Hydroxyapatite-Resin Composites Produced by Vat Photopolymerization and Post-Processing via In Situ Hydrolysis of Alpha Tricalcium Phosphate

Ci a ion: Oli e -U u ia, C.; D o á o á, L.; Gascón-Pé ez, S.; Slámeˇcka, K.; Ra aszo á, S.; ˇ Celko, L.; Mon u a , E.B. Hyd oxyapa i e- Resin Composi es P oduced by Va Pho opolyme iza ion and Pos -P ocessing ia In Si u Hyd olysis o Alpha T icalcium Phospha e. Ce amics 2023,6, 2282–2294. h ps://doi.o g/10.3390/ ce amics6040139 Academic Edi o : Ta iana Sa ono a Recei ed: 26 Sep embe 2023 Re ised: 17 No embe 2023 Accep ed: 20 No embe 2023 Published: 24 No embe 2023 Copy igh : © 2023 by he au ho s. Licensee MDPI, Basel, Swi ze land. This a icle is an open access a icle dis ibu ed unde he e ms and condi ions o he C ea i e Commons A ibu ion (CC BY) license (h ps:// c ea i ecommons.o g/licenses/by/ 4.0/). ce amics A icle Hyd oxyapa i e-Resin Composi es P oduced by Va Pho opolyme iza ion and Pos -P ocessing ia In Si u Hyd olysis o Alpha T icalcium Phospha e Ca olina Oli e -U u ia 1, Lenka D o á o á1, Sebas ián Gascón-Pé ez 1,† , Ka el Slámeˇcka 1,2, Simona Ra aszo á3, Ladisla ˇ Celko 1and Edga B. Mon u a 1,* 1Cen al Eu opean Ins i u e o Technology, B no Uni e si y o Technology, Pu kyˇno a 123, 61200 B no, Czech Republic; u u ia@ u b .cz (C.O.-U.); lenka.d o a [email p o ec ed] (L.D.); [email p o ec ed] (S.G.-P.); [email p o ec ed].cz (K.S.); ladisla [email p o ec ed].cz (L. ˇ C.) 2Facul y o Mechanical Enginee ing, B no Uni e si y o Technology, Technická2, 61669 B no, Czech Republic 3Facul y o Ci il Enginee ing, B no Uni e si y o Technology, Ve eˇ í95, 60200 B no, Czech Republic; [email p o ec ed].cz *Co espondence: [email p o ec ed].cz †Cu en add ess: Cen o Uni e si a io de Ciencias Exac as e Ingenie ías (CUCEI), Uni e sidad de Guadalaja a, Boule a d Ma celino Ga cía Ba agán 1421, Olímpica, Guadalaja a 44430, Mexico. Abs ac : Va pho opolyme iza ion is an addi i e manu ac u ing echnique ha u ilizes pho osen- si i e esins o ab ica e 3D polyme ic objec s wi h high p ecision. Howe e , hese objec s o en lack mechanical s eng h. This s udy in es iga ed he s eng hening o a esin based on epoxidized soybean oil ac yla e, speci ically designed o a pho opolyme iza ion, by he in si u o ma ion o hyd oxyapa i e nanoc ys als. Fi s , a s able alpha icalcium phospha e ( α -TCP)- esin eeds ock mix u e was de eloped (~30 ol.% α -TCP), which p o ed sui able o ab ica ing monoli hs as well as complex iply pe iodic minimal su ace (gy oid, diamond, and Schwa z) po ous s uc u es h ough a pho opolyme iza ion. The esul s demons a ed ha he inco po a ion o α -TCP pa icles led o a signi ican mechanical imp o emen o he esin. Second, pos -p in ing hyd o he mal ea men s we e u ilized o ans o m he α -TCP pa icles in o hyd oxyapa i e c ys als wi hin he esin. I was obse ed ha he space be ween hyd oxyapa i e c ys als wi hin he composi es was occupied by he cu ed esin, esul ing in a mo e compac , s onge , and mechanically mo e eliable ma e ial han he po ous hyd oxyapa i e p oduced by he hyd olysis o α -TCP mixed wi h wa e . Mo eo e , wa e abso p ion du ing he hyd o he mal ea men s caused he plas iciza ion o he cu ed esin. As a consequence, he hyd oxyapa i e- esin composi es displayed sligh ly lowe mechanical p ope ies compa ed o he as-p in ed α-TCP- esin composi e. Keywo ds: a polyme iza ion; alpha icalcium phospha e; hyd oxyapa i e; po ous composi e; mechanical s eng h 1. In oduc ion Va pho opolyme iza ion (VPP) is a g oup o addi i e manu ac u ing (AM) echnolo- gies ha uses ligh o selec i ely cu e a laye o a pho osensi i e liquid esin, p oducing laye -by-laye h ee-dimensional (3D) objec s. The high p ecision o ad anced ligh sou ces gua an ees high la e al esolu ion du ing he cu ing p ocess, esul ing in high-quali y p in ou s and allowing non-i adia ed a eas o emain liquid [ 1 ]. VPP-AM echnologies a e classi ied acco ding o he con igu a ion o he ligh sou ce in o s e eoli hog aphy (SLA), digi al ligh p ocessing (DLP), liquid c ys al display (LCD), con inuous liquid in e ace p oduc ion, wo-pho on polyme iza ion, and compu ed axial li hog aphy. Among hem, SLA was he i s and mos ly used AM echnology ha u ilizes an ul a iole (UV) lase o cu e he esin, ollowing a scanning pa h o each laye o he objec . On he con a y, DLP Ce amics 2023,6, 2282–2294. h ps://doi.o g/10.3390/ce amics6040139 h ps://www.mdpi.com/jou nal/ce amics Ce amics 2023,62283 and LCD cu e a comple e laye o he objec in a single s ep by p ojec ing he en i e image o he laye in he esin, hus educing p in ing ime. DLP uses a digi al ligh p ojec o o gene a e he image o he laye , whe eas LCD p oduces he image by selec i ely blocking a backligh , allowing he ligh o pass only h ough he a eas ha o m he laye . LCD p in e s a e mo e cos -e ec i e and consume less powe han DLP p in e s, making hem he mos common comme cially a ailable op ion. In addi ion, VPP echnologies a e ca ego ized as op-down o bo om-up se ups. The bo om-up app oach is mo e common, wi h he ligh sou ce posi ioned below a anspa en window a he bo om o he a , while he building pla o m mo es upwa ds