Woo-Kul Lee

Effect of surface modification on the in vitro calcium phosphate growth on the surface of poly(methyl methacrylate) and bioactivity.

Poly(methyl methacrylate) (PMMA) is a biocompatible polymer widely used for bone substitutes. Its surface properties, however, are not favorable for the induction of biological apatite which can be directly related to natural bone formation. In this study, the surface of PMMA was modified by NaOH treatment or sequential treatments with ethanol (EtOH) and NaOH. Results displayed that surface hydrophilicity was improved for increasing treatment time and NaOH concentration. Field-emission scanning electron microscope (FE-SEM) displayed that in vitro formation of calcium phosphate (CaP) coating was significantly promoted by the surface modifications. X-ray photon spectroscopy (XPS) examination elucidated that the films prepared on PMMA consisted of calcium and phosphorus and their values for Ca/P ratio were closed to octacalcium phosphate (OCP). Fourier transform infrared (FT-IR) spectra of the film coated on PMMA revealed a band characteristic of phosphate groups confirming that CaP films were formed and their characteristics were dependent on the surface properties of PMMA. Cellular assay demonstrated that the adhesion of osteoblast-like MG63 cells was significantly promoted on CaP-coated PMMA. Proliferation assay showed that CaP films appeared not to exert any cytotoxic effects on the growth of MG63 cells.

Association of collagen with calcium phosphate promoted osteogenic responses of osteoblast-like MG63 cells.

In this investigation, the effects of the association of the collagen (COLL) molecules with the calcium phosphate (CaP) film were examined with respect to both the physicochemical properties of the CaP films and the osteoblast responses, such as the adhesion, proliferation, differentiation, and mineralization. The COLL pre-adsorbed CaP film (CaPA) exhibited significant changes in the surface morphology compared to the COLL incorporated CaP film (CaPC). The adhesions of the osteoblast-like MG63 cells were similar on the CaPC or CaPA films. However, the proliferation of the MG63 cells on CaPC was comparable to CaP but considerably different than CaPA. The differentiation of the MG63 cells was greatly improved on CaPC and CaPA compared to CaP and more pronounced on CaPA. The presence of COLL within or on the CaP films significantly modulated the expression of the phenotypic genes, including osteopontin (OPN), alkaline phosphatase (ALP), and the transforming growth factor-β (TGF-β). The expression patterns of these genes elucidated that COLL that was present within or on the CaP film supported the osteoblast proliferation and differentiation. These positive effects were stronger for CaPA than CaPC. The bone-like nodules formed on all of the specimens. However, the mineralization of CaPC and CaPA was significantly higher than CaP, indicating that the association of CaP with COLL promoted the mineral deposition. Therefore, the association of the COLL molecules with the CaP film induced positive effects on the biomineralization. Overall, the incorporation of COLL efficiently enhanced the osteoblast responses of CaP. This system can be utilized in a drug delivery system using calcium phosphate. Although the incorporation effects were slightly higher for the osteoblast responses of CaPA than CaPC, CaPC can be used when the longer drug release times are desirable.

Fabrication of porous chitosan-polyvinyl pyrrolidone scaffolds from a quaternary system via phase separation.

Three-dimensional porous chitosan-polyvinyl pyrrolidone (PVP) scaffolds were fabricated for tissue engineering applications via liquid–liquid or liquid–solid phase separation. A mixture of an acidic aqueous solution with butanol as a non-solvent and a chitosan-PVP quaternary system were freeze-dried. We then studied the homogenous open pore structure and the minute pore distribution in order to improve the mass transfer and cell seeding efficiency while also obtaining the optimal ratio of PVP to provide high interconnectivity and to improve the open-pore structure. The properties of the porous chitosan-PVP scaffolds – including the microstructure, chemical release, water absorption properties, and cell proliferation tests were studied – and the results were compared against those obtained from conventional scaffolds. chitosan-PVP scaffolds with a porosity of over 70% were obtained, and the pore morphology on the surface and within the porous scaffolds showed the presence of homogenous open pores with excellent interconnectivity. As the PVP content increased, main pores (50–100 μm) and minute pores (4–10 μm) could be clearly observed. Also, the porous scaffold showed an improved efficiency for cell adhesion after the cells were cultured for 4 h. After 72 h, the cultured cells presented an increase in the cell proliferation and on the porous scaffolds. These results strongly suggest that the porous chitosan-PVP scaffolds can be widely used in tissue engineering, including for biopatches and artificial skin applications.

