Improvement of Mechanical Properties of UV/Heat Dual-Curable Adhesives for Liquid Crystal Display

유지용 명지대학교 대학원 2018 국내석사

Recently, many efforts have been dedicated to improve the device performance in liquid crystal (LC) display. In particular, the LC device of the 3D or tiled display needs narrow bezel design for seamless characteristics. However, this design might result in poor adhesion, high water permeability, and increased LC pollution of LC adhesive materials. So, narrow bezel designs in LC displays require an adhesive that possesses mechanical properties, including adhesive properties, water permeability, and acceptable LC pollution levels. Among adhesive components, the silane coupling agent plays an important role in adhesion between inorganic materials. In this study, we used three types of silane coupling agents, which are had various functional groups. These various types of coupling agents make physicochemical bonds with various resins and also physicochemical bonds with inorganic fillers and inorganic substrates. In this study, we prepared UV/heat dual-curable adhesives using photoreactive silane coupling agents, and then compared their performance with that of conventional adhesive containing alkyl-based silane coupling agent. The adhesive strength of the conventional silane coupling agent was measured as 31.86 kgf/cm2 and the adhesive strength of the photoreactive silane coupling agent was measured as 42.18 kgf/cm2. This shows 32 % enhanced results. The water permeability of the conventional silane coupling agent was measured as 8.28 g/m2·day and the water permeability of the photoreactive silane coupling agent was measured as 5.30 g/m2·day. This shows 36 % enhanced results. Also, the LC pollution level of the photoreactive silane coupling agent was decreased by 56 % compared with the conventional silane coupling agent. The heat-curing agent is also a key role in the adhesion between the epoxy resins. Generally, epoxy resin has good physical properties such as chemical resistance and excellent adhesion. The heat-curing agent including amine groups can be reacted with epoxy resins under certain heat condition through epoxy ring opening reaction. These heat-curing agents are essential for epoxy adhesives. And, conventional bi-functional heat-curing agents have limitations in enhancing mechanical properties. In this study, we use a multi-functional heat-curing agent that reacts with epoxy resin and evaluate the resulting mechanical properties by comparing them to those resulting from a conventional heat-curing agent. The heat curing level of the conventional heat-curing agent was measured as 90.03 % and the heat curing level of the multi-functional heat-curing agent was measured as 97.80 %. This shows 8 % enhanced results. The adhesive strength of the conventional heat-curing agent was measured as 11.41 kgf/cm2 and the adhesive strength of the multi-functional heat-curing agent was measured as 38.40 kgf/cm2. This shows 237 % enhanced results. The water permeability of the conventional heat-curing agent was measured as 12.25 g/m2·day and the water permeability of the multi-functional heat-curing agent was measured as 5.63 g/m2·day. This shows 54 % enhanced results. Also, the LC pollution level of the multi-functional heat-curing agent was decreased by 69 % compared with the conventional heat-curing agent. It is shown that the proposed adhesive offers excellent adhesive properties for narrow-bezel applications. In this study, a photoreactive silane coupling agent and a multi-functional heat curing agent were used to improve the mechanical properties of narrow bezel LC display adhesive. The silane coupling agent which react with organic-inorganic materials and multi-functional heat curing agent which has reacts with epoxy resin were optimized and dramatically improved mechanical properties. The results confirm that we were able to develop a high-performance LCD adhesive for various display devices successfully. 최근 액정 디스플레이의 제품 성능을 향상시키기 위해 많은 노력이 있다. 특히 3D 또는 타일 디스플레이의 액정 디스플레이는 아주 매끄러운 특성을 위해 내로 베젤 디자인이 필요하다. 그러나, 이 디자인은 접착력이 좋지 않고 높은 투수성과 LCD용 접착제와 액정간의 오염을 증가시킬 수 있다. 따라서 액정 디스플레이의 내로 베젤 디자인은 고 접착강도, 저 투습성 및 낮은 액정 오염 수준을 포함한 접착제를 필요로 한다. LCD용 접착 성분 중, 실란 커플링제는 유기 수지와 무기 기판 사이의 접착에 중요한 역할을 한다. 본 연구에서는 다양한 작용기를 가진 3 가지 종류의 실란 커플링제를 사용하였다. 이러한 다양한 커플링제는 다양한 수지와 물리 화학적 결합을 하고 무기 충진재 및 기판과 또한 결합을 한다. 본 연구에서 반응성의 실란 커플링제를 사용하여 자외선과 열에 이중으로 경화하는 접착제를 제조한 후 기존의 알킬계 실란 커플링제를 포함한 접착제와 성능을 비교 하였다. 일반적인 알킬 기반의 실란 커플링제의 접착강도는 31.86 kgf/cm2으로 측정 되었고, 광반응성 실란 커플링제의 접착강도는 42.18 kgf/cm2으로 측정되었다. 이는 기존대비 32 % 증진된 결과를 보여준다. 일반적인 알킬 기반의 실란 커플링제의 투습도는 8.28 g/m2·day로 측정되었고, 광반응성 실란 커플링제의 투습도는 5.30 g/m2·day로 측정되었다. 이는 기존대비 36 % 증진된 결과를 보여준다. 또한, 광반응성 실란 커플링제의 액정 오염정도는 기존 대비 56 % 감소된 결과를 보여준다. 또한, 열 경화제는 에폭시 수지 사이의 결합에서 중요한 역할을 한다. 일반적으로, 에폭시 수지는 우수한 내 화학성과 우수한 접착력을 가지고 있다. 아민 작용기가 포함된 열 경화제는 에폭시 개환 반응을 통해 특정 열 조건 하에서 에폭시 수지와 반응 할 수 있다. 이러한 경화제는 에폭시 접착제에 필수적이다. 하지만 일반적인 이 관능성의 열 경화제는 접착제의 기계적 특성을 향상 시키는데 한계가 있다. 이번 연구에서는 에폭시 수지와 반응하는 다 관능성 열 경화제를 사용하여 기존의 이 관능성 열 경화제의 특징과 비교하여 평가하였다. 일반적인 열 경화제의 경화율은 90.03 %이고, 다관능성 열 경화제의 경화율은 97.80 %이다. 이는 기존대비 8 % 증진된 결과를 보여준다. 일반적인 열 경화제의 접착강도는 11.41 kgf/cm2으로 측정 되었고, 다관능성 열 경화제의 접착강도는 38.40 kgf/cm2으로 측정되었다. 이는 237 % 증진된 결과를 보여준다. 일반적인 경화제의 투습도는 12.25 g/m2·day로 측정되었고, 다관능성 열 경화제의 투습도는 5.63 g/m2·day로 측정되었다. 이는 기존대비 54% 증진된 결과를 보여준다. 또한, 다관능성 열경화제의 액정 오염정도는 기존 대비 69 % 감소된 결과를 보여준다. 제안된 접착제는 내로 베젤 응용 분야에서 우수한 기계적 특성을 보여준다. 본 연구에서는 광 반응성 실란 커플링제와 다관능성 열 경화제는 내로 베젤 디스플레이 접착제의 기계적 물성을 증진시키는데 사용되었다. 유-무기 물질과 반응성이 있는 광 반응성 실란 커플링제와 에폭시 레진과 반응성이 있는 다관능성 열 경화제를 최적화 하여 기계적 물성을 증진시켰다. 그 결과들은 다양한 디스플레이용 고 성능 접착제 구현을 증명했다.

