Dong Yong Park

A new method of fabricating robust freeform 3D ceramic scaffolds for bone tissue regeneration

Fabrication of three‐dimensional (3D) scaffolds with appropriate mechanical properties and desired architecture for promoting cell growth and new tissue formation is one of the most important efforts in tissue engineering field. Scaffolds fabricated from bioactive ceramic materials such as hydroxyapatite and tricalcium phosphate show promise because of their biological ability to support bone tissue regeneration. However, the use of ceramics as scaffold materials is limited because of their inherent brittleness and difficult processability. The aim of this study was to create robust ceramic scaffolds, which have a desired architecture. Such scaffolds were successfully fabricated by projection‐based microstereolithography, and dilatometric analysis was conducted to study the sintering behavior of the ceramic materials. The mechanical properties of the scaffolds were improved by infiltrating them with a polycaprolactone solution. The toughness and compressive strength of these ceramic/polymer scaffolds were about twice those of ceramic scaffolds. Furthermore, the osteogenic gene expression on ceramic/polymer scaffolds was better than that on ceramic scaffolds. Through this study, we overcame the limitations of previous research on fabricating ceramic scaffolds and these new robust ceramic scaffolds may provide a much improved 3D substrate for bone tissue regeneration. Biotechnol. Bioeng. 2013; 110: 1444–1455.

Fiber-optic OCT sensor guided “SMART” micro-forceps for microsurgery

A handheld Smart Micromanipulation Aided Robotic-surgery Tool (SMART) micro-forceps guided by a fiber-optic common-path optical coherence tomography (CP-OCT) sensor is presented. A fiber-optic CP-OCT distance and motion sensor is integrated into the shaft of a micro-forceps. The tool tip position is manipulated longitudinally through a closed loop control using a piezoelectric motor. This novel forceps design could significantly enhance safety, efficiency and surgical outcomes. The basic grasping and peeling functions of the micro-forceps are evaluated in dry phantoms and in a biological tissue model. As compared to freehand use, targeted grasping and peeling performance assisted by active tremor compensation, significantly improves micro-forceps user performance.

Densification Behavior of Rhenium Alloy using Master Sintering Curve

This study investigated the densification behavior of rhenium alloys including W-25 wt.%Re and Re-2W- 1Ta (pure Re) during sintering. The dilatometry experiments were carried out to obtain the in-situ shrinkage in H2 atmo- sphere. The measured data was analyzed through shrinkage, strain rate and relative density, and then symmetrically treated to construct the linearized form of master sintering curve (MSC) and MSC as a well-known and straightforward approach to describe the densification behavior during sintering. The densification behaviors for each material were ana- lyzed in many respects including apparent activation energy, densification parameter, and densification ratio. MSC with a minimal set of preliminary experiments can make the densification behavior to be characterized and predicted as well as provide guideline to sinter cycle design. Considering the results of linearized form and MSC, it was confirmed that the W-25 wt.%Re compared to Pure Re is more easily densified at the relatively low temperature.

Development of Powder Injection Molding Process for a Piezoelectric PAN-PZT Ceramics

A powder injection molding process is developed and optimized for piezoelectric PAN-PZT ceramics. Torque rheometer experiments are conducted to determine the optimal solids loading, and the rheological property of the feedstock is evaluated using a capillary rheometer. Appropriate debinding conditions are chosen using a thermal gravity analyzer, and the debound specimens are sintered using sintering conditions determined in a preliminary investigation. Piezoelectric performance measures, including the piezoelectric charge constant and dielectric constant, are measured to verify the developed process. The average values of the measured piezoelectric charge constant and dielectric constant are 455 pC/N and 1904, respectively. Powder injection molded piezoelectric ceramics produced by the optimized process show adequate piezoelectric performance compared to press-sintered piezoelectric ceramics.

Investigation of powder size effects on sintering of powder injection moulded 17-4PH stainless steel

ABSTRACT Densification behaviours of 17-4PH stainless steel powders (SUS17-4PH) of three different particle sizes during the sintering were investigated. The samples with different mean particle sizes of 3.17, 4.22 and 8.30 µm were prepared through powder-binder mixing, injection moulding, and solvent and thermal debindings. The in situ shrinkage data measured by dilatometry tests were treated to analyse the densification behaviour of each sample. In order to characterise the densification behaviour with a minimum set of experiments, the master sintering curve (MSC), as well-known and straight-forward approach, was employed. After constructing the MSCs for powders of different particle sizes, the effects of particle size on the densification were analysed in many respects including shrinkage, strain rate, apparent activation energy, and work of sintering.

Variational approach to powder-binder separation in Poiseuille and Couette flows

To predict the time-evolution of powder separation in the Phillips model, we derive an essential condition under a viscosity model for non-Newtonian fluids which considers the effects of shear rate and particle volume fraction. Under the condition, the time-evolution is independent of initial conditions, and powder separation converges in time to smooth steady-states. The proposed condition also determines the existence and uniqueness of smooth steady-states and the degree of powder separation. Finally, we compare the theoretical prediction for the particle volume fraction to numerical verification for the purpose of confirming our prediction.

Development of hydrophobic forcep for robot surgery

The hydrophobic forcep for robot surgery was developed by powder injection molding and surface treatment. The processing conditions including filling behavior for powder injection molding was developed through MoldFlow simulation. After producing the surgical forcep, the surface treatment for hydrophobic surface was realized.