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4D printing untethered hydrogel soft robots for cargo delivery

4D printing untethered hydrogel soft robots for cargo delivery
Saeeun Jang
DGIST Authors
Saeeun JangSukho ParkHoe Joon Kim
Hoe Joon Kim
Issued Date
Awarded Date
4D printing; Hydrogel actuators; Soft robots; Stimuli-responsive hydrogel; Cargo delivery
Stimuli-responsive hydrogel have been utilized as materials for hydrogel actuators capable of wireless control in transporting objects. However, the production of complex 3D structures using molding or photolithography methods has been challenging. Actuators in the form of simple 2D grippers made using conventional methods have limitations in the shapes and sizes of objects that can be transported. Therefore, 4D printing has emerged as a method that is simple, repeatable, and allows for easy stacking of complex structures. However, 4D printed actuators have mainly focused on the printability of materials or complex shape transformations rather than performing tasks such as transporting cargo, and still face limitations in the size and shape of objects that can be transported.
To overcome these limitations, the untethered milli-gripper with six-arms was fabricated using a DIW 3D printer. The gripper can undergo bending deformation by swelling and shrinking through an electric field and can be moved to a desired position through a magnetic field. The untethered milli-gripper initially exists in a 2D plane state and transforms into a 3D state through bending deformation when an electric field is applied, providing a very large bending angle, allowing cargo delivery with any shape, size, or number. In addition, it was confirmed that the gripper can be made from biodegradable and biocompatible materials for application in the field of biomedical engineering. After 5 weeks, the remaining citric acid coated SPIONs that were biodegraded were found to be biocompatible, indicating that they can be used for various purposes in the field of biomedical in the future.
In addition, we overcame the limitations of existing grippers for cargo delivery by creating a structure that grasps cargo not by gripping, but by enclosing them, combining a lid with a cross-shaped hole and a hemisphere structure with an empty space. The lid part was made of a temperature-responsive hydrogel that can adjust the opening and closing of the cross-shaped holes depending on the temperature. Therefore, by irradiating NIR, it is possible to raise the temperature and control the opening and closing of the entrance, and an actuator that could move to the desired position using a magnetic field was developed. Since it is a structure that can be enclosed, it was demonstrated that objects of any shape or quantity can be enclosed, and even small living organisms can be safely transported. This research suggests that, through the analysis of the rheological properties of ink, 4D printing at high resolution is possible, and depending on the requirements of the application field, it can be utilized as a soft actuator that can respond to various external stimuli, including temperature and magnetic fields, by changing the type of stimuli-responsive hydrogel.
|외부자극 감응 하이드로겔은 외부 자극에 대해 무선 제어가 가능하다는 점에서 물체 운송을 수행하는 하이드로겔 액츄에이터의 재료로 활용된다. 그러나, 몰딩이나 포토리소그래피로 제작된 액츄에이터는 제작 방법의 한계로 인해 복잡한 3D 구조의 형태는 제작이 어려웠다. 기존의 방법으로 제작된 2D 집게 형태의 액츄에이터는 운반할 수 있는 물체의 모양과 크기가 제한적이었다. 따라서 간단하고 반복 가능하며 복잡한 구조의 적층이 용이한 4D printing이 등장하게 되었다. 하지만 4D printing으로 제작된 액츄에이터들은 물체 운송과 같은 역할을 수행하기 보다는 재료의 printability나 복잡한 형상변환에만 연구가 집중되어왔고, 보고된 화물 운반을 수행하는 4D printed 액츄에이터는 여전히 운반할 수 있는 물체의 크기나 형태에 제한을 받고 있다.
