3D printable and piezoelectric-conductive multifunctional hydrogel patch for human-machine interface sensing and enhanced wound healing = 인체-기계 인터페이스 센싱 및 상처 치유 개선을 위한 압전 전도성 생분해성 다기능 3D 프린팅 하이드로겔 패치

국문 초록 (Abstract)

본 석사논문은 기존 웨어러블 전극의 피부 자극, 신호 품질 저하, 환경 오염 문제를 극복하고자, 생체 적합성 높은 천연 고분자(GelMA 및 알지네이트) 기반의 이중 가교(Double Network, DN) 네트워크에 기계적 보강제인 TEMPO 산화 셀룰로오스 나노결정(TOCNCs, 4 wt%)과 압전-전도성 나노 물질인 MXenes(Ti₃C₂Tₓ, 2 wt%)을 최적 비율로 통합하여, 인체-기계 인터페이스(HMI) 센싱 및 향상된 상처 치유 기능을 동시에 수행하는 3D 프린팅 가능한 다기능성 하이드로겔 플랫폼(GACM 하이드로겔)을 개발하고 그 가능성을 입증하는 것을 목적으로 한다. 본 연구를 수행하기 위한 재료 및 방법론적으로 TOCNCs의 성공적인 표면 개질 및 MXenes의 층상 나노 시트 형태를 확인한 후, 물리적 이온 가교(CaCl₂/MgCl₂)와 화학적 공유 결합 가교(CDI/NHS)를 순차적으로 적용하여 안정적인 DN 구조를 확립하였다. 그 결과 GACM 하이드로겔은 TOCNCs의 보강 효과와 DN 네트워크의 시너지 덕분에 초기 GA 하이드로겔(11.54 kPa) 대비 압축 강도가 20.97 kPa로 크게 증가하고 접착력이 0.33 N으로 향상되었으며, 3D 프린팅에 필수적인 전단 박하 거동을 유지하여 격자, 벌집 등 복잡한 3차원 구조물로도 높은 정밀도로 출력 가능함을 입증하였다. 또한, 본 학위논문에 MXenes 나노물질 도입을 통해 전기 전도성이 0.92 mS/m에서 1.86 mS/m로 유의미하게 향상되었고, 80% 변형률에서 특히 1.77의 높은 게이지 팩터(GF)를 달성하여 큰 신체 움직임에 대한 민감한 센싱 능력을 보였다. 뿐만 아니라, 외부 압력 인가 시 최대 36.35 mV의 전압을 안정적으로 발생하는 압전 나노 발전기(PENG) 역할을 수행함으로써, 외부 전원 없이 자가 발전된 전기 자극을 통해 상처 치유를 촉진할 잠재력을 제시할 수 있었다. 생물학적 평가에서는 GACM 하이드로겔이 HaCaT 세포의 우수한 증식 및 이동 능력을 보이며 높은 생체 적합성을 입증하였고, 상처 환경(pH 5.0)에서 생리적 환경(pH 7.4) 대비 약물(커큐민)을 더 빠르게 방출하는 pH 반응성 약물 전달 특성과 Curcumin-MXenes의 시너지 효과를 통한 강력한 항균 활성을 확인하여 스마트 상처 드레싱으로서의 우수성을 입증하였다. 더불어, GACM 하이드로겔은 인체의 움직임을 정밀하게 감지하는 압전 센서로서 무선 인체-기계 인터페이스(HMI) 시스템에 성공적으로 적용되어 본 석사논문에서 웨어러블 기기를 이용한 손가락 움직임 전기신호를 감지하거나 센서로 움직임을 인식하도록 정밀하게 제어할 수 있었다. 최종적으로, 이러한 연구결과는 3D 프린팅 가능성, 뛰어난 기계적 안정성, 자가 발전 압전 센싱, 그리고 생체 적합성 및 감염 치료 기능을 하나의 플랫폼에 성공적으로 통합하여, 미래 헬스케어 모니터링, 재생 의학 및 차세대 바이오 일렉트로닉스 분야에서 혁신적인 발전을 이끌어낼 다재다능한 플랫폼임을 제시할 수 있을 것으로 사료된다.

다국어 초록 (Multilingual Abstract)