o c ea e each new laye . The na ow gap be ween he bo om o he a and he building pla o m enables be e Z esolu ion han he op-down se up, bu equi es low iscosi y esins o quickly ill he gap [ 2 ]. Mo eo e , each cu ed laye adhe es o he bo om o he a , equi ing he ca e ul li ing o he pla o m o de ach i be o e build- ing he nex laye . The coa ing o he a wi h a hyd ophobic laye educes he adhesi e o ce p e en ing delamina ion o de achmen o he objec om he building pla o m. The composi ion o he pho osensi i e esin is a balanced mix u e o oligome s, monome s, pho o ini ia o , and o he addi i es [ 3 ], ensu ing a as -cu ing p ocess a a speci ic wa eleng h ( ypically be ween 355 and 410 nm) wi h minimal pho opolyme iza- ion sh inkage. Comme cially a ailable esins a e gene ally sa e, o e s able p in ing pe o mance, and a e a ailable in a ious colo s, making hem ideal o p oducing models and p o o ypes. Howe e , s anda d esins used in VPP p in ing esul in p in ou s wi h poo mechanical p ope ies ha a e unsui able o s uc u al applica ions. Consequen ly, e o s ha e been made o imp o e mechanical beha io by ein o cing he cu ed esins wi h addi ional phases, leading o he de elopmen o polyme ic ma ix composi es [ 2 , 4 – 6 ]. Nano ille s play a c ucial ole in ein o cing he ma ix due o hei high speci ic su ace a ea, which c ea es a s ong in e phase wi h he ma ix [ 6 ]. This in e phase inc eases he mechanical s eng h h ough in e acial s ess ans e , c ack b idging, and c ack de lec ion. The homogeneous dispe sion o he nano ille is a mic os uc u al equi emen o hese mechanisms o ac e icien ly. Agglome a ions o he nano ille s gene a e s ess concen a- ion egions ha dec ease he ac u e esis ance. Howe e , main aining dispe sion du ing mixing and pho opolyme iza ion is challenging due o he endency o he nano ille s o educe hei high su ace ene gy and inc ease he en opy o he sys em by sel -agg ega ion. Addi ionally, ille s can abso b and sca e ligh [ 3 ] and signi ican ly inc ease he iscosi y o he esin [ 2 ], comp omising he VPP p ocess. Consequen ly, he e is a limi o he amoun o ein o cemen ha can be inco po a ed in o he esin. The e o e, an in iguing app oach is he in si u o ma ion o nano ille s wi hin he esin. Fo example, a sol–gel p ocess in acidic apo s and he he mal educ ion o me allic sal s we e used o induce he condensa ion o silica [ 7 ], and sil e [ 8 ] nanopa icles, espec i ely, inside VPP s uc u es. These app oaches ha e demons a ed he po en ial o double he mechanical s eng h; howe e , he achie ed alues emained below a couple o megapascals [7]. This wo k explo es a di e en app oach o ein o ce a comme cial VPP esin h ough inco po a ing hyd oxyapa i e nanoc ys als p oduced in si u by he hyd olysis o alpha icalcium phospha e ( α -TCP). α -TCP is equen ly used in calcium phospha e cemen s (CPCs) due o i s dissolu ion–p ecipi a ion eac ion when exposed o wa e , esul ing in he o ma ion o a mechanically en angled ne wo k o calcium-de icien hyd oxyapa i e (CDHA) nanoc ys als (Equa ion (1)) [ 9 , 10 ]. This eac ion e ec i ely ans o ms he α - TCP pas e in o a solid CDHA monoli h, wi h he mechanical s eng h inc easing as he con e sion p oceeds and he c ys al ne wo k de elops [10]. 3α-Ca3(PO4)2+ H2O→Ca9(HPO4)(PO4)5(OH) (1) In p e ious wo ks, non- eac i e calcium phospha e powde s ha e been inco po a ed in o pho osensi i e esins o p oduce dense ce amic s uc u es aided by VPP [ 11 – 17 ]. The goal o hese s udies was o achie e a maximum solid loading in he slu ies wi hou causing a de imen al inc ease in iscosi y ha could impai he laye -by-laye pho opolyme iza ion p ocess. The esin is emo ed a e ab ica ion by hea ing he composi e in ai , and hen he Ce amics 2023,62284 esul ing g een body is sin e ed a a high empe a u e o p oduce dense o po ous ce amic monoli hs. In con as , he p esen me hod enables he ab ica ion o ein o ced composi es a low empe a u e, wi hou he need o addi ional hea . The no el y o his wo k was o explo e i α -TCP powde inco po a ed in he esin eac s as a adi ional CPC and o de e mine i he pos -p in ing hyd olysis inc eases he mechanical s eng h o he cu ed composi e. Ini ially, an α -TCP-based esin sui able o LCD VPP was de eloped, ollowed by an examina ion o he chemical, mic os uc u al, and mechanical changes du ing hyd oxyapa i e o ma ion. Subsequen ly, h ee dis inc iply pe iodic minimal su ace (TPMS) po ous composi e s uc u es (i.e., gy oid, diamond, and Schwa z) we e p oduced o compa e hei comp ession beha io . 2. Ma e ials and Me hods 2.1. Feeds ock Ma e ials The pho opolyme izable ce amic- esin slu y used in all he expe imen s was based on α -TCP powde and a comme cial low- iscosi y esin ha polyme izes a 405 nm (whi e plan -based UV esin, Anycubic Co., Shenzhen, China). The exac o mula ion o he esin is no a ailable bu i is based on epoxidized soybean oil ac yla e monome , which polyme izes h ough he ee ac yla e adicals. The α -TCP was syn hesized by a solid-s a e eac ion be ween CaCO 3 and CaHPO 4 in a mola a io o 1:2. The syn hesis was pe o med a 1400 ◦ C o 2 h wi h a hea ing a e o 2.5 ◦ C/min, ollowed by ai quenching. The esul ing α -TCP block (150 g) was hen d y milled in a plane a y mill (F i sch Pul e ise e 6, Ida -Obe s ein, Ge many) o 15 min a 450 pm. An aga e ja (500 mL) and 25 aga e balls (diame e o 20 mm) we e used du ing he milling p ocess. The powde ac ion below 32 µ m was ob ained by sie ing, and i was mixed wi h he esin a a liquid o powde (L/P) a io o 0.70 mL/g (32 ol.