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Biological properties of surface modifed 316 LVM steel

Dyner, Aneta

Abstract

This paper aimed to investigate the selected physicochemical and biological properties of titanium dioxide thin flms depos ited by atomic layer deposition on 316LVM stainless steel dedicated for cardiovascular implants. The main challenge in surface modifcation of these implants is the complexity of the processes taking place in the circulatory system. The atomic layer deposition was carried out for a number of cycles 500 and temperature 200 °C for 316LVM stainless steel substrate. The surface topography and surface microstructure were examined. Mouse fbroblasts L929 and Human Dermal Fibroblasts (NHDF-Ad) were used for cytotoxicity assays. The following biocompatibility aspects were investigated in vitro: direct cytotoxicity, hemolysis, platelet activation and aggregation, and pro-infammatory cytokine levels. The titanium dioxide thin flms inherited the substrate topography. The surface microstructure was amorphous with the typical layer by layer growth. The flm improved the in vitro cell response in terms of cell viability. The cells were also able to proliferate and adhere; however, diferences in the cell morphology and the distribution of cell nuclei were observed. The host cell damage was not noted in terms of lactate dehydrogenase levels. The proposed surface modifcation reduced the hemolysis index and did not signifcantly afect platelet activation and aggregation. Acute cytotoxicity of the thin flms is not predicted basing on the in vitro pro-infammatory cytokine assay. The results of the biological tests may be basis for further biological assessment proving the full biocompatibility of the proposed surface modifcation dedicated for specifc cardiovascular implants.

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Vol.:(0123456789) 1 3 A chi es o Ci il and Mechanical Enginee ing (2023) 23:237 h ps://doi.o g/10.1007/s43452-023-00776-7 ORIGINAL ARTICLE Biological p ope ies o su ace modi ied 316 LVM s eel Ane aDyne 1· RomanMajo 2· ŁukaszMajo 2· JanuszSzewczenko3· K zysz o Lukaszkowicz4· Ka laČechBa abaszo á5· MaciejK zywiecki6· Ma cinBasiaga3 Recei ed: 14 Ap il 2023 / Re ised: 14 July 2023 / Accep ed: 18 Augus 2023 / Published online: 20 Sep embe 2023 © The Au ho (s) 2023 Abs ac This pape aimed o in es iga e he selec ed physicochemical and biological p ope ies o i anium dioxide hin ilms depos- i ed by a omic laye deposi ion on 316LVM s ainless s eel dedica ed o ca dio ascula implan s. The main challenge in su ace modi ica ion o hese implan s is he complexi y o he p ocesses aking place in he ci cula o y sys em. The a omic laye deposi ion was ca ied ou o a numbe o cycles 500 and empe a u e 200°C o 316LVM s ainless s eel subs a e. The su ace opog aphy and su ace mic os uc u e we e examined. Mouse ib oblas s L929 and Human De mal Fib oblas s (NHDF-Ad) we e used o cy o oxici y assays. The ollowing biocompa ibili y aspec s we e in es iga ed in i o: di ec cy o oxici y, hemolysis, pla ele ac i a ion and agg ega ion, and p o-in lamma o y cy okine le els. The i anium dioxide hin ilms inhe i ed he subs a e opog aphy. The su ace mic os uc u e was amo phous wi h he ypical laye by laye g ow h. The ilm imp o ed he in i o cell esponse in e ms o cell iabili y. The cells we e also able o p oli e a e and adhe e; howe e , di e ences in he cell mo phology and he dis ibu ion o cell nuclei we e obse ed. The hos cell damage was no no ed in e ms o lac a e dehyd ogenase le els. The p oposed su ace modi ica ion educed he hemolysis index and did no signi ican ly a ec pla ele ac i a ion and agg ega ion. Acu e cy o oxici y o he hin ilms is no p edic ed basing on he in i o p o-in lamma o y cy okine assay. The esul s o he biological es s