Interfacial Tension Kinetics of Nisin and β-Casein at an Oil-Water Interface

The concentration- and time-dependence of interfacial pressure of nisin and β-casein at ann-hexadecane-water interface were evaluated by using DuNoüy tensiometry. The two emulsifiers attained interfacial saturation at a bulk concentration of about 0.1 mg/ml, the reduction of the interfacial tension by nisin at that concenration being about equivalent to that of β -casein. The time dependence of interfacial tension recorded for each protein was described by using two kinetic models. In the first, the reduction of interfacial tension with time was considered to be a result of molecular penetration into the interface followed by rearrangement. Nisin exhibited more rapid penetration and rearrangement at the interface than did β -casein. In the second, the model allowed for the parallel, irreversible adsorption of protein into each of two states from solution, where state 2 molecules occupy greater interfacial area and are more tightly bound than state 1 molecules. The extent of adsorption in state 1 and state 2 was determined to be highly concentration dependent for each protein; adsorption occurs mostly in state 1 at high concentration and mostly in state 2 at low concentrations.

Enhanced biocompatibility and adhesive properties by aromatic amino acid-modified allyl 2-cyanoacrylate-based bio-glue

Cyanoacrylates have numerous advantages, including that they can be applied quickly during first aid and can provide good cosmetic outcomes, but they also have limitations in that they have a low bond strength and local tissue toxicity. Consequently, they are primarily used only in urgent applications. To improve both the biocompatibility and the mechanical properties of cyanoacrylate, allyl 2-cyanoacrylate (AC) was prepolymerized and mixed with a dopamine co-initiator. Various properties of prepolymerized AC (PAC)/dopamine mixtures were tested using mouse fibroblast cell (L-929), including their bond strength, setting time, crystallization intensity, and cytotoxicity. Enhanced mechanical properties and biocompatibility were confirmed, and a cytotoxicity test was used to determine the optimal conditions for prepolymerization of AC to be 130°C for 60min. A combination of 5mg of dopamine in 5ml of PAC achieved a high bond strength with cytotoxicity of the dopamine/PAC at approximately 1.5 times lower than that of PAC. These results indicate that dopamine/PAC materials can be extensively used as advanced bio-glues in various applications.

Bone nodule formation of Mg63 cells is increased by the interplay of signaling pathways cultured on vitamin D3‐entrapped calcium phosphate films

Abstract Since vitamin D3 is an important regulator of osteoblastic differentiation, a presently‐established vitamin D3‐entrapped calcium phosphate film (VCPF) was evaluated for hard tissue engineering. The entrapped vitamin D3 more rapidly induced bone nodule formation. To characterize the cellular events leading to regulations including faster differentiation, signal transduction pathways were investigated in osteoblastic MG63 cells at a molecular level. Major signaling pathways for MG63 cell proliferation including phosphatidylinositol‐3‐kinase, extracellular signal‐regulated kinase, c‐Jun N‐terminal kinase and focal adhesion kinase pathways were markedly down‐regulated when cells were cultured on calcium phosphate film (CPF) and VCPF. This agreed with our earlier observations of the immediate delay in proliferation of MG63 cells upon culture on CPF and VCPF. On the other hand, the p38 mitogen‐activated protein kinase (p38 MAPK) and protein kinase A (PKA) pathways were significantly up‐regulated on both CPF and VCPF. CPF alone could simulate differential behaviors of MG63 cells even in the absence of osteogenic stimulation and entrapment of vitamin D3 within CPF further amplified the signal pathways, resulting in continued promotion of MG63 cell differentiation. Interplay of p38 MAPK and PKA signaling pathways likely is a significant event for the promotion of differentiation and mineralization of MG63 cells.

Enhanced chemophysical properties by bis-GMA-modified allyl 2-cyanoacrylate-based bioadhesives for hard tissue

Abstract To improve the biocompatibility and physical properties of bioadhesives for hard tissue, allyl 2-cyanoacrylate (AC) was pre-polymerized and mixed with bisphenol A glycidyl methacrylate (bis-GMA) and hydroxyapatite (HA). Various properties of pre-polymerized AC (PAC)/bis-GMA mixtures were measured, including compressive and shear bond strength, polymerization shrinkage, surface properties, and cytotoxicity (tested using L929 cells); enhanced physical properties and biocompatibility were observed. In particular, the optimal ratio for PAC/bis-GMA/HA was determined to be 90/9/1 wt%, as per the results of the above-mentioned measurements. Polymerization shrinkage of PAC/bis-GMA samples decreased with increasing bis-GMA content (by up to 15 times compared to PAC alone). Furthermore, biocompatibility and mechanical strength improved with increasing bis-GMA or HA content. Therefore, bioadhesives prepared with these PAC/bis-GMA/HA mixtures showed enhanced chemophysical properties compared to commercial bioadhesives for hard tissue. These results indicate that PAC/bis-GMA/HA materials can be used widely as advanced bioadhesives in various fields.