojun Zhu, Tatsuya Osaki, Takahiro Kakegawa, Yunzhi Yang, Matteo Moretti, Junji Fukuda, Ali Khademhosseini

  Biomaterials. 10/2011; 32(30):7479-90.

  A major challenge in tissue engineering is to reproduce the native 3D microvascular architecture fundamental for in vivo functions. Current approaches still lack a network of perfusable vessels withA major challenge in tissue engineering is to reproduce the native 3D microvascular architecture fundamental for in vivo functions. Current approaches still lack a network of perfusable vessels with native 3D structural organization. Here we present a new method combining self-assembled monolayer (SAM)-based cell transfer and gelatin methacrylate hydrogel photopatterning techniques for microengineering vascular structures. Human umbilical vein cell (HUVEC) transfer from oligopeptide SAM-coated surfaces to the hydrogel revealed two SAM desorption mechanisms: photoinduced and electrochemically triggered. The former, occurs concomitantly to hydrogel photocrosslinking, and resulted in efficient (>97%) monolayer transfer. The latter, prompted by additional potential application, preserved cell morphology and maintained high transfer efficiency of VE-cadherin positive monolayers over longer culture periods. This approach was also applied to transfer HUVECs to 3D geometrically defined vascular-like structures in hydrogels, which were then maintained in perfusion culture for 15 days. As a step toward more complex constructs, a cell-laden hydrogel layer was photopatterned around the endothelialized channel to mimic the vascular smooth muscle structure of distal arterioles. This study shows that the coupling of the SAM-based cell transfer and hydrogel photocrosslinking could potentially open up new avenues in engineering more complex, vascularized tissue constructs for regenerative medicine and tissue engineering applications.

• In vitro evaluation of an injectable chitosan gel for sustained local delivery of BMP-2 for osteoblastic differentiation.

  Authors: Sungwoo Kim, Helen Tsao, Yunqing Kang, Daniel A Young, Milan Sen, Joseph C Wenke, Yunzhi Yang

  Journal of biomedical materials research. Part B, Applied biomaterials. 09/2011; 99(2):380-90.

  We investigated the effect of sustained release of bone morphogenetic protein-2 (BMP-2) from an injectable chitosan gel on osteoblastic differentiation in vitro. We first characterized the releaseWe investigated the effect of sustained release of bone morphogenetic protein-2 (BMP-2) from an injectable chitosan gel on osteoblastic differentiation in vitro. We first characterized the release profile of BMP-2 from the gels, and then examined the cellular responses of preosteoblast mouse stromal cells (W-20-17) and human embryonic palatal mesenchymal (HEPM) cells to BMP-2. The release profiles of different concentrations of BMP-2 exhibited sustained releases (41% for 2 ng/mL and 48% for 20 ng/mL, respectively) from the chitosan gels over a three-week period. Both cell types cultured in the chitosan gels were viable and significantly proliferated for 3 days (p < 0.05). Chitosan gels loaded with BMP-2 enhanced ALP activity of W-20-17 by 3.6-fold, and increased calcium mineral deposition of HEPM by 2.8-fold at 14 days of incubation, compared to control groups initially containing the same amount of BMP-2. In addition, schitosan gels loaded with BMP-2 exhibited significantly greater osteocalcin synthesis of W-20-17 at seven days, and of HEPM at both 7 and 14 days compared with the control groups (p<0.05). This study suggests that the enhanced effects of BMP-2 released from chitosan gels on cell differentiation and mineralization are species and cell type dependent.

• Enhanced mechanical performance and biological evaluation of a PLGA coated β-TCP composite scaffold for load-bearing applications.

  Authors: Yunqing Kang, Allison Scully, Daniel A Young, Sungwoo Kim, Helen Tsao, Milan Sen, Yunzhi Yang

  European polymer journal. 08/2011; 47(8):1569-1577.

