Joo L Ong

Publications of Joo L Ong

• Bilayer hydroxyapatite scaffolds for maxillofacial bone tissue engineering.

  Authors: Teja Guda, Sunho Oh, Mark R Appleford, Joo L Ong

  The International journal of oral & maxillofacial implants. 03/2012; 27(2):288-94.

  Purpose: The frequency of alveolar ridge resorption and crestal bone loss emphasizes the clinical need for bone graft substitutes to improve local bone quality prior to dental implant placement.Purpose: The frequency of alveolar ridge resorption and crestal bone loss emphasizes the clinical need for bone graft substitutes to improve local bone quality prior to dental implant placement. Microcomputed tomography has been extensively employed to estimate bone quality more objectively (ie, quantitatively) by relating it to architectural parameters. In the present study, the mechanical properties of open cellular fully interconnected bilayer hydroxyapatite scaffolds, which mimicked the cortical shell/trabecular core architecture of human bone, were investigated for suitability as bone graft substitutes for maxillofacial reconstruction. Materials and Methods: Hydroxyapatite scaffolds with different architectures were fabricated using polymeric template pore sizes of 450 or 340 Μm for the inner trabecular cores and 200 or 250 Μm for the outer cortical shells in three different core-to-shell volume ratios. The architectural and mechanical properties and fluid permeability of the scaffolds were compared to reported values for maxillofacial bone. Results: Whereas the elastic moduli of the scaffolds were comparable, their compressive strength was observed to be in the lower range of human mandibular trabecular bone. The microcomputed tomography architectural indices for the scaffolds were comparable to those of human trabecular bone at different locations in the human body, including the maxilla and mandible. Scaffold compressive strength, elastic modulus, and fluid conductance were 0.3 to 2.3 MPa, 40.9 to 668.1 MPa, and 8.8 to 49.9 x 10-10 m3s-1Pa-1, respectively. Conclusion: Open-pore bilayer scaffolds can be fabricated to exhibit sufficient mechanical integrity for maxillofacial bone graft applications to match specific bone site architecture while providing sufficient permeability to sustain bone regeneration.

• Antibacterial effect and cytotoxicity of Ag-doped functionally graded hydroxyapatite coatings.

  Authors: Xiao Bai, Stefan Sandukas, Mark Appleford, Joo L Ong, Afsaneh Rabiei

  Journal of biomedical materials research. Part B, Applied biomaterials. 11/2011;

  Functionally graded hydroxyapatite coatings (FGHA) doped with 1, 3, and 6.5 wt % silver (Ag) have been deposited on Titanium using ion-beam-assisted deposition. Scanning transmission electronFunctionally graded hydroxyapatite coatings (FGHA) doped with 1, 3, and 6.5 wt % silver (Ag) have been deposited on Titanium using ion-beam-assisted deposition. Scanning transmission electron microscopy on coating cross sections confirmed the presence of FGHA coating with mostly amorphous layers at the top and mostly crystalline layers toward the coating interface as well as the existence of 10-50 nm Ag particles distributed throughout the thickness of the coatings. Calcium release in phosphate buffered saline solution showed a high release rate of Ca at the beginning of the test, and a gradual decrease in release rate thereafter to a minimum level until day 7. Similarly, the release rate of Ag in ultra pure water was initially high in the first 4 h and then gradually decreased over a 7 days period. Antibacterial tests have shown a reduction in the viability of S. aureus in Ag-doped coatings particularly in samples with higher Ag concentrations of 3 and 6.5 wt %. Cytotoxicity tests using an osteoblast cell line, on the other hand, have demonstrated that the samples with 6.5 wt % Ag have a negative effect on osteoblast cell response, proliferation, and apoptosis as well as a negative effect on protein and osteocalcin production. It is notable that the samples with 3 wt % Ag or less presented minimal cytotoxicity compared with control surfaces. Considering both the antibacterial and cytotoxicity effects, it is suggested that the 3 wt % of Ag in FGHA coatings can be favorable. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2011.

• Hydroxyapatite/polylactide biphasic combination scaffold loaded with dexamethasone for bone regeneration.

  Authors: Jun-Sik Son, Su-Gwan Kim, Ji-Su Oh, Mark Appleford, Sunho Oh, Joo L Ong, Kyu-Bok Lee

  Journal of biomedical materials research. Part A. 09/2011; 99(4):638-47.

