Young Eun Park

In vitro and in vivo evaluation of bone formation using solid freeform fabrication-based bone morphogenic protein-2 releasing PCL/PLGA scaffolds

The aim of this study was to develop novel polycaprolactone/poly(lactic-co-glycolic acid) (PCL/PLGA) scaffolds with a heparin-dopamine (Hep-DOPA) conjugate for controlled release of bone morphogenic protein-2 (BMP-2) to enhance osteoblast activity in vitro and also bone formation in vivo. PCL/PLGA scaffolds were prepared by a solid freeform fabrication method. The PCL/PLGA scaffolds were functionalized with Hep-DOPA and then BMP-2 was sequentially coated onto the Hep-DOPA/PCL/PLGA scaffolds. The characterization and surface elemental composition of all scaffolds were evaluated by scanning electron microscope and x-ray photoelectron spectroscopy. The osteoblast activities on all scaffolds were assessed by cell proliferation, alkaline phosphatase (ALP) activity and calcium deposition in vitro. To demonstrate bone formation in vivo, plain radiograph, micro-computed tomography (micro-CT) evaluation and histological studies were performed after the implantation of all scaffolds on a rat femur defect. Hep-DOPA/PCL/PLGA had more controlled release of BMP-2, which was quantified by enzyme-linked immunosorbent assay, compared with Hep/PCL/PLGA. The in vitro results showed that osteoblast-like cells (MG-63 cells) grown on BMP-2/Hep-DOPA/PCL/PLGA had significantly enhanced ALP activity and calcium deposition compared with those on BMP-2/Hep/PCL/PLGA and PCL/PLGA. In addition, the plain radiograph, micro-CT evaluation and histological studies demonstrated that the implanted BMP-2/Hep-DOPA/PCL/PLGA on rat femur had more bone formation than BMP-2/Hep/PCL/PLGA and PCL/PLGA in vivo.

Long-term results of arthroscopic excision of unstable osteochondral lesions of the lateral femoral condyle

The purpose of this study was to evaluate the long-term functional and radiological outcomes of arthroscopic removal of unstable osteochondral lesions with subchondral drilling in the lateral femoral condyle. We reviewed the outcome of 23 patients (28 knees) with stage III or IV osteochondritis dissecans lesions of the lateral femoral condyle at a mean follow-up of 14 years (10 to 19). The functional clinical outcomes were assessed using the Lysholm score, which improved from a mean of 38.1 (SD 3.5) pre-operatively to a mean of 87.3 (SD 5.4) at the most recent review (p = 0.034), and the Tegner activity score, which improved from a pre-operative median of 2 (0 to 3) to a median of 5 (3 to 7) at final follow-up (p = 0.021). The radiological degenerative changes were evaluated according to Tapper and Hoovers classification and when compared with the pre-operative findings, one knee had grade 1, 22 knees had grade 2 and five knees had grade 3 degenerative changes. The overall outcomes were assessed using Hughstons rating scale, where 19 knees were rated as good, four as fair and five as poor. We found radiological evidence of degenerative changes in the third or fourth decade of life at a mean of 14 years after arthroscopic excision of the loose body and subchondral drilling for an unstable osteochondral lesion of the lateral femoral condyle. Clinical and functional results were more satisfactory.

Serial bone mineral density ratio measurement for fixator removal in tibia distraction osteogenesis and need of a supportive method using the pixel value ratio

Distraction osteogenesis is one of the common procedures for limb lengthening. However, attempts are being made constantly to establish objective guidelines for early and safe removal of a fixator using a sensitive and quantitative measurement technique. Dual-energy X-ray absorptiometry (DEXA) has been evaluated in the past for understanding callus stiffness, and the present study is a step further in this direction. The purpose of this study was to evaluate the correlation between bone mineral density ratio (BMDR) obtained by a DEXA scan and the pixel value ratio (PVR) on plain digital radiographs at each cortex and various callus pathways and callus shapes as described by Ru-Li’s classification. A retrospective analysis of 40 tibial segments in 23 patients operated upon for various indications for limb lengthening was carried out. There were 11 male and 12 female patients with a mean age of 18 years. The Ilizarov method was applied after monofocal osteotomy, and distraction and consolidation were monitored using digital radiographs and DEXA scanning. BMDR was positively correlated with PVR, and the optimal BMDR for removal of the fixator was found to be 0.511. PVR of all cortices, except the anterior cortex, showed significant positive correlation with BMDR of the regenerate. There was good correlation between BMDR and PVR in the homogenous or heterogenous pathway according to callus shape and pathway. Thus, this study shows that BMD measurement can provide an objective and noninvasive method for assessing the rate of new bone formation during tibial distraction osteogenesis. It can thus function as an effective adjunct to measure callus stiffness, along with PVR, using digital radiographs, especially in cases in which callus maturation and stiffness is doubtful. Further studies especially dealing with callus progression through the lucent pathway as well as those dealing with regenerate fractures may be needed to conclusively prove the efficacy of this method for measurement of callus maturation.

The design and implementation of a high performance management information tree for a TMN platform

In telecommunication management network (TMN) systems, a managed object (MO) is an OSI abstract view of a logical or physical system resource to be managed. Instances of MO classes can be thought as logically containing other instances. The full set of MO instances available across a management interface are organized in a management information tree (MIT). Managed objects in an MIT may be accessed either individually or collectively through an object-oriented query facility. The speed of MO selection operation highly affects the overall performance of the network management system. In this paper, we propose an MIT mechanism to reduce the MO selection time. This MIT consists of three kinds of nodes: MO node, MO class node and MO info node. A class level filtering (CLF) mechanism is developed based on the MIT to avoid unnecessary filtering time. After detailed provisions on this MIT, some evaluation results are given, and these results are checked against existing MIT.

A management information tree architecture supporting efficient managed object selection

This paper deals with the architecture, design and implementation of a management information tree (MIT) supporting efficient managed object (MO) selection. We present the architecture and mechanism of the MIT in detail and also show how the proposed architecture is implemented in a telecommunication management network (TMN) platform. In addition, we present a new mechanism decreasing MO selection delay, named class level filtering (CLF). The main idea of CLF is to use the class information of MO to exclude the scoped instances of improper MO classes from the conventional filtering. Analysis and performance tests in various cases are presented. The results show the superior performance of the MIT and CLF.

The design and implementation of a network management platform for TMN

Network management systems which administer actual network resources are developed based on a software system called network management platforms. Network management platforms provide major functions defined in TMN and interfaces to develop network management systems. Our research designs and implements a network management platform suitable to the TMN environment of today and tomorrow. This platform increases the efficiency in handling management information by completely separating managed object class information from instance information. In addition, the performance of the platform is significantly improved through a multi-structured management information tree (MIT) and a multi-staged arrangement of the execution of common management information services (CMIS). Furthermore, our platform allows a new management information base (MIB) to be added to the managed system in run-time, solving the problem of having to recompile and restart the network management system. In our research, we develop a new concept of class level filtering, which yields relatively high performance as the MIT becomes larger.