  Porous β-tricalcium phosphate (β-TCP) has been used for bone repair and replacement in clinics due to its excellent biocompatibility, osteoconductivity, and biodegradability. However, the applicationPorous β-tricalcium phosphate (β-TCP) has been used for bone repair and replacement in clinics due to its excellent biocompatibility, osteoconductivity, and biodegradability. However, the application of β-TCP has been limited by its brittleness. Here, we demonstrated that an interconnected porous β-TCP scaffold infiltrated with a thin layer of poly (lactic-co-glycolic acid) (PLGA) polymer showed improved mechanical performance compared to an uncoated β-TCP scaffold while retaining its excellent interconnectivity and biocompatibility. The infiltration of PLGA significantly increased the compressive strength of β-TCP scaffolds from 2.90 MPa to 4.19 MPa, bending strength from 1.46 MPa to 2.41 MPa, and toughness from 0.17 MPa to 1.44 MPa, while retaining an interconnected porous structure with a porosity of 80.65%. These remarkable improvements in the mechanical properties of PLGA-coated β-TCP scaffolds are due to the combination of the systematic coating of struts, interpenetrating structural characteristics, and crack bridging. The in vitro biological evaluation demonstrated that rat bone marrow stromal cells (rBMSCs) adhered well, proliferated, and expressed alkaline phosphatase (ALP) activity on both the PLGA-coated β-TCP and the β-TCP. These results suggest a new strategy for fabricating interconnected macroporous scaffolds with significantly enhanced mechanical strength for potential load-bearing bone tissue regeneration.

• Creation of bony microenvironment with CaP and cell-derived ECM to enhance human bone-marrow MSC behavior and delivery of BMP-2.

  Authors: Yunqing Kang, Sungwoo Kim, Ali Khademhosseini, Yunzhi Yang

  Biomaterials. 05/2011; 32(26):6119-30.

  Extracellular matrix (ECM) comprises a rich meshwork of proteins and proteoglycans, which not only contains biological cues for cell behavior, but is also a reservoir for binding growth factors andExtracellular matrix (ECM) comprises a rich meshwork of proteins and proteoglycans, which not only contains biological cues for cell behavior, but is also a reservoir for binding growth factors and controlling their release. Here we aimed to create a suitable bony microenvironment with cell-derived ECM and biodegradable β-tricalcium phosphate (β-TCP). More specifically, we investigated whether the ECM produced by bone marrow-derived mesenchymal stem cells (hBMSC) on a β-TCP scaffold can bind bone morphogenetic protein-2 (BMP-2) and control its release in a sustained manner, and further examined the effect of ECM and the BMP-2 released from ECM on cell behaviors. The ECM was obtained through culturing the hBMSC on a β-TCP porous scaffold and performing decellularization and sterilization. SEM, XPS, FTIR, and immunofluorescent staining results indicated the presence of ECM on the β-TCP and the amount of ECM increased with the incubation time. BMP-2 was loaded onto the β-TCP with and without ECM by immersing the scaffolds in the BMP-2 solution. The loading and release kinetics of the BMP-2 on the β-TCP/ECM were significantly slower than those on the β-TCP. The β-TCP/ECM exhibited a sustained release profile of the BMP-2, which was also affected by the amount of ECM. This is probably because the β-TCP/ECM has different binding mechanisms with BMP-2. The β-TCP/ECM promoted cell proliferation. Furthermore, the BMP-2-loaded β-TCP/ECM stimulated reorganization of the actin cytoskeleton, increased expression of alkaline phosphatase and calcium deposition by the cells compared to those without BMP-2 loading and the β-TCP with BMP-2 loading.

• A chitosan/beta-glycerophosphate thermo-sensitive gel for the delivery of ellagic acid for the treatment of brain cancer.

  Authors: Sungwoo Kim, Satoru K Nishimoto, Joel D Bumgardner, Warren O Haggard, M Waleed Gaber, Yunzhi Yang

  Biomaterials. 02/2010; 31(14):4157-66.

  We report here the development of a chitosan/beta-glycerophosphate(Ch/beta-GP) thermo-sensitive gel to deliver ellagic acid (EA) for cancer treatment. The properties of the Ch/beta-GP gels wereWe report here the development of a chitosan/beta-glycerophosphate(Ch/beta-GP) thermo-sensitive gel to deliver ellagic acid (EA) for cancer treatment. The properties of the Ch/beta-GP gels were characterized regarding chemical structure, surface morphology, and viscoelasticity. In vitro EA release rate from the EA loaded Ch/beta-GP gel and chitosan degradation rate were investigated. The anti-tumor effect of the EA loaded Ch/beta-GP gel on brain cancer cells (human U87 glioblastomas and rat C6 glioma cells) was evaluated by examining cell viability. Cell number and activity were monitored by the MTS assay. The Ch/beta-GP solution formed a heat-induced gel at body temperature, and the gelation temperature and time were affected by the final pH of the Ch/beta-GP solution. The lysozyme increased the EA release rate by 2.5 times higher than that in the absence of lysozyme. Dialyzed chitosan solution with final pH 6.3 greatly reduced the beta-GP needed for gelation, thereby significantly improving the biocompatibility of gel (p < 0.001). The chitosan gels containing 1% (w/v) of ellagic acid significantly reduced viability of U87 cells and C6 cells compared with the chitosan gels at 3 days incubation (p < 0.01, and p < 0.001, respectively).