  This study presents a novel design of a ceramic/polymer biphasic combination scaffold that mimics natural bone structures and is used as a bone graft substitute. To mimic the natural bone structures,This study presents a novel design of a ceramic/polymer biphasic combination scaffold that mimics natural bone structures and is used as a bone graft substitute. To mimic the natural bone structures, the outside cortical-like shells were composed of porous hydroxyapatite (HA) with a hollow interior using a polymeric template-coating technique; the inner trabecular-like core consisted of porous poly(D,L-lactic acid) (PLA) that was loaded with dexamethasone (DEX) and was directly produced using a particle leaching/gas forming technique to create the inner diameter of the HA scaffold. It was observed that the HA and PLA parts of the fabricated HA/PLA biphasic scaffold contained open and interconnected pore structures, and the boundary between both parts was tightly connected without any gaps. It was found that the structure of the combination scaffold was analogous to that of natural bone based on micro-computed tomography analysis. Additionally, the dense, uniform apatite layer was formed on the surface of the HA/PLA biphasic scaffold through a biomimetic process, and DEX was successfully released from the PLA of the biphasic scaffold over a 1-month period. This release caused human embryonic palatal mesenchyme cells to proliferate, differentiate, produce ECM, and form tissue in vitro. Therefore, it was concluded that this functionally graded scaffold is similar to natural bone and represents a potential bone-substitute material.

• Migration of co-cultured endothelial cells and osteoblasts in composite hydroxyapatite/polylactic acid scaffolds.

  Authors: Amita R Shah, Sarita R Shah, Sunho Oh, Joo L Ong, Joseph C Wenke, C Mauli Agrawal

  Annals of biomedical engineering. 07/2011; 39(10):2501-9.

  Regeneration of bone in large segmental bone defects requires regeneration of both cortical bone and trabecular bone. A scaffold design consisting of a hydroxyapatite (HA) ring surrounding aRegeneration of bone in large segmental bone defects requires regeneration of both cortical bone and trabecular bone. A scaffold design consisting of a hydroxyapatite (HA) ring surrounding a polylactic acid (PLA) core simulates the structure of bone and provides an environment for indirect and direct co-culture conditions. In this experiment, human umbilical vein endothelial cells (EC) and normal human primary osteoblasts (OB) were co-cultured to evaluate cell migration and interactions within this biphasic composite scaffold. Both cell types were able to migrate between the different material phases of the scaffold. It was also observed that OB migration increased when they were co-cultured with ECs, whereas EC migration decreased in co-culture. The results show that co-culture of ECs and OBs in this composite biphasic scaffold allows for migration of cells throughout the scaffold and that pre-seeding a scaffold with ECs can increase OB infiltration into desired areas of the scaffold.

• Porous hydroxyapatite scaffold with three-dimensional localized drug delivery system using biodegradable microspheres.

  Authors: Jun Sik Son, Mark Appleford, Joo L Ong, Joseph C Wenke, Jong Min Kim, Seok Hwa Choi, Daniel S Oh

  Journal of controlled release : official journal of the Controlled Release Society. 03/2011; 153(2):133-40.

  In this study, ionic immobilization of dexamethasone (DEX)-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres was performed on the hydroxyapatite (HAp) scaffold surfaces. It was hypothesizedIn this study, ionic immobilization of dexamethasone (DEX)-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres was performed on the hydroxyapatite (HAp) scaffold surfaces. It was hypothesized that in vivo bone regeneration could be enhanced with HAp scaffolds containing DEX-loaded PLGA microspheres compared to the use of HAp scaffolds alone. In vitro drug release from the encapsulated microspheres was measured prior to the implantation in the femur defects of beagle dogs. It was observed that porous, interconnected HAp scaffolds as well as DEX-loaded PLGA microspheres were successfully fabricated in this study. Additionally, PEI was successfully coated on PLGA microsphere surfaces, resulting in a net positive-charged surface. With such modification of the PLGA microsphere surfaces, DEX-loaded PLGA microspheres were immobilized on the negatively charged HAp scaffold surfaces. Release profile of DEX over a 4week immersion study indicated an initial burst release followed by a sustained release. In vivo evaluation of the defects filled with DEX-loaded HAp scaffolds indicated enhanced volume and quality of new bone formation when compared to defects that were either unfilled or filled with HAp scaffolds alone. This innovative platform for bioactive molecule delivery more potently induced osteogenesis in vivo, which may be exploited in implantable bone graft substitutes for stem cell therapy or improved in vivo performance. It was thus concluded that various bioactive molecules for bone regeneration might be efficiently incorporated with calcium phosphate-based bioceramics using biodegradable polymeric microspheres.