%). This mix u e was used as eeds ock in all he expe imen s. 2.2. Va Pho opolyme iza ion The ce amic s uc u es we e p oduced using a bo om-up LCD p in ing machine (Pho on Mono X, Anycubic Co., Shenzhen, China) wi h a pixel esolu ion o 50 µ m a a wa eleng h o 405 nm. The 3D models o he s uc u es we e c ea ed in a compu e design so wa e and we e sa ed as s e eoli hog aphy (STL) iles. These STL iles we e hen expo ed in o he p in e so wa e. The ab ica ion pa ame e s we e se as ollows: a laye hickness o 75 µ m, a no mal exposu e ime o 10 s, an o ime o 0.5 s, a bo om exposu e ime o 100 s, and a numbe o bo om laye s o 6. A e he p in ing p ocess, any excess o un eac ed eeds ock esin in he p in ou s was emo ed wi h e hanol, and an addi ional cu ing s ep a 405 nm was conduc ed o 2 min. The composi e s uc u es, a e polyme iza ion and p io o any ea men , we e labelled as α-TCP/R. 2.3. Hyd o he mal T ea men s The in es iga ion o chemical, mic os uc u al, and mechanical changes du ing CDHA o ma ion was pe o med using cylind ical α -TCP/R monoli hs wi h a diame e o 6 mm and a heigh o 12 mm. These cu ed monoli hs we e imme sed in wa e a di e en empe a u es and o di e en du a ions o ob ain CDHA- esin composi es. The imme sion condi ions included 37 ◦ C o 10 days (CDHA/R-37), 90 ◦ C o 1 day (CDHA/R-90), and 190 ◦ C o 30 min in an au ocla e (CDHA/R-190). Monoli hs consis ing solely o esin (Resin), and monoli hs composed o α -TCP powde mixed wi h 2.5% Na 2 HPO 4 solu ion (L/P = 0.70 mL/g) ha dened in wa e a 37 ◦ C o 10 days (CDHA-c l), we e used as e e ences. The addi ion o Na 2 HPO 4 solu ion aimed o enhance he cohesion o he α -TCP powde be o e imme sion in wa e . 2.4. Fab ica ion o Po ous S uc u es Th ee di e en ypes o TPMS po ous s uc u es we e ab ica ed wi h a po osi y o 50%. These s uc u es we e based on iso opic gy oid, diamond, and Schwa z uni cells, espec i ely. The po ous s uc u es we e cylinde s (20 mm diame e , 10 mm heigh ) Ce amics 2023,62285 designed in silico wi h 6-uni cells along he diame e . A e ab ica ion, he po ous s uc u es we e hyd o he mally ea ed a 90 ◦C o 1 day. 2.5. Physicochemical and S uc u al Cha ac e iza ion C ys alline phases we e iden i ied by X- ay di ac ion (XRD, Sma Lab 3 kW CF2, Rigaku, Japan). Measu emen s we e ca ied ou in B agg–B en ano pa a ocusing geome y a 40 kV and 30 mA, p oducing CuK α adia ion wi h λ = 0.154 nm. The scanning 2 θ ange was se be ween 10 and 90 ◦ , wi h a s ep o 0.02 ◦ and a scanning speed o 4 ◦ /min. Phase iden i ica ion was pe o med wi h PDXL so wa e (Rigaku, Japan), using s uc u al models o α -TCP (Ino ganic Cen e o Di ac ion Da a (ICDD) No. 01-070-0364), be a icalcium phospha e ( β -TCP, ICDD No. 01-070-2065), and hyd oxyapa i e (ICDD No. 01-073-1731). C ys alli e size was e alua ed om he XRD da a (hyd oxyapa i e peak (002) a a ound 25.8 ◦ ) using he Debye–Sche e app oxima ion wi h a b oadening cons an o 0.9 [ 18 ]. Chemical changes we e in es iga ed by a enua ed o al e lec ance Fou ie ans o m in a ed spec oscopy (ATR-FTIR, Vacuum FTIR Ve ex 70 , B uke , B emen, Ge many). Scans we e pe o med in he MIR spec al ange be ween 400 and 4000 cm −1 , a e aging 40 scans wi h a spec al esolu ion o abou 2 cm −1 . ATR-FTIR spec a we e analyzed in he OPUS so wa e (B uke , B emen, Ge many). Powde samples o XRD and FTIR analysis we e p epa ed by g inding wo cylinde s pe se ies wi h sandpape . The mic os uc u e was examined using scanning elec on mic oscopy (SEM, Ly a3, TESCAN, B no, Czech Republic) ope a ed a an accele a ion ol age o 5 kV. Be o e imaging, he su aces we e coa ed wi h a nanome ic ca bon laye . The mechanical s eng h and Young’s modulus in comp ession we e de e mined using a uni e sal es ing machine (Ins on 8874, No wood, MA, USA). The es s (n= 5) we e conduc ed a a cons an c osshead speed o 1 mm/min. The s ess–s ain cu es we e ob ained om he eco ded o ce- displacemen da a, wi h load chain compliance compensa ion. The mac o po osi y o he po ous s uc u es (n= 5) was es ima ed by g a ime ic analysis acco ding o he Equa ion (2). P=1−D1 D2100, (2) whe e D 1 is he appa en densi y o he po ous s uc u es, calcula ed by di iding he mass by he bulk olume, and D 2 is he expe imen al densi y o he CDHA/R-90 dense composi e (1.7 g/mL). The heigh and diame e o he samples we e measu ed wi h a callipe o de e mine he olume. 