藻類在細菌纖維素上的生物列印 @Srikkanth Balasubramanian
如果你能造出利用太陽能自供電、完全可回收、100%可生物降解、僅憑存在就能固碳、能過濾空氣中的毒素，並且還是有生命的家居用品——生物服裝、廚房電器，或是百葉窗和窗簾——是不是很妙？荷蘭代爾夫特理工大學（Delft University of Technology）的助理教授瑪麗·奧賓-塔姆（Marie Aubin-Tam）博士和她實驗室的博士後研究員斯里坎特·巴拉蘇布拉馬尼安（Srikkanth Balasubramanian），已經朝著實現這一目標邁進了一步。她們利用藻類創造了一種3D列印的光合作用材料。
瑪麗：“我們的研究興趣是3D列印由微藻製成的活體材料。雖然已經有一些3D列印藻類材料的例子存在了，但我們致力於開發一種在機械效能上足夠堅固，能夠實際應用的材料，因為這類材料大多基於水凝膠，往往非常脆弱。”
你可能沒聽說過水凝膠，但你一定用過。一次性嬰兒紙尿褲、奇亞籽布丁、玩具水珠：這些都是常見的水凝膠。但水凝膠的強度和硬度都不高，因此研究團隊希望研發出更為優質的材料。瑪麗的實驗室有一臺自制的3D印表機，可以用細菌生物墨水來列印材料，這種生物墨水是一種含有活細胞的溶液，可裝入3D印表機中。
同時，瑪麗他們也在研究一種名為萊茵衣藻
（Chlamydomonas reinhardtii）的微藻，但他們對於萊茵衣藻的興趣點在於它遊動時的物理特性，以及它遊動時如何帶動了周圍的水流。瑪麗想到或許可以將兩者結合起來。他們用活體微藻製成生物墨水，並將其列印在細菌纖維素上——一種可由細菌產生的纖維材料，生長於細菌培養物表面生長，剛產生時是橡膠狀薄膜，但乾燥後則像堅韌的紙張。
實驗方法中的巧妙之處在於，藻類生物墨水只有在接觸到氯化鈣時才會凝固。因此，瑪麗他們以細菌纖維素和氯化鈣為基底，將海藻酸鈉和微藻組成的生物墨水作為列印材料在基底上方進行列印。當藻類墨水被列印在細菌纖維素紙頂部時，它會接觸到擴散來的鈣並凝固，形成固定微藻細胞的海藻酸鹽水凝膠。
這種方法在第一次試驗中就立刻見效了，瑪麗和同事又接著嘗試了不同的條件，不同的設計，並測試了這種材料的機械效能。
細菌纖維素紙像襯墊一樣附著在列印品上，為打印出來材料提供了比單純的水凝膠列印更高的強度，讓它能夠承受扭曲和擠壓。這種材料自身可存活3天，如果每隔幾天給微藻們補充營養，就能將維持時間延長到一個月甚至更久。它能在光照或黑暗環境中儲存，溶解後完全可生物降解，藻類可被取出並直接放回印表機中，用於製造更多材料。
列印成型後，它的體積不會隨時間推移而顯著增加，但細胞數量會增多，葉綠素含量也隨之增加。最重要的是，整個列印過程的成本相對較低。
斯里坎特表示，他們的3D列印方法最大的優勢之一就是它非常經濟實惠。對於市場上已有的能夠列印活細胞的3D印表機，它們的價格範圍通常在幾萬到幾十萬人民幣之間，但他們的3D印表機僅需
……[檢視全文]New 3-D-Printed Material Is Tough, Flexible—and Alive
Sarah Vitak: This is Scientific American’s 60-Second Science. I’m Sarah Vitak.
What if you could create household objects—maybe bio-garments, kitchen appliances, or blinds and curtains—that powered themselves using the sun, were fully recyclable, 100 percent biodegradable, sequestered carbon just by existing, filtered toxins out of the air and were also—alive? Dr. Marie Aubin-Tam at Delft University and a postdoc researcher in her lab, Srikkanth Balasubramanian, have gotten one step closer to making that a reality. They have created a 3-D-printed photosynthetic material using algae.
Here is Dr. Aubin-Tam.
Marie Aubin-Tam: We were interested in 3-D printing living material that’s made of microalgae. And there were a couple examples of 3-D-printed algae material already out there, but we were interested in making one that will be enough mechanically robust to be used in real applications because a lot of these materials are based on hydrogels, which tend to be very fragile.
Vitak: You might not have heard of hydrogels, but you’ve certainly used them. Wet, disposable baby diapers, chia pudding, toy water beads: all of these are hydrogels you might have around your house. But hydrogels aren’t very strong or solid, so the team wanted to make something better.
They already had a 3-D printer that they had built in their lab to print materials with bacterial bioink—a solution that contains living cells that you load in a 3-D printer.
Aubin-Tam: We were also studying the microalgae Chlamydomonas reinhardtii but for a different purpose. We’re interested in the physics of how it swims and how it moves the flow around itself when it swims.
Vitak: They had the idea that maybe they could put the two together. They created a bioink out of the living microalgae and printed it onto bacterial cellulose—a fibrous material that can be produced by bacteria. It grows as a rubbery film on top of bacterial cultures, but when it’s dried out, it is like a tough paper.
The clever part of their method is that the algae bioink won’t solidify until it comes into contact with calcium chloride. So they put it in agar on a petri dish, then place the bacterial paper above and print on that. When the algae ink is printed on top of the paper, it comes into contact with the calcium that is diffusing through and solidifies.
Aubin-Tam:
It almost immediately, I think the first trial, it immediately worked. So we thought that it was very promising. And then, yeah, we tried different conditions, different designs. And then we test the mechanical properties of this material.
Vitak: The bacterial paper stays on the print like a backing and provides the material with more strength than hydrogel prints alone. It can handle twisting and crushing. The material can survive three days on its own and at least a month (probably longer) if fed with nutrients every couple days. It can be kept in light or dark. And it can easily be dissolved, and the algae can be removed and placed right back in the printer to make more material. And, of course, the material can also be dissolved and then is fully biodegradable.
The printed material won’t grow noticeably in volume over time, but the number of cells increase and so does the amount of chlorophyll. Best of all, this process is relatively inexpensive. Here is Dr. Balasubramanian.
Srikkanth Balasubramanian: And one biggest advantage of our approach with a 3-D printer is that it is really cost-effective because if you consider 3-D printers that are already available in the market that can print living cells, they are like they are in the price range of thousands to hundreds of thousands of dollars, but our 3-D printer is just like less than…[full transcript]
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