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March 12, 2012

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Device makes 3-D objects with “nano-precision”

March 12, 2012
Courtesy of Vi­en­na Uni­vers­ity of Tech­nol­o­gy
and World Science staff

A tech­nol­o­gy for manu­fac­tur­ing three-di­men­sion­al ob­jects with in­credibly fi­ne de­tails now works faster than ev­er be­fore, re­search­ers have an­nounced.

The “high-precision-3D-printer” at the Vi­en­na Uni­vers­ity of Tech­nol­o­gy is hun­dreds of times faster than si­m­i­lar de­vices, open­ing up new ar­eas of ap­plica­t­ion in­clud­ing med­i­cine, ac­cord­ing to the de­vel­op­ers.

A min­ia­ture ver­sion of St. Stephen's Ca­the­dral, Vi­en­na, cre­at­ed by two-photon li­thog­ra­phy. The hor­i­zon­tal line be­neath the pic­ture rep­re­sents a dis­tance of 50 micro­me­ters, or thou­sandths of a mil­li­me­ter. (Cour­te­sy U. of Vi­en­na)

In the tech­nique, ob­jects are cre­at­ed out of a liq­uid res­in that’s hard­ened at just the right spots by a fo­cused la­ser beam. Its fo­cal point is guid­ed through the syr­upy liq­uid by mov­a­ble mir­rors and leaves be­hind a hard­ened line of sol­id pol­y­mer, or plas­tic, just a few ten-thousandths of a mil­li­me­ter wide. The re­sults are fi­nely struc­tured sculp­tures as small as a grain of sand. 

“Un­til now, this tech­nique used to be quite slow,” said ma­te­ri­als sci­ent­ist Jür­gen Stampfl at the uni­vers­ity. The speed “used to be meas­ured in mil­li­me­ters per sec­ond – our de­vice can do five me­ters in one sec­ond,” a rec­ord for the tech­nique, called two-photon li­thog­ra­phy, he added.

The prog­ress was made pos­si­ble by com­bin­ing sev­eral new ideas. “It was cru­cial to im­prove the steer­ing mech­an­ism of the mir­rors,” said col­la­bo­ra­tor Jan Torg­ersen at the uni­vers­ity. The mir­rors are con­tin­u­ously mov­ing dur­ing the pro­cess, and their ac­celera­t­ion and de­celera­t­ion must be tuned very pre­cisely, he not­ed.

A tiny sculpture of a race car, 285 micro­me­ters long (Cour­te­sy U. of Vi­en­na)

“The res­in con­tains molecules, which are ac­ti­vat­ed by the la­ser light,” Torg­ersen added. “They in­duce a chain re­ac­tion in oth­er com­po­nents of the res­in, so-called monomers, and turn them in­to a sol­id.” The in­i­ti­a­tor mo­le­cules are only ac­ti­vat­ed if they sim­ul­ta­ne­oly ab­sorb from the beam two pho­tons, or light par­t­i­cles. This only hap­pens in the cen­ter of the beam, where the in­tens­ity is high­est. 

Oth­er tech­niques for manu­facturing such tiny 3-D objects exist, both in de­vel­op­ment and in in­dus­t­ri­al use. The tech­no­lo­gies generally go under the moni­ker “3-D printing,” due to si­mi­larities to ac­tual print­ing meth­ods. The ad­van­tage of this one is that sol­id ma­te­ri­al can be cre­at­ed an­y­where with­in the liq­uid res­in rath­er than only on top of a pre­vi­ously cre­at­ed lay­er, the de­vel­op­ers said. A team of chemists led by Rob­ert Liska at the uni­vers­ity de­vel­oped the in­gre­di­ents for the spe­cial liq­uid. Sci­en­tists at the school are al­so de­vel­op­ing res­ins that are bi­o­log­ic­ally com­pat­ible so that the two-photon li­thog­ra­phy could be used for med­i­cal de­vices, pos­sibly in­clud­ing ar­ti­fi­cial or­gans.

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A technology that allows for printing out three-dimensional objects with incredibly fine details now works faster than ever before, researchers have announced. A high-precision-3D-printer at the Vienna University of Technology is hundreds of times faster than similar devices, opening up new areas of application such as in medicine, according to the developers. In the technique, objects are created out of a liquid resin that’s hardened at precisely the correct spots by a focused laser beam. The focal point of the beam is guided through the syrupy liquid by movable mirrors and leaves behind a hardened line of solid polymer, or plastic, just a few ten-thousandths of a millimeter wide. The results are finely structured sculptures as small as a grain of sand. “Until now, this technique used to be quite slow”, said materials scientist Jürgen Stampfl at the university. “The printing speed used to be measured in millimeters per second – our device can do five meters in one second,” a record for the technique, called two-photon lithography, he added. The progress was made possible by combining several new ideas. “It was crucial to improve the steering mechanism of the mirrors,” said collaborator Jan Torgersen at the university. The mirrors are continuously moving during the printing, and their acceleration and deceleration must be tuned very precisely, he noted. “The resin contains molecules, which are activated by the laser light,” Torgersen added. “They induce a chain reaction in other components of the resin, so-called monomers, and turn them into a solid.” The initiator molecules are only activated if they simultaneously absorb from the beam two photons, or light particles. This only happens in the center of the beam, where the intensity is highest. There are other 3D-printing techniques, both in development and in industrial use. The advantage of this one is that solid material can be created anywhere within the liquid resin rather than only on top of a previously created layer, the developers said. A team of chemists led by Robert Liska at the university developed the ingredients for the special liquid. Scientists at the school are also developing resins that are biologically compatible so that the two-photon lithography could be used for medical devices, possibly including artificial organs.