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3D Printing

3D printing
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  INTRODUCTION3D printing was originally developed in 1984 by Ch! #ll and is an additive pro!ess o$ %a ing a three&di%ensional solid ob'e!t $ro% a digital %odel( 3D printingis a!hieved by laying down s!!essive layers o$ %aterial to $or% shapes( There has been re!ently a hge growth in the sales and se o$ 3D printing and the %ar et $or these in!reased by )9* $ro% )+11 to year )+1)( To print, the %a!hine reads thedesign $ro% an (stl $ile and lays down s!!essive layers o$ %aterial to bild a series o$ !ross se!tions( These layers, as de!ided by the C-D %odel, are 'oined or ato%ati!ally $se to !reate the $inal shape( This te!hni.e allows $or the ability to!reate al%ost any shape or geo%etri! $eatre(The printer resoltion /layer thi! nessand 0& resoltion2 are de$ined as either dpi /dots per in!h2 or %i!ro%eters( Typi!allayer thi! ness is arond 1++ %i!ro%eters /%2( #igher end %a!hines however /Ob'et Conne series and 3D 5yste%s6 7roet series2 !an print layers as thin as 1 %(The 0& resoltion o$ 3D printers is arond :+ to 1++ %(-%ong other ses, 3D printing has $ond pro%ise in the bio%edi!al $ield as a %eans to generate tisses!a$$olds ot o$ biodegradable poly%ers as well as potentially tisses by printing !ellsand %atri into a de$ined area(Crrent syntheti! bone gra$ts s$$er $ro% poor handling !hara!teristi!s, brittle%e!hani!al properties, and in!onsistent bioa!tivity( ;y blending a biodegradablea%phiphili! poly%er with hydroyapatite /#-2, the %ain %ineral !o%ponent in bone,we developed an i%proved syntheti! bone gra$t( The poly%er<#- !o%posites were$abri!ated in both )&D and 3&D $or%s by ele!trospinning and 3&D printing( These%aterials ehibited ni.e handling !hara!teristi!s s!h as high tensile elasti!ity/=)++* $ailre strain2 and sel$&sti$$ening properties pon hydration, allowing their $a!ile<stabile $iation arond an open de$e!t or within a !on$ined de$e!t( They are alsosperhydrophili!, enabling the absorption o$ a.eos !ell sspensions and proteintherapeti!s(  Design 7roperties>ow %e!hani!al strength is a %a'or !hallenge in poros s!a$$olds, and is pri%arily !ontrolled by pore vol%e and distribtion( This is also tre $or 3D printed!era%i! s!a$$olds and li%its their se to only non&load bearing and low&load bearingappli!ations( Opti%i?ed post pro!essing approa!hes and !o%positional %odi$i!ations!an i%prove %e!hani!al properties o$ !era%i! s!a$$olds( To investigate the e$$e!t o$  printing orientation and layer thi! ness on the %e!hani!al properties o$ greenspe!i%ens, !o%pression tests were per$or%ed on raw @p 1:+ spe!i%ens(The !o%pression strength, ong6s %odls and toghness o$ the 3D printed porossa%ples were deter%ined and !o%pared with ea!h other to $ind the opti%% printing!onditions( The sa%e test setp and para%eter were sed $or all other sa%ples(Cal!i% 5l$ate s!a$$olds not sb'e!ted to any post hardening de%onstrated lower !o%pressive strength, !o%pressive %odls and !o%pressive toghness than thosereported $or !an!ellos bone( The !o%pressive stress&strain !rves shown in Aigre13/aB!2 are !hara!teri?ed by the initial non&linear toe region $ollowed by the %ainlinear region and then the !on!ave shape till the $ailre point( The $l!tationsobserved in this region !old be attribted to the layer by layer !ollapse o$ the%i!rostr!tre nder !o%pression load( The average vales o$ !o%pressive strength,ong6s %odls and toghness o$ $ive sa%ples were shown in Aigre 14/aB!2(Aigre 13( Co%pressive 5tress&5train Crve $or di$$erent layer thi! ness in 0 /a2, /b2 and @ /!2 dire!tion printing(  Aigre 14( Co%parison o$ !o%pressive strength /a2, ong6s %odls /b2 andtoghness /!2 in sa%ples printed with di$$erent layer thi! ness in varios orientation(-!!ording to the !o%pressive stress&strain !rves in Aigre 13/aB!2, s!a$$oldsnderwent the elasti! displa!e%ent $ollowed by $ailre in strts and %i!ro!ra! sgeneration in the periphery wall o$ the s!a$$olds printed in 0 and  dire!tion throghthe hori?ontal strts( Aailre also o!!rred throgh the verti!al strts in the body o$ sa%ples printed in @ dire!tion( oreover, the lo!ation o$ $ailres is not !on!entratedin the %iddle o$ the s!a$$olds( This indi!ates that internal str!tre has a signi$i!antin$len!e on the %e!hani!al properties o$ 3D7 sa%ples(-s shown in Aigres 14/aB!2, di$$eren!e in printing orientation reslted in varios!o%pressive strengths( The !o%pressive strength o$ sa%ples printed