조직 접착 하이드로젤은 봉합사 및 스테이플과 같은 전통적인 상처 관리 방법을 보완하거나 대체하기 위해 개발되었으며, 상처 봉합, 지혈제, 실란트 및 다양한 의료 분야에서 사용되어왔다. 조직 접착제는 합성, 천연 고분자를 이용하여 만들 수 있다. 다양한 유형의 조직 접착제가 보고된 바 있지만, 여전히 접착 강도 및 생체 활성 부족과 같은 제한점이 있다. 따라서, 이상적인 접착제를 개발의 필요성이 부각되고 있으며 많은 연구자들이 자연에서 영감을 얻은 재료를 이용하여 조직 접착제 연구를 진행했다. 그 중에서도 홍합의 접착 단백질은 물이 존재하는 조건에서도 표면에 강하게 접착할 수 있기 때문에 큰 주목을 받았으며, 이러한 특성을 사용하기 위해, 카테콜 분자로 개질된 다양한 중합체 시스템이 보고되었다. 산소는 상처 치유 및 조직 재생에 필수적인 신호 전달 분자이며, 산소 농도에 따라 저산소 상태, 산소 정상 상태, 과산소 상태, 세 가지 조건으로 나눌 수 있다. 특히, 과산소 상태는 세포 내 반응성 산소 및 질소 종을 증가시킴으로써 살균 효과, 세포 증식, 콜라겐 합성 및 신생혈관 형성을 포함하는 상처 치유 과정을 촉진한다는 것이 입증되었다. 본 연구에서는 티올기가 도입된 젤라틴 (GtnSH), 도파민 염산염을 이용하여 과산화칼슘 매개 가교 반응을 통해 향상된 조직 접착력을 가지는 산소 발생 접착 하이드로젤을 연구하였다. 이 반응에서, 하이드로젤 네트워크는 이황화 결합 및 GtnSH와 폴리 도파민 사이의 마이클 유형 첨가를 통해 형성되었다. 또한, 도파민은 조직 표면의 작용기 (예, -NH2, -SH)와 반응하여 다양한 계면 결합을 할 수 있다. 과산화칼슘 및 도파민 농도에 따라 하이드로젤의 물리화학적 특성을 평가한 결과, 조절 가능한 상 전이 시간 (43초 ? 3분)과 기계적 특성 (40 ? 830 Pa)을 얻었으며, 과산화칼슘 농도가 증가함에 따라 더 많은 도파민 분자가 하이드로젤 매트릭스 내에 남아 있음을 입증하였다. 또한, 하이드로젤은 15-38kPa의 기존 피브린 젤보다 약 2배정도 향상된 조직 접착 강도를 보였고, 체외 (in vitro)에서 빠르게 산소를 생성하고 7일 동안 방출하였다. 쥐의 피하 및 상처 모델에 산소를 방출하는 그룹 (HG, G5D0.5C0.75)과 방출하지 않는 그룹 (NG, G5D0.5C0.75)을 적용한 결과, HG가 NG에 비해 증가된 신생혈관 형성 및 상처 치유를 촉진함을 확인하였다. 본 하이드로젤은 보다 진보된 상처 관리 및 다양한 조직 재생 분야에 있어 사용될 수 있는 잠재력을 가진다.
