Polymeric nanoparticles protect the resin-dentin bonded interface from cariogenic biofilm degradation

Thismanusc ip hasbeenpublishedonlinein:Ac aBioma e ialiaMay2019 h ps://doi.o g/10.1016/j.ac bio.2020.05.002   1 Ti le: Polyme ic nanopa icles p o ec he esin-den in bonded in e ace om ca iogenic bio ilm deg ada ion. Running i le: Nanopa icles an ideg ada ion ac i i y a bonded den in. Au ho s: Manuel Toledano-Oso ioa, Raquel Oso ioa, Fá ima S Aguile aa, An onio Luis Medina-Cas illob, Manuel Toledanoa*, Es ella Oso ioa, Se gio Acos ac, Ruoqiong Chend, Con ado Apa icioe. Ins i u ion: a Uni e si y o G anada, Facul y o Den is y, Den al Ma e ials Sec ion. Colegio Máximo de Ca uja s/n 18071 – G anada - Spain. b c d Uni e si y o G anada, NanoMyP. Spin-O En e p ise. Edi icio BIC-G anada. A . Inno ación 1. 18016 - A milla, G anada, Spain. Bio o ge lab, CIBER-BBN, Edi icio LUCIA, Uni e si y o Valladolid, Paseo Belen 19, Valladolid 47011, Spain. Depa men o Diagnos ic and Biological Sciences, School o Den is y, Uni e si y o Minneso a, Minneapolis, MN, USA. e MDRCBB-Minneso a Den al Resea ch Cen e o Bioma e ials and Biomechanics, Depa men o Res o a i e Sciences, School o Den is y, Uni e si y o Minneso a, Minneapolis, MN, USA. *Co esponding au ho : P o . Manuel Toledano. Uni e si y o G anada, Facul y o Den is y Den al Ma e ials Sec ion Colegio Máximo de Ca uja s/n 18071 – G anada - Spain. Tel.: +34-958243788 Fax: +34-958240809 2 ABSTRACT The objec i e was o assess doxycycline (Dox) and zinc (Zn) doped nanopa icles' (NPs) po en ial o p o ec he esin-den in in e ace om ca iogenic bio ilm. Th ee g oups o polyme ic NPs we e es ed: unloaded, loaded wi h zinc and wi h doxycycline. NPs we e applied a e den in e ching. The disks we e exposed o a ca iogenic bio ilm challenge in a D ip-Flow Reac o du ing 72 h and 7 d. Hal o he specimens we e no subjec ed o bio ilm o ma ion bu s o ed 72 h and 7 d. LIVE/DEAD® iabili y assay, nano-dynamic mechanical assessmen , Raman spec oscopy and ield emission elec on mic oscopy (FESEM) analysis we e pe o med. The measu ed bac e ial dea h a es, a 7 d we e 46% o he con ol g oup, 51% o he undoped-NPs, 32% o Dox-NPs, and 87% o Zn-NPs; being o al de ec ed bac e ia educed i e imes in he Dox-NPs g oup. Zn-NPs ea ed samples eached, in gene al, he highes complex modulus alues a he esin-den in in e ace o e ime. Rega ding he mine al con en , Zn-NPs- ea ed den in in e aces showed he highes mine aliza ion deg ee associa ed o he phospha e peak and he ela i e mine al concen a ion. FESEM images a e Zn-NPs applica ion pe mi ed o obse e emine aliza ion o he e ched and non- esin in il a ed collagen laye , and bac e ia we e sca cely encoun e ed. The combined an ibac e ial and emine alizing e ec s, when Zn-NPs we e applied, educed bio ilm o ma ion. Dox-NPs exe ed an an ibac e ial ole bu did no emine alize he bonded in e ace. Undoped-NPs did no imp o e he p ope ies o he in e aces. Applica ion o Zn-doped NPs du ing he bonding p ocedu e is encou aged. Keywo ds: den in, deg ada ion, in e ace, nanopa icle, bio ilm 3 1. In oduc ion In den is y, es o a ions based on adhesi e esins a e widesp ead due o he aes he ic p ope ies and he handling cha ac e is ics o hese ma e ials. Bu adhesi e es o a ions ha e a high ailu e a e. A e 8 yea s, composi e es o a ions had a leas 50% g ea e ailu e pe cen age and 3.5 imes highe seconda y decay incidence han amalgam [1]. The adhesi e bond laye in eg i y o composi e es o a ion, i.e, he quali y o he in e ace be ween he oo h and he es o a ion, is he mos impo an ac o ha de e mines he long- e m success o es o a ions [1–4]. In clinical den is y, he mos equen ly in ol ed subs a e o adhesion is den in [5]. The s uc u e o den in is comp ised o a ound 50 ol% mine al. This mine al is p esen in he o m o apa i e c ys alli es, cha ac e ized by a ca bona e en ichmen and calcium de iciency. I is dis ibu ed be ween den inal ubules which un pa allel. The o he 50 ol% is wa e , collagen and o he mino non-collagenous p o eins [6]. Den in adhesion is p omo ed when he subs a e’s mine al phase is emo ed by acids and he oids o med by mine al a e filled wi h adhesi e esin, which is subjec ed o an in si u polyme iza ion, c ea ing he hyb id laye (HL) [7]. Collagen is no easily pene a ed by esins, a e acid e ching. Di e en ial den in di usion dep h be ween acids and esins p oduces a demine alized/non- esin in il a ed collagen laye , loca ed igh a he bo om, and named bo om o he hyb id laye (BHL). I is conside ed an in e acial mic ogap and he weak link a he composi e es o a ions [1]. The BHL is suscep ible o deg ada ion by in insic hos -de i ed ma ix me allop o einases (MMPs) o bac e ial ac i i y [8]. Bac e ial mic oleakage is he mos common complica ion among composi e es o a ions, and seconda y ca ies is he p incipal ailu e cause [2,3,9]. Bio ilm o ma ion a he es o a ion- oo h in e ace [10] is p obably assis ed by he gap o med