may be basis o u he biological assessmen p o ing he ull biocompa ibili y o he p oposed su ace modi ica ion dedica ed o speci ic ca dio ascula implan s. Keywo ds A omic laye deposi ion· Modi ica ion o 316LVM· Ti anium dioxide· Biological e alua ion 1 In oduc ion Fo blood con ac ing de ices, a ious in e ac ions o he bioma e ials wi h blood and su ounding issues should be conside ed. Ci cula ing blood con ac ing de ices (s en s, hea al es, a i icial hea s, and en icula -assis de ices) should be subjec o h ombosis and hema ology assays. Depending on he ype o implan , in e ac ions wi h a i- ous ypes o cells should be in es iga ed. Pla ele esponse (pla ele ac i a ion and agg ega ion) is a help ul ool o de e mining non- h ombogenic p ope ies o he implan su ace. Hemolysis induced by ci cula ing blood con ac - ing de ice may be caused by mechanical and biomechanical ac o s and induce oxic e ec s o p omo e h ombosis [1]. The assessmen o cy o oxici y is a basic assay o all issue con ac ing medical de ices and may include a ious aspec s o he cellula esponse depending on he ype o con ac expec ed. Cy o oxici y can be de e mined by e alu- a ion o cell mo phology, cell damage, cell g ow h, o cel- lula ac i i y. S ainless s eel 316LVM is commonly used in * Ma cin Basiaga [email p o ec ed] 1 Manu ac u e o Medical Ins umen s CHIRMED Ma cin Dyne , Rudniki, Poland 2 Ins i u e o Me allu gy andMa e ials Science o Polish Academy o Sciences, Reymon a 25, 30-059K aków, Poland 3 Facul y o Biomedical Enginee ing, Depa men o Bioma e ials andMedical De ices Enginee ing, Silesian Uni e si y o Technology, Roose el a 40, 41-800Zab ze, Poland 4 Facul y o Mechanical Enginee ing, Depa men o Enginee ing Ma e ials andBioma e ials, Silesian Uni e si y o Technology, Kona skiego 18A S ., 44-100Gliwice, Poland 5 Nano echnology Cen e, CEET, VŠB-Technical Uni e si y o Os a a, Os a a, CzechRepublic 6 Ins i u e o Physics—CSE, Silesian Uni e si y o Technology, Kona skiego 22B S ., 44-100Gliwice, Poland A chi es o Ci il and Mechanical Enginee ing (2023) 23:237 1 3 237 Page 2 o 14 biomedical applica ions as co ona y and pulmona y s en s. As a e y needs mechanical suppo o i s healing wi hou isk o ecoil, s ainless s eel is conside ed o such appli- ca ions. Howe e , compa ed o o he me allic bioma e ials (e.g., Ti-based alloys), co osion esis ance o biomedical- g ade o s ainless s eel 316LVM is signi ican ly low. Passi e laye does no p o ec he s eel su icien ly when subjec ed o ex emely co osi e en i onmen s. The e o e, p o iding coa ings o co osion p o ec ion which does no change he mechanical p ope ies o he ma e ial a e subjec o cu en esea ch, as co osion o a me allic ma e ial is one o he mos impo an issues o be conside ed when i is designed o implan s. Taking in o accoun he abo e equi emen s, low- empe - a u e su ace modi ica ion echniques wi h abili y o co e geome ically complex su aces (minia u ized implan s) on all sides should be conside ed. The ALD echnology, which is a a ia ion o he CVD me hod, allows o he p oduc ion o ul a- hin, homogeneous and epea able coa ings wi h a wide ange o po en ial biological applica ions. In ALD, al e na ing pulses o p ecu so and eac an gases a e sepa- a ed by pu ging s eps wi h an ine ca ie gas (N2 o A ) o achie e sel -limi ing su ace eac ions. The ALD eac- ion ends when all a ailable si es on he eac i e su ace a e occupied. This ea u e is e e ed o as sel -limi ing, which enables ALD o deposi uni o m laye s o high con o ma ion and p ecisely con olled hickness on all ypes o subs a es [2]. Nume ous es s o coa ings using he ALD me hod show an imp o emen in he co osion esis ance o he subs a e depending on chemical composi ion (SiO2, Al2O3, SiO2/ TiO2, ZnO, and Z O2–Al2O3) o he laye s and ALD p ocess pa ame e s [3–7]. Some single aspec s o biological p op- e ies