• Anodic oxidized nanotubular titanium implants enhance bone morphogenetic protein-2 delivery.

  Authors: In-Ho Bae, Kwi-Dug Yun, Hyun-Seung Kim, Byung-Chul Jeong, Hyun-Pil Lim, Sang-Won Park, Kwang-Min Lee, Young-Chai Lim, Kyung-Ku Lee, Yunzhi Yang, Jeong-Tae Koh

  Journal of biomedical materials research. Part B, Applied biomaterials. 02/2010; 93(2):484-91.

  Implant failure has been attributed to loosening of an implant from the host bone possibly due to poor osseointegration. One promising strategy for improving osseointegration is to develop aImplant failure has been attributed to loosening of an implant from the host bone possibly due to poor osseointegration. One promising strategy for improving osseointegration is to develop a functional implant surface that promotes osteoblast differentiation. In this study, a titanium (Ti) surface was functionalized by an anodic oxidation process and was loaded with recombinant human bone morphogenetic protein-2 (rhBMP-2). The following four groups of Ti surfaces were prepared: machined (M), anodized machined (MA), resorbable blast medium (RBM), and anodized RBM (RBMA). The surfaces were characterized by scanning electron microscopy and contact angle measurements. The results showed that a Ti oxide layer (TiO(2)) was observed in the anodized surfaces in the form of nanotubes, approximately 100 nm in diameter and 500 nm in length. The hydrophilic properties of the anodized surfaces were significantly improved. The adsorbed rhBMP-2 loaded on the nonanodized surfaces and lyophilized showed spherical particle morphology. However, the adsorbed rhBMP-2 showed a dispersed pattern over the anodized surfaces. The velocity of the rhBMP-2 released from the surfaces was measured to determine if the anodized surface can improve in delivery efficiency. The results showed that the release velocity of the rhBMP-2 from the anodized surfaces was sustained when compared with that of the nonanodized surfaces. In addition, the rhBMP-2 released from the surface was found to be bioactive according to the alkaline phosphatase activity and the level of calcium mineral deposition. These results suggest that the TiO(2) nanotubular structure formed by anodizing is a promising configuration for sustained rhBMP-2 delivery.

• Effect of growth factors in combination with injectable silicone resin particles on the biological activity of dermal fibroblasts: A preliminary in vitro study.

  Authors: Jessica A Jennings, Robert M Crews, Joycelyn Robinson, Kelly Richelsoph, Judith A Cole, Joel D Bumgardner, Yunzhi Yang, Warren O Haggard

  Journal of biomedical materials research. Part B, Applied biomaterials. 11/2009;

  Injections of silicone fluid have been clinically evaluated to treat and prevent foot ulcers due to diminished plantar fat-pad in neuropathic diabetics. The objective of this study was to determineInjections of silicone fluid have been clinically evaluated to treat and prevent foot ulcers due to diminished plantar fat-pad in neuropathic diabetics. The objective of this study was to determine preliminary in vitro effects of an injectable form of silicone resin particles in combination with growth factors to determine the suitability of this potential therapy for prevention of diabetic foot ulcers. Basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and platelet-derived growth factor (PDGF-BB) were added to monolayer culture along with silicone resin particles (12 mum average diameter). Growth factors were also combined as follows: bFGF+PDGF-BB, EGF+PDGF-BB, and bFGF+EGF. Growth factors alone and in combination increased fibroblast proliferation, but the presence of particles did not significantly affect cellular proliferation. The addition of particles significantly increased fibronectin production 117% in the control group and 151% in the PDGF only group. Collagen production was increased with exposure to EGF and growth factor combinations, but the presence of particles did not lead to any significant differences, except an 81% increase in the bFGF group. These preliminary results suggest that a combination of PDGF and bFGF may be effective in stimulating proliferation and matrix production around injectable silicone resin particles to generate a fibrous tissue pad to alleviate the abnormal distribution of high pressures that contribute to diabetic foot ulcer formation. (c) 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2010.