be ween bo h s uc u es ha enables he coloniza ion o bac e ia [11], he eby acili a ing seconda y ca ies [3,12,13]. The pH dec ease caused by bac e ia acid p oduc ion, al e s he equilib ium and dissol es hyd oxylapa i e, leading o u he den in demine aliza ion [14–16]. Then, he exis ing gaps a he esin-den in bond in junc ion wi h an inc ease in le els o bac e ia a he pe ime e o 4 composi e ma e ials leads o a key ela ionship be ween mic obiology and adhesi e deg ada ion as c ucial elemen s in he ailu e o hese adhesi e es o a ions [1,17,18]. Bac e ia canno be elimina ed om he o al en i onmen , and hey ha e been shown o o m a mic o-ecosys em known as a bio ilm [1]. The educ ion o he pa hogenic impac o he bio ilm a he ma gin o he composi e es o a ion by enginee ing an i-ca iogenic ma e ials is desi ed [1,17–19]. Biocompa ible and non- eabso bable polyme ic nanopa icles (NPs), comp ised o me hac ylic acid, e hylene glycol dime hac yla e and 2-hyd oxye hyl me hac yla e co alen ly connec ed [20], has been p oposed o hinde he o ma ion o seconda y ca ies and ex end adhesi e es o a ions longe i y [21]. An ibac e ial and emine alizing agen s can be chemically a ached o he polyme ca ie h ough unc ional ca boxyl g oups ha a e along he su ace o he NPs [9,22]. Doxycycline and zinc ha e been p e iously doped on o hese NPs and an an ibac e ial [23] and an ibio ilm o ma ion e ec s we e demons a ed on hyd oxyapa i e discs [24]. Fu hemo e, NPs we e p e iously employed a he esin-den in bonded in e ace, and i was s a ed ha hey do no in e e e he bonding p ocess and also may p oduce collagen p o ec ion om den in MMPs [22,25]. The objec i e o his esea ch was o assess he doxycycline and zinc loaded-NPs po en ial o p o ec he esin den in in e ace om a ca iogenic bio ilm. Measu ing he e ec s o an ibac e ial agen s a he bonded in e ace in a simula ed o al en i onmen is challenging. A mul i ac o ial dele e ious e ec o bac e ia a he bonded in e ace has been epo ed [26]. A LIVE/DEAD® s aining echnique con ibu es o de e mine he p esence and g ow h o he bio ilm a he esin-den in in e ace [17]. Bac e ial localiza ion may also be quali a i ely analyzed by scanning elec on mic oscopy. Nano-DMA ep esen s a c ucial ool o de ec he bonded in e ace deg ada ion ough educ ion in mechanical p ope ies o he bonded in e ace ha p ima y esul ed om den in demine aliza ion [27]. High biochemical speci ici y analysis o he esin-den in in e ace h ough complemen a y Raman spec oscopy has also been p oposed [28]. The null hypo hesis o be es ed is ha in il a ion o doxycycline and zinc loaded-NPs in o e ched den in, p e ious o he esin applica ion s ep, does no exe p o ec ion o he hyb id 5 laye om he in i o deg ada ion ac i i y o a ca iogenic bio ilm. 2. Ma e ials and me hods 2.1. Nanopa icles ab ica ion and loading PolymP-n Ac i e nanopa icles we e used (NanoMyP®, G anada, Spain). These pa icles a e syn he ized ollowing a polyme iza ion p ecipi a ion p ocedu e. NPs a e composed by a main monome , 2-hyd oxye hyl me hac yla e, a c oss-linke , e hylene glycol dime hac yla e, and a unc ional monome , me hac ylic acid. De ailed desc ip ion o NPs composi ion and p oduc ion is a ailable [20]. NPs zinc-doping is ob ained ia imme sion o 25 mg o NPs in 25 ml aqueous solu ions o ZnCl2 (40 mgL-1), o in 25 ml o doxycycline hycla e aqueous solu ion (Sigma Ald ich, ChemieGmbh, Rieds , Ge many) a 750 mgL-1, du ing 30 min unde cons an shaking o 20 and 90 min espec i ely. Suspensions we e hen subjec ed o a cen i uga ion p ocess o 20 min (7,800 pm/G- o ce=6,461) and he pa icles washed in phospha e bu e ed solu ion (PBS) and de ached om he supe na an [25,29]. The a ained abso p ion equilib ium o zinc as a ime unc ion and ZnCl2 solu ion concen a ions was p e iously assessed [30] and he maximum a ained zinc complexa ion alue (2 µg Zn/mg NPs) was used o load NPs in he p esen s udy. Doxycycline doping alues o NPs as a unc ion o incuba ion ime and doxycycline concen a ions was also measu ed [30] and he maximum doxycycline adso p ion alue o 27.1 µg Dox/mg NPs was selec ed o load NPs o he p esen esea ch. I has been p e iously shown ha he size o NPs does no change a e loading, and no agglome a ion is p oduced. Hyd odynamic size dis ibu ion o nanopa icles is NPs 250.1 ± 7.5 nm, Dox-NPs 244.4 ± 9.8 nm and Zn-NPs 225.9 ± 8.9 nm [31]. 2.2. Mul ispecies bio ilm s ocks F ozen (-80ºC) mul ispecies bio ilm s ocks om mul iple subjec s we e used. Plaque was collec ed om den al es o a ions ma gins [32]. Uni e si y o Minneso a Ins i u ional Re iew Boa d app o ed he o iginal human plaque sampling p o ocol used o p epa e he s ocks. Employed s ocks om mic ocosm bio ilms we e ep esen a i e o he o al mic obio a. Bio ilm alida ion and a comple e bio ilm cha ac e iza ion may be ound in Rudney e al., [33]. 