3. Resul s 3.1. Polyme iza ion P ocess and as P in ed S uc u es The ab ica ion o CDHA- esin composi es by LCD VPP was success ully accom- plished (Figu e 1). The composi e esin based on α -TCP had low iscosi y, allowing smoo h low o he esin be ween laye s wi hou equi ing addi ional mechanical aid. Fu he mo e, he composi e esin did no ha den spon aneously due o he hyd olysis o α -TCP, making i possible o s o e he esin p o ec ed om ligh o a leas one yea wi hou any no iceable changes in iscosi y o he modi ica ion o he XRD pa e n. The α -TCP/R p in ou s appea ed whi e in colo as bo h he esin and α -TCP we e o iginally whi e. The composi es exhibi ed a ce amic-ma e su ace, whe eas he pu e esin was b igh e (Figu e 2a). The α -TCP emained un eac ed du ing he pho opolyme iza ion p ocess, as he XRD pa e n o he α -TCP/R monoli hs mainly showed peaks indexed as α - TCP, one addi ional di ac ion peak associa ed wi h he cu ed esin, and a ela i ely small p esence o he β -TCP phase (Figu e 3). Consis en ly, he mic os uc u e o he α -TCP/R composi e consis ed o un eac ed α -TCP pa icles embedded in he esin ma ix (Figu e 2a). The Resin i sel showed a smoo h mic os uc u e (Figu e 2a) and XRD c ys allini y wi h a main di ac ion peak a 35.5◦(Figu e 3). Ce amics 2023,62286 Ce amics2023,6,FORPEERREVIEW 5   The ab ica iono CDHA- esincomposi esbyLCDVPPwassuccess ullyaccom- plished(Figu e1).Thecomposi e esinbasedonα-TCPhadlow iscosi y,allowing smoo h lowo  he esinbe weenlaye swi hou  equi ingaddi ionalmechanicalaid.Fu - he mo e, hecomposi e esindidno ha denspon aneouslydue o hehyd olysiso α- TCP,makingi possible os o e he esinp o ec ed omligh  o a leas oneyea wi hou  anyno iceablechangesin iscosi yo  hemodi ica iono  heXRDpa e n.  Figu e1.STLmodelsandVPPCDHA/R-90po ouss uc u es. Theα-TCP/Rp in ou sappea edwhi eincolo asbo h he esinandα-TCPwe e o iginallywhi e.Thecomposi esexhibi edace amic-ma esu ace,whe eas hepu e esinwasb igh e (Figu e2a).Theα-TCP emainedun eac eddu ing hepho opolyme - iza ionp ocess,as heXRDpa e no  heα-TCP/Rmonoli hsmainlyshowedpeaksin- dexedasα-TCP,oneaddi ionaldiff ac ionpeakassocia edwi h hecu ed esin,anda ela i elysmallp esenceo  heβ-TCPphase(Figu e3).Consis en ly, hemic os uc u e o  heα-TCP/Rcomposi econsis edo un eac edα-TCPpa iclesembeddedin he esin ma ix(Figu e2a).TheResini sel showedasmoo hmic os uc u e(Figu e2a)andXRD c ys allini ywi hamaindiff ac ionpeaka 35.5°(Figu e3).  Figu e2.Mic os uc u eo VPPcomposi es.(a)α-TCP/Rmonoli h(le )andcu ed esinwi hou  ce amicpowde ( igh ).(b)Hyd o he mally ea edCDHA- esincomposi es. Figu e 1. STL models and VPP CDHA/R-90 po ous s uc u es. Ce amics2023,6,FORPEERREVIEW 5   The ab ica iono CDHA- esincomposi esbyLCDVPPwassuccess ullyaccom- plished(Figu e1).Thecomposi e esinbasedonα-TCPhadlow iscosi y,allowing smoo h lowo  he esinbe weenlaye swi hou  equi ingaddi ionalmechanicalaid.Fu - he mo e, hecomposi e esindidno ha denspon aneouslydue o hehyd olysiso α- TCP,makingi possible os o e he esinp o ec ed omligh  o a leas oneyea wi hou  anyno iceablechangesin iscosi yo  hemodi ica iono  heXRDpa e n.  Figu e1.STLmodelsandVPPCDHA/R-90po ouss uc u es. Theα-TCP/Rp in ou sappea edwhi eincolo asbo h he esinandα-TCPwe e o iginallywhi e.Thecomposi esexhibi edace amic-ma esu ace,whe eas hepu e esinwasb igh e (Figu e2a).Theα-TCP emainedun eac eddu ing hepho opolyme - iza ionp ocess,as heXRDpa e no  heα-TCP/Rmonoli hsmainlyshowedpeaksin- dexedasα-TCP,oneaddi ionaldiff ac ionpeakassocia edwi h hecu ed esin,anda ela i elysmallp esenceo  heβ-TCPphase(Figu e3).Consis en ly, hemic os uc u e o  heα-TCP/Rcomposi econsis edo un eac edα-TCPpa iclesembeddedin he esin ma ix(Figu e2a).TheResini sel showedasmoo hmic os uc u e(Figu e2a)andXRD c ys allini ywi hamaindiff ac ionpeaka 35.5°(Figu e3).  Figu e2.Mic os uc u eo VPPcomposi es.(a)α-TCP/Rmonoli h(le )andcu ed esinwi hou  ce amicpowde ( igh ).(b)Hyd o he mally ea edCDHA- esincomposi es. Figu e 2. Mic os uc u e o VPP composi es. ( a ) α -TCP/R monoli h (le ) and cu ed esin wi hou ce amic powde ( igh ). (b) Hyd o he mally ea ed CDHA- esin composi es. Ce amics2023,6,FORPEERREVIEW 6    Figu e3.XRDpa e nso composi es ab ica edbyVPP.Composi ecomponen s(ResinandCDHA- c l)a eincluded o compa ison.Righ handplo isade ailed iewo  hepa e nsin he ange20– 41°. 3.2.Hyd o he malT ea men  Thede elopmen o anen angledne wo ko nanoc ys alsin hecomposi esdemon- s a ed he ans o ma iono α-TCPin oCDHAdu inghyd o he mal ea men s(Figu e 2b).Ingene al, hese ea men s esul edinana e agediame alexpansiono 3.1±0.8%. TheCDHA o ma ionoccu edmo e apidlya ahighe hyd olysis empe a u ease i- dencedby hedec easein hein ensi yo  hecha ac e is icα-TCPdiff ac ionpeaksand heinc easingin ensi yo hyd oxyapa i e- ela edpeakswi hinc easing empe a u e(Fig- u e3).Inpa icula ,a 190°C, heα-TCPdiff ac ionpeaksalmos disappea ed,al hough hehyd o he mal ea men las edonly30min.Thein ensi yo  hediff ac ionpeaks e- la ed oβ-TCP emainedunchangeda 37°Cbu p og essi elyinc easeda ahighe  eac- ion empe a u e,consis en wi hp e iouswo ks ha  epo ed hepolymo phic ans o - ma iono α-TCPin oβ-TCPunde hyd o he malcondi ions[19,20].The empe a u eo  hehyd o he mal ea men alsoin luenced hemic os uc u eo  heCDHA- esincom- posi es.Pla e-likeCDHAnanoc ys alswe ep oducedin heCDHA/R-90composi eand heCDHA-c l,whe easneedle-likeCDHAnanoc ys alswe e o medin heCDHA/R-37 andCDHA/R-190composi es(Figu e2b).Thec ys alsizewasde e mined obe23.5nm o CDHA/R-37,29.6nm o CDHA/R-90,and32.3nm o CDHA/R-190,indica ing as e  g ow ho