• In vivo performance of bilayer hydroxyapatite scaffolds for bone tissue regeneration in the rabbit radius.

  Authors: Teja Guda, John A Walker, Beth E Pollot, Mark R Appleford, Sunho Oh, Joo L Ong, Joseph C Wenke

  Journal of materials science. Materials in medicine. 02/2011; 22(3):647-56.

  The objective of this study was to investigate the in vivo biomechanical performance of bone defects implanted with novel bilayer hydroxyapatite (HAp) scaffolds that mimic the cortical and cancellousThe objective of this study was to investigate the in vivo biomechanical performance of bone defects implanted with novel bilayer hydroxyapatite (HAp) scaffolds that mimic the cortical and cancellous organization of bone. The scaffolds maintained architectural continuity in a rabbit radius segmental defect model and were compared to an untreated defect group (negative control) and autologous bone grafts (positive control). Micro-CT evaluations indicated total bone and scaffold volume in the experimental group was significantly greater than the defect group but lesser than the autologous bone graft treatment. The flexural toughness of the scaffold and the autograft groups was significantly greater than the flexural toughness of the defect group. Interestingly, the absolute density of the bone mineral as well as calcium to phosphorus (Ca/P) ratio in that mineral for the scaffold and autograft contralateral bones was significantly higher than those for the defect contralaterals suggesting that the scaffolds contributed to calcium homeostasis. It was concluded from this study that new bone regenerated in the bilayer HAp scaffolds was comparable to the empty defects and while the HAp scaffolds provided significant increase in modulus when compared to empty defect and their flexural toughness was comparable to autografts after 8 weeks of implantation.

• Stability of antibacterial self-assembled monolayers on hydroxyapatite.

  Authors: Nelson Torres, Sunho Oh, Mark Appleford, David D Dean, James H Jorgensen, Joo L Ong, C Mauli Agrawal, Gopinath Mani

  Acta biomaterialia. 02/2010; 6(8):3242-55.

  Open fractures are common in battlefields, motor vehicle accidents, gunshot wounds, sports injuries, and high-energy falls. Such fractures are treated using hydroxyapatite (HA)-based bone graftOpen fractures are common in battlefields, motor vehicle accidents, gunshot wounds, sports injuries, and high-energy falls. Such fractures are treated using hydroxyapatite (HA)-based bone graft substitutes. However, open fracture wounds are highly susceptible to bacterial infections. Hence, this study was focused on incorporating antibacterial properties to HA using silver (Ag) carrying self-assembled monolayers (SAMs). Also, the stability of Ag carrying SAMs on HA was investigated under sterilization and physiological conditions. Initially, the -COOH terminated phosphonic acid SAMs of two different chain lengths (11 carbon atoms - shorter chain and 16 carbon atoms - longer chain) were deposited on HA. Antibacterial SAMs (ASAMs) were prepared by chemically attaching Ag to shorter and longer chain SAMs coated HA. X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle goniometry collectively confirmed the attachment of Ag onto SAMs coated HA. The bacterial adhesion study showed that the adherence of Staphylococcus aureus was significantly reduced on ASAMs coated HA when compared to control-HA. The stability studies showed that gas plasma, dry heat and autoclave degraded most of the ASAMs on HA. UV irradiation did not damage the shorter chain ASAMs as vigorously as other treatments, while it degraded the longer chain ASAMs completely. Ethylene oxide treatment did not degrade the longer chain ASAMs unlike all other treatments but it severely damaged the shorter chain ASAMs. Both shorter and longer chain ASAMs significantly desorbed from the HA surfaces under physiological conditions although longer chain ASAMs exhibited better stability than shorter chain ASAMs. This study demonstrated the potential for using ASAMs to provide antibacterial properties to HA and the need for developing techniques to improve stability of SAMs under sterilization and physiological conditions.

• Histomorphometric Analysis of Delayed Implantation After Horizontal Distraction Osteogenesis of the Mandible in Dogs.

  Authors: Ju-Rim Sun, Su-Gwan Kim, Seong-Yong Moon, Sung-Chul Lim, Joo L Ong

  Implant dentistry. 10/2009; 18(5):413-419.