6 2.3. Den in disks p epa a ion The den in disks p epa a ion was made ollowing Li e al., 2014 [18]. Disk specimens we e made using bo ine inciso s. The bo ine ee h we e s o ed in 1.0% Chlo amine T solu ion. The media was eplaced once a week by eshly p epa ed solu ions and s o ed in 4◦C be o e use. The c owns we e cu o a he cemen -enamel junc ion (CEJ) wi h a low-speed diamond saw (Isome , Buehle , LakeBlu , IL, USA) unde cooling wa e o p o ide he oo den in po ion. These specimens we e hen immed down in o den in cylinde s o 5 mm in diame e (concen ic and pa allel wi h he enla ged oo canals), and he oo canals we e enla ged o 2 mm in diame e using Ga es–Glidden d ills. The cylinde s we e ans e sely cu o p oduce ound disks o abou 4 mm. A e his p ocess, hey we e insed 3 imes wi h dis illed wa e , s o ed in 1.0% Chlo amine T solu ion o 7 days a 4◦C be o e being used. A o al o 88 disks we e p epa ed. 2.4. Den in-composi e disks ab ica ion The disks we e hen insed in dis illed wa e and d ied ou . To p oceed wi h he composi e illing, a common adhesion p o ocol was ollowed. The inne su ace o he disks was subjec ed o an e ching p ocess wi h 35% phospho ic acid du ing 20 s. The disks we e subsequen ly insed wi h dis illed wa e and sligh ly d y. Disks we e andomly di ided in o ou g oups (n=22), ega ding NPs applica ion: 1) NPs we e no applied (e hanol was used ins ead o he NPs suspension); 2) undoped NPs; 3) Dox-NPs; and 4) Zn-NPs. The di e en NPs in e hanol suspensions (10 mg/ml) we e hen applied on he e ched su aces o he disks be o e he adhesi e applica ion. Single Bond (SB) (3 M ESPE, S . Paul, MN, USA) adhesi e, was placed o he inne su ace and polyme ized, ollowing manu ac u e ’s ins uc ions. The disks we e comple ely illed wi h Z-100TM (3 M ESPE, S . Paul, MN, USA), which was applied inc emen ally and ligh cu ed o 40 s. The wo su aces o he disks we e hen g ound la (180-g i ) (Figu e 1). 2.5. In i o bio ilm challenging model Six een samples om each g oup we e andomly selec ed (n=64). Be o e being exposed o bio ilm, he bo om and he side su aces o disks we e co e ed wi h acid esis an nail 7 a nish. F om he uppe su ace, only he ou e pa o he disk was nail a nished (lea ing unp o ec ed he esin-den in in e ace and he esin su ace). Samples we e imme sed o 5 min in 75% e hanol, ai -d ied and s e ilized unde UV ligh o 20 minu es [32]. The ollowing s eps we e pe o med inside he high e iciency pa icula e ai (HEPA) enclosu e. The unp o ec ed (no co e ed wi h nail a nish) esin-den in in e ace and esin su aces we e coa ed wi h 10µl il e s e ilized whole sali a o 5 minu es. 10µl o mul ispecies bio ilm solu ion (769NS) om a 1:100 dilu ion o he bac e ial s ock we e inocula ed on he op o he sali a coa ing o ano he 5 minu es. Disks whe e hen placed in a well pla e (one disk pe well) and co e ed wi h 1.5 ml o s e ile basal mucin medium (BMM) and incuba ed a 37°C, 5% CO2 o 24 h. A e his pe iod, he samples we e ans e ed in o a 4 channel D ip-Flow Reac o wi h a 37ºC incuba o wi h a pump a e o 0.28 ml/minu e. Two ime poin s we e es ablished o analyzing he bio ilm samples: 72 h (24 h o pla e + 48 h o eac o ) and 1 week (24 h o pla e + 6 d o eac o ). Hal o he samples (n=32) we e subjec ed o each ime poin . The o he wen y- ou samples, 3 om each g oup we e incuba ed ollowing he same p ocedu e bu wi hou bac e ia inocula ion. A e ge ing hem ou o he eac o di e en ea men s we e ca ied ou depending on he analyzing me hod. 2.6. LIVE/DEAD® iabili y assay Th ee disks pe each g oup, om hose subjec ed o bac e ia challenge, we e gen ly subme ged in o 0.9% NaCl o emo e he una ached bac e ia. Fo cell iabili y assessmen , he luo escen s ains solu ion was p epa ed (L7012, LIVE/DEAD® BacLigh Bac e ial Viabili y Ki , The moFishe Scien i ic, Wal ham, MA, USA) by adding 3 µl o SYTO9 g een s ain and 3 µl o P opidium iodide ed s ain o 1 ml o s e ilized Milli-Q ul apu e wa e . 100 µl o s aining solu ion was added. A e 20-30 min in ligh -p o ec ed incuba ion a oom empe a u e, he bio ilms g own on op he unp o ec ed a eas o he disks we e analyzed by con ocal lase scanning mic oscopy (CLSM) wi h a mul ipho on con ocal mic oscope (A1R-HD, Nikon Ins umen s Inc., Japan). A 25x wa e imme sion objec i e (Apo LWD, 1.1 NA) was used o di ec ly isualize he bio ilms. Fluo escence emissions we e collec ed a 488 nm o Sy o9 (li ing cells) and a 561 nm o p opidium iodide (dead cells). 