具熱響應之聚(N-異丙基丙烯醯胺)/瓊脂糖互穿式水凝膠的特性與應用

Abstract

自1956年來聚(N-異丙基丙烯醯胺)在生醫領域的研究不斷地推陳出新，其受溫度刺激響應的特性也使對它的應用與研究跨足了其它如物理學、環境科學、能源等領域，聚(N-異丙基丙烯醯胺)是屬於一種具有可逆體積相變過程的材料，因為其結構上的功能性官能基團會受溫度高低而選擇與水分子或自身產生氫鍵，由此達到親疏水性轉換與發生體積相變。為了提高應用性，先前的研究將其合成互穿式高分子網路的水凝膠，同時保有溫敏性與加強機械性質或增加其他的響應模式。 本研究開發出兩種不同型式的水凝膠，一種是用浸潤法使聚(N-異丙基丙烯醯胺)分子擴散進瓊脂糖的網路基底形成半互穿式高分子網路，另一種是採用紫外線誘導共聚合法合成出聚(N-異丙基丙烯醯胺-co-聚乙二醇二甲基丙烯酸酯)與瓊脂糖的互穿式高分子網路水凝膠，兩種水凝膠都是將瓊脂糖與聚(N-異丙基丙烯醯胺)做結合，來開拓與以往不同的研究方向。 在本研究中主要分為兩個部分，第一部分為研究了瓊脂糖基底的聚(N-異丙基丙烯醯胺)互穿式高分子網路水凝膠的性質，發現當聚(N-異丙基丙烯醯胺)會改變瓊脂糖水凝膠的溶脹特性，比起純的瓊脂糖水凝膠在溶脹平衡時可以保有更多水分。另外，聚(N-異丙基丙烯醯胺)也會改變透射度與機械性質，並且可以用溫度去操控其變化，我們提出了一個模型去解釋這個獨特的現象，當聚(N-異丙基丙烯醯胺)進入水凝膠網路時會因為氫鍵膠護作用而與瓊脂糖支架結合，加強其結構並使折射率匹配，造成有較大的彈性模數與透射度變化，但當溫度高於聚(N-異丙基丙烯醯胺)的濁點時，聚(N-異丙基丙烯醯胺)會改變成與自身或同類分子產生氫鍵，進而改變自身的折射率，而與此同時因為與瓊脂糖網路分離，進而造成機械性質改變。 第二部分為基於前一部分觀測的性質，設計三種不同的加熱方式與應用。第一種應用是基於通過溫度變化可逆地切換機械性能，以通過圖案化加熱系統生產具有不同局部機械強度的材料。第二種應用是智慧隔熱窗戶，它包含了一個可調節透射率的內層，其受紅外線加熱到相變溫度就會自動關閉，使室內不會接收過多的紅外線而升溫。第三種應用則是在水凝膠的表面輸送膠體粒子，當水凝膠表面的聚(N-異丙基丙烯醯胺)分子相變時會將水分排出，故可利用紅外雷射掃描加熱水凝膠表面產生不對稱的流場，發現半互穿式高分子網路水凝膠與互穿式高分子網路水凝膠的產生的流場模式不同。並利用這種不對稱流場加以設計雷射掃描路徑製造出可以排開、聚集與單向輸送膠體粒子的表面流場，最後將材料做成微流道的基底，測試此材料輸送粒子的在微流道中的可行性。

The research of poly(N-isopropylacrylamide) (PNIPAAm) has been persistently innovated in the biomedicine field since 1956. Because of the unique thermoresponsivity, the field of research has been also stepped into others, such as physics, environmental science and energy. PNIPAAm is a kind of polymers which exhibit reversible switching between swollen state and shrunken state. Through the functional groups of its structure bounds to water molecules or themselves by hydrogen bonds depending on the temperature, it can achieve hydrophilic-hydrophobic conversion and volume phase transition process. For improving its applicability, the research in previous studies is synthesizing of an interpenetrating polymer network hydrogel to enhance its mechanical properties or add other response modes and maintain thermoresponsivity simultaneously. In this study, two types of IPN hydrogels were developed. One is forming semi-IPN hydrogels by making the PNIPAAm molecules diffuse into the agarose networks as immersing method, the other is synthesized of IPN hydrogels from agarose, NIPAAm monomer and polyethylene glycol dimethacrylate (PEGDA) by ultraviolet‐radiation induced graft‐copolymerization. Both of these hydrogels are combined agarose network with PNIPAAm or its derivative to extend different research directions from the past. In this study, it has been mainly divided into two parts. The first part start with observing the properties of agarose/PNIPAAm s-IPNs or agarose/P(NIPAAm-co-PEGDA) IPNs. PNIPAAm molecules change the swelling properties of hydrogels, and conduce to s-IPNs retaining more water than pure agarose hydrogels when swelling are balanced. In addition, they also change the transmittance and mechanical properties, and both of the properties are switchable by temperature changes. We have proposed a model to explain this unique phenomenon. When PNPAAm molecules diffuse into the agarose network, they will be combined with the agarose scaffold due to the hydrogen bond interaction, leading to strengthen its structure and lead to the refractive index matching, resulting in a large change in elastic modulus and transmittance. If the temperature is higher than the cloud point of this system, PNIPAAm will change hydrogen bonds formation from with water molecules to itself or other the same molecules, thereby changing the hydrogel’s refractive index and mechanical properties. The other part is based on the observed properties of the previous part, designing three kinds of applications by different heating methods. The first application is based on the reversibly switching mechanical properties by temperature changing to produce the material with different local mechanical strengths by patterned heating systems. The second one is smart thermal insulation window, which is involves an interlayer designed by the characteristic of switchable transmittance. When the window is heated to the phase transition temperature by infrared, the interlayer will be automatically close, so that the room will not receive too much the infrared to heat up. The last one is transporting colloidal particles on the surface of the hydrogel. When the PNIPAAm on the surface of the hydrogel change phase by using infrared laser scanning heating, the water will be discharged to generate an asymmetric flow field on the surface. It is found that the flow fields generated on the s-IPN or IPN surface are different. Based on these asymmetric flow fields, the laser scanning path is designed to create their kinds of surface flow fields which lead to colloidal particles repulsion, aggregation or unidirectional delivery. Finally, the material is made into the base of the micro-channel, and the feasibility of particle transport in the micro-channel has been tested.