CDHAc ys alsa ahighe hyd olysis empe a u e. IRabso p ionspec ashow hep esenceo cha ac e is icbandso phospha e(PO43−) g oupsinbo h heα-TCP/Randhyd o he mally ea edCDHA- esincomposi es(Figu e 4).In enseb oadbandsbe ween900and1200cm−1andbe ween500and650cm−1 ep e- sen  hesymme ics e ching ib a ionand hebending ib a iono  hePO43−g oups, espec i ely.Sha peningo  hebanda ound1030cm−1and hespli ingo  hebandbe- ween550and650cm−1in o wopeakscon i m he ans o ma iono α-TCPin ohyd ox- yapa i e.Fu he mo e, hep esenceo OH-g oupsin hehyd oxyapa i ec ys allines uc- u ewascon i medby heweakabso p ionbandsbe ween3700and3900cm−1and he sub lyappea ingOH-banda 630cm−1asashoulde o  hePO43−band.A la weakab- so p ionbanda app oxima ely850cm−1isassocia edwi hP-OHs e cho  heHPO42− g oup,whichis ypical o calcium-de icien apa i es, husshowing he o ma iono  CDHA a he  hans ochiome ichyd oxyapa i e,whichis ypical o  hehyd oxyapa i e s uc u e o medbyα-TCPhyd olysis[10]. TheFTIRspec umo  hecu ed esindemons a esa ypicalhigh-in ensi ybando  heca bonylg oupa 1730cm−1.Thebandso igina ing omC=Cs e chappea a 1630 and1440cm−1,and hebando C–O–Cs e ching ib a iono es e issi ua edbe ween Figu e 3. XRD pa e ns o composi es ab ica ed by VPP. Composi e componen s (Resin and CDHA-c l) a e included o compa ison. Righ hand plo is a de ailed iew o he pa e ns in he ange 20–41◦. 3.2. Hyd o he mal T ea men The de elopmen o an en angled ne wo k o nanoc ys als in he composi es demons a ed he ans o ma ion o α -TCP in o CDHA du ing hyd o he mal ea men s ( Figu e 2b) . In gene al, hese ea men s esul ed in an a e age diame al expansion o 3.1 ±0.8% . The CDHA o ma ion occu ed mo e apidly a a highe hyd olysis empe a u e as e idenced by he dec ease in he in ensi y o he cha ac e is ic α -TCP di ac ion peaks and he inc easing in ensi y o hyd oxyapa i e- ela ed peaks wi h inc easing empe a u e (Figu e 3). In pa icula , a 190 ◦ C, he α -TCP di ac ion peaks almos disappea ed, al hough he hyd o he mal ea men las ed only 30 min. The in ensi y o he di ac ion peaks ela ed Ce amics 2023,62287 o β -TCP emained unchanged a 37 ◦ C bu p og essi ely inc eased a a highe eac ion empe a u e, consis en wi h p e ious wo ks ha epo ed he polymo phic ans o ma ion o α -TCP in o β -TCP unde hyd o he mal condi ions [ 19 , 20 ]. The empe a u e o he hyd o he mal ea men also in luenced he mic os uc u e o he CDHA- esin composi es. Pla e-like CDHA nanoc ys als we e p oduced in he CDHA/R-90 composi e and he CDHA-c l, whe eas needle-like CDHA nanoc ys als we e o med in he CDHA/R-37 and CDHA/R-190 composi es (Figu e 2b). The c ys al size was de e mined o be 23.5 nm o CDHA/R-37, 29.6 nm o CDHA/R-90, and 32.3 nm o CDHA/R-190, indica ing as e g ow h o CDHA c ys als a a highe hyd olysis empe a u e. IR abso p ion spec a show he p esence o cha ac e is ic bands o phospha e (PO 43− ) g oups in bo h he α -TCP/R and hyd o he mally ea ed CDHA- esin composi es (Figu e 4). In ense b oad bands be ween 900 and 1200 cm −1 and be ween 500 and 650 cm −1 ep esen he symme ic s e ching ib a ion and he bending ib a ion o he PO 43− g oups, espec- i ely. Sha pening o he band a ound 1030 cm −1 and he spli ing o he band be ween 550 and 650 cm −1 in o wo peaks con i m he ans o ma ion o α -TCP in o hyd oxyapa i e. Fu he mo e, he p esence o OH- g oups in he hyd oxyapa i e c ys alline s uc u e was con i med by he weak abso p ion bands be ween 3700 and 3900 cm −1 and he sub ly appea ing OH- band a 630 cm −1 as a shoulde o he PO 43− band. A la weak abso p ion band a app oxima ely 850 cm −1 is associa ed wi h P-OH s e ch o he HPO 42− g oup, which is ypical o calcium-de icien apa i es, hus showing he o ma ion o CDHA a he han s ochiome ic hyd oxyapa i e, which is ypical o he hyd oxyapa i e s uc u e o med by α-TCP hyd olysis [10]. Ce amics2023,6,FORPEERREVIEW 7   1100–1200cm −1 .Bandsassocia edwi hepoxyandoxi anea ep esen be ween800and 900cm −1 .Theweakbanda 3400cm −1 co esponds o heOHg oupsc ea ed om he ing openingo epoxidedu ingac yla ion.CHabso p ionbandsa e isiblebe ween2800and 3000cm −1 .The e o e, heResinshows hecha ac e is icchemicalbondso epoxidized ac yla epolyme s,whichisconsis en wi h hepho ocu ablemonome used.Thecha ac- e is icbandso  he esina ealsop esen in heFTIRspec umo  heCDHA- esincom- posi esand heα-TCP/Rcomposi e.Abso p ionbandsin he angeo 2300–2400cm −1 a e associa edwi h hep esenceo a mosphe icca bondioxideabso bedon hesu aceo  he samples.  