512 x 512 and 1024 x 1024 pixel 8 a eas we e scanned, and he Z-s acks we e eco ded e e y 0.375 µm. Images we e analyzed using an image analysis so wa e (ImageJ B, Na ional Ins i u es o Heal h, Be hesda, Ma yland, USA), by measu ing oxel in ensi ies om wo-channel images, and he e o e calcula ing he cell iabili y pe cen age wi hin he s acks. Subs ac ion o he backg ound signal was pe o med. 2.7. Nanodynamic mechanical (NanoDMA) assessmen Th ee di e en disks om each g oup we e subjec ed o nanoDMA. Disks we e sligh ly polished (2400 o 4000 g i and 1 µm diamond pas e) and ho oughly washed wi h deionized wa e . P ope y mappings we e ealized using a Ti-750D T iboInden e (Hysi on, Inc., Minneapolis, MN) equipped wi h nano-DMA III, a comme cial nano-DMA package. The nanoinden e ip was calib a ed agains a used qua z sample using a quasis a ic o ce se poin o 5 µN o main ain con ac be ween he ip and he sample su ace. A dynamic (oscilla o y) o ce o 5 µN was supe imposed on he quasis a ic signal a a equency o 200 Hz. Based on a calib a ion modulus o he ip alue o 1.1400E+3 N/mm2 o he used qua z, he bes - i sphe ical adius app oxima ion o ip was ound o be 150 nm, o he selec ed nano-DMA scanning pa ame e s. Modulus mapping o ou samples was conduc ed by imposing a quasis a ic o ce se poin , Fq =5 µN, o which we supe imposed a sinusoidal o ce o ampli ude FA=1.8 µN and equency =200 Hz. Da a om egions app oxima ely 20×20 µm in size we e collec ed using a scan a e o 0.2 Hz. Each scan esul ed in a 256×256 pixel da a a ay. Specimens we e scanned in he hyd a ed condi ion. Regions o in e es o analysis we e selec ed jus below he adhesi e laye . Unde s eady condi ions (applica ion o a quasis a ic o ce) he inden a ion modulus o he es ed sample, E, was ob ained by applica ion o di e en models ha ela e he inden a ion o ce, F, and dep h, D [34]. Da a om he hyb id laye (HL), bo om o hyb id laye (BHL) we e acqui ed, as ep esen ed in he Fig. 1. 2.8. Raman spec oscopy The same den in su aces men ioned abo e we e subsequen ly s udied by Raman spec oscopy. Fo his analysis, a dispe si e Raman spec ome e /mic oscope (Ho iba Scien i ic Xplo a, Villeneu e d´Ascq, F ance) wi h a 785-nm diode lase h ough a X100/0.90 NA ai 15 educed om 24 h o 7 d o one hi d, howe e i should also be no ed ha he o al bac e ial coun s a he bonded in e ace was educed abou i e imes. I is hypo hesized ha su i ing bac e ia a e 7 d, we e ewe in numbe , bu mos esis an o doxycycline e ec . A he con a y in he case o Zn-NPs he o al bac e ial coun s was simila a e 24 h and 7 d, bu he an ibac e ial ac i i y (dead o inju ed cells) was almos wo- old a e 7 d han a 24 h ime- poin , showing a slowe an ibac e ial ac i i y o Zn-NPs. I has been p e iously epo ed [41] ha LIVE/DEAD® dyes may no be used as an exac quan i a i e measu emen o cell dea h. P opidium iodide s ained cells ( ed cells) may be alsely iden i ied as dead cells, and ep esen cells ha a e inju ed, dead o s a ing iable cells. The e o e ed cells pe cen ages should be aken wi h cau ion. When analyzing FESEM images o hose g oups (Zn-NPs and Dox-NPs a e 7 d), i is clea ha bac e ia we e no easily obse ed a any o he bonded in e aces (Figs. 4b, 4d, 4g, 4h), co obo a ing LIVE/DEAD esul s. In he es o he g oups, bio ilm s uc u es ancho ed and de eloped adhe ence and pene a ion h ough he BHL in den in specimens incuba ed no only a 72 h, bu also a e 7 d (Figs. 3bSI, 3dSI). Den in emine aliza ion a he hyb id laye was encoun e ed when Z-NPs we e applied (Figs. 4g,4h). Howe e , an ad anced den in demine aliza ion was also obse ed a FESEM images o in e aces ea ed wi h Dox- NPs (Figs. 4b, 4d). T ough Raman analysis i was demons a ed ha all g oups e lec ed demine aliza ion a he esin-den in in e ace (Table 2), as he symme ic bending mode ( 2) o phospha e (PO43-) a 431 cm-1 was g ea e han a 446 cm-1 peaks [37] in all cases. I should be conside ed ha NPs a e no e ained by physical abso p ion, bu o ming p ima y bonds wi h demine alized collagen. Dislodging du ing he den in bonding will no occu as pa icle binding o demine alized collagen is p oduced. I may be explained by (1) he esul o he high a ini y be ween he nega i ely cha ged polyme ic NPs (−43.3 mV) and he posi i ely cha ged demine alized den in collagen and (2) due o he binding o COO− g oups om NPs o NH+ si es a den in collagen. Then, pa icle e en ion a he demine alized den in su ace is p oduced, and i is impo an as NPs collagen binding is necessa y o exe a emine aliza ion e ec [25,45]. I is also impo an o s ess ha es ed NPs loca ed a he esin- den in bonded in e ace do no p oduce speci ic spec al ea u es o luo escence ha may 16 o e lap o obscu e Raman signals, as p e iously demons a ed ough a de ailed Raman analysis o he di e en subs a es (polyme s and den in) a hese bonded in e aces demons a ed [45]. E en when he comple e Raman spec a we e p o ided, jus he ele an spec al ea u es we e assigned and commen ed in he p esen manusc ip , some mo e in o ma ion abou Raman analysis o den in bonded in e ace ea ed wi h he p esen expe imen al NPs is p esen ed somewhe e else [45]. Bo h he s o age modulus (E') and he loss modulus (E'') a e in ol ed in he iscoelas ic exp ession o he complex modulus (E*), only E* will be discussed. The complex modulus is a measu e o he ma e ial esis ance o dynamic de o ma ion [46]. The demine alized BHL is he Achilles’s heel o adhesion o den in, p obably, which mos likely de e mine he low es o a ion longe i y [1]. A 7 d o s o age, he BHL o specimens ea ed wi h Zn-NPs and exposed o bio ilm