6.2 Pressure driven Microsyringe

Transcription

1 . Pessue diven Miosyinge Te deposition system developed t Cento Intediptimentle di ie E. Piggio t te Univesity of Pis onsists of stinless steel syinge wit mion glss pilly needle (fig.) [, ]. Te needle is onneted to te syinge el nd eld in ple y smll o-ing. A solution of te polyme in voltile solvent is pled inside te syinge, wi s pity of out ml. Fig. Pofiles of needle tip Te syinge, wi s no plunge ut is diven y filteed ompessed i t pessue of out mmhg, is fitted to te z-xis of -xis steppe-moto miopostioning system wit esolution of. mion. A pln sustte, genelly glss slide of dimensions X m, is fixed on te x nd y xes of te miopositione, nd is mde to move unde te syinge duing deposition. In peliminy expeiments, it ws setined tt te most epoduile tenique fo otining smoot, even mio-sized pttens ws to pply low nd onstnt pessue (te tn pulsed pessue) to te syinge nd to llow te polyme to e dgged oss te sufe of te sustte, mu like witing wit n ink pen. Dops of polyme e dwn long te sustte, keeping te syinge tip just ig enoug to ensue tt it does not ontt te sustte. A semti illusttion of te pessue ontolled deposition system is sown in figue. Eletoni pessue egulto Compessed Ai Mio syinge Positioning pltfom Fig. Semti illusttion of te pessue ontolled deposition system 8

2 Te entie system inluding vlves, pessue sensos nd position ontolles is intefed to nd ontolled y PC toug GPIB d. Appopite softwe to dive te system, witten in C, llows simple pttens su s lines, etngul, exgonl o tingul gids, nd spils to e deposited. Moe omplex pttens e esy to design nd inopote into te softwe. Te pessue senso nd ssoited ontol system llows te pplied pessue to e ontolled to witin ±mmhg, nd te veloity of te sustte wit espet to te syinge to e vied etween. nd. mm/s. E polyme onenttion ws deposited in vious onditions of pplied pessue nd x, y moto veloity in ode to detemine nge of optimum opeting onditions. DP system Te DP system is omposed of tee motoized plnes mounted on oust luminium suppot to fom tee xes noml to e ote. Te system ws pojeted wit CAD softwe (fig.). Evey plne is tuted y fou pses ipol steppe moto wit n ngul esolution of.8 /step, dovetiled to sew wit. mm step, tt tnsfoms te line motion into ngul motion wit menil oeffiient equl to.88 µm/. Tis solution deeses lmost ompletely te menil ply in te pesene of invesion of motion nd it is le to ensue ig level of pessue even in pesene of ig eletions. Steppe motos wee osen euse tey do equie expensive position sensos. Inft, if diven oetly, it is possile to detemine position of te slide t evey instnt wit ig degee of uy, if te end position is known wen te system is eset. Te dive od Fig. Menil stutue pojeted wit CAD softwe Te teistion equied of te steppe moto dive fo te system wee s follows: to e le to give uent of. Amps 9