Figu e4.ATR-FTIRspec ao composi es ab ica edbyVPP.Composi ecomponen s(Resinand CDHA-c l)a eincluded o compa ison. 3.3.MechanicalCha ac e iza ion Thecomp essi es ess–s aincu eso  hes udiedma e ialswe e ep oducibleand exhibi eddis inc mechanicalbeha io o pu ecomponen sandcomposi es(Figu e5a). TheCDHA-c lma e ialwasweakandb i le,while heResindemons a edplas icbe- ha io wi hayields eng h ha wassigni ican lyhighe  han hecomp essi es eng h o  heCDHA-c l.Theplas icde o ma iono  heResin ollowedanon-linea s ainha d- ening end,and he es swe es oppedbe o e heResin ac u ing.Bo hCDHA-c land heResinhadsimila Young’smodulus alues(Figu e5c).Thes ess–s aincu eso  he composi es,including heα-TCP/R,displayed h eedis inc domains:anini iallinea elas- ic egion, ollowedbynea lylinea s ainha deninga e yielding,and inally, as s ain so eninga e  ailu ea  hecomp essi es eng h(Figu e5a). Figu e 4. ATR-FTIR spec a o composi es ab ica ed by VPP. Composi e componen s (Resin and CDHA-c l) a e included o compa ison. Ce amics 2023,62288 The FTIR spec um o he cu ed esin demons a es a ypical high-in ensi y band o he ca bonyl g oup a 1730 cm −1 . The bands o igina ing om C=C s e ch appea a 1630 and 1440 cm −1 , and he band o C–O–C s e ching ib a ion o es e is si ua ed be ween 1100–1200 cm−1 . Bands associa ed wi h epoxy and oxi ane a e p esen be ween 800 and 900 cm −1 . The weak band a 3400 cm −1 co esponds o he OH g oups c ea ed om he ing opening o epoxide du ing ac yla ion. CH abso p ion bands a e isible be ween 2800 and 3000 cm −1 . The e o e, he Resin shows he cha ac e is ic chemical bonds o epoxidized ac yla e polyme s, which is consis en wi h he pho ocu able monome used. The cha ac e is ic bands o he esin a e also p esen in he FTIR spec um o he CDHA- esin composi es and he α -TCP/R composi e. Abso p ion bands in he ange o 2300–2400 cm −1 a e associa ed wi h he p esence o a mosphe ic ca bon dioxide abso bed on he su ace o he samples. 3.3. Mechanical Cha ac e iza ion The comp essi e s ess–s ain cu es o he s udied ma e ials we e ep oducible and exhibi ed dis inc mechanical beha io o pu e componen s and composi es (Figu e 5a). The CDHA-c l ma e ial was weak and b i le, while he Resin demons a ed plas ic beha io wi h a yield s eng h ha was signi ican ly highe han he comp essi e s eng h o he CDHA-c l. The plas ic de o ma ion o he Resin ollowed a non-linea s ain ha dening end, and he es s we e s opped be o e he Resin ac u ing. Bo h CDHA-c l and he Resin had simila Young’s modulus alues (Figu e 5c). The s ess–s ain cu es o he composi es, including he α -TCP/R, displayed h ee dis inc domains: an ini ial linea elas ic egion, ollowed by nea ly linea s ain ha dening a e yielding, and inally, as s ain so ening a e ailu e a he comp essi e s eng h (Figu e 5a). Ce amics2023,6,FORPEERREVIEW 8    Figu e5.Resul so comp ession es so composi emonoli hsandcomposi ecomponen s.(a)Com- p essi es ess–s aincu eswi h hehighes andlowes  alues.(b)Yields eng handcomp essi e s eng h.Thecomp essi es eng ho  heResinco esponds o hes essa 20%s ain.(c)Young’s modulus.Ba plo sshowa e age±SD alues(n=5). Asexpec ed,all hecomposi eswe es onge  hanbo h heResinandCDHA-c l. Howe e ,con a y oexpec a ions, heα-TCP/Rcomposi ewas hes onges one,wi h heyieldandcomp essi es eng h ha we e wiceashighas ha o  heResin(Figu e5b), and heYoung’smodulus ha was en imeshighe (Figu e5c).Hyd o he mally ea ed composi eswe e ound obeweake  han heα-TCP/Rcomposi edue owa e abso p ion in he esinma ix,causingplas iciza ionbyin e molecula hyd oca bonglidingeffec s [21].None heless,wa e abso p ionalsoenabled hehyd olysiso α-TCP o o minsi u ein o cingnanome icCDHAc ys als(Figu e2b).Thec ys alscoun e ac edma ixso - eningandminimized helosso mechanicals eng h.Themo phologyanddeg eeo  o ma iono CDHAp oducedby hediffe en hyd o he mal ea men sin luenced he mechanicalp ope ies.TheCDHA/R-37composi eexhibi ed helowes yieldandcom- p essi es eng h(Figu e5b)due o heincomple e ans o ma iono α-TCPin oCDHA (Figu e3).Incon as ,CDHA/R-90andCDHA/R-190,whichnea ly ullycon e edin o CDHA, e ainedhighe mechanicals eng h.Mo eo e ,CDHA/R-90wassligh lys onge  hanCDHA/R-190because hepla e-likec ys almo phologygene a ess onge c ys al in e locking hanneedle-likemo phologya  hesamepo osi y[22].I iswo hno ing ha  hedeclineinYoung’smodulus ollowedasigni ican lydiffe en  end han hecomp es- si es eng h.Ingene al, hehyd o he mal ea men s esul edina h ee- old educ ion inYoung’smoduluswi h espec  o heas-p in edcondi ion(α-TCP/R).Mo eo e , he e wasa u he  educ ioninYoung’smoduluswi hahighe  empe a u eandsho e  eac- ion ime,indica ing ha  empe a u eplayedamo esigni ican  oleinwa e adso p ion wi hin hecomposi es han ime. 3.4.TPMSPo ousComposi eS uc u es Th eeTPMSpo ousCDHA/R-90s uc u eswe e ab ica ed odemons a e hesui - abili yo  heα-TCP-based esininp oducingcomplex3Dobjec s(Figu e1).Thepo ous s uc u esexhibi edhigh ideli y,wi hwell-de inededgesandcon ou s(Figu e6).The su aceso  hes uc u eswe e oughwi hape iodicpa e ngene a edbylaye -by-laye  ab ica ion(Figu e7b,c),whichis ypical o VPPpa s[23].Thea e ageexpe imen al po osi ywas31.5±6.1% o Schwa z,36.7±5.9% o gy oid,and30.2±3.0% o diamond s uc u es.Asexpec ed, hepo ouss uc u esexhibi edlowe comp essi es eng h han hemonoli hiccomposi e.Inaddi ion, hes ess–s ain esponseo  hepo ouss uc u es Figu e 5. Resul s o comp ession es s o composi e monoli hs and composi e componen s. ( a ) Com- p essi e s ess–s ain cu es wi h he highes and lowes alues. ( b ) Yield s eng h and comp essi e s eng h. The comp essi e s eng h o he Resin co esponds o he s ess a 20% s ain. ( c ) Young’s modulus. Ba plo s show a e age ±SD alues (n= 5). As expec ed, all he composi es we e s onge han bo h he Resin and CDHA-c l. Howe e , con a y o expec a ions, he α -TCP/R composi e was he s onges one, wi h he