Full Leng h A icle
Sol-gel TiO
2
-based coa ings in 3D p in ed po ous Ti-6Al-4V alloy s uc u es
as e icien an ibac e ial d ug deli e y sys ems: Tho ough s uc u al and
biological cha ac e iza ion
Anna Knaislo ´
a
a,*
, Diana Ho ka co ´
a
b
, E a Jablonsk´
a
c
, Dalibo Voj ˇ
ech
a
a
Depa men o Me als and Co osion Enginee ing, Uni e si y o Chemis y and Technology, P ague. Technick´
a 5 166 28 P ague, Czech Republic
b
Depa men o Glass and Ce amics, Uni e si y o Chemis y and Technology, P ague. Technick´
a 5 166 28 P ague, Czech Republic
c
Depa men o Biochemis y and Mic obiology, Uni e si y o Chemis y and Technology, P ague. Technick´
a 5 166 28 P ague, Czech Republic
ARTICLE INFO
Keywo ds:
Dode hick
Gy oid
Sol-gel coa ings
3D p in ing
Hyd oxyapa i e
sil e
ABSTRACT
The applica ion o sol-gel coa ings on i anium-based ma e ials o e s a p omising app oach o enhancing hei
bioac i i y, an ibac e ial p ope ies, and adhesion, pa icula ly o biomedical applica ions. This s udy ocuses,
o he i s ime, on he p epa a ion and cha ac e iza ion o sol-gel TiO
2
-based coa ings con aining hyd oxy-
apa i e and sil e in 3D-p in ed po ous gy oid and dode hick s uc u es. TiO
2
-based coa ings on he s anda d
w ough Ti-Al-V alloy ods we e used as a e e ence. The coa ings we e applied ia he speci ic dip-coa ing
p ocess de eloped by he au ho eam. The mic os uc u al analysis e ealed ha he sol-gel coa ings on he
e e ence w ough od samples we e homogeneous and well-adhe ed. The coa ings on he po ous gy oid and
dode hick s uc u es exhibi ed some localized c acking due o he complex geome y o he po ous s uc u es.
Bioac i i y was e alua ed h ough he s anda d in i o simula ed body luid es s, con i ming hyd oxyapa i e
p ecipi a ion on HA-con aining coa ings. An ibac e ial p ope ies we e assessed agains Esche ichia coli,
demons a ing nea ly 100 % bac e ial inhibi ion o Ag-con aining coa ings. Cy o oxici y es s wi h L929
ib oblas cells indica ed ha coa ings wi h lowe Ag concen a ions in sol we e non- oxic, while highe Ag
concen a ions in sol esul ed in educed cell iabili y, pa icula ly in gy oid s uc u es.
1. In oduc ion
Ti anium and i s alloys, pa icula ly Ti–6Al–4 V, a e widely used in
biomedical applica ions due o hei excellen mechanical p ope ies
and biocompa ibili y, making hem sui able o long- e m implan a ion
[1]. Sol-gel i ania-based coa ings applied o Ti-6Al-4 V biomedical alloy
ab ica ed ia 3D p in ing ep esen a g owing a ea o esea ch, espe-
cially in biomedical and enginee ing ields. These coa ings a e p ima ily
u ilized o enhance su ace p ope ies, including bioac i i y, adhesion,
co osion esis ance, an ibac e ial pe o mance and pho oca aly ic ac-
i i y [2,3]. While hey ha e been applied o compac , plana implan
su aces, he e a e no scien i ic epo s, o ou knowledge, ha explo e
hei applica ion on 3D-p in ed po ous Ti-6Al-4 V s uc u es. Po ous
a chi ec u es, howe e , o e a e y high speci ic su ace a ea, which
makes hem sui able candida es o hos ing d ugs o an ibac e ial
agen s. Gy oid and dodecahed on la ice s uc u es a e pa icula ly ad-
an ageous due o hei abili y o mimic he a chi ec u e o na u al
abecula bone [4,5]. Gy oids, being iply pe iodic minimal su aces,
p o ide a high su ace-a ea- o- olume a io and excellen mechanical
s eng h, [6] making hem ideal o bone sca old applica ions [7,8].
Likewise, dodecahed on (dode hick) s uc u es a e complex po ous
ne wo ks ha o e high load-bea ing capaci y and unable po osi y,
imp o ing mechanical s abili y, luid pe meabili y, and educing s ess
shielding [9,10].
