전기수력학 젯 프린팅을 이용한 폴리다이아세틸렌을 함유하는 실크피브로인 미세 패턴화 및 센서 응용

Abstract

전기수력학적 분사 인쇄법 (Electrohydrodynamic (EHD) jet printing) 은 인가된 전압에서 기인한 전기장을 이용하여 잉크를 노즐의 팁에서 기판으로 방출시키는 프린팅 기술이다. 이 기술은 종래의 잉크젯 프린팅 기술과 비교할 때 더 우수한 해상도와 잉크 선택성을 지녀 각광받고 있다. 또한 적용 전압, 적용 전압의 지속 시간 및 주기, 노즐과 기판 사이의 거리, 기판의 이동속도 등을 조절하여 다양한 패턴을 제조할 수 있다. 누에나방으로부터 생성된 실크 피브로인은 생체 적합성, 생분해성, 비독성 특성이 우수하여 의료용 소재로 각광받고 있는 물질이다. 근래에는 용매 침지, 염 침출, 동결 건조와 같은 방법으로 실크 피브로인에 다공성 구조를 형성할 수 있음이 보고되고 있다. 다공성 물질은 일정 크기의 기공과 더 큰 비표면적을 지녀 흡착제, 특정 물질의 지지체, 촉매, 센서 등으로의 응용 연구가 활발히 진행되고 있다. 본 연구에서는 실크 피브로인의 센서 물질 지지체로의 응용에 주목하였다. 센서 물질을 담지하는 이상적인 고분자 지지체는 센서 물질을 지지하여 쉽게 변형되지 않는 기계적 물성을 지녀야 하고, 센서 물질과 검출 물질 사이에 충분한 공간이 확보되어 확산에 의해 구조 내 전 영역의 센서 물질이 성공적으로 신호를 발현할 수 있어야 하며, 넓은 비표면적을 지녀 많은 센서 물질을 고정할 수 있는 구조인 다공성 형태를 지녀야 한다. 본 연구에서는 생체 적합성이 우수한 다공성 실크 피브로인을 EHD jet printing 기술로 미세 패턴화 하였고, 패턴 내에 pH, 열, 화학 가스와 같은 외부 자극에 의해 색 전이 및 형광 발현 특성을 지니는 폴리다이아세틸렌을 고정시켜 센서로서 응용하였다. 뿐만 아니라 메탄올 처리로 인해 실크 피브로인 내 이차 구조의 베타 병풍 구조 특성이 강화되어 물 불용성과 기계적 안정성을 지니게 되었다. 다공성 구조 및 기판의 소수성으로 인하여 향상된 단위 면적당 비표면적으로 인해 상대적으로 많은 물질을 지지할 수 있는 지지체로서의 기반이 마련되었다. 폴리다이아세틸렌의 안정적인 고정을 위해 실크 피브로인 표면에 자외선/오존 처리를 통해 카복실 산 작용기를 도입하였고 이를 아민 작용기로 치환하였다. 아민 작용기와 다이아세틸렌 리포좀과의 아마이드화 (amidization) 반응을 유도하여 다이아세틸렌 리포좀을 다공성 실크 피브로인 표면에 성공적으로 고정 할 수 있었다. 254 nm의 자외선 파장을 조사하여 폴리다이아세틸렌을 광중합 하였고 이를 열 및 용매로 자극하여 적색의 형광 발현을 관찰함으로써 다공성 실크 피브로인의 센서 지지체로서의 응용 가능성을 확인하였다.|Electrohydrodynamic (EHD) jet printing is the technique that uses electric fields to eject ink from the tip of nozzle to the substrate. This technology has attracted huge attention in recent years because it shows higher resolution and broader ink selectivity than conventional ink-jet printing. In addition, various patterns can be easily fabricated by adjusting operating parameters such as applied voltage, working distance, frequency of the applied voltage, and pulse duration. Silk fibroin (SF) from the domestic bombyx mori has been widely used in the field of medicine owing to its high biocompatibility, biodegradability, and non-toxicity. In recent years, several studies have reported that SF can be formed as porous structure by using several methods such as salt leaching, freeze drying, and solvent immersion. The porous structure has become very attractive in the field of sensors, catalyst, adsorbent, and supporter because the porous structures can provide large specific surface area and uniform pores. Ideal polymeric supporter for sensor application has several important requirements. Firstly, it should have mechanical property that are not easily deformed when it supports the sensor materials. Secondly, sufficient space must be provided between the sensor materials and analytes so that the sensing signal can be successfully expressed throughout whole structure by diffusion of analytes. Lastly, it should be a structure with high specific surface area which can immobilize a lot of sensor materials. The porous silk fibroin is one of the candidates satisfying these requirements. Therefore, in this research, the porous silk fibroin was used as a supporter for sensor materials. In this research, an EHD jet printing technique was used to fabricate micron-sized biocompatible porous SF patterns, and polydiacetylenes (PDAs) were immobilized onto the surface of SF patterns for sensor applications. PDAs are conjugated polymers exhibiting novel properties such as color change or fluorescence emission by external stimuli like heat, solvent, and pH, which is essential for sensor applications. A β-sheet component in SF were increased by methanol treatment leading to the improved water insolubility and mechanical stability. The high specific surface area per unit area of the SF patterns could be obtained by printing the SF ink on the hydrophobic substrates. The combination of the porous structure of SF and high aspect ratio of the pattern can realize an excellent supporter for sensor material immobilization. To immobilize PDAs on the surface of the porous SF patterns, firstly, carboxylic acid groups were introduced onto the surface of the porous SF patterns by UV/ozone irradiation, and then they were substituted for amine groups. Finally, through