HaeYong Kweon

A novel degradable polycaprolactone networks for tissue engineering

Polycaprolactone (PCL) macromer was obtained by the reaction of PCL diol with acryloyl chloride and confirmed using Fourier transform infrared and nuclear magnetic resonance spectrometer. Novel degradable PCL networks were prepared through photopolymerization of the PCL macromer. Thermal, mechanical, and morphological characteristics as well as degradability and biocompatibility of the PCL networks were investigated. Differential scanning calorimetry showed that the melting temperature and the calculated weight average crystallinity of PCL networks were decreased with a decrease of molecular weight of PCL diols due to the increased crosslinking density. Thermal stability of PCL networks was higher than that of PCL diols. PCL networks showed faster degradation, and higher compressive modulus and compressive recovery ratios than those of PCL itself because of their low crystallinity and the modification of terminal groups. The porosity of the PCL networks can be controlled by the amounts and size of porogen used. MG-63 osteoblast cell was attached and proliferated on PCL networks. PCL networks therefore may have considerable potential as scaffold for tissue engineering.

Structural characteristics and properties of the regenerated silk fibroin prepared from formic acid.

Structural characteristics and thermal and solution properties of the regenerated silk fibroin (SF) prepared from formic acid (FU) were compared with those of SF from water (AU). According to the turbidity and shear viscosity measurement, SF formic acid solution was stable and transparent, no molecular aggregations occurred. The sample FU exhibited the beta-sheet structure, while AU random coil conformation using Fourier transform infrared (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry. The effects of methanol treatment on samples were also examined. According to the measurement of crystallinity (XRD) and crystallinity index (FTIR), the concept of long/short-range ordered structure formation was proposed. Long-range ordered crystallites are predominantly formed for methanol treated SF film while SF film cast from formic acid favors the formation of short-range ordered structure. The relaxation temperatures of SF films measured by dynamic thermomechanical analysis supported the above mechanism due to the sensitivity of relaxation temperature on the short-range order.

Structural and thermal characteristics of Antheraea pernyi silk fibroin/chitosan blend film

Abstract Antheraea pernyi silk fibroin (SF)/chitosan blend films were prepared by mixing aqueous solution of A. pernyi SF and acetic acid solution of chitosan. The conformation of A. pernyi SF in blend films was revealed to be a β-sheet structure, mainly due to the effect of acetic acid used as a mixing solvent. According to the Fourier transform infrared (FTIR) spectra, NH groups of SF and C O and NH2 groups of chitosan might have participated in a specific intermolecular interaction among themselves. The exotherm of SF was not exhibited in blend films due to the precrystallization of SF induced by acetic acid. The blend films showed two distinct maximum decomposition temperatures at around 294 (chitosan component) and 369°C (A. pernyi component), which could be indirect evidences of a phase separation. Scanning electron microscopy (SEM) results confirmed that the phase separation occurred in A. pernyi SF/chitosan blend film. Blending with A. pernyi SF can enhance the thermal decomposition stability of chitosan.

Thermal behavior of regenerated Antheraea pernyi silk fibroin film treated with aqueous methanol

The regenerated Antheraea pernyi silk fibroin films prepared from calcium nitrate solution were treated with 80% aqueous methanol. The thermal and dynamic thermomechanical behaviors of the films were investigated through TGA, DSC and DMTA. IR spectroscopy was used for the conformational changes with methanol treatments. The treatment time of aqueous methanol highly influenced the thermal behavior of regenerated films. As the methanol treatment time increased up to 60 min, the thermal decomposition behavior did not differ significantly compared with untreated films while the endo/exo transition was gradually decreased, with the exotherm finally disappearing. The dynamic mechanical thermal behavior was also affected by the treatment time of aqueous methanol. The onset temperature of storage modulus drop or damping peak shifted to a higher temperature due to the increase in crystallinity induced by the methanol treatment. The thermal transition was strongly dependent on the formation of β-sheet crystal conformation of the regenerated films upon methanol treatment.

Comparison of methods for the repair of acute tympanic membrane perforations: Silk patch vs. paper patch

We investigated the effects of repairing large tympanic membrane (TM) perforations in rats with a thin silk patch compared with the commonly used paper patch. We performed bilateral myringotomies of 1.8 mm in diameter on 50 adult Sprague–Dawley rats with intact TMs. The perforations in the right ears of 40 rats were treated with a silk patch, and the perforations in the left ears of the same rats were treated with a paper patch. Ten rats acted as controls. The mean healing times of the TM perforations on the silk‐patch–treated ears and the paper‐patch–treated ears were 7.2±1.48 and 9.1±1.11 days, respectively (control 10.38±1.70 days). The difference between silk‐patch– and paper‐patch–treated ears was statistically significant, with a mean difference of 1.9 days (0.6–4.5 days). The mean perforation closure times were significantly shorter in silk‐patch– and paper‐patch–treated ears than in the control animals. The endoscopic and histological findings of this study provide evidence that silk‐patch treatment accelerates wound healing and shortens TM perforation closure time. We suggest that the silk patch may prove to be an effective material for repairing TM perforations in human patients in an outpatient clinical setting.