Bioadhesive hydrogels have been used as wound closures, hemostatic agents, tissue sealants and other medical applications. They emerged to complement or replace traditional wound care methods such as sutures and staples. Bioadhesives can be made from synthetic, natural polymers, and materials inspired by nature. While various types of bioadhesives have been reported, it is still challenging to overcome some limitations, such as poor adhesion strength and lack of bioactivities. Recently, many researchers have been tried to use bio-inspired materials for developing adhesives. Among them, mussel foot protein has received considerable attention because it can adhere to various surfaces underwater conditions. To use this distinctive property in bioadhesive researches, different catechol-modified polymer systems have been reported. Molecular oxygen is an essential signaling molecule in wound healing and tissue regeneration. Oxygen tension can be divided into three conditions depending on concentrations. Normoxia is the condition of a normal level of oxygen. Hypoxia refers to a condition of low oxygen tension, typically in the range of 1-5% of oxygen and hyperoxia means excess oxygen higher than normal partial pressure. In particular, it is demonstrated that hyperoxic condition promotes the wound healing process including oxidative killing effect, cell proliferation, collagen synthesis, and angiogenesis by increasing intracellular reactive oxygen and nitrogen species (RONS). Right after the injury, tissues surrounding the wound undergoes hypoxia due to the damaged vessels. Although this condition could stimulate the initial wound healing process, it requires sufficient oxygen supply to sustain the next step of the process. Herein, we present the preparation of novel oxygen-generating bioadhesive hydrogels based on gelatin. The thiolated gelatin (GtnSH)-polydopamine (PD) hydrogels were formed via calcium peroxide (CaO2)-mediated crosslinking reaction. In this reaction, the polymer networks were crosslinked through disulfide bonds, and Michael type addition between the GtnSH and dopamine hydrochloride (DA). Additionally, DA reacts with functional groups (e.g., -NH2, -SH) of tissue surfaces resulting in diverse interfacial bindings. We investigated the physicochemical properties of the hydrogels depending on CaO2 and DA concentrations, resulting in tunable phase transition time (43 sec ? 3 min) and mechanical properties (40 ? 830 Pa). We demonstrate that as increasing CaO2 contents, more DA molecules were remained within the hydrogel matrices since CaO2 facilitated dopamine oxidation and in situ polymerization. Also, the hydrogels showed controllable tissue adhesive strength in wet conditions (15 ? 38 kPa), and rapidly generated oxygen up to 70% pO2 and released for seven days in vitro. We evaluated the cytotoxicity of the hydrogels using human dermal fibroblasts (HDFs), confirming the excellent cell viability (> 85% compared to the control). Furthermore, we implanted the hyperoxic gels (HG, G5D0.5C0.75) and normoxic gels (NG, G5D0.5C0.75) in the subcutaneous pocket of mice and applied critical defect model to analyze in vivo effects of the hydrogels. Interestingly, we found that the HG group facilitated wound closing and healing with enhanced neovascularization compared to the NG. Our GtnSH-PD hydrogel is a promising system for advanced wound management applications such as hemostatic agents, tissue sealants, and bioglues. Great tissue adhesiveness and oxygen-generating properties of the hydrogels have the potential for tissue regenerative materials.
Chapter 1. General Introduction1.1. Tissue adhesive biomaterials 11.1.1. Synthetic polymer 11.1.2. Natural polymers 31.1.3. Nature-inspired materials 61.2. Oxygen in wound healing process 101.2.1. Wound healing process 101.2.2. The role of hyperoxia in wound healing process 131.2.3. Current strategies for oxygen therapies 151.2.3.1. Oxygen-delivery system 151.2.3.2. Oxygen-generating system 151.3. Research Motivation and Approaches 18Chapter 2. Oxygen-generating Tissue Adhesive Hydrogels2.1. Introduction 202.2. Objectives 242.3. Experimental Section 252.3.1. Materials 252.3.2. Synthesis and preparation of the GtnSH-PD hydrogels 262.3.3. Phase transition time and rheological analysis 262.3.4. Quantification of released H2O2 concentrations 282.3.5. Oxidation kinetics of dopamine 282.3.6. Dopamine-releasing kinetics from the hydrogel matrixes 282.3.7. Measurement of dissolved oxygen (DO) level 292.3.8. Cytocompatibility of the GtnSH-PD hydrogels 292.3.9. Measurement of tissue adhesive strength 302.3.10. In vivo degradation of GtnSH-PD hydrogels 302.3.11. In vivo biocompatibility and angiogenic effect of the hydrogels 312.3.12. In vivo wound healing study 312.3.13. In vivo hemostatic ability test 322.3.14. Histological analysis 322.3.15. Statistical Analysis 322.4. Results and Discussion 332.4.1. Tunable physicochemical properties of the hydrogels 332.4.2. Generation and decomposition of H2O2 from the hydrogels 362.4.3. CaO2-mediated in situ polymerization of dopamine 402.4.4. Controllable oxygen tension of the hydrogels 432.4.5. Improved tissue adhesive properties of the hydrogels 452.4.6. Cytocompatible oxygen-generating bioadhesive 472.4.7. In vivo degradability of the hydrogels 502.4.8. In vivo angiogenic effect and enhanced wound healing ability 522.4.9. In vivo hemostatic capacity of the hydrogels 54Chapter 3. Conclusion and Future Direction