Evaluation of micro-shear bond strength of self-adhesive giomer to bovine tooth

김은진 Graduate School, Yonsei University 2024 국내석사

Self-adhesive flowable giomer (SAG) has been used in dental practice recently to simplify clinical procedures and shorten chair times. However, there are only few studies evaluating its bond strength to enamel and dentin, resulting in a lack of evidence. This in vitro study aimed to evaluate the micro-shear bond strength (μ-SBS) of SAG bonded with or without a dental bonding system to enamel and dentin, both before and after thermocycling. Sound bovine teeth were used as the tooth substrates. For μ-SBS tests, enamel and dentin specimens were prepared for SAG (Beautifil Kids SA - BK), a self-adhesive flowable composite (Vertise Flow - VF), and a nanohybrid flowable giomer (Beautifil Flow Plus F03 - BF). Two adhesive modes were tested for BK and VF (with self-etching adhesive and no adhesive), and one for BF (with self-etching adhesive). The μ-SBS test was conducted after 24 h and after thermocycling for 10,000 cycles using a universal testing machine. For all materials, when self-etching adhesive was used, the μ-SBS was significantly higher than that of no adhesive group (p < 0.05). No statistically significant difference was found between the restorative materials under any condition. Thermocycling had no significant effect on the μ-SBS of BK. In self-etching adhesive group, mixed failure was predominant for all materials. However, in no adhesive group, adhesive failure and mixed failure were observed at similar levels for all materials. The bonding performance of self-adhesive material to the dental substrate was significantly weaker without adhesive compared to conventional adhesive. No statistically significant difference was found between the restorative materials under any condition. BK and BF were negligibly affected by thermocycling, but VF was affected. Therefore, this study showed that self-adhesive flowable composite has lower bond strength stability in enamel and dentin compared to SAG. 자가 접착성 유동성 자이오머 (SAG)는 최근 진료 과정을 단순화하고 진료 시간을 단축하기 위해 도입되었지만, 법랑질과 상아질에 대한 결합 성능에 대한 정보는 적다. 이 연구의 목적은 열순환 전후에 법랑질과 상아질에 다양한 방식으로 결합된 SAG의 미세전단결합강도를 평가하는 것이었다. 치아 시편을 위해 건전한 소 치아가 사용되었다. 미세전단결합강도 시험을 위해 법랑질 및 상아질 시편에 SAG (Beautifil Kids SA - BK), 자가 접착성 유동성 복합레진 (Vertise Flow - VF) 및 나노하이브리드 유동성 자이오머 (Beautifil FlowPlus F03 - BF)를 적용했다. BK, VF에는 두 가지 (자가 부식 접착제 포함, 접착제 없음) 접착모드가, BF에 대해서는 한 가지 (자가 부식 접착제 포함) 접착 모드가 수행되었다. 미세전단결합강도 시험은 24시간 후, 열순환 후 만능 시험기를 사용하여 측정되었다. 자가 부식 접착제를 포함한 접착모드에서는 모든 재료에 대해 접착제가 없는 접착모드에 비해 상당히 높은 미세전단결합강도를 보였다 (p < 0.05). 열순환은 BK의 미세전단결합강도에 큰 영향을 미치지 않았다. 자가 부식 접착제를 포함한 군에서는 모든 재료에서 혼합 실패가 우세했으나 접착제가 없는 군에서는 모든 재료에서 접착 실패와 혼합 실패가 유사한 수준으로 관찰되었다. 접착제가 없는 접착모드에서 자가접착 재료의 치아에 대한 접착 성능은 기존 접착제에 비해 상당히 약했다. 어떤 조건에서도 수복 재료 간에 통계적으로 유의미한 차이는 관찰되지 않았다. BK, BF는 열순환의 영향을 무시할 수 있는 것으로 나타났으나, VF는 열순환의 영향을 받았다. 따라서 본 연구에서는 자가 접착성 유동성 복합레진이 자가 접착성 유동성 자이오머에 비해 법랑질과 상아질의 결합 강도 안정성이 낮다는 것을 보여주었다.