• Lyophilization to improve drug delivery for chitosan-calcium phosphate bone scaffold construct: A preliminary investigation.

  Authors: Benjamin T Reves, Joel D Bumgardner, Judith A Cole, Yunzhi Yang, Warren O Haggard

  Journal of biomedical materials research. Part B, Applied biomaterials. 06/2009;

  Lyophilization was evaluated in chitosan-calcium phosphate microspheres and scaffolds to improve drug delivery of growth factors and antibiotics for orthopedic applications. The dual delivery of anLyophilization was evaluated in chitosan-calcium phosphate microspheres and scaffolds to improve drug delivery of growth factors and antibiotics for orthopedic applications. The dual delivery of an antibiotic and a growth factor from a composite scaffold would be beneficial for treatment of complex fracture sites, such as comminuted fractures and segmental bone defects. The aim of this investigation was to increase the loading capacity of the composite by taking advantage of the increased porosity, due to lyophilization, and to produce an extended elution profile using a secondary chitosan-bead coating. The physiochemical properties of the composite were investigated, and loading and elution studies were performed with alkaline phosphatase (ALP), bone morphogenetic protein-2 (BMP-2), and amikacin. Lyophilization was found to increase the surface area of scaffolds by over 400% and the porosity of scaffolds by 50%. Using ALP as a model protein, the loading capacity was increased by lyophilization from 4.3 +/- 2.5 to 24.6 +/- 3.6 mug ALP/mg microspheres, and the elution profile was extended by a supplemental chitosan coating. The loading capacity of BMP-2 for composite microspheres was increased from 74.4 +/- 3.7 to 102.1 +/- 8.0 mug BMP-2/g microspheres with lyophilization compared with nonlyophilized microspheres. The elution profiles of BMP-2 and the antibiotic amikacin were not extended with the supplemental coating. Additional investigations are planned to improve these elution characteristics for growth factors and antibiotics. (c) 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009.

• Novel template-casting technique for fabricating beta-tricalcium phosphate scaffolds with high interconnectivity and mechanical strength and in vitro cell responses.

  Authors: Yongxing Liu, Joong-Hyun Kim, Daniel Young, Sungwoo Kim, Satoru K Nishimoto, Yunzhi Yang

  Journal of biomedical materials research. Part A. 04/2009;

  A novel template-casting method was developed to produce completely interconnected, macroporous biodegradable beta-tricalcium phosphate (beta-TCP) scaffolds, whose architecture and chemistry can beA novel template-casting method was developed to produce completely interconnected, macroporous biodegradable beta-tricalcium phosphate (beta-TCP) scaffolds, whose architecture and chemistry can be fully manipulated by varying the templates and casting materials. The processing route includes preparation of beta-TCP slurry; casting and shaping into preformed templates comprised of paraffin beads; solidifying, drying; and sintering. Structural, chemical, and mechanical properties of the prepared macroporous scaffolds were characterized using micro computed tomography, scanning electron microscopy, x-ray diffractometry, Fourier transform infrared spectroscopy, and mechanical testing. Human embryonic palatal mesenchymal cells were used to evaluate cell proliferation within the scaffolds in vitro. The scaffolds consisted of interconnected macropores and solid struts, leading to a reticular network. Two groups of scaffolds with larger pores, approximately 600-800 mum and smaller pores approximately 350-500 mum, were demonstrated. The interconnected windows between neighboring macropores were 440 +/- 57 mum in diameter for the larger-pored scaffolds, and 330 +/- 50 mum for the smaller-pored scaffolds. The scaffolds were highly crystallized and composed dominantly of beta-tricalcium phosphate (beta-TCP) accompanied by minor phase of hydroxyapatite (HA). The hydroxyl group was clearly detected by FTIR on the scaffolds. High mechanical strength (9.3 MPa) was demonstrated by the completely interconnected scaffolds with approximately 79% porosity. The human embryonic palatal mesenchymal (HEPM) cells proliferated well on the smaller-pored and larger-pored scaffolds, exhibiting a significantly higher level of proliferation in the first 11 days of culture on the smaller pored scaffolds. High levels of differentiation were also evidenced in both pore sizes of scaffolds. (c) 2009 Wiley Periodicals, Inc. J Biomed Mater Res, 2009.