in @ dire!tionwas $ond to be very low $or the printed poros sa%ples that is !riti!al $or thedepowdering and handling steps 3+E( 5!a$$olds printed in 0 and  dire!tion withlayer thi! ness o$ +(1 %% had the less !o%pressive strength, however, in!reasinglayer thi! ness $ro% +(+8F: %% to +(11): and +(1): %% had a %ore positive e$$e!ton the %e!hani!al properties o$ the s!a$$old(-s shown in Aigre 14/a2 and 14/!2, althogh the sa%ples with layer thi! ness o$ +(+8F: %% printed in @ dire!tion have the least !o%pressive strength bt ehibit %oretoghness !o%pared to sa%ples with +(1 %% layer thi! ness(-s shown in Aigres 14/a2 and 14/!2, s!a$$olds with layer thi! ness o$ +(1 %%de%onstrated low !o%pressive strength, ong6s %odls and toghness in both 0and  printing orientations( ;y in!reasing the layer thi! ness to +(11): and +(1):%%, the !o%pressive strength in!reased, and the plasti! region was etended,sggesting higher toghness in three orientation o$ 0,  and @( Conversely, thes!a$$olds printed with +(1 %% layer thi! ness de%onstrated a lower level o$ plasti!de$or%ation and generally $ailed shortly a$ter rea!hing the pea load that is %oreevident in @ printing orientation, /Aigre 13/!22( -s it !an be seen, the greatesti%prove%ent in !o%pressive strength and toghness were all obtained when s!a$$oldswere printed with +(11): %% layer thi! ness in 0 printing dire!tion(  It see%s that an in!rease o$ layer thi! ness and de!rease o$ shear $or!es reslt in better powder spreading, stability and ni$or%ity whi!h i%prove the strength(#owever, when layer thi! ness de!reases, the n%ber o$ layers is in!reased( This %ayreslts in higher integrity that in trn will in!rease the strength o$ the spe!i%ens too)3E( It is also worthy to note that, as shown in Aigre 14/a2, nder the sa%e binder satration, with a de!rease o$ layer thi! ness $ro% +(1 to +(+8F: %%, the !o%pressivestrength wold so%ehow in!rease( In s!h !ase, as layer thi! ness de!reases, thesprayed binder wold penetrate better in verti!al and lateral dire!tions over thesr$a!e reslting in less e%pty spa!es between powder parti!les and in!reasing thestrength o$ the spe!i%en( Generally, binder spreading in verti!al dire!tion is %orethan that in lateral dire!tion( 5o, the verti!al dire!tion will be satrated with the binder  be$ore the lateral binder spreading is !o%plete( #owever, it see%s that when thesele!ted layer thi! ness is less than a !ertain threshold, the binder wold !o%pletely penetrate verti!ally and the powder gets satrated, while this is not the !ase in lateraldire!tion( 5o, in!o%plete spreading o$ the binder laterally wold de!rease the sa%pleintegrity and strength( Arther%ore, with a de!rease o$ layer thi! ness $ro% +(1): and+(11): to +(1 %%, the binder penetrates $aster to the botto% o$ the layer( #owever, the previos printed layer prevents the binder $ro% $rther spreading whi!h reslts innonni$or%ity in the inter$a!e layers( There$ore $inding the opti%% layer thi! nessis !riti!al $or printing s!h poros s!a$$olds(The %e!hani!al behavior depends on the orientation o$ the powder spreading and binder 'etting( Aor s!a$$olds printed in  dire!tion the !o%pressive load was applied parallel to the !onstitent layers and the dire!tion o$ binder 'etting( Hhile $or thosesa%ples printed in 0 orientation, the !o%pressive load was applied parallel to the!onstitent layers bt perpendi!lar to the dire!tion o$ binder 'etting( Aor sa%ples printed in @ orientation, the !o%pressive load was applied perpendi!lar to both, the!onstitent layer and the binder 'etting(5!a$$olds printed in 0 orientation present higher !o%pressive strength and %odls in!o%parison with the s!a$$olds printed in  and @ dire!tions( These reslts sggest thatthe printing orientation and layer thi! ness have a great in$len!e on the %e!hani!al properties o$ 3D7 parts( #owever, these reslts are in !ontrast to the stdy reslt o$ (Castilho et al(-!!ording to Aigre 14/a2, the wea est average !o%pressive strength was shown bythe sa%ples printed in @ dire!tion( -lso, %ore average strength was observed insa%ples printed in 0 dire!tion and this set also showed the lowest standard deviation(The sa%ples printed in  dire!tion have the %ean !o%pressive strength( -lthogh,this set showed the highest standard deviation re$erring to the signi$i!ant diversitya%ong strength vales(It shold be noted that de to the low strength o$ sa%ples printed in @ dire!tion, they bro e in the depowdering step(
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