  PURPOSE:: Insufficient alveolar width is known to impede successful implantation and is a major obstacle to successful oral reconstruction using intraosseous implants. The aim of this study was toPURPOSE:: Insufficient alveolar width is known to impede successful implantation and is a major obstacle to successful oral reconstruction using intraosseous implants. The aim of this study was to evaluate the osseointegration at implantation after consolidation in distracted narrow alveolar bone. MATERIALS:: Three adult mongrel dogs weighing 9 to 10 kg were studied. The lower premolars were extracted and horizontal distraction was performed using a distraction device after 8 weeks. Eight weeks after consolidation period, SLA surface implants were installed. The dogs were killed after 4 weeks implantation. RESULTS:: The preoperative and postoperative buccolingual widths of alveolar ridge were 2.7 ± 2.1 mm and 4.8 ± 2.5 mm, respectively. Direct bone contact was achieved, with no significant difference in new bone formation observed between implants placed in the distracted and undistracted bone after 4 weeks. CONCLUSIONS:: It was concluded from this study that horizontal distraction is a useful technique in augmenting a narrow alveolar ridge necessary for implant placement.

• Evaluation of peri-implant tissue in nonsubmerged dental implants: a multicenter retrospective study.

  Authors: Young-Kyun Kim, Su-Gwan Kim, Hee-Kyun Oh, Yong-Geun Choi, Yong-Seok Cho, Young-Hak Oh, Jun-Sik Son, Joo L Ong

  Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics. 09/2009; 108(2):189-95.

  OBJECTIVES: The objective of this study was to evaluate the peri-implant's hard and soft tissue response associated with the 1-stage, nonsubmerged, endosseous dental implant. STUDY DESIGN: AOBJECTIVES: The objective of this study was to evaluate the peri-implant's hard and soft tissue response associated with the 1-stage, nonsubmerged, endosseous dental implant. STUDY DESIGN: A multicenter retrospective clinical evaluation was performed on 339 nonsubmerged implants placed in 108 patients at 5 clinical centers between January 2003 and December 2007. RESULTS: After a mean follow-up period of 30 months, the mean crestal bone resorption in 339 implants was 0.43 mm. The survival and success rates were observed to be 99.1% and 95.1%, respectively. The mean calculus, inflammatory, and plaque indices were 0.13, 0.37, and 0.73, respectively, and the mean width of buccal keratinized mucosa was observed to be 2.43 mm. CONCLUSION: The short- to intermediate-term evaluation of the 1-stage, nonsubmerged, endosseous implant yields relatively high survival and success rates.

• Histomorphometric evaluation of immediately loaded SSII implants of different surface treatments in a dog model.

  Authors: Woo-Jin Jeon, Su-Gwan Kim, Sung-Chul Lim, Joo L Ong, Daniel Sunho Oh

  Journal of biomedical materials research. Part A. 08/2009; 90(2):396-400.

  This study compared splint (experimental) and nonsplint (control) methods for immediately loaded implants and examined the bone-implant contact rate for smooth, oxidized, and resorbable blast mediumThis study compared splint (experimental) and nonsplint (control) methods for immediately loaded implants and examined the bone-implant contact rate for smooth, oxidized, and resorbable blast medium (RBM) surfaces. The first through fourth mandibular premolars were extracted from six young adult dogs. Twelve weeks after extraction, implantation was performed at the extraction sites. The SSII OSSTEM implant had one of three surface treatments: smooth, oxidized, or RBM. Sixteen weeks after implantation, the dogs were euthanized; the hemimandibles were obtained and processed histologically to obtain nondecalcified sections. Longitudinal sections were made for each implant and analyzed using light microscopy. Independent of the splinting method, a significantly higher bone-implant contact was observed for implants with oxidized and RBM surfaces when compared with implants with smooth surfaces. Irrespective of the splinting method, immediately loaded implants with oxidized and RBM surfaces may result in higher bone-implant integration when compared with implants with smooth surfaces.

• Deposition and investigation of functionally graded calcium phosphate coatings on titanium.