The sol-gel p ocess in ol es he ans o ma ion o a colloidal solu ion
(sol) in o a h ee-dimensional gel ne wo k, allowing p ecise con ol o e
coa ing composi ion, hickness, and su ace cha ac e is ics [11].
Ti ania-based sol-gel coa ings a e pa icula ly ad an ageous o
biomedical applica ions due o hei biocompa ibili y, os eoin eg a ion
capabili y, an ibac e ial ac i i y, and esis ance o co osion [12–14].
Coa ings doped wi h hyd oxyapa i e (HA) and sil e ni a e (AgNO₃) can
u he enhance bone in eg a ion and in oduce an ibac e ial p ope ies
[15]. Pos -deposi ion hea ea men imp o es coa ing adhesion and
c ys allini y, con e ing amo phous TiO₂ in o mo e s able ana ase o
* co esponding au ho .
E-mail add ess: [email p o ec ed] (A. Knaislo ´
a).
Con en s lis s a ailable a ScienceDi ec
Applied Su ace Science Ad ances
jou nal homepage: www.sciencedi ec .com/jou nal/applied-su ace-science-ad ances
h ps://doi.o g/10.1016/j.apsad .2025.100816
Recei ed 27 May 2025; Recei ed in e ised o m 21 July 2025; Accep ed 6 Augus 2025
Applied Su ace Science Ad ances 29 (2025) 100816
A ailable online 14 Augus 2025
2666-5239/© 2025 The Au ho (s). Published by Else ie B.V. This is an open access a icle unde he CC BY license ( h p://c ea i ecommons.o g/licenses/by/4.0/ ).
u ile phases, he eby imp o ing long- e m du abili y and biological
pe o mance [16,17]. On 3D-p in ed i anium subs a es, sol-gel coa -
ings os e cell a achmen and p oli e a ion while o ming a p o ec i e
laye agains oxida ion and deg ada ion [16,18]. The inclusion o sil e
also p o ides an an imic obial e ec , helping p e en pos -implan a ion
in ec ions [19].
Se e al s udies conduc ed a ou uni e si y ha e ocused on he
de elopmen and cha ac e iza ion o i anium-based coa ings on i a-
nium subs a es o biomedical applica ions. These included he use o
sol-gel and dip-coa ing echniques wi h a ious addi i es such as sil e ,
calcium, and phospha e o imp o e implan pe o mance. The coa ings
we e e alua ed o adhesion, an ibac e ial ac i i y, bioac i i y, and
cy ocompa ibili y, showing p omising esul s such as s ong adhesion,
an imic obial e ec s agains Esche ichia coli and S. epide midis, p o-
mo ion o hyd oxyapa i e o ma ion, and non- oxici y o cells. Some o
ou esea ch also explo ed coa ings on po ous i anium, TiSi alloys, and
he e ec s o calcium i ana e powde addi ions o sol-gel o mula ions
[20–27]. Howe e , he applica ion o sol-gel coa ings o 3D-p in ed
po ous s uc u es emains uns udied. This is pa icula ly challenging
due o he need o comple e and uni o m con ac be ween he iscous
sol and he in e nal su aces o ine po es. The e o e, he aim o his
s udy was o p epa e and cha ac e ize sol-gel i ania-based coa ings,
wi h sil e (Ag) and comme cial hyd oxyapa i e (HA, Ca₁₀(PO₄)₆(OH)₂),
on h ee di e en i anium-based subs a es: a Ti-6Al-4 V alloy od, a
3D-p in ed po ous Ti-6Al-4 V gy oid s uc u e, and a 3D-p in ed po ous
i anium dode hick s uc u e. The coa ings we e assessed in e ms o
bioac i i y and an ibac e ial p ope ies o e alua e hei po en ial o
biomedical applica ions.
2. Ma e ial and me hods
2.1. Sample p epa a ion
The ini ial subs a e o he sol-gel coa ing was a machined w ough
TiAl6V4 alloy od, 15 mm in diame e and 3 mm in heigh , wi h a
su ace a ea o 4.94 cm
2
. This od unde wen g inding wi h P400, P600,
and P800 g i silicon ca bide ab asi e pape s (g inde Buehle Me aSe
250). Subsequen ly, he od was cleaned ul asonically in e hanol o 10
min.