Restoration of peri-implant defects in immediate implant installations by Choukroun platelet-rich fibrin and silk fibroin powder combination graft.

OBJECTIVE The objective of this study was to determine the capability of silk fibroin powder as a biomaterial template for the restoration of peri-implant defects when mixed with Choukroun platelet-rich fibrin (PRF) in vivo. STUDY DESIGN Ten New Zealand white rabbits were used for this study. Using a trephine bur (diameter 7.0 mm), 2 monocortical defects were prepared. Subsequently, 2 dental implants were installed into the tibia (diameter 3.0 mm, length 10.0 mm). In the experimental group, the peri-implant defect was filled with a combination graft of silk fibroin powder and Choukroun PRF. The control was left in an unfilled state. The animals were killed at 8 weeks. Subsequently, a removal torque test and a histomorphometric analysis were done. RESULTS The removal torque for the experimental group was 30.34 +/- 5.06 N.cm, whereas it was 21.86 +/- 3.39 N.cm for the control. The difference between the 2 groups was statistically significant (P = .010). Mean new bone formation was 51.93 +/- 27.90% in the experimental group and 11.67 +/- 15.12% in the control (P = .003). Mean bone-to-implant contact was 43.07 +/- 21.96% in the experimental group and 15.37 +/- 23.84% in the control (P = .002). CONCLUSION A peri-implant defect can be successfully repaired by the application of Choukroun PRF and silk fibroin powder.

Development of nano-hydroxyapatite graft with silk fibroin scaffold as a new bone substitute.

PURPOSE This study involves a comparison between the bone regeneration of nano-hydroxyapatite (nHA), as derived from eggshells either with or without silk fibroin scaffolds, and the unfilled control in the rabbit calvarial bony defect model. MATERIALS AND METHODS Sixteen 4-month-old New Zealand white rabbits, with a mean weight of 2.8 kg (range, 2.5-3.0 kg), were used in this experiment. After the formation of bilateral parietal bony defects (diameter, 8.0 mm), either an nHA or an nHA+silk fibroin combination (nHA+silk) was grafted. The control was unfilled defect. The bone regeneration was evaluated by micro-computed tomography (μCT) and histomorphometric analyses at 4 and 8 weeks. RESULTS All measured variables of the μCT analysis were significantly higher in the grafted groups (nHA and nHA+silk) than in the unfilled control groups at both 4 and 8 weeks after operation (P < .05). On histomorphometric analysis, there was no significant difference between the groups at 4 weeks after operation. However, the nHA group exerted significantly higher bone regeneration (40.16% ± 8.27%) compared with the unfilled control group (25.66% ± 10.98%) or the nHA+silk group (16.62% ± 3.05%) (P < .05). CONCLUSION The nHA from eggshells exerted better bone formation than the unfilled control group on both μCT and histomorphometric analyses. Considering the rapid healing in bony defect and easy availability, the nHA from the eggshells could prove to be a good new bone substitute.

Effect of methyl alcohol on the morphology and conformational characteristics of silk sericin

Effects of methyl alcohol on the morphology and conformational characteristics of silk sericin (SS) were studied. Scanning electron microscope showed that morphology of SS lyophilized was dramatically changed from sponge-like structure to spherical fine particle type. X-ray diffraction method, infrared spectroscopy, and differential scanning calorimetry showed that the conformation of SS was random coil structure regardless of the addition of methyl alcohol. On the other hand, circular dichroism showed that the molecular states of SS were more densely packed.

Semi-interpenetrating polymer networks composed of silk fibroin and poly(ethylene glycol) for wound dressing

Semi-interpenetrating polymer networks (SIPNs) composed of silk fibroin (SF) and poly(ethylene glycol) (PEG) were prepared by photopolymerization of a PEG macromer in the presence of SF to improve the mechanical properties of SF sponge as wound dressing. The morphological structure of the SF/PEG SIPNs was observed to be composed of an interconnected microporous surface and a cross-sectional area. SF/PEG SIPNs showed non-cytotoxicity evaluated by a cell proliferation method using L929 fibroblasts. Wound contraction treated with SF/PEG SIPNs sponges was faster than that of Vaseline gauze as a control. Histological observation confirmed that the deposition of collagen in the dermis was organized by covering the wound area with SF/PEG SIPNs. The above results indicated that SF/PEG SIPNs could be used as wound dressing.

Accelerated healing with the use of a silk fibroin membrane for the guided bone regeneration technique.

OBJECTIVE The purpose of this study was to evaluate the bone regeneration ability of silk fibroin (SF) membrane. STUDY DESIGN Fourier-transform infrared (FT-IR) and solubility test against distilled water were performed with 3 different types of SF membrane (SM1, SM2, and SM3). Subsequently, microscopic computerized tomography (μ-CT) and histomorphometric analyses were performed in rabbit calvarial defect model after SF membrane application at 4 and 8 weeks after surgery. RESULTS FT-IR showed that the conformation of the SF membrane was a random coil structure and that SM1 was the least soluble. When SM1 was used in the animal model, the groups with SM1 had significantly higher new bone formation than the uncovered control in both the μ-CT and the histomorphometric analyses (P < .05). CONCLUSIONS The SF membrane had more new bone formation compared with the uncovered control.