• Development of chitosan-ellagic acid films as a local drug delivery system to induce apoptotic death of human melanoma cells.

  Authors: Sungwoo Kim, Yongxing Liu, M Waleed Gaber, Joel D Bumgardner, Warren O Haggard, Yunzhi Yang

  Journal of biomedical materials research. Part B, Applied biomaterials. 12/2008;

  This study was designed to develop a local chemotherapy device using chitosan as a local drug carrier and ellagic acid (EA) as an anticancer drug. We fabricated chitosan-ellagic acid (Ch-EA) filmsThis study was designed to develop a local chemotherapy device using chitosan as a local drug carrier and ellagic acid (EA) as an anticancer drug. We fabricated chitosan-ellagic acid (Ch-EA) films with concentrations of 0, 0.05, 0.1, 0.5, and 1% (w/v) of EA and examined the films using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and contact angle measurement. The WM115 human melanoma cell line as a skin cancer model was used to evaluate cell response to the films with the MTS assay and apoptosis assay, and HS68 human newborn fibroblast cell line as a control. With the increase in the concentration of the EA, the composite films exhibit increasing amide and ester groups and diffraction peaks of the crystallized EA and greater surface roughness and hydrophilicity. The chitosan films with 0.5 and 1% (w/v) of EA were found to have a potent antiproliferative effect on the melanoma cells by inducing apoptotic cell death. Localized effect of composites on cell behaviors has been clearly demonstrated. Our study demonstrated that the novel Ch-EA film can be potentially used in local chemotherapy. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2009.

• Chitosan-coated stainless steel screws for fixation in contaminated fractures.

  Authors: Alex H Greene, Joel D Bumgardner, Yunzhi Yang, Jon Moseley, Warren O Haggard

  Clinical orthopaedics and related research. 08/2008; 466(7):1699-704.

  Stainless steel screws and other internal fixation devices are used routinely to stabilize bacteria-contaminated bone fractures from multiple injury mechanisms. In this preliminary study, weStainless steel screws and other internal fixation devices are used routinely to stabilize bacteria-contaminated bone fractures from multiple injury mechanisms. In this preliminary study, we hypothesize that a chitosan coating either unloaded or loaded with an antibiotic, gentamicin, could lessen or prevent these devices from becoming an initial nidus for infection. The questions investigated for this hypothesis were: (1) how much of the sterilized coating remains on the screw with simulated functional use; (2) is the unloaded or loaded chitosan coating bacteriostatic and biocompatible; and (3) what amount and rate does an antibiotic elute from the coating? In this study, the gentamicin eluted from the coating at a detectable level during 72 to 96 hours. The coating was retained at the 90% level in simulated bone screw fixation and the unloaded and loaded chitosan coatings had encouraging in vitro biocompatibility with fibroblasts and stem cells and were bacteriostatic against at least one strain of Staphylococcus aureus. The use of an antibiotic-loaded chitosan coating on stainless steel bone screws and internal fixation devices in contaminated bone fracture fixation may be considered after optimization of antibiotic loading and elution and more expanded in vitro and in vivo investigations with other organisms and antibiotics.

• Novel fabrication of nano-rod array structures on titanium and in vitro cell responses.

  Authors: Yongxing Liu, Weihui Chen, Yunzhi Yang, Joo L Ong, Kanji Tsuru, Satoshi Hayakawa, Akiyoshi Osaka

  Journal of materials science. Materials in medicine. 07/2008; 19(7):2735-41.

  Nano-scale rod arrays of titania were fabricated on titanium surface by a glass phase topotaxy growth (GPT) method, which was featured by an interfacial reaction between sodium tetraborate coatingNano-scale rod arrays of titania were fabricated on titanium surface by a glass phase topotaxy growth (GPT) method, which was featured by an interfacial reaction between sodium tetraborate coating and the preheated metallic titanium at elevated temperature. The samples were characterized by thin-film X-ray diffraction (XRD), scanning electron microscope (SEM), profilometer and contact angle measurement. Thin-film XRD analysis indicated that the nano-rod arrays were composed of pure rutile titania phase. SEM images showed that these rutile rods were 100-200 nm wide and 1-2 mum long. The nano-rod arrays had significantly higher average roughness (P < 0.05) and greater hydrophilicity (P < 0.05) compared to the control. Human embryonic palatal mesenchymal (HEPM) cells were grown to evaluate in vitro cell responses to the nano-rod array structures in terms of cell attachment and proliferation. An equivalent high attachment rate of 94% was observed after 4-h incubation, but a lower proliferation rate was observed on the nano-rod array after 12-day culture compared to the control (P < 0.05).