  Authors: Xiao Bai, Stefan Sandukas, Mark R Appleford, Joo L Ong, Afsaneh Rabiei

  Acta biomaterialia. 06/2009;

  A series of calcium phosphate coatings with graded crystallinity were deposited onto heated titanium substrates using ion beam assisted deposition. The microstructure of the coating was examinedA series of calcium phosphate coatings with graded crystallinity were deposited onto heated titanium substrates using ion beam assisted deposition. The microstructure of the coating was examined using transmission electron microscopy (TEM). The coating thickness observed to be in a range of 594-694nm. The degree of crystallinity and microstructural grain size of the coating showed a clear decrease with increasing distance from the substrate-coating interface. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of PO(4)(3-), and X-ray photoelectron spectroscopy (XPS) analysis on the coating top surface showed that the atomic Ca/P ratio was in the range of 1.52+/-0.15 to 1.61+/-0.07. The biological response to the coatings was also evaluated using an osteoblast precursor cell culture test. More cells and a higher integrin expression of cell attachment sites were observed on the coating surface when compared to the control group (blank titanium surface). The pull-off test showed average adhesion strengths at the coating-substrate interface to be higher than 85.12+/-5.37MPa. Nanoindentation tests indicated that the Young's moduli of all coatings are higher than 91.747+/-3.641GPa and microhardness values are higher than 5.275+/-0.315GPa. While the adhesion strength results helped us to identify the best setup for substrate temperature and processing parameters to begin the deposition, the culture test and XPS results helped identifying the optimum parameters for the last stage of deposition. TEM, X-ray diffraction, FTIR and nanoidentation results were used to further evaluate the quality of the coating and optimization of its processing parameters.

• Evaluation of sinus bone resorption and marginal bone loss after sinus bone grafting and implant placement.

  Authors: Young-Kyun Kim, Pil-Young Yun, Su-Gwan Kim, Bum-Soo Kim, Joo L Ong

  Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics. 02/2009; 107(2):e21-8.

  OBJECTIVE: The objective of this study was to evaluate the sinus bone graft resorption and marginal bone loss around the implants when allograft and xenograft are used. STUDY DESIGN: Sinus boneOBJECTIVE: The objective of this study was to evaluate the sinus bone graft resorption and marginal bone loss around the implants when allograft and xenograft are used. STUDY DESIGN: Sinus bone grafting and implant placement (Osstem, Korea) were performed on 28 patients from September 2003 to January 2006. In group I, a total of 49 implants were placed in 23 maxillary sinus areas of 16 patients together with bone graft using xenograft (Bio-Oss) and a minimal amount of autogenous bone. In group II, 24 implants were placed in 13 maxillary sinus areas of 12 patients together with bone graft using a minimal amount of autogenous bone and equal amounts of allograft (Regenaform) and Bio-Oss in group II. RESULTS: Early osseointegration failures of 3 implants in 3 patients (group I: 1 patient, 1 implant; group II: 2 patients, 2 implants) were observed, and revisions were performed for these 3 implant sites, followed by complete prosthodontic treatments. The average height of the remaining alveolar bone before the surgery, immediately after the surgery, and 1 year after the surgery was 4.9 mm, 19.0 mm, and 17.2 mm, respectively, in group I. In group II, the average height of the remaining alveolar bone was 4.0 mm, 19.2 mm, and 17.8 mm before the surgery, immediately after the surgery, and 1 year after the surgery, respectively. The average marginal bone loss 1 year after prosthodontic loading and after 20.8 months' follow-up was 0.6 mm and 0.7 mm, respectively, in group I. A 93.9% success rate was observed for group I, with 3 implants showing bone resorption of >1.5 mm within 1 year of loading. For group II, the average marginal bone loss 1 year after prosthodontic loading and after 19.7 months' follow-up was 0.7 mm and 1.0 mm, respectively. An 83.3% success rate was observed for group II, with 4 implants showing bone resorption of >1.5 mm within 1 year of loading. CONCLUSIONS: Based on the observations in this study, it was concluded that mixed grafting with demineralized bone matrix for maxillary sinus bone grafting has no significant short-term merit regarding bone healing and stability of implants compared with anorganic bovine bone alone.

• A comparative study of two noninvasive techniques to evaluate implant stability: Periotest and Osstell Mentor.