challenge showed he highes E* (Fig. 2), deno ing ad anced in a ib illa emine aliza ion [47]. Complex modulus ou comes show ha he g een and/o yellow egions obse ed a he bo om o he hyb id laye , when Zn-NPs we e applied and analyzed a e 7 d (Fig. 2aSI), had highe alues han he es o he specimens, sugges ing he occu ence o minimal i any demine aliza ion, and hus den in emine aliza ion [21] (Fig. 2). In gene al, complex modulus alues o den in ea ed wi h Zn-NPs we e be ween wo and ou imes old hose o con ol g oup, and i is consis en wi h o he s udies [31,45]. Zinc has been p e iously shown o p oduce calcium/phospha e p ecipi a ion and den in emine aliza ion wi h a high inc ease in mechanical p ope ies [48]. I has also been shown when his new mine al is o med in he p esence o zinc, an exchange be ween Zn2+ and Ca2+ occu s in i o, o ming a subs i u ed apa i e compound h ough an isomo phous subs i u ion [49]. A highe nanoha dness and lowe solubili y was ound in his zinc-subs i u ed mine alized laye [49,50]. Den in ea ed wi h Zn-NPs a e 7 d p esen s Raman bands a 579, 590, cm-1 ( 4 asymme ic bending mode PO43-) e lec ed he lowes peak alues among g oups (Table 2), e oking he in si u p esence o sound den in [37]. The lowes in ensi y a io plo showed a 579/ 959, 590/ 959 (Table 2), also demons a ed den in emine aliza ion a he in e ace [37,51]. This mine al p ecipi a ion p omo ed ac i e den in emodeling wi h inc eased ma u i y which was 17 sus ained on a high collagen quali y pa ame e (1.37) ( a io 1674 cm-1/1690 cm-1) [40] (Table 2) and highe mechanical p ope ies [31,45]. These new mine al o ma ions, absen in he es o he g oups, we e obse ed as mul iple od-like igu es ha illed he in a ubula den in lumen a bo h pe i ubula and in e ubula den in [45] (Fig. 4h). To p e en s ess concen a ion zones and o a oid c ack p opaga ion ac oss he su ace, he emine alized den in should abso b mechanical shock wa es. E* esul s e ealed ha he e is homogenei y in he mechanical p ope ies dis ibu ion be ween HL and BHL, when samples we e ea ed wi h bo h Dox-NPs and Zn-NPs (Fig. 2). HL in bo h g oups showed highe E* han he BHL (1.28 and 1.03 old, espec i ely) enabling, he eby, he ene gy dissipa ion ac oss hei s uc u es. Thus, a 7 d o s o age, nano-DMA e ealed ha he e is he e ogenei y in he mechanical p ope ies dis ibu ion a bo h HL and BHL in he g oup o samples ea ed wi h Dox-NPs, exposed o bio ilm challenge, making he issue p one o c acking [52,53]. This b eakdown o den in, p e e en ially occu ed a he HL [54], p ecisely whe e bands a 579, 590, cm-1 showed he highes peak alues (41.68 and 38.75, espec i ely), which sugges s he g ea es demine aliza ion zone [37] among all g oups (Table 2). The ailu e coincided wi h he o med gap in he esin-den in in e ace which clea ly caused he HL o be de ached om he BHL (Fig. 4e). The p esence o hese c acks suppo s he assump ion ha he c acks can acili a e acids pene a ion. Howe e , seconda y ca ies o ma ion may be impai ed [55], due o bo h he inhibi o y e ec o MMPs by doxycycline [56] and he an ibac e ial p ope ies o Dox- NPs [23,24]. Dox-NPs applica ion did no induce mine als p ecipi a ion o den in emine aliza ion (Fig. 3) [31]. Howe e , he ein o ced den in mic os uc u e and he ela i ely imp o ed mechanical p ope ies (Fig. 2) a e p obably due o he high collagen-c osslinking ha was ob ained a e Dox-NPs applica ion [45,57,58] (Table 2). The main componen o AGE (ad ance glyca ion end p oduc s) is he pen osidine [40]. Pen osidine Raman signal a ained he highes alues in Zn-NPs- ea ed samples (14.38) (Table 2) when compa ed wi h he es o g oups, indica ing ad anced sca olding o collagen and g ea e po en ial o u he emine aliza ion [40]. E en a 72 h o s o age, Dox-NPs- ea ed den in a ained he lowes 18 s o age modulus (Fig. 2 SI) (Table 1SI) wi h minimal emine aliza ion (Figs. 3SIe, 3SI ). Raman peaks de ec ed a 1400cm-1 co espond o bonds o Ca-COO and can be associa ed wi h Ca-Dox complexes ha a ec he p ima y nuclea ion, in e e ing wi h mine al p ecipi a ion and inhibi ing mine aliza ion [59]. Ca-COO peaks became highe o e ime (Fig. 3 ), and his abili y o chela e calcium ions, may be esponsible o some de e io a ion o he mechanical p ope ies [59] (Fig. 2). The ini ial bu s o Doxycycline elease om NPs, which has been p e iously desc ibed [23] was con i med by he hie a chical clus e analysis (HCA) o he Raman spec a a e 72 h (Fig. 3c). The h ee plo s co esponded o he di e en HCA a iances ha appea ed below 750 cm-1 Raman shi s. They s ill appea ed bu became lowe a e 7 d (Fig. 3d), p obably indica ing mino d ug elease om he deli e y sys em a e his ime (NPs) [23,59]. A 7 d o s o age, Dox p esence inc eased a he esin-den in in e ace and so he Dox-Ca complexes (Fig. 3 ). This ou come wa an ed he an ibac e ial p ope ies [24] o Dox-NPs o e ime. The lowe nano-DMA ou comes when bo h con ol o undoped-NPs g oups we e exposed o bio ilm challenge 