• Bulletin of the Korean Chemical Society
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• v.24 no.10
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• pp.1485-1489
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• 2003

The gelation for di-(2-ethylhexyl) phthalate (DEHP)-plasticized poly(vinyl chloride) was studied by measuring time-resolved small-angle X-ray scattering (SAXS) and a flow of the solutions in test tube. It was found that for the gelation there were three regimes. At Regime I, the solution rapidly changed to a gel, and the SAXS intensity showed a peak and the peak intensity increased, keeping the peak angle constant. Applying the SAXS intensity to the kinetic analysis of the liquid-liquid phase separation, it was revealed that the spinodal decomposition proceeded to develop a periodic length of 29.9 nanometer in size, a hydrogen-bonding-type association in polymer rich phase followed, and then it induced fast gelation rate. At Regime II, the gelation slowly occurred and the SAXS intensity was not observed, suggesting that a homogeneous gel network was formed by a hydrogen-bonding. At regime III, the solution was a homogeneous sol.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.42
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• pp.18.1-18.9
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• 2020

Background: Bone grafting has been considered the gold standard for hard tissue reconstructive surgery and is widely used for large mandibular defect reconstruction. However, the midface encompasses delicate structures that are surrounded by a complex bone architecture, which makes bone grafting using traditional methods very challenging. Three-dimensional (3D) bioprinting is a developing technology that is derived from the evolution of additive manufacturing. It enables precise development of a scaffold from different available biomaterials that mimic the shape, size, and dimension of a defect without relying only on the surgeon's skills and capabilities, and subsequently, may enhance surgical outcomes and, in turn, patient satisfaction and quality of life. Review: This review summarizes different biomaterial classes that can be used in 3D bioprinters as bioinks to fabricate bone scaffolds, including polymers, bioceramics, and composites. It also describes the advantages and limitations of the three currently used 3D bioprinting technologies: inkjet bioprinting, micro-extrusion, and laserassisted bioprinting. Conclusions: Although 3D bioprinting technology is still in its infancy and requires further development and optimization both in biomaterials and techniques, it offers great promise and potential for facial reconstruction with improved outcome.

• Journal of Biomedical Engineering Research
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• v.40 no.4
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• pp.137-142
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• 2019

Numerous efforts are being made to develop an ideal dermal filler that should be bio-compatibility, non-immunogenicity, long-lasting and biodegradable without a toxic secretion. Biomaterials of dermal fillers are hyaluronic acid filler, calcium filler, PMMA filler and collagen filler depending on the ingredient. Although hyaluronic acid (HA) is most widely used, it has shortages such as short shelf life and low mechanical strength compare to extracellular matrix (ECM). The cartilage ECM composed of collagen type II, proteoglycans, glycosaminoglycans (GAGs) and in a minor part with glycoproteins. In this study, we developed a cartilage ECM injectable filler capable of improving biocompatibility and longevity compared with hyaluronic acid (HA) fillers. The ECM hydrogel was cross-linked by the reaction of N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) for mechanical enhancement. Prepared ECM filler was compared with cross-linked HA by butanediol diglycidyle ether (BDDE), which is the most widely used natural polymers for dermal filler. In the results, the articular cartilage ECM hydrogel has great potential as a dermal filler to improve the biophysical and biological performance.

• Journal of Radiopharmaceuticals and Molecular Probes
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• v.6 no.2
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• pp.171-176
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• 2020

Covalent organic frameworks (COFs) are porous crystalline polymers in which organic units are linked by covalent bonds and have a regular arrangement at the atomic level. Recently, the COFs have been much attention in bio-medical area such as bio-imaging, drug delivery, and therapeutics. These 2D nanoparticles are proving their value in nanomedicine due to their large surface area, functionalization through functional groups exposed on the surface, chemical stability due to covalent bonding, and high biocompatibility. The high ω-electron density and crystallinity of COFs makes it a promising candidate for bioimaging probes, and its porosity and large surface area make it possible to be utilized as a drug delivery vehicle. However, the low dispersibility in water, the cytotoxicity problems of COFs are still challenged to be solved in the future. In this regard, several efforts that increase the degree of dispersion through functionalization on the surface of COFs for the application to the biomedical field have been reported. In this review, we would like to describe the advantages and limitations of COFs for bio-imaging and anti-cancer treatment.