  Authors: Ji-Su Oh, Su-Gwan Kim, Sung-Chul Lim, Joo L Ong

  Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics. 01/2009;

  OBJECTIVES: The purpose of this study was to examine the usefulness of Periotest and Osstell Mentor (a resonance frequency analysis) as nondestructive analytical tools for determining implantOBJECTIVES: The purpose of this study was to examine the usefulness of Periotest and Osstell Mentor (a resonance frequency analysis) as nondestructive analytical tools for determining implant stability in clinics, to evaluate the precision of both instruments, and to determine the applicability of these measured values as clinically relevant indices. STUDY DESIGN: Four adult mongrel dogs weighing about 12 to 15 kg were used in this study. Bilateral extractions of the first through the fourth mandibular and maxillary premolars were performed and a total of 48 commercially pure titanium screw implants (USII Plus; OSTEM Implant, Seoul, Republic of Korea) were placed at 4 weeks after extraction. All implants (10 mm length and 3.3 mm diameter) were self-tapping and surface-treated with resorbable blast media (RBM). Periotest values (PTVs) obtained from Periotest, and Implant Stability Quotient (ISQ) obtained from Osstell Mentor, were measured at the time of implantation, and 3 and 6 weeks after implantation. At 3 and 6 weeks after implantation, 4 dogs were humanely killed and histomorphometric analysis was performed. The new peri-implant bone formation rate (NBFR) was measured. RESULTS: The PTV value was lower and ISQ value was higher at 6 weeks when compared with data collected at 3 weeks after implantation. The PTVs of the maxilla were higher than the mandible and the ISQ values of the maxilla were lower than the mandible. Based on the NBFR, the 6-week group showed higher bone formation when compared to the 3-week group, correlating to the observed PTV and ISQ values. Additionally, the NBFR was higher in the maxilla than the mandible. No significant difference between PTV and ISQ was also observed when PTV and ISQ were compared to NBFR. CONCLUSION: The results indicated that the Periotest and Osstell Mentor, both noninvasive diagnostic devices, were useful and comparably reliable, showing a strong association with each other in assessing implant stability.

• A short-term study on immediate functional loading and immediate nonfunctional loading implant in dogs: Histomorphometric evaluation of bone reaction.

  Authors: Joo-Young Lee, Su-Gwan Kim, Seong-Yong Moon, Sung-Chul Lim, Joo L Ong, Kwang-Min Lee

  Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics. 12/2008;

  OBJECTIVES: The purpose of this study was to evaluate implant stability after short-term immediate loading in a canine model. STUDY DESIGN: The control group used in this study was immediateOBJECTIVES: The purpose of this study was to evaluate implant stability after short-term immediate loading in a canine model. STUDY DESIGN: The control group used in this study was immediate nonfunctional loading and the experimental group was immediate functional loading. Each group was measured for its periotest value (PTV) and bone-to-implant contact (BIC) ratio. RESULTS: Statistically significant differences in PTV and BIC ratio were not observed between the control and the experimental groups. CONCLUSION: It was concluded that implant stability can be achieved even with immediate loading.

• Stress corrosion cracking of an aluminum alloy used in external fixation devices.

  Authors: Jacob L Cartner, Warren O Haggard, Joo L Ong, Joel D Bumgardner

  Journal of biomedical materials research. Part B, Applied biomaterials. 09/2008; 86B(2):430-7.

  Treatment for compound and/or comminuted fractures is frequently accomplished via external fixation. To achieve stability, the compositions of external fixators generally include aluminum alloyTreatment for compound and/or comminuted fractures is frequently accomplished via external fixation. To achieve stability, the compositions of external fixators generally include aluminum alloy components due to their high strength-to-weight ratios. These alloys are particularly susceptible to corrosion in chloride environments. There have been several clinical cases of fixator failure in which corrosion was cited as a potential mechanism. The aim of this study was to evaluate the effects of physiological environments on the corrosion susceptibility of aluminum 7075-T6, since it is used in orthopedic external fixation devices. Electrochemical corrosion curves and alternate immersion stress corrosion cracking tests indicated aluminum 7075-T6 is susceptible to corrosive attack when placed in physiological environments. Pit initiated stress corrosion cracking was the primary form of alloy corrosion, and subsequent fracture, in this study. Anodization of the alloy provided a protective layer, but also caused a decrease in passivity ranges. These data suggest that once the anodization layer is disrupted, accelerated corrosion processes occur.

• Clinical evaluations of OSTEON as a new alloplastic material in sinus bone grafting and its effect on bone healing.

  Authors: Young-Kyun Kim, Pil-Young Yun, Sung-Chul Lim, Su-Gwan Kim, Hyo-Jung Lee, Joo L Ong

  Journal of biomedical materials research. Part B, Applied biomaterials. 08/2008; 86(1):270-7.