7 d co ela ed wi h e ealed a eas o demine aliza ion (Figs. 4b, 4d, espec i ely) as a p oduc o incomple e esin imp egna ion o demine alized den in. E en a 72 h o s o age, undoped-NPs ea ed den in showed he lowes loss modulus, among g oups a bo h he HL (2.61 GPa) and he BHL (2.51 GPa) (Table 1SI) (Fig. 2gSI). This also co ela ed wi h he high RMC alues (Table 2) ha we e ob ained a e applying unloaded-NPs. RMC exp esses he ela i e p esence o mine als [phospha e, (PO43-)] e e ed o p o eins (phenyl g oup), [60]. The Raman peak o phenyl in den in ea ed wi h undoped-NPs showed he low in ensi y ha was ob ained in he p esen s udy (43.06) among he g oups in which NPs we e applied (Table 2). This ac e lec ed he p esence o sca ce ma ix con en and damaged collagen (Figs. 4c, 4d), which indi ec ly aised he quo ien RMC (Table 2) [57]. The lack o esin in il a ion and p ope den in emine aliza ion in specimens ea ed wi h undoped-NPs allow he bac e ia o ha e access o colonize he demine alized den in collagen, along he in e ace [61] (Figs. 4b, 4d). As a esul , bac e ia could pene a e h ough he demine alized po es, oids, c acks and open ubules [31] allowing he p esence o ma u e bio ilm wi hin he s uc u es o he esin-den in in e ace, e en a 72 h o s o age (Figs 4b, 4d, 3bSI, 3dSI). 19 Acco dingly, i is specula ed ha bac e ia and he exis ence o demine alized den in a he BHL, may syne gis ically p omo e seconda y oo h ca ies o ma ion. The bonded in e ace is hen deg aded by o al bac e ia leakage a he gaps o he BHL. Bac e ia can di ec ly colonize and bind o demine alized collagen p esen in den in [2], o ming a bio ilm and in ec ing he den inal issues [17]. Bac e ia, h ough adhesins p esen a he cell memb ane and in junc ion wi h o he collagen-binding p o ein and se ine p o eases, ancho age and colonize he non- esin co e ed o unp o ec ed collagen, whe e hey exe hei p o eoly ic and demine alizing ac ion [32,62], p omo ing in e acial deg ada ion. Zinc and doxycycline a e an ibac e ial [63] and also po en ma ix me allop o einases (MMPs) inhibi o s; he eby, hey a e collagen p o ec o s [56]. This poin has gained clinical ele ance a e s udies pe o med by Fine , as i was demons a ed ha den inal pa hogenic bac e ia p oduce MMPs ha may deg ade collagen acili a ing den in in asion [64]. Consis en wi h hese esul s i was also shown ha a MMPs inhibi o wi h no an ibac e ial ac i i y was able o enhance ma ginal in eg i y and o educe in e acial bac e ial ing ess and bac e ial biomass in den in- esin bonded in e aces [65]. The mine al p ecipi a ion in specimens ea ed wi h Zn-NPs (Fig. 4h) lead o a educed bac e ial pene a ion, when compa ed wi h hose ea ed wi h Dox-NPs (Fig. 4 ), a e 7 d o bio ilm challenge. The e o e, he emine alizing and an ibac e ial e ec s we e combined when Zn-NPs we e applied. In his manusc ip , we ha e a ained a posi i e ou come in one o he highes no ewo hy a eas o conce n in adhesi e den is y, he s abili y o he den in bonding in e ace. This wo k p o ides a amewo k o u he esea ch ying o de elop u u e ma e ials wi h in insic an imic obial e ec s, and ma e ials which will no only unc ionally es o e den in bu also s imula e biological esponses ha inc ease emine aliza ion and na u al den in epai [66]. The p esen s udy used a mul ispecies bio ilm om a s ock o plaque mic ocosm bio ilm. This complex and clinically ele an bio ilm p o ides expe imen al condi ions ha can be used o assess he po en ial clinical e icacy o he expe imen al NPs [41]. Howe e , i is impo an o no e ha he an imic obial NPs do no selec i ely kill ce ain pa hogens. They ac 20 as b oad spec um an imic obials. As such, hey indisc imina ely will a ec commensal bac e ia, which can comp omise he balance o species in he heal hy o al bio ilm. Fu he esea ch abou po en ial e ec s on bio ilm dysbiosis should be pe o med. The p esen esea ch is new no only ega ding he use o hese unique loaded NPs bu also, because o he mul iple complemen a y esea ch es ing and cha ac e iza ion echniques and ools pe o med o e alua e he e ec o he bac e ial challenge, a he bonded esin-den in in e ace. Nanomechanical, mo phological and chemical conside a ions we e inno a i ely aken oge he o analyze he da a and d aw conclusions. The esul s o his esea ch a e clinically ele an . Bu his s udy also has some limi a ions: 1) an ibio ics may p oduce bac e ial esis ance and dysbiosis which a e cu en global conce ns; he e o e, u he esea ch is needed o asce ain he long- e m e ec o es ed NPS a he bonded in e ace, 2) he employed d ip low eac o does no ake in o conside a ion he e ec o mechanical loading in gap o ma ion, bac e ial pene a ion and he consequen demine aliza ion, i dese es u u e esea ch, 3) he use o bo ine adicula den in, 3) he pe pendicula di ec ion o he den inal ubules espec o he bonded in e ace which a ies om he o ien a ion ound in eal clinical condi ions and 4) c ea ing ca i ies wi h a high C ac o , a