Seong-Joo Heo

Tissue-engineered growth of bone by marrow cell transplantation using porous calcium metaphosphate matrices

In this study we investigated not only osteoblastic cell proliferation and differentiation on the surface of calcium metaphosphate (CMP) matrices in vitro but also bone formation by ectopic implantation of these cell-matrix constructs in athymic mice in vivo. Interconnected porous CMP matrices with pores 200 microm in size were prepared to use as scaffolds for rat-marrow stromal-cell attachment. Cell-matrix constructs were cultured in vitro, and cell proliferation and ALPase activities were monitored for 56 days. In addition to their being cultured in vitro, cell-matrix constructs were implanted into subcutaneous sites of athymic mice. In vitro these porous CMP matrices supported the proliferation of osteoblastic cells as well as their differentiation, as indicated by high ALPase activity. In vivo the transplanted marrow cells gave rise to bone tissues in the pores of the CMP matrices. A small amount of woven bone formation was detected first at 4 weeks; osteogenesis progressed vigorously with time, and thick lamellar bones that had been remodeled were observed at 12 weeks. These findings demonstrate the potential for using a porous CMP matrix as a biodegradable scaffold ex vivo along with attached marrow-derived mesenchymal cells for transplantation into a site for bone regeneration in vivo.

Chitosan nano-/microfibrous double-layered membrane with rolled-up three-dimensional structures for chondrocyte cultivation

With an aim to mimic natural extracellular matrix, we fabricated the nano- and microfibrous matrix with chitosan by electrospinning nanofibers onto predefined microfibrous mesh for effective chondrocytes cultivation. Rolling the double-layered nano-/microfibrous membranes produced three-dimensional (3-D) scaffolds that exhibited the interconnected open pore structure in their scanning electron microscopy images. In vitro chondrocyte culture experiment showed that this nano-/microfibrous 3-D matrix provided a significantly greater microenvironment for chondrocytes to proliferate and produce glycosaminoglycan as compared with only microfibrous 3-D matrix. This difference could be explained by the result on 2-D membrane, where chitosan nanofibrous surface substantially facilitated the cellular attachment and proliferation, and efficiently prevented phenotypic changes of chondrocytes, when compared with chitosan microfibrous membrane and film. In this regard, the nano-/microfibrous 3-D matrix we fabricated in this study would possess a great potential as a system for effective chondrocyte cultivation and also for application to cartilage regeneration therapy.

Marginal bone loss around three different implant systems: radiographic evaluation after 1 year

This study was designed to radiographically evaluate the effect of surface macro-and microstructures within the coronal portion of the external hex implant at the marginal bone change after loading. The fifty-four patients included in the study were randomly assigned to treatment groups with rough-surface implants (TiUnite, n = 45), a hybrid of smooth and rough surface implants (Restore, n = 45) or rough-surface with microthreads implants (Hexplant, n = 45). Clinical and radiographic examinations were conducted at the time of implant loading (baseline) and at 1-year post-loading. A three-level mixed-effect ancova was used to test the significance of the mean marginal bone change of the three implant groups from baseline to 1-year follow-up. At 1-year, significant differences were noted in marginal bone loss recorded for the three groups (P < 0.0001). The rough surface with microthread implants had a mean crestal bone loss of 0.42 +/- 0.27 mm; the rough surface implants, 0.81 +/- 0.27 mm; and the hybrid surface implants, 0.89 +/- 0.41 mm. Within the limitations of this study, a rough surface with microthreads at the coronal part of implant maintained the marginal bone level against functional loading better than implants without these two features.

A 3-year prospective radiographic evaluation of marginal bone level around different implant systems

The aim of this study was to evaluate the change of marginal bone level radiographically around three different implant systems after 3 years in function. Fifty-four patients were included and randomly assigned to three treatment groups of rough-surface implants (TiUnite, n = 37), hybrid of smooth and rough-surface implants (Restore, n = 38) and rough surface with microthread implants (Hexplant, n = 45). Clinical and radiographic examinations were conducted at the time of implant loading (baseline), 1 and 3 years after loading. A three-level mixed-effect analysis of covariance (ancova) was used to test the significance of the mean marginal bone change of the three implant groups. A total 120 of 135 implants completed the study. None of the implants failed to integrate. Significant differences were noted in the marginal bone loss recorded for the three groups (P < 0.0001). At 3 years, the rough surface with microthread implants had a mean crestal bone loss of 0.59 +/- 0.30 mm; the rough-surface implants, 0.95 +/- 0.27 mm; and the hybrid surface implants, 1.05 +/- 0.34 mm. Within the limitations of this study, rough-surface implants with microthread at the coronal part might have a long-term positive effect in maintaining the marginal bone level against functional loading in comparison with implants without these two features.

Enhanced fibronectin-mediated cell adhesion of human osteoblast by fibroblast growth factor, FGF-2

Using specific recombinant human fibronectin peptide (hFNIII9-10) that contains the binding site for integrin, we found that the fibroblast growth factor, FGF-2, enhances fibronectin-mediated adhesion in human osteoblast-like MG63 cells. The mechanism of the synergistic adhesion was due to the activation of extracellular-regulated kinase (ERK)-type MAPK upon interaction of integrin to hFNIII9-10 and its downstream activation of signaling pathways.