  PURPOSE: The objective of this study was to clinically evaluate the use of OSTEON as a sinus graft material and to measure the effect of healing at 4 and 6 months after surgery. MATERIALS ANDPURPOSE: The objective of this study was to clinically evaluate the use of OSTEON as a sinus graft material and to measure the effect of healing at 4 and 6 months after surgery. MATERIALS AND METHODS: After sinus graft using OSTEON in 17 patients, bone specimens were collected from lateral sinus using 2.0-mm trephine bur at the time of 4 or 6 months after surgery. Histology of the bone specimens was prepared and the percentage of newly formed bone fraction, lamellar bone/woven bone ratio (LB/WB), and newly formed bone/graft material ratio (NB/GM) were measured to indicate the suitability of the materials and the successful healing of the graft. RESULTS: The morphology of OSTEON was observed to be interconnected, with 77% porosity and a pore size of 300-500 microm. After implantation, the mean percentage of newly formed bone fraction after 4 months and 6 months surgery was 40.6 and 51.9%, respectively. Statistical analysis indicated no significant difference (p = 0.135) in the newly formed bone fraction between the two postoperative periods. The mean LB/WB ratio after 4 months and 6 months surgery was 0.14 and 0.45, respectively, with significant difference observed between the two postoperative periods (p = 0.027). Additionally, the mean NB/GM ratio after 4 months and 6 months surgery was 1.95 and 7.72, respectively, with significant difference observed between the two postoperative periods (p = 0.046). CONCLUSION: It was concluded that OSTEON is suitable for use in sinus graft application since desirable time-dependent healing was demonstrated.

• 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).

• In vivo study on hydroxyapatite scaffolds with trabecular architecture for bone repair.

  Authors: Mark R Appleford, Sunho Oh, Namsik Oh, Joo L Ong

  Journal of biomedical materials research. Part A. 06/2008;

  The objective of this research was to investigate the bone formation and angio-conductive potential of hydroxyapatite (HA) scaffolds closely matched to trabecular bone in a canine segmental defectThe objective of this research was to investigate the bone formation and angio-conductive potential of hydroxyapatite (HA) scaffolds closely matched to trabecular bone in a canine segmental defect after 3 and 12 weeks post implantation. Histomorphometric comparisons were made between naturally forming trabecular bone (control) and defects implanted with scaffolds fabricated with micro-size (M-HA) and nano-size HA (N-HA) ceramic surfaces. Scaffold architecture was similar to trabecular bone formed in control defects at 3 weeks. No significant differences were identified between the two HA scaffolds; however, significant bone in-growth was observed by 12 weeks with 43.9 +/- 4.1% and 50.4 +/- 8.8% of the cross-sectional area filled with mineralized bone in M-HA and N-HA scaffolds, respectively. Partially organized, lamellar collagen fibrils were identified by birefringence under cross-polarized light at both 3 and 12 weeks post implantation. Substantial blood vessel infiltration was identified in the scaffolds and compared with the distribution and diameter of vessels in the surrounding cortical bone. Vessels were less numerous but significantly larger than native cortical Haversian and Volkmann canals reflecting the scaffold architecture where open spaces allowed interconnected channels of bone to form. This study demonstrated the potential of trabecular bone modeled, highly porous and interconnected, HA scaffolds for regenerative orthopedics. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 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.

• Osteogenic activity of the mixture of chitosan and particulate dentin.

  Authors: Sun-Sik Park, Su-Gwan Kim, Sung-Chul Lim, Joo L Ong

  Journal of biomedical materials research. Part A. 02/2008;

  To evaluate the healing effect of a mixture of chitosan and particulate dentin, a 8-mm-diameter critical size defect was created in the calvarium of 75 rats. The rats were divided into fourTo evaluate the healing effect of a mixture of chitosan and particulate dentin, a 8-mm-diameter critical size defect was created in the calvarium of 75 rats. The rats were divided into four experimental groups and a control group (no treatment). The defects in the experimental groups were grafted either with pig particulate dentin (group 1), a mixture of particulate dentin and plaster of Paris (group 2), particulate dentin and chitosan (group 3), or chitosan only (group 4). Rats in each group were sacrificed 2, 4, and 8 weeks after implantation. All experimental groups showed more new bone formation when compared to the control group. Additionally, all groups exhibited more bone growth at 8 weeks than at 4 weeks after implantation. It was concluded from this study that defects treated with particulate dentin powder-chitosan mixture may mediate an excellent effect on the formation of new bones. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2008.