Synthesis and Properties of UV Laser Debondable Temporary Bonding and Debonding Adhesives for 3D Multi-chip Packaging Process

이승우 서울대학교 대학원 2015 국내박사

Recently, mobile devices with a focus on smartphone require both high performance and lightness at the same time, so TSV (Through Silicon Via) 3D multi-chip package technology was emerging. In order to realize this technique, temporary bonding and debonding adhesive is required to process silicon wafer and handling. However, using the existing adhesive handling a thin silicon wafer having a thickness of less than 50 μm is not easy. There are two main reasons for this. First, to maintain the high purity, it is required to have over 200 oC processing temperature during the process of bonding and debonding. Due to this thermal degradation, it generates low molecular weight substances and cause contamination to the thin silicon wafer. Second, while debonding, strong adhesive force can crack or cracking the thin silicon wafer and generate defects. In this study, the perspective on temporary bonding for TSV (Through Silicon Via) 3D multichip packaging and the perspective on debonding afterwards are divided into each technique elements, and these elements are to be used to newly synthesize the adhesive. Plus, the mechanisms of curing and debonding are to be analyzed through these property evaluations. In this study, the non-solvent type urethane acrylic adhesive was designed and manufactured to improve the disadvantages such as the phenomenon on flowing adhesive out from the silicon wafer after the spinning coating which the conventional solvent-based adhesive have during temporary bonding, the phenomenon of uneven coating thickness by contaminated wafer surface from the solvent evaporation and the phenomenon on the contamination of the work area. During the urethane synthesis, isophorone diisocyante was used as a hard segment and silicone-based diols (not conventional hydrocarbon-based diols) was used as a soft segment to improve the heat resistance of the polymer structure. Also, designing for dual curing adhesive that further introduce a photo-curing after thermal curing was made (rather than a single curable adhesive, such as the conventional light curing or thermal curing) to improve the heat resistance. A multi-functional acrylic monomer was end-capped to one end of the synthesized urethane oligomer and a monomer containing a fluorine was end-capped to the other end for to analyze the measurement of the number of functional groups of the multifunctional acrylic monomer, the density of the UV irradiation energy, hardening behavior, thermal stability and the peel strength depending on the amount of photoinitiator used. As a result, the number of functional acrylic monomer was in mono <di << tri, hexa order and increase on the indirect cure rate using the Gel-minute law was confirmed. This has initial reaction in the light-curing, which give an increase of the reaction sites and hence an increase in the crosslinking density. After tri-acrylate, it is confirmed that the gel fraction was not further increased by 60%, which can be interpreted that the reaction activity is falling by the radical trap of unreacted oligomers. The Gel fraction was confirmed to become constant at 60% when the UV irradiation energy density is at 400 mJ/cm2 or more. To decrease the peel strength due to the increase density of the UV energy, the pulsed irradiation method, which examine by dividing each into 100 mJ/cm2, was introduced to derive the molecular weight distribution of the polymer in a state in which heterogeneous. (The steady irradiation method, which is used primarily during irradiation, is not used.) In the steady irradiation method, the PDI value is 5.9, but the pulsed irradiation method showed 16.1 of high PDI value. This characteristic allowed showing lower intensity levels on the peel strength measurement of pulsed irradiation method than the steady irradiation method, concluding that the pulsed irradiation method is more suitable considering both temporary bonding and debonding. Type and the reaction mechanism of the photoinitiator was found through the existing studies, and the purpose of this study was to evaluate and analyze by varying the amount of light curing initiator. As a result, the gel fraction became constant without any further increase when adding the binder contrast of 2 phr or more photoinitiators. This is considered as an important research data on the optimal composition ratio of the initial dose, given a side reaction due to unreacted initiator, which can occur when an excess of added photoinitiator. Thermal decomposition behavior results, seen by varying the amount of UV energy density and photo initiator for the thermal stability and by using thermogravimetric analysis, was confirmed that the thermal stability is maintained at a high temperature condition over 250 oC. This can interpret that the heat resistance was improved by the introduction of dual-cure mechanism and the adhesive synthesis containing all hybrid type of silicone-based, epoxy-based, fluorine-based functional group. On the other hand, this study used the method of edge zone debonding, using the UV laser, to consider both temporary bonding and debonding. While the conventional method requiring a bonding temperature of 200 ~ 220 oC, this study was able to proceed the bonding at a low temperature of 80 ~ 150 oC. Furthermore, this study has done debonding within two minutes using a UV laser, rather than the conventional way in which this process takes time over 6 hours by a penetration of the solvent. For this purpose, BTHPEMA (2- [3- (2-Benzotriazol-2-yl) -4-hydroxyphenyl] ethyl methacrylate) was introduced when preparing the adhesive. When debonding, identification (BTHPEMA playing a role of being the LTHC (light to heat conversion)) for debonding progression of the polymer film formation by the heat cure adhesive was made through thermal curing mechanism of epoxy functionality by the FTIR-ATR analysis and the gel fraction measurement. Absorbency, for a UV laser of a synthesis adhesive, was determined according to wavelength using a UV-visible spectroscopy. As a result, 355 nm in wavelength bands indicate the absorption of up to 60% of the binder prepared in accordance with the increase amount of BTHPEMA comparison 0.4 phr input, and the UV laser absorbency of the adhesive synthesized was adjustable by varying the blending ratio. Moreover, it was confirmed that the joined debonding was composed in the effective energy density conditions of the UV laser irradiation with 5.65 to 6.72 J/cm2.