yield and comp essi e s eng h ha we e wice as high as ha o he Resin (Figu e 5b), and he Young’s modulus ha was en imes highe (Figu e 5c). Hyd o he mally ea ed composi es we e ound o be weake han he α -TCP/R composi e due o wa e abso p- ion in he esin ma ix, causing plas iciza ion by in e molecula hyd oca bon gliding e ec s [ 21 ]. None heless, wa e abso p ion also enabled he hyd olysis o α -TCP o o m in si u ein o cing nanome ic CDHA c ys als (Figu e 2b). The c ys als coun e ac ed ma ix Ce amics 2023,62289 so ening and minimized he loss o mechanical s eng h. The mo phology and deg ee o o ma ion o CDHA p oduced by he di e en hyd o he mal ea men s in luenced he mechanical p ope ies. The CDHA/R-37 composi e exhibi ed he lowes yield and com- p essi e s eng h (Figu e 5b) due o he incomple e ans o ma ion o α -TCP in o CDHA (Figu e 3). In con as , CDHA/R-90 and CDHA/R-190, which nea ly ully con e ed in o CDHA, e ained highe mechanical s eng h. Mo eo e , CDHA/R-90 was sligh ly s onge han CDHA/R-190 because he pla e-like c ys al mo phology gene a es s onge c ys al in e locking han needle-like mo phology a he same po osi y [ 22 ]. I is wo h no ing ha he decline in Young’s modulus ollowed a signi ican ly di e en end han he comp es- si e s eng h. In gene al, he hyd o he mal ea men s esul ed in a h ee- old educ ion in Young’s modulus wi h espec o he as-p in ed condi ion ( α -TCP/R). Mo eo e , he e was a u he educ ion in Young’s modulus wi h a highe empe a u e and sho e eac ion ime, indica ing ha empe a u e played a mo e signi ican ole in wa e adso p ion wi hin he composi es han ime. 3.4. TPMS Po ous Composi e S uc u es Th ee TPMS po ous CDHA/R-90 s uc u es we e ab ica ed o demons a e he sui - abili y o he α -TCP-based esin in p oducing complex 3D objec s (Figu e 1). The po ous s uc u es exhibi ed high ideli y, wi h well-de ined edges and con ou s (Figu e 6). The su aces o he s uc u es we e ough wi h a pe iodic pa e n gene a ed by laye -by-laye ab ica ion (Figu e 7b,c), which is ypical o VPP pa s [ 23 ]. The a e age expe imen al po osi y was 31.5 ± 6.1% o Schwa z, 36.7 ± 5.9% o gy oid, and 30.2 ± 3.0% o diamond s uc u es. As expec ed, he po ous s uc u es exhibi ed lowe comp essi e s eng h han he monoli hic composi e. In addi ion, he s ess–s ain esponse o he po ous s uc u es di e ed, showing in gene al a quasi-b i le beha io wi hou a p onounced s ain-ha dening egion (Figu e 7a). This dis inc ion is explained by local ensile s esses ac ing on he walls o he s uc u es, leading o hei localized ailu e. The p esence o cup and cone ac u es obse ed on he ac u e su aces (Figu e 7b,c) u he suppo s his hypo hesis, as hey a e ypical o polyme s subjec ed o ension [ 24 ]. In he gy oid s uc u es, c acks p opaga ed a an angle o app oxima ely 45 ◦ o he applied loading (Figu e 7b), whe eas in he diamond s uc u es, c acks p opaga ed pa allel o he loading (Figu e 7c). In bo h cases, se e al c acks p opaga ed h ough he laye s a he han be ween hem. A a nea ly cons an po os- i y and di e en po e size, he Schwa z s uc u e was s onge (34.9 MPa) han gy oid (16.3 MPa) and diamond (16.1 MPa) s uc u es, which showed simila s ess–s ain esponses wi h signi ican s aining. Ce amics2023,6,FORPEERREVIEW 9   diffe ed,showingingene alaquasi-b i lebeha io wi hou ap onounceds ain-ha d- ening egion(Figu e7a).Thisdis inc ionisexplainedbylocal ensiles essesac ingon hewallso  hes uc u es,leading o hei localized ailu e.Thep esenceo cupandcone ac u esobse edon he ac u esu aces(Figu e7b,c) u he suppo s hishypo hesis, as heya e ypical o polyme ssubjec ed o ension[24].In hegy oids uc u es,c acks p opaga eda anangleo app oxima ely45° o heappliedloading(Figu e7b),whe eas in hediamonds uc u es,c acksp opaga edpa allel o heloading(Figu e7c).Inbo h cases,se e alc acksp opaga ed h ough helaye s a he  hanbe ween hem.A anea ly cons an po osi yanddiffe en po esize, heSchwa zs uc u ewass onge (34.9MPa) hangy oid(16.3MPa)anddiamond(16.1MPa)s uc u es,whichshowedsimila s ess– s ain esponseswi hsigni ican s aining.  Figu e6.Imageso CDHA/R-90po ouss uc u es.(a)Schwa zla e al iew,(b)Schwa z op iew, (c)gy oidla e al iew,and(d)diamondla e al iew.  Figu e7.Mechanicalbeha io o CDHA/R-90po ouss uc u es.(a)Comp essi es ess–s ain cu es,andimageso  ac u esu acesin(b)gy oidand(c)diamondTPMSpo ouss uc u es.Thin a owspoin  o hecupandcone ac u esanddashellipsesshowexampleso  hepe iodic ough su ace. 4.Discussion Theobjec i eo  hiss udywas oenhance hemechanicals eng ho pho osensi i e esins oexpand hepo en ialapplica ionso VPPpa sbeyondmodellingandp o o yp- ing.Thehyd olysiso α-TCPwasexplo edasas aigh o wa dme hod o o mnanome - ichyd oxyapa i e ein o cemen c ys alsinacomme cialpho ocu ing esin.The esin i sel didno induce hehyd olysiso α-TCPdue o heabsenceo wa e molecules,en- su ing hes abili yandp in abili yo  he eeds ockmix u eo e anex endedpe iod.Fu - he mo e, heα-TCPpa icleshadaminimalimpac onligh abso p ionandsca e inga  Figu e 6. Images o CDHA/R-90 po ous s uc u es. ( a ) Schwa z la e al iew, ( b ) Schwa z op iew, (c) gy oid la e al iew, and (d) diamond la e al iew. Ce amics 2023,62290 Ce