• Science of Emotion and Sensibility
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• v.19 no.3
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• pp.43-50
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• 2016

The uniform nanofibers of polyurethane with different contents of Juniperus Chinensis extracts were successfully prepared by electrospinning method. Polyurethane is widely used as functional polymers in the industrials, medical field as their properties can be tailor-made by adjusting their compositions. Juniperus Chinensis has been reported for anti-tumor, anti-bacterial, anti-fungal, and anti-viral activities. PU/Juniperus Chinensis extracts composite nanofibers were produced at different Juniperus Chinensis extracts concentrations (0.25, 0.5, 1, 1.5wt.%). The effects of the major parameters in electrospinning process such as tip to collector distance (TCD), voltage, polymer concentration on the average diameter of electrospun nanoweb were investigated. As results, 12wt% PU solution concentration, 8kV applied voltage and 15cm tip to collector distance were identified as optimum conditions for electrospinning the composite nanofibers. The diameter and morphology of the nanocomposite nanofibers were confirmed by a scanning electron microscopy (SEM). The resulting fibers exhibited a uniform diameter ranging from 435nm~547nm. It has been found that the average diameters of fibers decreased by the adding of Juniperus Chinensis extracts. These nanowebs can be used for medical materials, protective clothing, and antimicrobial filters.

• The Journal of Advanced Prosthodontics
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• v.8 no.6
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• pp.504-510
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• 2016

PURPOSE. Polyamide polymers do not provide sufficient bond strength to auto-polymerized resins for repairing fractured denture or replacing dislodged denture teeth. Limited treatment methods have been developed to improve the bond strength between auto-polymerized reline resins and polyamide denture base materials. The objective of the present study was to evaluate the effect of surface modification by acetic acid on surface characteristics and bond strength of reline resin to polyamide denture base. MATERIALS AND METHODS. 84 polyamide specimens were divided into three surface treatment groups (n=28): control (N), silica-coated (S), and acid-treated (A). Two different auto-polymerized reline resins GC and Triplex resins were bonded to the samples (subgroups T and G, respectively, n=14). The specimens were subjected to shear bond strength test after they were stored in distilled water for 1 week and thermo-cycled for 5000 cycles. Data were analyzed with independent t-test, two-way analysis of variance (ANOVA), and Tukey's post hoc multiple comparison test (${\alpha}=.05$). RESULTS. The bond strength values of A and S were significantly higher than those of N (P<.001 for both). However, statistically significant difference was not observed between group A and group S. According to the independent Student's t-test, the shear bond strength values of AT were significantly higher than those of AG (P<.001). CONCLUSION. The surface treatment of polyamide denture base materials with acetic acid may be an efficient and cost-effective method for increasing the shear bond strength to auto-polymerized reline resin.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.585-596
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• 2012

PVDF(poly vinylidene fluoride) and P(VDF-TrFE)(poly vinylidene fluoride-tetrafluoroethylene) are the typical piezoelectric polymers with unique properties. Even they are inferior to conventional piezoelectric ceramics PZT in electromechanical conversion efficiency and interior loss, though they are superior in receiving sensitivity and frequency bandwidth. Their acoustic impedances are relatively close to water or biological tissue and it is easier to make thin film than other piezoelectric materials. Futhermore, the film is so flexible that it is easy to attach on a complex surface. Those properties are suitable for the ultrasound transducers which are useful for medical and biological application, so that various types of polymer transducers have been developed. In this paper, several important considerations for design and fabrication of piezoelectric polymer transducers were described and their effect on the transducer performance were demonstrated through the KLM model analysis. Then, it was briefly reviewed about the structures of the polymer transducers developed for obtaining images as well as the characteristics of the images in several important medical and biological application fields.