Calcium Carbonate와 fibrin adhesive의 병용이 성견 2급 치근분지부 치주조직 재생에 미치는 영향

서은표 전남대학교 대학원 2000 국내석사

본 실험은 성견의 하악 소구치에 2급 분지부 골 결손을 형성하고 calcium carbonate와 fibrin adhesive의 병용이 치주조직의 재생에 미치는 영향을 평가하고자 하였다. 실험은 잡종 성견 6마리를 이용하였으며 실험군은 모두 4개 군으로 나누었다. 대조군은 골 결손부에 외과적 처치만 시행한 군, 실험 I군은 골 결손부에 calcium carbonate를 이식 후 치주판막으로 봉합한 군, 실험 II군은 골 결손부에 외과적 처치 후 fibrin adhesive만 적용한 군, 실험 III군은 골 결손부에 calcium carbonate 이식 후 fibrin adhesive로 고정하고 치주판막으로 봉합한 군으로 하였다. 희생은 각각 술 후 2, 4, 12주에 시행하였고 광학 현미경적 관찰을 시행하여 다음과 같은 결론을 얻었다. 임상적으로 1주 째 소견에서는 모든 군에서 염증소견이 관찰되었지만 2, 4, 12주 소견에서는 전 실험기간을 통하여 모든 군에서 치유는 양호하였다. 광학 현미경적 관찰시 대조군에서는 모든 군에서 홈부위까지 상피가 하방 증식되었으며 4주, 12주 째에서는 홈부근에서 신생 치조골 형성이 관찰되었다. 실험 I군에서는 상피가 홈부위까지 하방 증식되었고 이식재는 골 결손부에서 대부분 탈락되어 관찰되지 않았다. 4주, 12주 째 소견에서는 홈부근에서 신생골 형성이 관찰되었다. 실험 II군에서는 사용된 fibrin adhesive가 2주 째 소견에서 완전히 흡수되어 관찰되지 않았으나 상피의 하방 증식은 모든 관찰시기에서 억제되었다. 결합조직성 부착은 대조군보다 증가하였고 홈부근에서 신생 백악질과 치조골 형성이 관찰되었다. 실험 III군에서는 상피의 하방 증식은 관찰되지 않았고 이식재가 골 결손부에서 계속적으로 유지되었으며 2주 째에 홈부근에서 치조골의 형성이 관찰되었다. 4주 째에서는 홈상방으로 신생 백악질과 치조골이 형성되었으며 12주 째에서는 백악질과 치조골이 치관측 2/3까지 재생되었다. 이상의 결과로 볼 때 2급 분지부 결손에서 calcium carbonate이식과 fibrin adhesive를 병용하였을 때 치유기간 동안에 이식재의 안정과 상피의 하방 증식 억제 및 신생 백악질 치조골 형성 촉진등 치주조직의 재생 효과가 우수하리라 사료된다. The purpose of this study was to evaluate the effect of combined use of fibrin tissue adhesive and porous resorbable calcium carbonate on the periodontal regeneration of the class II furcation defects in dogs. Class II furcation defect was surgically created on the second, third, and fourth premolars bilaterally in the mandibles of six mongrel dogs. The experimental sites were divided into four groups according to the treatment modalities: Control-surgical debridement only; Group I-calcium carbonate grafting; Group II-application of fibrin adhesive only; Group III-application of fibrin adhesive after calcium carbonate grafting. The animals were sacrificed at 2, 4, and 12 weeks after periodontal surgery and the decalcified specimens were prepared for histologic and histometric examination. The results are as follows : Clinically, there were no inflammatory response in all groups after 2, 4, and 12 weeks. In the Control group, junctional epithelium migrated apically to the reference notch. In Group I, graft materials exfoliated from the defect throughout the experimental periods and new bone was seen in the notch area at 4 and 12 weeks’ specimens. At 2 weeks, fibrin adhesive was indistinguishable in group II. In Group III, the graft material was maintained in the defect throughout the experimental periods and the amount of periodontal tissue regeneration was greater than other groups. These results suggest that the use of fibrin tissue adhesive in conjunction with porous resorbable calcium carbonate would improve the stability of graft material and inhibit the epithelial downgrowth and contribute to periodontal regeneration.

Flexible Adhesive Patch Based on Synergetic Crack Trapping Effects with Kirigami and Micropillar Hybrid Structures