The second subs a e o he sol-gel coa ing was a 3D-p in ed
TiAl6V4 alloy gy oid, 15 mm in diame e and 3 mm in heigh , wi h a
su ace a ea o 9.90 cm
2
, calcula ed a e age po osi y 66 % (Fig. 1a)
[28–31]. The gy oid was ul asonically cleaned in e hanol o 3 ×10
min.
The hi d subs a e o he sol-gel coa ing was a 3D-p in ed i anium
dode hick (la ice: 1.35), 15 mm in diame e and 3 mm in heigh , wi h a
su ace a ea o app oxima ely 14 cm
2
, calcula ed a e age po osi y 63 %
(Fig. 1b) [28–31]. The dode hick was ul asonically cleaned in e hanol
o 2 ×10 min.
2.2. Composi ion and condi ions o he p epa a ion o sols
The basic i anium sol (T sol) was p epa ed by g adually mixing
e a-n‑bu yl‑o ho i ana e (Sigma Ald ich Me ck), T i on X-100 (Ro h),
1 mol/l HNO
3
(p.a., Lach-Ne ), ace ylace one (p.a., Lach-Ne ), and
e hanol (den.), ollowed by s i ing a labo a o y empe a u e o 24 h
and aging a labo a o y empe a u e o 24 h. The aged T sol had a
iscosi y o 4.8 mPas ( iscome e RV1). The basic sol was hen di ided
in o h ee 25 ml aliquo s: he i s aliquo emained unmodi ied (T sol),
AgNO
3
wi h a sil e concen a ion o 0.04 mol/l was added o he sec-
ond, and AgNO
3
wi h a sil e concen a ion o 0.06 mol/l was added o
he hi d. A e dissol ing he AgNO
3
, comme cial hyd oxyapa i e wi h a
concen a ion o 0.2 mol/l was added o he sols (TAN04HA sol,
TAN06HA sol).
A dip-coa e (IDLab) was used o coa ing. The dipping speed was 20
cm/min, he wi hd awal speed was 6 cm/min, and he dwell ime in he
sol was 30 s, wi h a sol s i ing speed o 200 pm (IKA). Coa ing was
pe o med a labo a o y empe a u e.
2.3. Hea ea men condi ions o coa ed subs a es
The coa ed samples we e d ied a labo a o y empe a u e, and hen
hea - ea ed in ai a 400 ◦C o 120 min using a hea ing a e o 2 ◦C/min
(Clasic). The samples we e cooled o oom empe a u e o e nigh .
2.4. Measu emen o he selec ed p ope ies
The adhesion o he coa ings o he machined w ough od subs a e
was assessed using an adhesi e ape es , acco ding o ASTM D3359–02
[32]. A 6 ×6 g id o sc a ches was made on he coa ings. Following ape
applica ion (Pe macel 99), loading, and peeling, he coa ing su aces
we e isually cha ac e ized, and he deg ee o adhesion was de e mined
using a classi ica ion scale.
The bioac i i y o all coa ing ypes on he h ee subs a e ypes was
e alua ed acco ding o ISO 23,317 [33]. Coa ed samples (n =2 pe
condi ion) we e imme sed in a simula ed body luid solu ion, main-
aining a cons an su ace a ea- o- olume a io (S/V), o 21 days a 36.5
◦C. The simula ed body luid solu ion was eplaced e e y 7 days. A e
he in i o es , he samples we e d ied a labo a o y empe a u e and
cha ac e ized.
Using a omic abso p ion spec opho ome e (AAS, Agilen 280 FS)
he concen a ion o Ca
2+
was de e mined, and UV–VIS (Shimadzu UV-
2450) was used o measu e he concen a ion o (PO
4
)
3-
ions in SBF
solu ions be o e and a e he 21-day in i o es .
The an ibac e ial ac i i y o he coa ings was measu ed s a ically in a
low box (Sa eFas Eli e) o 24 h a labo a o y empe a u e using E. coli
(s ain DMB3138). The coa ed subs a es we e imme sed in o suspen-
sion o physiological solu ion (NaCl, 9 g.l
-1
) wi h bac e ia concen a ion
o 10
4
CFU.ml
-1
o 24 h a he labo a o y empe a u e in he da k. A
consis en su ace a ea- o- olume a io (S/V) was main ained ac oss
Fig. 1. (OM) Su aces o : a) 3D p in ed TiAl6V4 alloy gy oid; b) 3D p in ed i anium dode hick.