• Analytical Science and Technology
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• v.15 no.1
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• pp.72-79
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• 2002

Di-(2-ethylhexyl)phthalate (DEHP) may be released from plasticized poly(vinyl chloride) (PVC) articles. In the cases of various methods for the quantitative analysis of migrating DEHP, there are much differences in migrating quantity according to the experimental methods. It is therefore important to make the comparison and analysis between these two results. A study of DEHP migration from blood and infusion bags has been carried out in different methods to evaluate the amount of DEHP migration using gas chromatograph and UV-vis spectrophotometry. Five PVC bags were cut into plane sheets in size of $40{\times}10{\times}0.4mm$, then were immersed in extraction solvent for an hour to release DEHP. It was determined by a gas chromatograph that $23.2{\sim}70.9{\mu}g/mL$ of DEHP was extracted. While extraction solvent was injected into PVC bags which were then placed for an hour to leach DEHP out. It was checked by a UV-vis spectrophotometer that the concentration of DEHP in extraction solvent was $24.8{\sim}41.3{\mu}g/mL$. Two results show different values according to the extraction conditions and experimental methods and the gas chromatographic results were converted into UV-vis spectroscopic results on condition that DEHP would be extracted equally per unit time and unit contact area. It was concluded that DEHP migrating amounts are approximately equal in two analytical methods.

• The Journal of Korean Academy of Prosthodontics
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• v.59 no.1
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• pp.71-78
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• 2021

Implant treatment, which was first attempted in fully edentulous patients, is now widely used in partially edentulous, and a single tooth missing patients. Moreover, implant treatment has become an essential treatment modality in modern dentistry. The material of fabricating implant prostheses has also become more diverse than before, one of which is the use of high-performance polymers. The frequency of using high-performance polymers, which have been used in the medical field, is also increased in the dental field compared to the past. In the first case, a PEKK abutment and a PFG crown (cement-screw-retaining type) were fabricated in the lower left second premolar, and in the second case, a PEKK abutment and a monolithic zirconia crown (cement-screw-retaining type) were fabricated in the missing upper left first molar, and in the third case two PEKK abutments and a splinted PFM crowns (cement-screw-retaining type) were fabricated and connected to the upper right first and second molar implants. Through these procedures the patients obtained esthetically and functionally satisfactory results after 4 years of follow-up.

• Fibers and Polymers
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• v.7 no.4
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• pp.389-397
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• 2006

The beneficial effects of graduated compression stockings (GCS) in prophylaxis and treatment of venous disorders of human lower extremity have been recognized. However, their pressure functional performances are variable and unstable in practical applications, and the exact mechanisms of action remain controversial. Direct surface pressure measurements and indirect material properties testing are not enough for fully understanding the interaction between stocking and leg. A three dimensional (3D) biomechanical mathematical model for numerically simulating the interaction between leg and GCS in dynamic wear was developed based on the actual geometry of the female leg obtained from 3D reconstruction of MR images and the real size and mechanical properties of the compression stocking prototype. The biomechanical solid leg model consists of bones and soft tissues, and an orthotropic shell model is built for the stocking hose. The dynamic putting-on process is simulated by defining the contact of finite relative sliding between the two objects. The surface pressure magnitude and distribution along the different height levels of the leg and stress profiles of stockings were simulated. As well, their dynamic alterations with time processing were quantitatively analyzed. Through validation, the simulated results showed a reasonable agreement with the experimental measurements, and the simulated pressure gradient distribution from the ankle to the thigh (100:67:30) accorded with the advised criterion by the European committee for standardization. The developed model can be used to predict and visualize the dynamic pressure and stress performances exerted by compression stocking in wear, and to optimize the material mechanical properties in stocking design, thus, helping us understand mechanisms of compression action and improving medical functions of GCS.