Donghyuk Lee Ulsan National Institute of Science and Technology 2023 국내석사

Wearable sensors have been spotlighted for their versatile uses of sensing temperature, strain, and biomarker-analysis wearable devices. Due to its wearability, conventional methods like chemically reactive and non-chemically reactive adhesives (HMAs, PSAs) for conformal adhesion are commonly used. However, the target surface being damaged, biocompatibility, residues, and problems with reusability have all been noted as limitations of conventional methods. To overcome those limitations of conventional methods, bioinspired adhesive microstructures mimicking fibrillar adhesion strategies from Gecko’s foot and Tree frog’s foot have been proposed for securing conformal contacts on target surfaces, residue-free, biocompatible, and less-stimuli on target surfaces characteristics. Furthermore, recent studies using the kirigami-inspired macro-crack trapping method found that making small cuts can significantly improve a patch’s resistance to peeling. Herein, we propose a hybrid micro-tip and macro-kirigami adhesive patch-based pressure insensitive strain sensor that can conformally contact with target surfaces while more accurately and steadily sensing the surface mechanical deformation. In this thesis, starting with biomimetics microfibrillar adhesives from native creatures to recent micro fabrications for dry adhesive uses, adhesion performances depending on some parameters such as modulus of polymers, diameter, spacing ratio (SR), extruding tip size and pillar-tip’s shape morphology would be introduced. The adhesion test has been conducted on a normal adhesion test machine, which can apply the pre-load 4 N uniformly to the back side of the adhesion patch sample (1 cm x 1 cm) and contact on a glass substrate. Low modulus polymers give better adhesion performance following the target surface roughness well with its easy-to-deform characteristics against the normal load. As the diameter of each micropillar decreases, the adhesion increases. However, the repeatability of the small-diameter pillars cannot be confirmed due to a structural vulnerability against the normal load. Regarding the SR, as the value of the SR decreases, adhesion pillars intensify, resulting in increases in the effective contact area, enhancing the adhesion strength. The extruding tip is also a key factor in the enhancement of the patch’s normal adhesion. This thesis examines how the diameter of each pillar affects how much the normal adhesion strength depends on tip length. Moreover, the hexagonal shape of pillars and tips can have additional advantages for friction and peeling resistance. In a microscale adhesive strategy, the low SR ratio, and long extruding tip micro hexagonal fibrillar structures with low modulus polymer are adopted for a strain sensor, securing conformal contacts in this thesis. In the macro field of adhesive, kirigami-inspired crack trapping methods have been recently reported for enhancing the peeling resistance of the adhesive patch. Simple cut patterns are applied to the overall adhesive patch, altering stiff and compliant regions by changing the bending rigidity, contact width, the characteristic length scale of the stress field, resulting in changing crack directions suddenly, or delaying the crack propagation in a simple manner called “pinning site”. In the same manner, the microfibrillar adhesive structures can trap micro-scale cracks because they contain numerous tiny pinning sites from split contacts of individual pillars. Integrating both kirigami and micropillar structures, the adhesive patch can have synergetic crack trapping effects. Micropillar structures have strong advantages of normal adhesion and breathability. Kirigami-inspired macrostructures have strong advantages of peeling resistance enhancement and tunability. As a result, kirigami and micropillar hybrid structures can help air/water permeability for skin and demonstrate a maximum peeling strength that is about 58 times greater than that of a steady-state counter sample. In addition to having excellent flexibility, this hybrid smart adhesive patch can easily follow rounded surfaces, confirming conformal contacts on target surfaces. We finally present a flexible adhesive patch for a wearable strain sensor made of selectively coated low-dimensional conductive nanomaterial (SWCNTs) with kirigami and micropillar hybrid structures. Our previous research reported that the micropillar-based strain sensor can distinguish between a strain and normal pressure simultaneously, which allows it to detect a strain with greater accuracy. Using the selective coating method, SWCNTs are uniformly coated on the overall adhesive patch, except the direct contact part with target surfaces, to maintain adhesion and peeling strength. Moreover, with the hybrid adhesive patch, the strain sensor was successfully attached to the curved target surfaces without any complete detachment while the external bending stress was imposed repeatedly about 230 times. We have verified that the strain sensor works with the physical motion monitoring attached to a human wrist by using it in this application.

Fabrication of Wet-Responsive Bioinspired Adhesives and Their Applications

Hoon Yi Graduate School of UNIST 2020 국내박사

Inspired by the fascinating adhesion properties of various creatures in nature, various bioinspired adhesives have been developed. Since the bioinspired adhesives exhibit excellent adhesion strength and reversible adhesion, they have strong potential for a wide variety of applications including wearable devices, nanoscale manufacturing techniques, and soft robotics. However, the bioinspired adhesives made of conventional elastomeric materials have limited adhesion strengths to rough surfaces and limited controllability on adhesion strengths, which limits their practical applications. As the challenges mainly result from the fixed physical property (e.g. elastic modulus of material) of the elastomer-based adhesives, utilization of stimuli-responsive materials that enable active modulation of their mechanical properties on demand is expected to be an effective solution overcoming the limitations. Wet-responsive hydrogels are tunable in their shape, volume, and mechanical properties based on hydration/dehydration in an active and reversible manner. Therefore, it is expected that bioinspired adhesives made of the wet-responsive hydrogels could overcome the aforementioned challenges. In this dissertation, we propose wet-responsive bioinspired adhesives made of hydroxypropyl cellulose (HPC) hydrogel and polyethylene dimethacrylate (PEGDMA) hydrogel that exhibit superior surface adaptability and high adhesion-on/off switchability, respectively. For superior adaptability, a bioinspired adhesive comprised of wet-responsive HPC is proposed as it enables adaptation to a rough surface due to its controllable swelling behavior. By hydration/dehydration, the elastic modulus of the HPC hydrogel can be modulated on demand. In the presence of a small amount of water, the individual bioinspired HPC microstructures in the adhesive can be easily deformed along the rough surface with the decreased elastic modulus of the HPC. As dehydrated, the elastic modulus of HPC microstructures is recovered with maintaining the deformed morphology. Through these processes, the surface roughness-adapted HPC adhesive exhibits strong adhesion strength. Furthermore, the adaptable HPC adhesive is reusable as the deformed microstructures can recover their original shapes based on a shape-memory capability of HPC. In order to develop the bioinspired adhesive that exhibits actively controllable and switchable adhesion on demand, PEGDMA hydrogel with swelling behavior is utilized as it has shape-reconfigurable property. The prepared PEGDMA adhesive shows high adhesion strengths against substrates with the aid of bioinspired nano‐ or microstructure array in the dry state (adhesion-on state). When the adhesive is exposed to water, a hydration‐induced shape transformation of the array and macroscopic film bending occur, switching the adhesion off with an extremely high adhesion switching ratio. Also, the switchable adhesion behavior of the adhesive is maintained over repeating cycles of hydration and dehydration, indicating their ability to be used repetitively. As the rough surface adaptation and adhesion on/off properties of the developed adhesives only require water droplets, they have a wide range of applications in diverse fields. Specifically, the adhesives have a strong potential for use in a biomedical field as the HPC and PEGDMA hydrogels are biocompatible. Accordingly, we demonstrate several unique biomedical practical applications of the developed adhesives. Firstly, with the adaptable HPC adhesive, an attachable photonic skin is developed as a wearable skin-like sensor. The photonic skin consisting of an HPC mechanochromic sensor and the adaptable adhesive can firmly laminate to diverse substrates including human skins, detecting mechanical signals from various target objects. Secondly, the adhesion-switchable PEGDMA adhesive is utilized for a nanotransfer printing (nTP). We demonstrate that diverse metallic and semiconducting nanomembranes can be transferred from donor substrates to either rigid or flexible surfaces including biological tissues with the PEGDMA adhesive in a reproducible and robust fashion. In total, this dissertation presents the fabrication of wet-responsive bioinspired adhesives and their applications. The overall contents consist of three main themes, that are as follow: (1) fabrication of bioinspired adhesives with optimized geometries, (2) rough surface-adaptable adhesive made of wet-responsive HPC hydrogel and (3) adhesion-switchable adhesive made of wet-responsive PEGDMA hydrogel.