3 to give peision of. µm miostep opetion to e esily onnetle wit ontol od to e menilly omptile wit k stndd 9 DIN 9, tt ontins ll eletoni devies utilised. Te ontol od, instlled in PC, nd dopted in tis system gives mjo flexiility nd llows ompete feedk. Tis od llows simultneously ontol of pi of motos in synonous mode o in n intepolted mnne. Tis ltte metod llows synonizing te movement of xes in su wy, tt fo e eletion te veloity nd motion dietion seleted, te pofile of te omined motion is lwys etiline. Tis od s miopoesso DSP nd is le to utonomously detemine te optiml sequene of impulses fo pefet ontol of te motion of e moto, esponding ontempoily to te ommnd sent to te PC us wit speifi two pots eseved I/O. At ny instnt te motion pmetes nd te tjetoies to follow n e estlised nd modified. Softwe wit te possiility of poviding onstnt feedk nd wit wi te opeto n see nd t on te deposition pmetes in el time duing miofition poess ws developed. Fo e moto, sequene of vile fequeny impulses e geneted y te dive od oding to te ommnds sent toug te I/O od of te PC. Pessue egulto Te mio fition tenique wit te pessue diven mio syinge needs soue of ompessed i, wose pessue n e egulted wit exteme peision. Tis teisti ws otined using n utomti pessue egulto ontolled y n integted miopoesso. Wit tis devie it is possile to: ve pessue nge of -.9 MP; pogmme it toug keyod ommnds visulize te imposed pessue in MP on digit disply Te pessue egulto is onneted to te PC wit n AD/DA od AD/DA od Te AD/DA od s input nd output it nnels. Te dynmi nge fo te nlogue pmete in input is ± V to ± mv. Tis od ws used to ontol te pessue s well s te lse senso, desied in te following. Te output nnel s nge etween to V. Senso lse To esolve te polems onneted wit te non plnity of te sustte nd to edue polem of tip ekge it is neessy vlue wit ig peision nd fo l te plne of mio fition te distne etween te needle nd te sustte. A lse senso ws used to mesue te tip-sustte distne utomtilly onneted to te PC. Te senso sould ve tese teistis: ig esolution low sensitivity to te extenl envionment ig stility pity to opete wit diffeent mteils non-destutive, non-ontt smll dimensions so s to e esily instlled ne te syinge.

4 A system wit lse tingultion ws seleted. Te pysil piniple used is sown in figue. Fig. Opeting piniple of te lse senso. Te ollimted em is inident on te tget o sufe nd te position of te efleted em is deteted y te senso wit get peision. Vitions etween te ligt soue nd te tget e tnsdued into line movement of position of te efleted ligt spot eeived y te senso. Tis infomtion is ten nlysed y n eletoni iuit wit n integted miopoesso in te devie nd onveted into pmete popotionl to te distne. Tis senso s esolution of mion t efeene distne of mm nd n output in uent popotionl to te distne fom te tget. Te senso element is line y CCD t ig esolution tt tnsfoms te ligt infomtion tt ives fom te sufe unde exmintion into n eleti vlue. A omplete seme of te miofition system is sown in figue.

5 AD/DA Pessue egulto Mio- Compute Powe supply Moto ontol od Lse Senso IIS Contol softwe Fig. Te omplete eletoni seme of te miofition system Te miosyinge softwe ws sed on simple onept: te esiest wy to design ptiul stutue is to dw it wit ig peision, ig esolution pen. Fo tis system esy to use softwe wit te following teistis s een developed: possiility to visulize on te seen te ptten to e miofited efoe stt of deposition; edit te ptten wit gpi intefe ting dietly on te dwing of te stutue to deposit; simultion of deposition to visulize ny eos duing te design of te stutue; visulize in one window te stte of te system wit position ontol s well s, of te pessue nd of te lse senso, llowing to te opeto to t on tese pmetes t ny instnt; llow te elistion nd te visulition of D stutues in file mnne nd wit utomti teniques. Te softwe ws developed in Windows wit Visul Studio softwe. Te gpi window tt ppes to te opeto is sown in figue.

6 Fig. Gpi window of te softwe Te deposition plne is sque of side mm nd tis gives esolution of µm pe pixel. At te igt of te deposition plne is te window fo ontol of te elements tt onstitute te ptten nd unde tis ontol tee is window tt llows modifitions nd visulistion of te sptil oodintes eltive to te deposition plne. At te top igt tee is te utton tt stt te deposition pse wi n e el o simulted. Unde tis ottom tee e te ontols of te position of te needle wile elises te stutue. Unde tee is te uttons fo pessue ontol. Te lst utton t te ottom igt in te window is te ontol of te position of te needle eltive to te sustte, deteted wit te lse senso. An impotnt fetue pf tis system is tt te opeto n design stutue wit ptiul geomety, nd tis stutue n e dwn on te softwe, o impoted fom note pogm, nd te sffold n e elised immeditely.. Fluid dynmi model of Miosyinge deposition A fluid-dynmi model, wi enles te pedition of widt nd eigt of te pttens, ws developed. Te model is foused on te onditions t te tip of te needle, just efoe te fluid is expelled. We ssume tt tee is vey simple geomety t te tip, nd tt te fluid exits in te fom of disete dops, wi e emispeil in spe. As sown in figue 7, te foes in ply t te tip wee te dops fom e: te weigt of te dop, mg. te diving pessue, P te dditionl pessue due to vpou pessue of te solvent nd te ed of polyme solution in te pilly needle, P *. te sufe tension etween dop nd glss, γ