we e also s udied, indica ing he in luence o ALD p ocess pa ame e s on a ious aspec s o biocompa ibili y [8–18]. The hi d-gene a ion s en s cu en ly used in clinical p ac ice a e he esul o many yea s o esea ch aimed a minimizing he isk o es enosis and h ombosis. While he p oblem o es enosis has been e ec i ely sol ed by he use o mode n an i-p oli e a i e d ugs and ma ices o biodeg adable d ug- eleasing polyme s, he p oblem o la e h ombosis has no been ully sol ed. The use o dual an i- pla ele he apy is s ill he s anda d a e s en ing, which in some cases inc eases he isk o bleeding. The op imal s en su ace should p e en he adso p ion o ib inogen, p e en he adhesion, agg ega ion, and ac i a ion o pla ele s, inhibi he adhesion and p oli e a ion o smoo h muscle cells, and p omo e he adhesion and g ow h o endo helial cells. Va i- ous su ace modi ica ion echniques based on deposi ion o i anium dioxide, has been widely used o biomedical appli- ca ions, showing a posi i e in luence on a ious aspec s o biocompa ibili y. The p esence o hyd oxyl g oups on he su ace p omo es osseoin eg a ion in bone implan s. The same p ope y can be also used in su ace modi ica ion o s en s, consis ing o su ace immobiliza ion leading o gene a ion o ni ic oxide o p omo e eendo helializa ion [18]. The ongoing in ensi e esea ch in o he c ea ion o biocompa ible implan su aces in con ac wi h he ci cula - ing blood indica es he lack o sa is ac o y solu ions in his ield, mainly due o he complexi y o he physiological p o- cesses occu ing in he ca dio ascula sys em. In his case, he biological es ing p og am should co e many aspec s o biocompa ibili y. The combina ion o biological p ope ies wi h he app op ia e physicochemical p ope ies o implan s is also an impo an ac o in luencing he selec ion o app o- p ia e p ocess pa ame e s o implan su ace modi ica ion. The aim o his s udy is o in es iga e he biological p op- e ies o i anium dioxide hin ilms deposi ed by a omic laye deposi ion on 316 LVM s ainless s eel dedica ed o ci cula ing blood con ac ing medical de ices. The p ecu so s used in he ALD p ocess (TiCl4/H2O) a e he mally s able up o high empe a u es, bu he co osi e byp oduc HCl may be ha m ul o he deposi ion ins umen s; he e o e, deposi- ion empe a u e 200°C was p oposed o he ALD p ocess. The mos impo an aspec s o he biocompa ibili y we e s udied, including: di ec cy o oxici y, pla ele ac i a ion and agg ega ion, hemolysis, and p edic ion o acu e oxici y. 2 Ma e ials andme hods 2.1 Ma e ials The es specimens a e desc ibed in Table1. 5 pcs. o each specimen we e used o es ing. A e age alues a e p esen ed in he es esul s. The es sample o 316LVM was subjec o p elimina y su ace inishing ypical o s en ab ica ion and deposi ion o TiO2 by he means o ALD. Table 1 Specimen desc ip ion Specimen code Specimen desc ip ion 316LVM S ainless s eel 316LVM, annealed, elec opolished (H3PO4/H2SO4), passi a ed (40% HNO3), au ocla ed 316LVM-TiO2S ainless s eel 316LVM, annealed, elec opolished (H3PO4/H2SO4), passi a ed (40% HNO3) ALD-TiO2- coa ed (500 cycles, 200°C), au ocla ed, pu ging gas ni ogen A chi es o Ci il and Mechanical Enginee ing (2023) 23:237 1 3 Page 3 o 14 237 The es ma e ial was 316LVM s ainless s eel in he annealed s a e in he o m o discs wi h diame e d = 14mm and hickness g = 3mm. Modi ica ion o he su ace o he analyzed bioma e ial was ca ied ou using such p ocedu es as: elec ochemical polishing, passi a ion, applica ion o a TiO2 coa ing using he low- empe a u e A omic Laye Depo- si ion (ALD) me hod, as well as medical s e iliza ion. To ensu e he equi ed physical and chemical p ope ies o he 316LVM s eel su ace, condi ions o i s su ace ea men ha e been de eloped. The i s su ace ea men was elec- ochemical polishing, which was ca ied ou in a ba h based on a mix u e o o hophospho ic acid