Gelatin-based Zinc Ion-releasing Bioadhesives for Wound Management

김성은 인천대학교 일반대학원 2023 국내석사

The need to deal with various diseases, the rising number of surgical cases, and the growing aging population drive the demand for wound care and healing products. Wound management has become a big issue in the wound care market, especially as wound dressings such as sutures, gauzes, films, and hydrogels are developed to achieve ideal wound management. However, there are still disadvantages to overcome, including weak adhesion, incomplete hemostasis, and difficulty in treating irregular wound sites. Therefore, tissue adhesives are attracting much attention in clinical applications due to their excellent mechanical strength and good adhesive properties at wound sites. Since tissue adhesives contact with the wound in direct, it should be biocompatible and participate in wound healing. Although bioadhesives have been developed through various natural, synthetic, and bioinspired materials, developing bioadhesives that promote wound healing with strong adhesiveness remains challenging. Polymeric hydrogels are a three-dimensional network of hydrophilic polymers. In situ cross-linked hydrogels have a form of hydrogels that can be injected via sol-to-gel phase transition by crosslinking reactions. They can be used as materials for bioadhesives due to their suitable properties such as biocompatibility, biodegradable, high moisture content, controllable release behavior, and easy treatment on irregular wound sites with high adhesiveness. Hence, in situ crosslinked hydrogels have drawn attention from researchers in various biomedical applications. Recently, many researchers have endeavored to develop bioactive hydrogel adhesives with high adhesiveness that can actively intervene in the wound-healing process. They modulate the immune response by releasing bioactive molecules such as growth factors, cytokines, and inorganic elements. Among the inorganic elements, there is growing evidence that zinc ions (Zn2+) play essential roles in wound healing, such as hemostasis, immunomodulation, proliferation, angiogenesis, and collagen deposition. In particular, it has been demonstrated that long-term Zn2+-release can promote wound healing and tissue regeneration by providing an appropriate Zn2+ environment. Herein, we represent Zn2+-releasing adhesive hydrogels via a ZnO2-mediated cross-linking reaction. As ZnO2 is decomposed, Zn2+ is released, and H2O2 is generated as an intermediate product. In situ cross-linked hydrogel network is formed via a ZnO2-mediated disulfide bond formation and thiol-ene reaction between thiolated gelatin (GtnSH) and maleimide-conjugated gelatin (GtnMI). Bioactive hydrogel adhesives had controllable physicochemical properties, including rapid gelation time (3 - 26 sec), mechanical strength (520 - 810 Pa), and proteolytic degradation (completely degraded in 24 hours). We investigated that our hydrogels exhibited prolonged Zn2+ and H2O2 release behavior in a sustained manner for up to 21 days and they were not excessed amounts, which were not expected to be toxic. Notably, we also demonstrated that our biocompatible hydrogels had strong adhesive strength (142 - 165 kPa) than commercial product, fibrin glue (64 kPa) and were effectively attached to various tissue surfaces. Moreover, we evaluated the hemostatic ability of the hydrogels in vivo, showing a high absorption capacity that enhanced the physical barrier effect and induced the efficient hemostatic effect (total blood loss 35 mg). Also, we proved that our adhesive hydrogels relieved an inflammatory response by improving M2 macrophage polarization. In addition, we investigated the capability of hydrogels to promote the wound-healing process through cell infiltration and vascular recruitment via Zn2+-mediated VEGF gene upregulation in vivo. In conclusion, we suggest that our Zn2+-releasing adhesive hydrogels possess great potential as bioactive hydrogel adhesives for wound management.

Bio-Inspired Stimuli-Responsive Smart Adhesive Systems for Macroscopic/Microscopic Applications