7 dynmi fition etween fluid nd glss, wi is funtion of te visosity, µ, of te solution. P * P µ mg s γ Fig. 7 Foes in ply t needle tip Consideing equiliium onditions, we n wite simple system of equtions lning foes nd enegy. Two equtions n tus e otined. v * mg PS µ π γ π osθ P S x (.) * mg PV µ v 8γπ P V mv wee m te mss of te dop, of volume V, density,, nd dius eigt of te dop ove te sustte te dius of te tip; mg γ, [] (.) π θ te ngle of ontt etween solution nd glss nd v is te veloity of te dop. By expessing te mss of te dop s /π, nd going fom Ctesin to ylindil o-odintes, x osφ. We ssume tt tee is no vition in spe of dop nd Φ π, so tt dxd. Tus, we otin:

8 8 os * * P g v P g P g v P g π µ π ϑ µ (.) wi n e expessed s funtion of te dius of te dop v v v wee Eqution. n e integted wit espet to to otin te veloity of te dop s funtion of, te dimete of te tip, giving: K v ln ) ( (.) wi n e sustituted into., giving n eqution tt depends only on. In ode to simplify te eqution, we n ssume ln, sine is smll. An t degee eqution is otined, wi n e witten s: (.) wee: 8 * π π π µ π π P g P g (.) (.) * os P g P g θ µ

9 A MATLAB outine ws witten to solve equtions nd. Te vlue of te onstnt K, fo e pessue, ws otined y esolving eqution fo, wee te veloity of te fluid is zeo (ondition of no-slip of fluid) t te wlls of te tip of te needle. Known vlues of visosity, ontt ngle, density of polyme solution, nd dimete of tip of needle wee input fo nge of pessues (PP*) etween nd mmhg nd oesponding veto of K vlues ws otined. Fo ll pessues gete ten mmhg, K is ppoximtely onstnt fo given polyme solution (etween. - m/s nd. - m/s fo PCL nd etween - m/s nd 7. - m/s fo PLLA). K epesents te limiting vlue of veloity of te dops fo vey smll tip dimetes, nd s expeted deeses wit deesing solution visosity. Te oots of eqution wee found y inputting nge of pessues, PP*, etween nd mmhg. Of te solutions otined, we seleted te el solution tt ws losest to te expeimentlly mesued vlue of lf widt of te pttens. In genel only one of te oots ws suitle. Te vlue of te dditionl pessue P *, ws ten otined y omping te nominl pessue pplied to otin given line lf-widt (oesponding to ). Te diffeene etween expeimentl pplied pessue nd PP* ws tken to e P*. Using tis metod, P* ws onstnt wit vlue of out P o 7 mmhg fo ll pessues ove mmhg. Using tis tenique, te uve otined fom te expeimentl dt ( ) ( ) K K K ( ) ) ( ) ( 9 K K

10 fits te uve otined fom te model lmost pefetly. Te dt e pesented in figues 8,, nd d, in wi line widts fo te polymes t diffeent onenttions e plotted s funtion of pplied pessue. X % PCL % PCL % PCL widt (m i on ) 7 pes s ue (m m Hg ) Fig.8 Widt line of PCL s funtion of pessue fo diffeent onenttion X % PLLA % PLLA % PLLA wid t (mi on) 8 8 pes s ue (m m Hg) Fig. 8 Widt line of PLLA s funtion of pessue fo diffeent onenttion 7

11 w id t (m io n) 7 pe s sue (m mhg) Fig.8 Widt line of lend of PCL nd PLLA s funtion of pessue Widt (mion) 8 Pessue (mmhg) Fig. 8d Widt line of lend of PLGA s funtion of pessue 8