amidization reaction between 10,12-pentacosadiynoic acid (PCDA) liposome and amine-functionalized SF, the PCDA liposome was successfully immobilized onto the surface of SF dot patterns. The PCDA liposome was photopolymerized under UV irradiation at 254 nm, and sensor capability was examined by exposing the PDA-immobilized SF patterns to the external stimuli such as solvent and heat. Fluorescence signals were successfully revealed after heat exposure. In conclusion, PDA-embedded SF sensor patterns with relatively enhanced fluorescence signals were successfully produced and the solvatochromic and thermochromic sensing ability of PDA-embedded SF patterns were demonstrated.; Electrohydrodynamic (EHD) jet printing is the technique that uses electric fields to eject ink from the tip of nozzle to the substrate. This technology has attracted huge attention in recent years because it shows higher resolution and broader ink selectivity than conventional ink-jet printing. In addition, various patterns can be easily fabricated by adjusting operating parameters such as applied voltage, working distance, frequency of the applied voltage, and pulse duration. Silk fibroin (SF) from the domestic bombyx mori has been widely used in the field of medicine owing to its high biocompatibility, biodegradability, and non-toxicity. In recent years, several studies have reported that SF can be formed as porous structure by using several methods such as salt leaching, freeze drying, and solvent immersion. The porous structure has become very attractive in the field of sensors, catalyst, adsorbent, and supporter because the porous structures can provide large specific surface area and uniform pores. Ideal polymeric supporter for sensor application has several important requirements. Firstly, it should have mechanical property that are not easily deformed when it supports the sensor materials. Secondly, sufficient space must be provided between the sensor materials and analytes so that the sensing signal can be successfully expressed throughout whole structure by diffusion of analytes. Lastly, it should be a structure with high specific surface area which can immobilize a lot of sensor materials. The porous silk fibroin is one of the candidates satisfying these requirements. Therefore, in this research, the porous silk fibroin was used as a supporter for sensor materials. In this research, an EHD jet printing technique was used to fabricate micron-sized biocompatible porous SF patterns, and polydiacetylenes (PDAs) were immobilized onto the surface of SF patterns for sensor applications. PDAs are conjugated polymers exhibiting novel properties such as color change or fluorescence emission by external stimuli like heat, solvent, and pH, which is essential for sensor applications. A β-sheet component in SF were increased by methanol treatment leading to the improved water insolubility and mechanical stability. The high specific surface area per unit area of the SF patterns could be obtained by printing the SF ink on the hydrophobic substrates. The combination of the porous structure of SF and high aspect ratio of the pattern can realize an excellent supporter for sensor material immobilization. To immobilize PDAs on the surface of the porous SF patterns, firstly, carboxylic acid groups were introduced onto the surface of the porous SF patterns by UV/ozone irradiation, and then they were substituted for amine groups. Finally, through amidization reaction between 10,12-pentacosadiynoic acid (PCDA) liposome and amine-functionalized SF, the PCDA liposome was successfully immobilized onto the surface of SF dot patterns. The PCDA liposome was photopolymerized under UV irradiation at 254 nm, and sensor capability was examined by exposing the PDA-immobilized SF patterns to the external stimuli such as solvent and heat. Fluorescence signals were successfully revealed after heat exposure. In conclusion, PDA-embedded SF sensor patterns with relatively enhanced fluorescence signals were successfully produced and the solvatochromic and thermochromic sensing ability of PDA-embedded SF patterns were demonstrated.