• Fabrication and characterization of functionally graded nano-micro porous titanium surface by anodizing.

  Authors: Hyun-Seung Kim, Yunzhi Yang, Jeong-Tae Koh, Kyung-Ku Lee, Doh-Jae Lee, Kwang-Min Lee, Sang-Won Park

  Journal of biomedical materials research. Part B, Applied biomaterials. 06/2008;

  The purpose of this study was to fabricate and characterize nanotubular structure on machined titanium (MA) and resorbable blast media (RBM) treated titanium by anodizing. The anodized MA and RBMThe purpose of this study was to fabricate and characterize nanotubular structure on machined titanium (MA) and resorbable blast media (RBM) treated titanium by anodizing. The anodized MA and RBM were characterized with scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy disperse spectra, X-ray photoelectron spectra, and nano-indentation and scratch test. Highly ordered nanotubular layers of individually 100 nm in diameter and 500 nm in length approximately were formed regardless of the substrates. The nanotubular layers consisted mainly of amorphous TiO(2) with trace fluorine. The nanotubular surfaces on both the substrates significantly reduced water contact angles and elastic modulus compared with those prior to anodizing. The anodizing treatment significantly increased the surface roughness of the smooth MA, but significantly decreased the surface roughness of the roughened RBM. The critical delamination forces of the nanotubular layer were not obtained due to the limitation of surface roughness. The anodized RBM consisted of a nano-micro porous graded structure, or a nanotubular amorphous fluoride containing TiO(2) layer on top of micro-roughened titanium surface, which is expected to significantly improve the surface area that can be used to deliver drugs and growth factors and alleviate the interfacial elastic modulus mismatch as to enhance osseointegration when compared with conventional dental and orthopedic implant devices with smooth or acid etched surface. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2008.

• Design and characterization of a novel chitosan/nanocrystalline calcium phosphate composite scaffold for bone regeneration.

  Authors: Betsy M Chesnutt, Ann M Viano, Youling Yuan, Yunzhi Yang, Teja Guda, Mark R Appleford, Joo L Ong, Warren O Haggard, Joel D Bumgardner

  Journal of biomedical materials research. Part A. 03/2008;

  To meet the challenge of regenerating bone lost to disease or trauma, biodegradable scaffolds are being investigated as a way to regenerate bone without the need for an auto- or allograft. Here, weTo meet the challenge of regenerating bone lost to disease or trauma, biodegradable scaffolds are being investigated as a way to regenerate bone without the need for an auto- or allograft. Here, we have developed a novel microsphere-based chitosan/nanocrystalline calcium phosphate (CaP) composite scaffold and investigated its potential compared to plain chitosan scaffolds to be used as a bone graft substitute. Composite and chitosan scaffolds were prepared by fusing microspheres of 500-900 mum in diameter, and porosity, degradation, compressive strength, and cell growth were examined. Both scaffolds had porosities of 33-35% and pore sizes between 100 and 800 mum. However, composite scaffolds were much rougher and, as a result, had 20 times more surface area/unit mass than chitosan scaffolds. The compressive modulus of hydrated composite scaffolds was significantly higher than chitosan scaffolds (9.29 +/- 0.8 MPa vs. 3.26 +/- 2.5 MPa), and composite scaffolds were tougher and more flexible than what has been reported for other chitosan-CaP composites or CaP scaffolds alone. Using X-ray diffraction, scaffolds were shown to contain partially crystalline hydroxyapatite with a crystallinity of 16.7% +/- 6.8% and crystallite size of 128 +/- 55 nm. Fibronection adsorption was increased on composite scaffolds, and cell attachment was higher on composite scaffolds after 30 min, although attachment rates were similar after 1 h. Osteoblast proliferation (based on dsDNA measurements) was significantly increased after 1 week of culture. These studies have demonstrated that composite scaffolds have mechanical properties and porosity sufficient to support ingrowth of new bone tissue, and cell attachment and proliferation data indicate composite scaffolds are promising for bone regeneration. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2008.

• The integration of chitosan-coated titanium in bone: an in vivo study in rabbits.