The relationship between implant stability quotient values and implant insertion variables: a clinical study

The aim of this study was to determine whether resonance frequency analysis can be integrated into the routine clinical evaluation of the initial healing of dental implants. In addition, this study was designed to verify whether there was a correlation between implant stability quotient (ISQ) values, maximum insertion torque values, angular momentum and energy, and to evaluate the importance of different clinical factors in the determination of ISQ values and maximum insertion torque values at implant insertion. Two different implant designs of 81 dental implants in 41 patients were evaluated using ISQ values. Maximum insertion torque values were obtained during the placement procedure. Two new methods were used to calculate the angular momentum developed due to implant installation as well as the energy absorbed by the bone. A linear correlation between ISQ values and maximum insertion torque values at the initial implant surgery was found (P < 0·01). There was a correlation between ISQ values and angular momentum (P < 0·05), although ISQ values and energy did not show a significant linear correlation at the initial surgery (P > 0·05). There was a correlation between maximum insertion torque values, each parts angular momentum, and their energies during installation (P < 0·01). The sequence of the variables that influenced ISQ values was implant location, design, diameter, and gender of the patient. The results of this experiment suggest that both ISQ values and new methods to calculate angular momentum and energy can help to predict implant stability.

Biofunctional porous anodized titanium implants for enhanced bone regeneration

Efficient osseointegration is a key factor in dental implants to reduce the total time-course of therapy. Titanium implants with anodized surface gained much interest for their enhanced osseointegration. Anodized implant combined with bioactive drugs is an ideal candidate for enhance bone regeneration. Previously delivery of drugs from the metal implants has been attempted by utilizing a polymeric dip-coating method. However, the entire surface coating with polymer can diminish the advantageous surface roughness of anodized implants and cause contact inhibition between bone and implant surface. In this study, fibroblast growth factor-2 (FGF-2) loaded poly(lactide-co-glycolide) nanoparticles were partially coated on anodized Ti discs by an electrospray deposition. Nanoparticle coated anodized discs maintained their native porous structure and provided a sustained release of FGF-2 for more than 2 weeks with 40% initial burst. In vitro study confirmed the influence of polymeric nanoparticles and the release of growth factors from the Ti disc. Nanoparticle-coated groups significantly enhanced cell spreading and differentiation. For in vivo evaluation, the anodized titanium implants were applied to rabbit tibia model. The osseointegration was estimated by bone to implant contact of best three consecutive threads at the border of the implant. The mean osteointegration value of FGF-2 releasing implant groups (70.1%) was significantly higher than that of untreated implants (47.1%). We believe that the electrospray deposition technique is a particularly attractive approach for the coating of medical devices with porous surface to maintain their surface topography while allowing a sustained delivery of growth factors for bone regeneration.

Effect of bone quality and implant surgical technique on implant stability quotient (ISQ) value

PURPOSE This study investigated the influence of bone quality and surgical technique on the implant stability quotient (ISQ) value. In addition, the influence of interfacial bone quality, directly surrounding the implant fixture, on the resonance frequency of the structure was also evaluated by the finite element analysis. MATERIALS AND METHODS Two different types of bone (type 1 and type 2) were extracted and trimmed from pig rib bone. In each type of bone, the same implants were installed in three different ways: (1) Compaction, (2) Self-tapping, and (3) Tapping. The ISQ value was measured and analyzed to evaluate the influence of bone quality and surgical technique on the implant primary stability. For finite element analysis, a three dimensional implant fixture-bone structure was designed and the fundamental resonance frequency of the structure was measured with three different density of interfacial bone surrounding the implant fixture. RESULTS In each group, the ISQ values were higher in type 1 bone than those in type 2 bone. Among three different insertion methods, the Tapping group showed the lowest ISQ value in both type 1 and type 2 bones. In both bone types, the Compaction groups showed slightly higher mean ISQ values than the Self-tapping groups, but the differences were not statistically significant. Increased interfacial bone density raised the resonance frequency value in the finite element analysis. CONCLUSION Both bone quality and surgical technique have influence on the implant primary stability, and resonance frequency has a positive relation with the density of implant fixture-surrounding bone.

Effect of Biomimetic Deposition on Anodized Titanium Surfaces

Surface energy and hydrophilicity of implant surfaces have been known to play an important role in subsequent cellular responses on the implant surface. The aim of the present study was to evaluate the effects of biomimetic deposition of anodized surfaces on surface wettability, surface energy, and osteoblast responses. Ti discs with 2 different surface topographies (machined and anodized) were immersed in Hanks’ balanced salt solution (HBSS) and modified simulated body fluid (SBF) solution for 2 weeks at physiologic conditions of 37°C, initial pH of 7.4, and p(CO2) of 0.05 atm. Scanning electron microscopic (SEM) observation and energy-dispersive spectroscopic (EDS) microanalysis showed the deposition of calcium phosphate (CaP) onto anodized Ti surfaces immersed in modified SBF. Surface energy, surface wettability, and osteoblast responses, including cell attachment capacity, cell proliferation rate, and cell differentiation level, significantly increased on anodized Ti surfaces immersed in modified SBF. The effects of biomimetic deposition with modified SBF on physiochemical surface characteristics and cell biological responses were greater on anodized surfaces than on machined surfaces. These results indicate that biomimetic deposition with effective SBF may enhance the interaction between anodized Ti surfaces and their biological environment, consequently improving bone healing of dental Ti implants.

Microarray-based expression analysis of human osteoblast-like cell response to anodized titanium surface

An anodized surface significantly enhanced the adhesion of human osteoblast-like MG-63 cells to titanium. Using cDNA microarray analysis, five genes were differentially expressed while the rest remained unaltered. The results demonstrated that the anodized surface enhances cellular adhesion without significantly affecting the pattern of gene expression.