Hochan Lee Graduate School of UNIST 2020 국내박사

Smart adhesive systems with actively controllable and switchable adhesions on demand in response to external signals such as temperature, light, humidity, electric current have attracted lots of atterntions thanks to their various potential applications in both of macroscopic and microscopic fields including medical patch, skin adhesive, robotics, transport and transfer, wearble device and so on. Many researches for the realization of smart adhesive systems which can be employed to the broad applications have been widely achieved, however it is still required to develop new smart adhesive systems with high-performance and unique adhesive properties containing high adhesive strength, high on/off switching ratio of adhesion, fast response, low preload, excellent durability, etc. To satisfy the increasing demands for the development a high-performance smart adhesive system, in this thesis, we employed two approaches of the biological mimicry of switchably adherable creatures in nature and the adoption of smart materials. In nature, many creatures having magnificient switchable adhesion systems for their static/dynamic locomotion already exist, such as anisotropic van der Waals force adhesion of gecko, capillary-force adhesion of insects and tree frog, pressure-induced adhesion of octopus. These switchable adhesive systems in nature can be a key to realize newly improved smart adhesive systems by mimicking the adhering mechanism and structures of the creatures. Besides, the adoption of smart materials in smart adhesive systems, where their physical and chemical properties can be significantly changeable by the external stimuli such as thermal, optical, elctrical, acidic, and chemical changes, can give a capability of on-demand control of adhesion to the smart adhesive systems. In this thesis, we introduce the novel platform of high-performance smart adhesive systems with superior adhesive properties, realized by the combination of biological inspiration and smart materials. First in Chapter 1, a definition and various types of smart adhesive systems with the recent research trends, switchable adhesion in nature, adhesive systems inspired by nature, and smart materials for the smart adhesive systems, following a summary of key components in the smart adhesive systems for the practical applications, are briefly introduced. In Chapter 2, an octopus-inspired thermo-responsive smart adhesive pad whose adhesive properties can be controlled on demand by external heat is demonstrated, realized via the combination of thermo-responsive hydrogel, pNIPAM, and microcavity-structured PDMS elastomer. The thermo-responsive smart adhesive pad shows the outstanding adhesive performance with extremely high adhesive strength and on/off ratio of adhesion without any preload and consequently it can be applied to transfer printing of sensitive and fragile semiconducting micro/nanomembranes as microscopic applications. In Chapter 3, an octopus-inspired light-responsive smart adhesive pad with actively controllable adhesion on demand in response to external near-infrared light is introduced, fabricated via the rGO/pNIPAM light-responsive hydrogel composite on microcavity-structured PDMS elastomeric support. The light-responsive hydrogel smart adhesive pad exhibits remotely controllable adhesion and fast response time with excellent adhesive strength and on/off ratio of adhesion. This smart adhesive pad is applied to adhesive patch as macroscopic application. In Chapter 4, the summary and future perspective of our smart adhesive systems are described. Our bioinspired smart adhesive systems realized by stimuli-responsive hydrogel actuations on microstructured elastomeric support can suggest a new concept for a high-performance smart adhesive system to be applied to various practical industries.

Analysis and Measurement of Stress Distributions in Gecko Toes and Synthetic Adhesives

Eason, Eric Verne ProQuest Dissertations & Theses Stanford Universit 2015 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The adhesive pads on gecko toes are complex systems containing structures at different size scales. Each toe is covered in flaps of skin called lamellae, which are in turn covered in arrays of microscopic hair-like structures known as setae. The tip of each seta splits into hundreds of even smaller nanoscale structures (spatulae) which produce adhesion through intermolecular van der Waals forces. Using this adhesive system, geckos can stick to a wide range of surfaces. One of the most interesting properties of gecko adhesive is controllable adhesion. An adhesive is called controllable if the stickiness can be switched on or off so it can be easily and repeatedly attached and detached. In gecko adhesive, the adhesion is controlled by the shear force: geckos can control their adhesive simply by applying a downwards shear force to their toes.In previous work, a controllable synthetic adhesive was developed that used shear force to control the adhesion similarly to gecko adhesive. The synthetic adhesive consisted of wedge-shaped microstructures made of polydimethylsiloxane (PDMS) silicone rubber, known as microwedges. This thesis presents a new micromachining manufacturing process for microwedge adhesives, which produces stronger adhesives with more varied geometries, enabling practical applications such as grasping and climbing devices for robots and humans. In addition, this thesis investigates the distribution of adhesive stress in natural gecko adhesive and synthetic microwedge adhesive through a combination of experimental measurements and theoretical modeling.In order for an adhesive system to produce the maximum possible adhesive force, the force must be uniformly distributed over the adhesive area. However, until now it was unknown how forces are distributed in gecko adhesive. To address this question and gain understanding of the gecko’s adhesive system, the stress distribution over the toes of a live tokay gecko (Gekko gecko) was measured using a custom optical tactile sensor with 100 µm spatial resolution based on frustrated total internal reflection (FTIR).Additionally, the stress distribution in the synthetic microwedge adhesive is investigated with a theoretical model that describes the elastic deformation and adhesive interactions of adhesive microstructures. Adhesion is modeled using a cohesive zone model, where the normal and tangential forces generated along the side of the microwedge depend on the separation distance between the microwedge and the surface. Deformation is modeled using a geometrically exact beam model, where the microwedge is treated as a tapered beam undergoing bending, axial, and shear deformation. This modeling approach accurately reproduces the limit curve in force space of microwedge adhesive, describing the relationship between normal and shear force that gives rise to controllable adhesion.In both the tokay gecko toe and the synthetic adhesive, the stress distributions were found to be nonuniform. In the gecko, the normal stress varied significantly at the lamella scale, with compressive stresses observed in some areas even though the net stress over the toe was tensile. Likewise, the model predicts that the normal stress on an adhesive microwedge varies from tensile to compressive along the adhesive interface, with a net stress that is several times smaller than the maximum stress. If the stresses were distributed uniformly, both systems would be capable of supporting much larger loads (around 20 times larger for tokay gecko toes and 5 times larger for microwedges).The proposed model may be useful in evaluating new microwedge structures with modified geometry in order to design a structure that distributes stress more uniformly. Along with the capabilities of the new micromachining process, this could lead to the development of stronger controllable adhesives.