amics2023,6,FORPEERREVIEW 9   diffe ed,showingingene alaquasi-b i lebeha io wi hou ap onounceds ain-ha d- ening egion(Figu e7a).Thisdis inc ionisexplainedbylocal ensiles essesac ingon hewallso  hes uc u es,leading o hei localized ailu e.Thep esenceo cupandcone ac u esobse edon he ac u esu aces(Figu e7b,c) u he suppo s hishypo hesis, as heya e ypical o polyme ssubjec ed o ension[24].In hegy oids uc u es,c acks p opaga eda anangleo app oxima ely45° o heappliedloading(Figu e7b),whe eas in hediamonds uc u es,c acksp opaga edpa allel o heloading(Figu e7c).Inbo h cases,se e alc acksp opaga ed h ough helaye s a he  hanbe ween hem.A anea ly cons an po osi yanddiffe en po esize, heSchwa zs uc u ewass onge (34.9MPa) hangy oid(16.3MPa)anddiamond(16.1MPa)s uc u es,whichshowedsimila s ess– s ain esponseswi hsigni ican s aining.  Figu e6.Imageso CDHA/R-90po ouss uc u es.(a)Schwa zla e al iew,(b)Schwa z op iew, (c)gy oidla e al iew,and(d)diamondla e al iew.  Figu e7.Mechanicalbeha io o CDHA/R-90po ouss uc u es.(a)Comp essi es ess–s ain cu es,andimageso  ac u esu acesin(b)gy oidand(c)diamondTPMSpo ouss uc u es.Thin a owspoin  o hecupandcone ac u esanddashellipsesshowexampleso  hepe iodic ough su ace. 4.Discussion Theobjec i eo  hiss udywas oenhance hemechanicals eng ho pho osensi i e esins oexpand hepo en ialapplica ionso VPPpa sbeyondmodellingandp o o yp- ing.Thehyd olysiso α-TCPwasexplo edasas aigh o wa dme hod o o mnanome - ichyd oxyapa i e ein o cemen c ys alsinacomme cialpho ocu ing esin.The esin i sel didno induce hehyd olysiso α-TCPdue o heabsenceo wa e molecules,en- su ing hes abili yandp in abili yo  he eeds ockmix u eo e anex endedpe iod.Fu - he mo e, heα-TCPpa icleshadaminimalimpac onligh abso p ionandsca e inga  Figu e 7. Mechanical beha io o CDHA/R-90 po ous s uc u es. ( a ) Comp essi e s ess–s ain cu es, and images o ac u e su aces in ( b ) gy oid and ( c ) diamond TPMS po ous s uc u es. Thin a ows poin o he cup and cone ac u es and dash ellipses show examples o he pe iodic ough su ace. 4. Discussion The objec i e o his s udy was o enhance he mechanical s eng h o pho osensi i e esins o expand he po en ial applica ions o VPP pa s beyond modelling and p o o yping. The hyd olysis o α -TCP was explo ed as a s aigh o wa d me hod o o m nanome ic hyd oxyapa i e ein o cemen c ys als in a comme cial pho ocu ing esin. The esin i sel did no induce he hyd olysis o α -TCP due o he absence o wa e molecules, ensu ing he s abili y and p in abili y o he eeds ock mix u e o e an ex ended pe iod. Fu he mo e, he α -TCP pa icles had a minimal impac on ligh abso p ion and sca e ing a he p in ing wa eleng h due o a low e ac i e index o 1.63 [ 11 ]. This cha ac e is ic allowed o he inco po a ion o a ela i ely high- olume ac ion o ein o cemen pa icles (32 ol.%) wi hou hinde ing he selec i e pho opolyme iza ion o he esin and, consequen ly, he laye -by-laye ab ica ion o TPMS po ous s uc u es. The ac ion o α -TCP pa icles inco po a ed in he esin (55.4 w .%) exceeded he ac ion o o he ille s ypically added o pho opolyme izable esins (usually below 20 w .% [ 25 – 29 ]), bu i emained ela i ely low (0.7 mL/g) compa ed o he L/P a io used in comme cial o mula ions o CPCs (e.g., 0.22–0.25 mL/g [ 30 ]). The selec ed expe imen al L/P a io allowed quick and smoo h low o he esin be ween laye s wi hou he need o a ecoa ing mechanism, which is no ypically included in s anda d VPP p in e s, and a oided addi ional s eps ha could inc ease he p ocessing ime. Based on he obse a ions and he pe o mance o o he esins con aining calcium phospha e pa icles [ 12 ], i is possible o inc ease he ac ion o α -TCP up o a leas 60 ol.% while main aining a cu ing dep h abo e 0.9 mm. The inco po a ion o mic ome ic α -TCP pa icles alone had a signi ican ein o cing e ec on he cu ed esin (Figu e 5). This esul ed in he Young’s modulus ou imes highe and comp essi e s eng h in he uppe ange o ensile s eng h compa ed o o he pa icle- ein o ced pho ocu able esins [ 25 , 27 , 31 – 33 ]. The ein o cemen e ec can be a ibu ed o he close and con inuous in e acial con ac be ween he pa icles and he polyme ic ma ix, which is p omo ed by s ong molecula in e ac ions, i.e., hyd ogen bonds and o he dipole–dipole a ac ions. P e ious s udies ha e explo ed he mixing o β -TCP pa icles wi h non-pho ocu able poly(me hyl me hac yla e) (PMMA) cemen s o imp o e he a ach- men wi h bone issue [ 34 – 36 ]. Howe e , unlike he indings o his s udy, he pa icles educed he mechanical s eng h in he absence o a compa ibilize due o hyd ophobic– hyd ophilic immiscibili y. In con as , when he app op ia e compa ibilize was u ilized along wi h 50 w .% o pa icles, he comp essi e s eng h imp o ed o app oxima ely 80 MPa ( s. 58 MPa in he composi e wi hou he compa ibilize ) [ 37 ]. This highligh s he impo ance o he chemical in e ac ions a he molecula scale in in luencing he mechanical beha io . Howe e , no no iceable band shi s o in e ac ions we e obse ed in he FTIR analyses o he composi es in his s udy and u he esea ch u ilizing esins wi h lowe chemical complexi y is equi ed o gain a deepe unde s anding o hese in e ac ions.