  Authors: Joel D Bumgardner, Betsy M Chesnutt, Youling Yuan, Yunzhi Yang, Mark Appleford, Sunho Oh, Ronald McLaughlin, Steven H Elder, Joo L Ong

  Implant dentistry. 04/2007; 16(1):66-79.

  PROCEDURE: Much research is directed at surface modifications to enhance osseointegration of implants. A new potential coating is the biopolymer, chitosan, the deacetylated derivative of the naturalPROCEDURE: Much research is directed at surface modifications to enhance osseointegration of implants. A new potential coating is the biopolymer, chitosan, the deacetylated derivative of the natural polysaccharide, chitin. Chitosan is biocompatible, degradable, nontoxic, and exhibits osteogenic properties. The aim of this research was to investigate the hypothesis that chitosan-coated titanium supports bone formation and osseointegration. MATERIALS AND METHODS: Chitosan (1 wt% of 92.3% deacetylated chitosan in 1% acetic acid) was solution cast and bonded to rough ground titanium pins (2-mm diameterx4-mm long) via silane reactions. Calcium phosphate sputter-coated titanium and uncoated titanium pins were used as controls. Two chitosan-coated pins, and 1 each of calcium phosphate coated and uncoated pins were implanted unilaterally in the tibia of 16 adult male New Zealand white rabbits. At 2, 4, 8, and 12 weeks, undecalcified sections were histologically evaluated for healing and bone formation. RESULTS: Histological evaluations of tissues in contact with the chitosan-coated pins indicated minimal inflammatory response and a typical healing sequence of fibrous, woven bone formation, followed by development of lamellar bone. These observations were similar to those for tissues interfacing the control calcium phosphate-coated and uncoated titanium implants. Quantitative comparisons of the bone-implant interface were not possible since 31% of the implants migrated into the tibial marrow space after implantation due to insufficient cortical bone thickness to hold pins in place during healing. CONCLUSION: These data support the hypothesis that chitosan-coatings are able to develop a close bony apposition or the osseointegration of dental/craniofacial and orthopedic implants.

• Effects of applied voltages on hydroxyapatite coating of titanium by electrophoretic deposition.

  Authors: Xianwei Meng, Tae-Yub Kwon, Yunzhi Yang, Joo L Ong, Kyo-Han Kim

  Journal of biomedical materials research. Part B, Applied biomaterials. 09/2006; 78(2):373-7.

  Hydroxyapatite (HA) coatings were deposited on titanium substrates by electrophoretic deposition (EPD) at constant voltage and dynamic voltage, respectively. Various surface morphologies wereHydroxyapatite (HA) coatings were deposited on titanium substrates by electrophoretic deposition (EPD) at constant voltage and dynamic voltage, respectively. Various surface morphologies were observed under different type of voltages. Under a constant voltage of 20 V, a dense HA coating could be prepared. Under a constant voltage of 200 V, big HA particles were deposited and the coating was porous. Under a dynamic voltage, a continuous gradient HA coating could be obtained. HA coatings were characterized with a field emission-scanning electron microscopy (FE-SEM) and an X-ray diffraction (XRD). XRD indicated no significant HA decomposition when the coatings were sintered for 2 h at 800 degrees C.

• Preparation and characterization of anodized titanium surfaces and their effect on osteoblast responses.

  Authors: Kyo-Han Kim, Tae-Yub Kwon, Shin-Yoon Kim, Inn-Kyu Kang, Sukyoung Kim, Yunzhi Yang, Joo L Ong

  The Journal of oral implantology. 02/2006; 32(1):8-13.

  In this study, titanium (Ti) surface was modified by anodizing with a mixture of beta-glycerophosphate sodium and calcium (Ca) acetate, and the anodized surfaces were characterized by scanningIn this study, titanium (Ti) surface was modified by anodizing with a mixture of beta-glycerophosphate sodium and calcium (Ca) acetate, and the anodized surfaces were characterized by scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. In vitro osteoblast response to anodized oxide was also evaluated. The anodic oxide produced was observed to have interconnected pores (0.5-2 microm in diameter) and intermediate roughness (0.60-1.00 microm). In addition, anodic oxide was observed to have amorphous and anatase oxide. Calcium and phosphorus ions were deposited on the Ti oxide during anodization. Osteoblast differentiation, as indicated by alkaline phosphatase production, was enhanced on anodized surfaces. It was thus concluded from this study that Ca phosphate can be deposited on Ti surfaces by anodization. It was also concluded that the phenotypic expression of osteoblast was enhanced by the presence of Ca phosphate and higher roughness on anodized Ti surfaces.