Effect of zwitterionic resin-based adhesive on biofilm resistance at the interface of the orthodontic bracket and tooth

Kim, Eun Ju 연세대학교 일반대학원 2026 국내박사

In orthodontic treatment, the complex structure of the orthodontic bracket-adhesive-tooth interface can cause the formation of biofilm and enamel demineralization. Resin-based composite is a commonly used orthodontic adhesive and has effective bonding strength. But it is vulnerable to biofilm adhesion due to the basic characteristic of composite resin. Resin-based materials incorporated with polybetaine amphiphilic ions such as 2-methacryloyloxyethyl phosphorylcholine (MPC) and sulfobetaine methacrylate (SBMA) can inhibit bacterial adhesion and formation of biofilm. Zwitterionic molecules (MPC or SBMA) can form a hydration shell, which can prevent nonspecific adsorption of proteins. Therefore, the purpose of this study was to develop an orthodontic adhesive containing a polybetaine zwitterions mixture with biofilm-resistance effect. For the aim of this study, physical and mechanical properties of orthodontic adhesive with zwitterionic mixture were characterized, and effectiveness of resistance to bacterial adhesion in the complex bracket-adhesive-tooth interface was investigated. Two types of zwitterionic powders, MPC and SBMA (MS), were blended in different weight percentages (1 wt% and 3 wt%) to prepare the experimental groups, designated as MS1 and MS3, respectively. A control group (MS0) without adding zwitterionic complexes was also included. The fundamental properties as an orthodontic adhesive were confirmed by measuring flowability, shear bond strength (SBS) and adhesive remnant index (ARI). Also, the wettability of each adhesive was evaluated by measuring the contact angle. In addition, scanning electron microscopy analysis to examine the cross-sectional surface of enamel with bonded brackets. To evaluate the attached bacteria between orthodontic adhesive and surface of teeth, the sterilized specimens in human saliva and MacBain medium, after incubating for 48 hrs, were analyzed by mean fluorescence intensity (MFI) in a region of interest (ROI) using confocal laser scanning microscopy (CLSM). There were no significant differences in flow among groups (P > 0.05), with values below 17 mm for all groups. SBS was highest in the MS0 group and decreased significantly with higher MS content (P < 0.001). MS3 showed a significantly lower contact angle compared to MS0 (P < 0.01). SEM images showed uniform bonding without any gaps between the bracket and tooth surface. MS3 exhibited reduced biofilm formation and lower fluorescence intensity, indicating better bacterial resistance (P < 0.05). In conclusion, the orthodontic adhesive containing a zwitterionic mixture meets clinical requirement and resist biofilm adhesion. Despite reductions in SBS, all adhesives remained at minimum acceptable levels. The 3 wt% zwitterionic adhesive effectively suppressed biofilm formation. 교정치료 시 브라켓과 접착제 그리고 치면 사이에서는 구강 위생 관리가 제한적이므로 세균성 바이오필름이 쉽게 형성되어 법랑질 탈회가 발생할 수 있다. 레진 계열 접착제는 브라켓 접착 시 흔히 사용되는 재료이며 강한 결합력을 보여주는 반면, 복합레진의 특성상 바이오필름의 부착에 취약하다. 양극성 이온을 포함하는 레진 계열 접착제는 치면에서의 세균 부착을 방지하여 바이오필름의 형성을 억제할 수 있다. 양극성 이온은 재료 표면에 수화층을 형성함으로써 단백질의 부착을 제한하는 특성을 지니고 있음이 알려져 있다. 본 연구의 목적은 바이오필름 형성을 억제하는데 효과적인 폴리베테인 양극성 화합물이 함유된 교정용 접착제를 개발하는 것이다. 폴리베테인 양극성 화합물을 포함하고 있는 교정용 접착제가 임상적으로 요구되는 접착제의 기계적 특성을 충족하는지 확인하고, 교정용 브라켓과 접착제 및 치아 표면의 복합 구조에서 세균의 부착을 억제하는데 효과적인지 분석하는 것이다. 교정용 접착제에 양극성 이온 화합물인 2-methacryloyloxyethyl phosphorylcholine (MPC)와 sulfobetaine methacrylate (SBMA)의 혼합물을 1, 3 wt%로 첨가하여 실험군 (MS1과 MS3)으로 설정하였고, 양극성 이온 화합물을 첨가하지 않은 교정용 레진 접착제를 대조군 (MS0)으로 설정하였다. 실험을 위한 각 샘플들이, 교정용 접착제가 갖춰야 할 기계적 특성에 부합하는지 평가하기 위하여 흐름성을 측정하고 전단결합강도 및 접착제 잔류지수를 분석하였으며 젖음성을 평가하였다. 또한 주사전자현미경을 이용하여 브라켓이 부착된 치아의 접착단면을 관찰하여 접합정도를 알아보고 미세누출 여부를 관찰하였다. 접착단면을 살펴본 후 이 부위에 부착된 세균의 양을 평가하기 위하여 타액과 McBain 용액에 멸균된 실험 표본을 넣어 48시간 동안 배양한 후 공초점 레이저주사현미경을 이용한 표면형광강도 분석을 수행하였다. 대조군과 실험군의 흐름성은 17 mm 이하로 측정되어 통계적으로 유의한 차이를 나타내지 않았다 (P > 0.05). 전단결합강도의 값은 대조군에서 가장 높았고, 양극성 이온 화합물의 함유 농도가 증가함에 따라 감소하는 경향을 보였다 (P < 0.001). MS3 그룹은 대조군에 비해 통계적으로 유의하게 접촉각이 작았다 (P < 0.01). 대조군과 실험군 모두에서 치면 접착에서의 간극이 관찰되지 않았으며, MS3 그룹에서 바이오필름 형성과 형광강도가 감소한 것으로 나타났으므로 세균 저항성이 가장 높다고 할 수 있다 (P < 0.05). 결론적으로, 양극성 이온 화합물을 함유한 교정용 접착제는 전단결합강도가 감소하였으나 임상적으로 사용이 가능한 기계적 특성을 지니며 바이오필름의 부착을 억제하는 효과를 나타내었다. 3 wt%의 양극성 이온 화합물을 함유하고 있는 레진 접착제는 바이오필름 형성을 감소시킬 수 있다.