and sul u ic acid (VI). This p ocess was ca ied ou un il he su ace oughness o Ra < 0.16µm, ecommended o blood con ac ing implan s, was ob ained. Then, he samples we e chemically passi a ed in 40% HNO3 acid. These a e he basic s ages o shaping he su ace o me al bioma e ials used o implan s wi h minia- u ized geome ic ea u es. Then, a laye o TiO2 was depos- i ed on he p epa ed samples using he ALD me hod. TiCl4 (Ti anium (IV) chlo ide) + H2O was used as a p ecu so . The pa ame e s o he deposi ion a e desc ibed in Table2. The las s age o he p oposed su ace ea men included medical s e iliza ion, which was ca ied ou using he s eam me hod in an au ocla e a empe a u e T = 135°C and p es- su e p = 2.1ba . 2.2 Mic os uc u e Cha ac e iza ion o he mic os uc u e o he su ace laye was pe o med using ansmission elec on mic oscopy (TEM). The mic os uc u e was cha ac e ized by he TEM echnique in he so-called b igh - ield obse a ion BF TEM, scanning ansmission elec on mic oscopy (STEM), and high- esolu ion TEM (HRTEM). Quali a i e chemical analysis was pe o med by X- ay spec oscopy wi h ene gy dispe sion (EDS). Comp ehensi e TEM analysis was pe - o med using TECNAI G2 F20 (200kV) FEG (FEI) and THEMIS (200kV) FEG (The mo Fishe Company) mic o- scopes. Thin ilms o TEM obse a ion we e p epa ed by he ocused gallium ion beam (FIB) echnique on an SCIOS II DualBeam (The moFishe Company) equipped wi h an EasyLi insi u mic omanipula o . 2.3 Su ace opog aphy Su ace opog aphy es ing was pe o med using an op i- cal p o ilome e 3D Su ace Me ology Mic oscope Leica DCM8. Su ace scans we e p ocessed in Leica Map so wa e, esul ing in a e age Sa alues and 3D su ace isualiza ions. 2.4 Cell iabili y assay The cell iabili y assay was pe o med by he di ec me hod acco ding o he PN-EN ISO 10993-5:2009 s anda d [19] on ib oblas s (L929 ATCC). The supplemen ed P omoCell Fib oblas G ow h Medium 2 en iched wi h an ibio ics (SIGMA ALDRICH An ibio ic An imico ic Solu ion) was used as a medium. Cell iabili y was assessed a e a 24-h incuba ion using luo escence mic oscopy. FDA ( luo escein diace a e) and PI (p opidium iodide) we e used in cell s ain- ing. The esea ch was ca ied ou using a Ca l Zeiss Exci e 5 scanning lase con ocal mic oscope. Image analysis and cell coun ing we e pe o med using ZEN 2008 so wa e and AxioVision 4 Module Au oMeasu e. The cy o oxici y s udies we e complemen ed by he di ec me hod o es ing he le el o lac a e dehyd ogenase (LDH), a subs ance eleased om damaged cells. Human ib oblas cells (L929 ATCC) we e used o he s udy, and Fib oblas G ow h Medium 2 (P omoCell) en iched wi h supplemen s and an ibio ics was used as he cul u e medium. A e incu- ba ion, he medium was aken om he abo e samples and cen i uged, and hen, he supe na an was aken om he cen i uged solu ion o he analysis o LDH le el using he colo ime ic Roche Cy o oxici y Assay Ki . 2.5 S udies o cell g ow h, p oli e a ion, andadhesion The p oli e a ion s udy was pe o med on Human De mal Fib oblas s in he adul skin e sion (NHDF-Ad). The s udy quali a i ely assessed cell mo phology, g ow h, adhesion, and di ec ion o elonga ion p ocesses based on he appea - ance o he cy oskele on, as well as he appea ance and dis ibu ion o cell nuclei and hei abili y o p oli e a e. Table 2 Technological condi ions o he ALD me hod TiCl4Ca ie gas low a e (N2/A ) [sccm] 200 P ecu so in oduc ion ime [s] 0,1 Chambe pu ging ime [s] 4,0 H2O Szybkość p zepływu gazu nośnego (N2) [sccm] 200 Reagen in oduc ion ime [s] 0,1 Chambe pu ging ime [s] 5,0 Chambe empe a u e [°C] 200 Numbe o cycles 500 A chi es o Ci il and Mechanical Enginee ing (2023) 23:237 1 3 237 Page 4 o 14 Fig. 1 TEM BF esul s o he ALD o TiO2 coa ing Fig. 2 STEM + EDS esul s o he ALD o TiO2 coa ing A chi es o Ci il and Mechanical Enginee ing (2023) 23:237 1 3 Page 5 o 14 237 