• The effect of sputtered calcium phosphate coatings of different crystallinity on osteoblast differentiation.

  Authors: Patricia Berube, Yunzhi Yang, David L Carnes, Robert E Stover, Edward J Boland, Joo L Ong

  Journal of periodontology. 11/2005; 76(10):1697-709.

  BACKGROUND: Coating titanium implants with hydroxyapatite (HA) has been suggested to increase osseointegration by stimulating early osteoblast function. The goal of this study was to determine theBACKGROUND: Coating titanium implants with hydroxyapatite (HA) has been suggested to increase osseointegration by stimulating early osteoblast function. The goal of this study was to determine the extent to which the crystalline content of the HA surface affected osteoblast function in vitro. METHODS: Osteoblasts were isolated from fetal rat calvaria. Titanium coupons were sputter coated and analyzed. Mineralized nodule formation on plastic using von Kossa staining was compared to tetracycline and procion dye labeling. Cell proliferation, adhesion, alkaline phosphatase activity, morphology and spreading, and cytoskeletal arrangement were analyzed. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the expression of mRNA for specific proteins. RESULTS: The percent crystallinity of coatings was 0% (HA1), 1.9% +/- 0.4% (HA2), and 66.4% +/- 2.8% (HA3). The nodule formation and cell number were greatest on titanium and HA3 compared to HA1 and HA2 (P < 0.01). At weeks 2 to 4, all samples showed strong alkaline phosphatase, osteocalcin, monocyte-colony stimulating factor (M-CSF), and receptor activator of nuclear factor kappa B ligand (RANKL) expression, but the specific activity of alkaline phosphatase decreased. Cell adherence was greater than 60% of applied cells for all surfaces except HA3. The cells were significantly more elongated on titanium, with no difference on the HA-coated surfaces. Actin filaments were arranged peripherally at 5 hours but arranged parallel to the long axis of the cell at 20 hours. CONCLUSIONS: Procion labeling is a valid method for evaluating mineralized nodule formation on opaque surfaces. There were no major differences in osteoblast function using titanium or high-crystalline coatings, and most functions were decreased on amorphous or low-crystalline coatings.

• Ectopic osteoinduction and early degradation of recombinant human bone morphogenetic protein-2-loaded porous beta-tricalcium phosphate in mice.

  Authors: Ge Liang, Yunzhi Yang, Sunho Oh, Joo L Ong, Changqiong Zheng, Junguo Ran, Guangfu Yin, Dali Zhou

  Biomaterials. 08/2005; 26(20):4265-71.

  The present study investigated the ectopic osteoinduction and early degradation of recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded porous beta-tricalcium phosphate (beta-TCP) in mice.The present study investigated the ectopic osteoinduction and early degradation of recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded porous beta-tricalcium phosphate (beta-TCP) in mice. The porous beta-TCP with 50 microg of rhBMP-2 (n = 25) and porous beta-TCP (control group, n = 25) were implanted into muscle pouches in the right and left thigh of 28-day-old mice (n = 25), respectively. At every time point (3, 7, 14, 21 and 28 days after implantation), five mice were euthanized and the histological examinations of implantation sites were performed. In addition, the alkaline phosphatase (ALP) activity was also quantitatively analyzed. For the rhBMP-2-loaded group, blood vessel formation and immature cartilage was observed within the porous beta-TCP 3 days after implantation. Mature cartilage was observed 7 days after implantation of rhBMP-2-loaded porous beta-TCP. Newly formed woven bone, lamellar bone as well as marrow were observed 14 and 21 days after implantation of the rhBMP-2-loaded porous beta-TCP. Lamellar bone and marrow were observed 28 days after implantation of the rhBMP-2-loaded porous beta-TCP. For the control group, no bone or cartilage was observed at all time points. However, multinucleated giant cells and fibrous tissues were observed in the control group at 7 and 28 days after implantation, respectively. At 21 and 28 days after implantation, porous beta-TCP was observed to fragment indicating early degradation of the porous beta-TCP in both groups. In addition, ALP was observed to be significantly higher in the rhBMP-2-loaded beta-TCP as compared to the control beta-TCP. It was concluded from this study that the rhBMP-2-loaded porous beta-TCP induced blood vessel and ectopic bone formation.