이러한 한계점을 극복하기 위해, 6개의 팔을 갖는 무선 밀리 그리퍼를 제작하였고, DIW 방식의 3D 프린터로 제작되었다. 전기장에 의해 팽창 및 수축을 겪어 굽힘 변형이 가능하고, 자기장에 의해 원하는 위치로 이동이 가능하다. 무선 밀리 그리퍼는 초기에는 2D 평면 상태로 존재하다가 전기장이 입력되면 굽힘 변형을 겪으면서 3D 상태로 변하고, 굉장히 큰 굽힘 각도를 제공하기 때문에 cargo의 모양이나 크기, 개수에 제한 받지 않고 운송할 수 있음을 입증하였다. 또한, 생체의료학에 응용될 수 있도록 생분해되며 생적합한 재료로 제작되었으며, 5주에 걸쳐 생분해 된 후 남은 구연산 코팅된 산화철 입자는 생적합하기 때문에 추후, 생체 내 의료 분야에 다양한 목적으로 수행될 수 있음을 확인하였다.
또한, 십자가 형태의 구멍이 있는 뚜껑과 빈공간이 존재하는 반구 구조체를 결합시킨 구조를 제작함으로써 물체를 집는 것이 아니라 담지하는 형태로 제작하여 기존 그리퍼의 물체 운송 한계점을 극복하였다. 뚜껑 부분은 온도감응 하이드로겔로 제작하여 온도에 따라 십자가 형태 구멍의 개폐 조절을 할 수 있도록 하였다. 따라서 근적외선을 쬐어주면 온도가 올라가 입구 부분의 개폐 조절이 가능하고, 자기장을 이용해 원하는 위치로 이동이 가능한 액츄에이터를 제작하였다. 빈 공간에 담지 할 수 있는 형태 이기 때문에 담지하고자 하는 물체의 모양이나, 개수에 제한 받지 않고, 작은 크기의 살아있는 생명체도 안전하게 운반 가능함을 입증하였다. 이 연구는 잉크의 유변학적 특성 분석을 통해 고해상도로 4D printing 가능하기 때문에 응용 분야의 요구사항에 따라 자극 반응성 hydrogel의 유형을 바꾸어 온도 뿐만 아니라 다양한 외부 자극에 감응하며 자기장 응답이 동시에 가능한 soft actuator로도 활용될 수 있는 가능성을 제시한다.
Table Of Contents
Ⅰ. Introduction 1
Ⅱ. 4D printing of biodegradable and biocompatible untethered milli-gripper using electro and magneto-active hydrogel 6
2.1 Background and motivation 6
2.2 Experimental section 11
2.2.1 Materials 11
2.2.2 Methods 11
Synthesis of the citric acid coated SPIONs 11
Hydrogel ink for 4D printing 11
Untethered milli-gripper 3D printing protocol 12
Measurement swelling ratio of the untethered milli-gripper 13
Biocompatibility test of the untethered milli-gripper 13
Biodegradability test of the untethered milli-gripper 14
2.3 Result and discussion 15
4D printing process of the untethered milli-gripper 15
Characterization of the citric acid coated SPIONs 24
Various magnetic locomotion of the untethered milli-gripper 27
Bending behavior of the untethered milli-gripper 29
Cargo delivery test of the untethered milli-gripper 36
Biocompatibility and biodegradability test of the untethered milli-gripper 44
2.4 Conclusion 48
Ⅲ. Multi-material 4D printing of hydrogel carrier actuated by NIR and magnetic stimulus 50
3.1 Background and motivation 50
3.2 Experimental section 56
3.2.1 Materials 56
3.2.2 Methods 56
Synthesis of the citric acid coated SPIONs 56
Synthesis of printing multi-inks 57
Rheological measurement of multi-inks 57
3D printing protocol 58
3.3 Result and discussion 59
Rheological properties of multi-inks and 4D printing parameters setting 59
4D printing process and results 68
Characterization of the citric acid coated SPIONs 70
Temperature responsive characterization of the hydrogel carrier 72
Various magnetic manipulation of the hydrogel carrier 80
Cargo delivery test of the hydrogel carrier 82
Various application of the hydrogel carrier 88
Robustness test of the hydrogel carrier on external disturbance 90
Difference between hydrogel carrier and previous hydrogel gripper 93
3.4 Conclusion 97
IV. Future work 99
V. References 101
요약문 115
Department of Robotics and Mechatronics Engineering
Related Researcher
  • 박석호 Park, Sukho 로봇및기계전자공학과
  • Research Interests Biomedical Micro/Nano Robotics; Biomedical Devices and Instruments
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