o ing gaps o ma ion and bac e ial coloniza ion. This implies ha cau ion mus be implemen ed when ying o ex apola e he cu en ou comes o clinical condi ions. Fu u e clinical s udies ocusing on he esin-den in in e ace deg ada ion a e encou aged. 5. Conclusions The combined an ibac e ial and emine alizing e ec s o Zn-NPs a he den in in e ace dec eased he hyb id laye deg ada ion media ed by he es ed in i o ca iogenic bio ilm. The e was a signi ican bac e ial iabili y educ ion, o e ime, when Dox-NPs we e applied. Applica ion o Dox-NPs on den in also p oduced ad anced sca olding o collagen bu did no acili a e esin-den in in e ace emine aliza ion. 21 Disclosu e The au ho s epo no con lic s o in e es in his wo k. Acknowledgemen s This wo k was suppo ed by he Minis y o Economy and Compe i i eness and Eu opean Regional De elopmen Fund [MAT2017-85999P MINECO/AEI/FEDER/UE] and Uni e si y o G anada Resea ch & T ans e P og am. The au ho s acknowledge P o esso Joel D. Rudney, Uni e si y o Minneso a o acili a ing he use o mic obiology acili ies and access o he plaque samples. Mul ipho on con ocal lase mic oscope was pe o med a he Uni e si y o Minneso a Imaging Cen e s (h p://uic.umn.edu). Re e ences [1] P. Spence , Q. Ye, J. Pa k, E.M. 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Clegho n, Ex i o de ec ion and cha ac e iza ion o ea ly den al ca ies by op ical cohe ence omog aphy and Raman spec oscopy, J. Biomed. Op . 10 (2005) 031118. 31 Figu e 1. Figu e 1. Schema ic illus a ion p esen ing disks p epa a ion mode and he obse a ion zone o all expe imen al p ocedu es ( he esin-den in bonded in e ace). Regions o in e es o analysis we e selec ed jus below he adhesi e laye . HL: Hyb id Laye ; BHL: Bo om o Hyb id Laye ; PD: Pe i ubula Den in; ID: In e ubula Den in; : esin ag; T: den inal ubule. 32 Figu e 2. Figu e 2. (a,b) Complex Modulus (GPa) a he di e en esin-den in bonded in e aces, measu ed a bo h hyb id laye (HL) (a) and bo om o hyb id laye (BHL) (b) loca ions espec i ely. HL and BHL we e analyzed independen ly. Simila capi al le e s indica e no signi ican di e ences be ween bio ilm g oups wi hin he same NPs g oup and ime-poin s (p<0.01). Compa isons wi hin he same bio ilm and NPs g oups a e indica ed wi h simila lowe case le e s, indica ing no signi ican di e ences be ween ime-poin s (72 h and 7 d o s o age) (p<0.01). Numbe s indica e signi ican di e ences among NPs g oups, wi hin he same bio ilm and ime-poin s g oups (p<0.05). 33 Figu e 3. Figu e 3. 2D mic o-Raman map (20 x 20 µm) o he phospha e peak (961 cm-1) in ensi ies a he esin-den in in e ace ob ained a e Dox-NPs (a) and Zn-NPs (b) applica ion, a 7 d o s o age wi h bio ilm challenge. Raman spec a om hie a chical clus e analysis (HCA) esul s o samples ea ed wi h Dox-NPs, a 72 h (c), 7 d (d) o s o age wi h bio ilm challenge. Th ee le els o HCA clus e ing a e shown. Va iances o dis inc colo s ha e di e ences in Raman spec al dis ibu ion and chemical composi ion. Each pe cen age clus e is assigned o a di e en colo ( ed, g een and blue). Raman spec a om hie a chical clus e analysis (HCA) esul s a he hyb id laye o samples ea ed wi h Zn-NPs, a 72 h and 7 d o s o age wi h bio ilm challenge (e). A unca ed segmen (1200-1500 Raman shi s, cm-1) o mic o-Raman analysis ( ) co esponding o he double peak o doxycycline (1252 cm-1, 1270 cm-1) and calcium-doxycycline complexes (1400 cm-1) a bo h 72 h and 7 d s o age ime in bio ilm challenge, may be obse ed. 34 Figu e 4. 35 Figu e 4. Field emission scanning elec on mic oscopy images o he esin-den in in e - di usion zone es ed a e 7 d o s o age. a, b: Den in in e ace bonded wi h Single Bond adhesi e and wa e /e hanol as p e- ea men . Open (a ows) and illed (poin e s) den inal ubules we e obse ed c ossing o e he den in su ace. Demine alized collagen ibe s (as e isks) below he hyb id laye (HL) and mul iple bac e ia (double a ows) we e disco e ed in a. A a highe magni ica ion (b), non-mine alized and esin unp o ec ed collagen ibbe s (a ows) we e appa en . Collagen ibbe s showed educed diame e . Bac e ial ancho age on unp o ec ed collagen was e iden in b (poin e s) [Scale ba : 3 µm (a), 1 µm (b)]. c, d: Den in in e ace in which undoped-NPs we e in il a ed be o e bonding. Mine al deposi s (double a ows), denuded collagen ibe s (a ows) and adhesi e esin (as e isks) we e shown. Collagen ibbe s exhibi ed diame e s o abou 100 nm, and pe iodical s ia ions ( iangles). A p o use bac e ial conso ium colonized he in il a ed den in (poin e s), in c. Dis up ed collagen ibbe s showing loose ends which a e non mine alized o esin p o ec ed we e e iden in d (a ows). Solely ew indi idual (poin e s) o associa ed ( aced a ows) NPs appea ed on o he deg aded den in su ace. Localized mine aliza ion was e iden (double a ows) [Scale ba : 1 µm (c), 100 nm (d)]. e, : Den in in e ace whe e Dox-NPs we e in il a ed be o e bonding. A e icula pa e n o s agge ed and