The cul u e was ca ied ou in a dedica ed supplemen ed medium in an incuba o a 37°C, 99% humidi y and 5% CO2. Cells we e ixed wi h o maldehyde, pe meabilized wi h T i onX-100 and blocked in 0.1% bo ine se um albu- min (BSA) solu ion in T is-bu e ed saline (TBS). To assess cell p oli e a ion, In i ogen™ DAPI D1306 by The mo Fig. 3 STEM + EDS esul s o he ALD o TiO2 coa ing Fig. 4 HRTEM esul s o he ALD o TiO2 coa ing Fig. 5 Example mo phology o he su ace o uncoa ed 316LVM samples, op ical p o- ilome y, × 50 A chi es o Ci il and Mechanical Enginee ing (2023) 23:237 1 3 237 Page 6 o 14 Fishe was used o s ain cell nuclei, allowing o nuclea and ch omosomal coun e s aining. DAPI emi s blue luo escence when bound o AT egions o DNA. Alexa Fluo 488 om The mo Fishe (a abbi IgG seconda y an ibody) wi h g een luo escence was used o F-ac in ( ib illa ac in) s aining. Ac in is an elemen o he cy oskele on in ol ed in cell di i- sion, main enance, and changes in he shape and mo emen o he cell. Fluo escen ly labeled ac in is an impo an ool o s udying he s uc u al dynamics o he cy oskele on in he li ing and ixed cells. 2.6 E alua ion o  hee ec o bioma e ial on ed blood cells The aim o he in i o s udies was o e alua e he e ec o ex ac s con ac ed wi h ma e ials on p ese ed whole blood componen s. The es s we e ca ied ou in acco dance wi h he PN-EN ISO 10993-4:2018-02 [20] and ASTM F 756–00 [21] s anda ds. The es s we e ca ied ou on human whole blood (KPK) ob ained om he Regional Cen e o Blood Dona ion and Hemo he apy in Ka owice. The blood was an icoagula ed wi h CPDA p ese a i e luid. The esea ch included h ee s udy g oups: • Blank es : CCP ees anding a oom empe a u e, no subjec ed o he condi ions o he expe imen , • Nega i e con ol: CCP wi hou con ac wi h he es ma e ial, subjec ed o expe imen al condi ions (slow mixing). • S udy g oup: ma e ials con ac ed wi h CCP in expe i- men al condi ions. The KPK was subjec ed o a 3-h con ac wi h he es ed ma e ials and ex ac s a a empe a u e o 37°C, in a slow- mixing sys em. The impac o he es ed ma e ials on ed blood cell pa ame e s was de e mined by assessing he deg ee o hemolysis, de e mined by calcula ing he hemoly- sis index o he es ed ma e ials. Fig. 6 Example mo phology o he su ace o samples wi h TiO2 laye , op ical p o ilom- e y, × 50 Table 3 A e age alues o su ace a i hme ic mean high and ough- ness Modi ica ion o su ace Sa, nm Ra, nm 316LVM 11.63 9.34 316LVM-TiO211.52 9.89 Fig. 7 Con ocal mic oscopy o uncoa ed 316LVM samples—all channels A chi es o Ci il and Mechanical Enginee ing (2023) 23:237 1 3 Page 7 o 14 237 2.7 S udies o  h ombogenic p ope ies Me hods de eloped by Sanak e al. [22] we e used o he s udy. P-selec in ac i a ing ma ke s and he ib inogen an i- gen-binding si e in he GP IIb–IIIa assembly (PAC-1) we e used as indica o s o pla ele ac i a ion and CD 61 ma ke was used o agg ega ion assessmen . Posi i e and nega i e con ols we e p epa ed o analyze he amoun o agg ega es. Nega i e con ol was ob ained om human blood d awn on sodium ci a e. A posi i e con ol was p epa ed by mixing blood wi h adenosine di-phospha e (ADP). 3 Resul s 3.1 Mic os uc u e The esul s o he conduc ed mic os uc u e es s a e p e- sen ed in Figs.1, 2, 3, 4. S udies using di ac ion con as showed on he c oss-sec ion he g ow h o a omic laye by a omic laye , co ec o he ALD echnique, a a dis ance o abou 5nm om he subs a e (Fig.4). Fu he on, he s uc- u e was amo phous. In addi ion, undesi able blis e s we e also no iced, which may indica e a poo e quali y o adhe- sion o he coa ing o he subs a e (Fig.1). The amo phous na u e o he coa ing was also con i med by scanning ans- mission elec on mic oscopy (STEM) and high- esolu ion HRTEM images (Fig.3 and 4). The esul s o STEM + EDS Fig. 8 Con ocal mic oscopy o uncoa ed 316LVM samples—sepa a ed channels