This thesis aims to develop and demonstrate the potential of a 3D printable multifunctional hydrogel platform (GACM hydrogel). This platform integrates a biocompatible natural polymer (GelMA and Alginate) based Double Network (DN) with TEMPO-oxidized cellulose nanocrystals (TOCNCs, 4 wt%) as a mechanical reinforcement and piezoelectric-conductive MXenes (Ti3C2Tx, 2 wt%) at an optimal ratio. The primary objective is to overcome the limitations of existing wearable electrodes, such as skin irritation, signal degradation, and environmental pollution, while simultaneously enabling Human-Machine Interface (HMI) sensing and enhanced wound healing capabilities. Regarding the materials and methodology employed in this study, a stable DN structure was established by confirming the successful surface modification of TOCNCs and the laminar nanosheet morphology of MXenes, followed by the sequential application of physical ionic crosslinking (CaCl2/MgCl2) and chemical covalent crosslinking (CDI/NHS). Consequently, due to the reinforcing effect of TOCNCs and the synergistic nature of the DN network, the GACM hydrogel exhibited a significant increase in compressive strength to 20.97 kPa compared to the initial GA hydrogel (11.54 kPa), as well as improved adhesiveness of 0.33 N. Furthermore, the hydrogel maintained shear-thinning behavior essential for 3D printing, proving its capability to print complex three-dimensional structures, such as lattice and honeycomb patterns, with high precision. In terms of electrical properties, the incorporation of MXenes nanomaterials significantly enhanced electrical conductivity from 0.92 mS/m to 1.86 mS/m. Notably, the material achieved a high Gauge Factor (GF) of 1.77 at 80% strain, demonstrating sensitive sensing capabilities for large body movements. Moreover, by functioning as a Piezoelectric Nanogenerator (PENG) capable of stably generating a maximum voltage of 36.35 mV under external pressure, the study presented the potential to promote wound healing through self-powered electrical stimulation without the need for an external power source. Biological evaluations demonstrated the high biocompatibility of the GACM hydrogel, evidenced by the excellent proliferation and migration abilities of HaCaT cells. The material also proved its superiority as a smart wound dressing by confirming pH-responsive drug delivery properties, releasing drugs (Curcumin (CuR)) faster in an acidic wound environment (pH 5.0) compared to a physiological environment (pH 7.4), and exhibiting strong antibacterial activity through the synergistic effect of CuR and MXenes. Additionally, the GACM hydrogel was successfully applied to a wireless HMI system as a piezoelectric sensor for precise motion detection, allowing for the sensing of finger movement electrical signals via wearable devices and the precise control of movements using the sensor. In conclusion, these findings suggest that this versatile platform—successfully integrating 3D printability, superior mechanical stability, self-powered piezoelectric sensing, biocompatibility, and infection treatment functions—holds the potential to drive innovative advancements in future healthcare monitoring, regenerative medicine, and next- generation bioelectronics.

목차 (Table of Contents)

• Abstract Ⅰ
• Contents Ⅲ
• List of Tables Ⅵ
• List of Figures Ⅶ
• List of Abbreviations IX
• Chapter Ⅰ. Introduction 1
• 1. Introduction 2
• 1.1. Background 2
• 1.2. Scope and objectives 5
• Chapter Ⅱ. Literature Review 7
• 2. Literature Review 8
• 2.1. Hydrogel network structure and fabrication 8
• 2.1.1. Hydrogel network formation through crosslinking mechanisms 9
• 2.1.2. Integration of hydrogels with 3D printing technology with nanocellulose 13
• 2.2. CNCs-based conductive hydrogels 17
• 2.2.1. Characteristics and role of CNCs in biocomposites 17
• 2.2.2. Imparting conductivity with conductive polymers 17
• 2.2.3. Imparting conductivity with carbon-based materials 20
• 2.2.4. Imparting Conductivity with Transition-Metal Carbides/Nitrides (MXenes) 23
• 2.3. Piezoelectric Nanogenerator (PENG) Hydrogels 25
• 2.3.1. Fundamentals of PENG 25
• 2.3.2. Applications of conductive and PENG hydrogels 25
• 2.3.2.1. Wearable motion sensing for human-machine interfaces 25
• 2.3.2.2. Electrical stimulation (ES) for accelerated tissue regeneration 26
• Chapter Ⅲ. Materials and Method 28
• 3. Materials and method 29
• 3.1. Materials 29
• 3.2. Preparation and characterization of TEMPO oxidation nanocellulose 29
• 3.3. Synthesis and characterization of MXenes 30
• 3.4. Preparation of piezoelectric composite hydrogel 30
• 3.5. General characterization of hydrogel 31
• 3.5.1. Morphological characterization 32
• 3.5.2. Mechanical test 32
• 3.5.3. Swelling and degradation rate 32
• 3.5.4. 3D printing performance of hydrogels 33
• 3.6. Characterization of conductive and piezoelectric GACM hydrogel 33
• 3.6.1. Adhesive performance of GACM hydrogel 33
• 3.6.2. Drug release and antibacterial activity 33
• 3.6.3. Conductivity and sensing activities 34
• 3.6.4. Piezoelectric activity 35
• 3.7. In vitro studies 41
• 3.8. In vivo studies 42
• 3.9. Statistical analysis 42
• Chapter Ⅳ. Results and Discussion 44
• 4. Results and Discussion 45
• 4.1. Characterization of synthesized nanomaterials 45
• 4.1.1. Morphology and chemical structure of TOCNCs 45
• 4.1.2. Structural characterization of MXenes nanosheets 46
• 4.2. Physicochemical properties of composite hydrogels 50
• 4.2.1. Morphology, chemical composition, and thermal stability 51
• 4.2.2. Swelling and biodegradation behavior 53
• 4.3. Mechanical, adhesive, and 3D printing properties 55
• 4.3.1. Mechanical properties of hydrogels 55
• 4.3.2. Rheological properties and 3D printing performance 59
• 4.4. Drug release kinetics and antibacterial activity 61
• 4.5. Real-time motion sensing and human-machine interface analysis 63
• 4.5.1. Conductivity and electromechanical sensitivity 63
• 4.5.2. Piezoelectric output performance 66
• 4.6. In vitro studies 70
• 4.7. In vivo studies 72
• Chapter Ⅴ. Conclusions 78
• 5. Conclusions 79
• Chapter Ⅵ. Future Perspectives 81
• 6. Future Perspectives 82
• References 83
• Abstract (in Korean) 98
• List of publication 100