demine alized collagen ib ils (a ows) was obse ed below he HL, c ossing o e he in e ubula den in a he BHL. Wi hin he esin-den in in e ace, a gap de aching he HL om he BHL was o med (double a ows). Minimal amoun o bac e ia was ad e ed (poin e s) on o he non emine alized den in, in e. A high magni ica ion, s agge ed and demine alized collagen ib ils (a ows) we e obse ed co e ing wo neighbo demine alized and non esin-in il a ed ubules, which appea ed o ally emp y, in . A pe i ubula den in, mine al o med a colla a ound each ubule lumen obse ed (as e isks). Mine alized collagen ibe s and NPs o med he ubula wall (poin e s) [Scale ba : 1 µm (e), 300 nm ( )]. g, h: Den in in e ace whe e Zn-NPs we e in il a ed be o e bonding. The esin composi e (RC) and he adhesi e (ADH) we e isible. Thick HL was obse ed and mine alized collagen ib ils we e no no iceable below new mine al deposi s. Tubules we e sca cely obse ed (a ows). Mine aliza ion was de ec ed as a dense ne wo k o mul ilaye ed mine al deposi s on he den in su ace (as e isks) and bac e ial we e ha dly encoun e ed, in g. In e ubula (ID) and pe i ubula den in (PD) appea ed en i ely emine alized. Tubules we e almos o ally occluded (poin e s). A comple e emine alized web o collagen ibbe s (double a ows) we e disco e ed a he bo om o he hyb id laye (BHL) in h. Fib ils exhibi ed a wid h o a ound 100-200 nm and he ypical 67-nm pe iodici y ( iangles). Minimal amoun o bac e ial colonized he specimens. [Scale ba : 3 µm (g), 300 nm (h), 100 nm (inse )]. 36 Supplemen a y Ma e ial Ti le: Polyme ic nanopa icles p o ec he esin-den in bonded in e ace om ca iogenic bio ilm deg ada ion. Running i le: Nanopa icles an ideg ada ion ac i i y a bonded den in. Au ho s: Manuel Toledano-Oso ioa, Raquel Oso ioa, Fá ima S Aguile aa, An onio Luis Medina- Cas illob, Manuel Toledanoa*, Es ella Oso ioa, Se gio Acos ac, Ruoqiong Chend, Con ado Apa icioe. Ins i u ion: a Uni e si y o G anada, Facul y o Den is y, Den al Ma e ials Sec ion. Colegio Máximo de Ca uja s/n 18071 – G anada - Spain. b c d Uni e si y o G anada, NanoMyP. Spin-O En e p ise. Edi icio BIC-G anada. A . Inno ación 1. 18016 - A milla, G anada, Spain. Bio o ge lab, CIBER-BBN, Edi icio LUCIA, Uni e si y o Valladolid, Paseo Belen 19, Valladolid 47011, Spain. Depa men o Diagnos ic and Biological Sciences, School o Den is y, Uni e si y o Minneso a, Minneapolis, MN, USA. e MDRCBB-Minneso a Den al Resea ch Cen e o Bioma e ials and Biomechanics, Depa men o Res o a i e Sciences, School o Den is y, Uni e si y o Minneso a, Minneapolis, MN, USA. *Co esponding au ho : P o . Manuel Toledano. Uni e si y o G anada, Facul y o Den is y Den al Ma e ials Sec ion Colegio Máximo de Ca uja s/n 18071 – G anada - Spain. Tel.: +34-958243788 Fax: +34-958240809 Email: [email p o ec ed] 37 Figu e 1SI. Figu e 1SI. Con ocal mic og aphs (25 x) ha ep esen ed a 2D maximum p ojec ion o he se ies along ixed axis o he bio ilm a esin-den in in e aces c ea ed using phospho ic acid and a den al adhesi e wi h di e en expe imen al nanopa icles (NPs). a. Specimen wi hou NPs applica ion (con ol) a e 72 h o bac e ial g ow h; b. Undoped nanopa icles (Undoped-NPs) a e 72 h o bio ilm g ow h; c. Bac e ial bio ilm was de eloped du ing 72 h in specimens in which Zn-nanopa icles (Zn-NPs) we e applied; d. Dox-doped nanopa icles (Dox-NPs) we e used; he image was aken a e 72 h o bac e ial g ow h. LIVE/DEAD® BackLigh Bac e ial Viabili y Ki was employed o assess cells in eg i y. Li e cells a e in g een and dead/inju ed cells in ed. Scale ba s a e 30 µm. 38 Figu e 2SI. 39 Figu e 2SI. 2D maps (20 x 20 µm) pe o med a scanning mode by nano-DMA analysis o he complex modulus (E*), a he esin-den in in e ace ea ed wi h Zn-NPs, ob ained a 7 d (a) and 72 h (e, ) ime poin s. In he colo scheme shown, he ed colo co esponds o he highes alue o he locally measu ed moduli, likely co esponding o he highes esis ance o de o ma ion o he in e ubula den in (as e isks). E* e e ed o pe i ubula den in appea s in blue colo (poin e s). The pixel da a a ay a he mapping is o ganized acco ding o E* dis ibu ion ha concu s wi h a clea delimi a ion be ween in e ubula and pe i ubula den in ( aced a ows). Scanning mode nano-DMA analysis o he map o he s o age modulus (E') a he esin-den in in e ace ea ed wi h Zn-NPs a 7 d (b) and Dox-NPs a 72 h ime poin s ( ). In he colo scheme shown, he ed colo co esponds o he highes alue o he locally E' alue moduli, po en ially associa ed o he highes abili y o he in e ubula den in o s o age ene gy, yellowish- ed and yellowish-g een in b and espec i ely, a he mappings. 2D scanning mode nano-DMA analysis o he map o he loss modulus (E") a he esin-den in in e ace ea ed wi h Zn-NPs (c). High loss moduli, o iscous beha io alues (as e isks), we e obse ed in c a in e ubula den in (yellow and ed), in con as wi h he hyb id laye (blue) (poin e s) and he bo om o he hyb id laye (g een) (a ows). 40 Figu e 3SI.