Fig. 9 Con ocal mic oscopy o TiO2-coa ed samples—all channels Fig. 10 Con ocal mic oscopy o TiO2-coa ed samples—sepa a ed channels; ed—dead cells, g een—ali e cells, and g een + ed—all channels A chi es o Ci il and Mechanical Enginee ing (2023) 23:237 1 3 237 Page 8 o 14 con i med he p esence o Ti a oms in he coa ing, which was also homogenously dis ibu ed along he hin ilms (Fig.2). The absence o subs a e o igina ed a oms in he coa ing was con i med. 3.2 Su ace opog aphy Example su ace opog aphies o he subs a e and TiO2-coa ed specimens a e p esen ed in Figs.5 and 6. Sa (a i hme ic mean heigh ) and Ra (a i hme ic a e age alue o il e ed oughness) alues a e p esen ed in Table3. Simila geome ical ea u es o he su ace a e clea ly isible, which indica es he endency o he laye o inhe i he subs a e su ace opog aphy. 3.3 Cell iabili y assay The esul s o he conduc ed cell su i al s udies a e shown in Figs.7, 8, 9, 10, 11. Analyzing he con ocal mic oscopy pho o, weak g ow h on he 316LVM s eel subs a e was obse ed. The cells had a cha ac e is ic ound shape, which indica es he poo iabili y o cells wi h ac i e mi ochond ia and a la ge numbe o nec o ic cells. In u n, su ace modi ica ion by applying a TiO2 coa ing imp o ed he biological p ope ies. A dec ease in cy o oxici y was obse ed. The cells on he su ace o he coa ing ha e an elonga ed shape and a educed numbe o nec o ic cells was ound. Fib oblas cells belong o he g oup o adhe en cells. In he case o he co ec , om he poin o iew o subs a e biology, memb ane pola i- za ion occu s and he ac in cy oskele on is ac i a ed. The cells elease he so-called phyllo- and lamellipodia, which is a posi i e phenomenon. Based on he s udies, su i al a es o 95% and 100% we e ound o he 316LVM and 316LVM wi h TiO2 samples, espec i ely. Acco ding o ISO 10993, educ ion o cell iabili y by mo e han 30% is conside ed a cy o oxic e ec , bu his was no obse ed in he analyzed samples. Figu e12 shows a g aph o LDH lac a e dehyd oge- nase le els. The lowe he alue o he es ed sample, he smalle he amoun o sec e ed isoenzyme, which means less cy o oxici y. Fo he es ma e ials, all alues a e in he same ange as he LDH alue o he con ol ma e ial, which was polys y ene (PS) in his s udy. The posi i e con ol was p esen ed as a c i ical alue o 0.6, which indi- ca es a 50% p obabili y o cell memb ane damage. 3.4 S udies o cell g ow h, p oli e a ion, andadhesion The esul s o he pe o med cell p oli e a ion s udies a e shown in Figs.13 and 14. Analyzing he con ocal Fig. 11 Numbe o iable cells s. all cells 316LVM 316 LVM + TiO2 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 0 2000 4000 6000 8000 1000012000 1400016000 180002 0000 Viable cells All cells 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 316LVM 316LVM+TiO2 PS (nega e con ol) Posi e con ol LDH [O.D.] Cy o oxici y in di ec con ac Fig. 12 LDH le el o es ed samples in di ec con ac A chi es o Ci il and Mechanical Enginee ing (2023) 23:237 1 3 Page 9 o 14 237 mic oscopy images, bo h he 316LVM e e ence sample and he TiO2 coa ing show a ypical no mal appea ance o ib oblas s wi h a spindle elonga ed shape, ocal adhesion (b igh elonga ed spo s), and a ied di ec ion o elonga- ion. In bo h cases, nume ous ound o o al cell nuclei can be seen, some in he di iding phase (close o each o he o pa ially o e lapping blue spo s). In he case o he TiO2 coa ing, a g ea e di e si y o he cy oskele on and a di e en densi y and leng h o ac in ilamen s can be obse ed. Places a e also isible wi h inc eased densi y o cell nuclei. In case o uncoa ed samples, in e up ions o he ac in ibe s con inui y in he o m o da k lines we e obse ed. On bo h he 316LVM e e ence sample and he TiO2 coa ing, ound da k spo s a e obse ed. Fig. 13 Example pho os o p oli e a ion s udies aken wi h a scanning lase mic oscope o sample 316LVM