A. Knaislo ´
a e al.
Applied Su ace Science Ad ances 29 (2025) 100816
2
sample ypes. Two independen es s we e pe o med. Following he
in e ac ion pe iod, 100 µL aliquo s o he suspension we e aken and
sp ead on o wo Pe i dishes wi h aga (LB). Fou dishes om each
coa ing and subs a e ype we e incuba ed in a biological he mos a a
36.5 ◦C o 24 h. A e incuba ion, he dishes we e pho og aphed, and
he colonies o su i ing bac e ia we e coun ed using he compu e
p og am NIS-Elemen s AR 3.10 and isually compa ed o he e e ence
sample (suspension wi hou con ac wi h he samples).
Cy o oxici y measu emen s o all h ee coa ing ypes on bo h sub-
s a e ypes we e pe o med acco ding o ISO 10,993–5 [34]. Samples
we e s e ilized in 70 % e hanol o 2 h. A e d ying, he samples we e
imme sed in MEM +5 % FBS medium (Minimum Essen ial Medium,
Fe al Bo ine Se um) wi h an ibio ics in 50 mL ubes a 37 ◦C on an
o bi al shake (130 pm) o 24 h. The ex ac ion a io was 1.25 cm
2
/ml.
Each ma e ial was es ed in iplica e. L929 cells (ATCC CCL-1) we e
seeded in a 96-well pla e in MEM +10 % FBS medium (10,000 cells/-
well) and cul u ed o 24 h in an incuba o (37 ◦C, 5 % CO
2
). A e 24 h,
he ma e ial ex ac s we e added o he subcon luen cell laye . Six
echnical eplica es (wells) we e used o each sample. The ex ac ion
medium alone (MEM +5 % FBS wi h an ibio ics) se ed as he nega i e
con ol, and he medium wi h de e gen (0.5 % T i on X-100) se ed as
he posi i e ( oxic) con ol. The sil e concen a ion in he ex ac s was
measu ed using ICP-OES. Following 24 h o incuba ion wi h he ex ac s,
he me abolic ac i i y o he cells was assessed using he esazu in es .
The ex ac s we e emo ed, and a solu ion o esazu in ( inal concen-
a ion 25 µg/ml) in MEM medium wi hou phenol ed was pipe ed on o
he cells. A e 1.5 h, he luo escence o he o med eso u in (ex/em
560/590 nm) was measu ed. The ela i e me abolic ac i i y was
exp essed as a pe cen age o he nega i e (una ec ed) con ol.
2.5. Cha ac e iza ion o he subs a es and coa ings
The subs a es and coa ings be o e and a e es s we e cha ac e ised
by scanning elec on mic oscope (Hi achi S4700, 15 kV, 20 µA) and by
he op ical mic oscope (Olympus BX 51). The phase composi ion o he
TAN04HA, TAN06HA coa ings a e i ing and a e in i o es ing was
analysed by XRD on he de ice PANaly ical X´Pe PRO wi h so wa e
High Sco e Plus (30 mA, 40 kV, Cu).
3. Resul s and discussion
3.1. Mic os uc u e o he p epa ed samples
Fo uni o mi y, he su aces o he machined w ough TiAl6V4 alloy
ods unde wen mechanical g inding (Fig. 2a). Howe e , aces o
sc a ches emained a e cleaning. Subsequen cleaning wi h e hanol
e ealed small sphe ical sphe uli es, anging om uni s o ens o mi-
c ome e s, on he gy oid samples. While he gy oid su ace a ea was
calcula ed based on cell shape and numbe , elec on mic oscope images
showed a la ge ac ual su ace a ea due o he pe asi e p esence o
hese sphe uli es (Fig. 2b). These su ace i egula i ies may signi ican ly
in luence he quali y and p ope ies o subsequen ly p epa ed coa ings.
Fu he cha ac e iza ion and es ing o hese no el gy oid-shaped bio-
ma e ials will be essen ial.
Following ul asonic cleaning wi h e hanol, he su aces o he
dode hick subs a es displayed 3D-p in ed g id laye s (1.35 mm hole
size) a anged in a sca old s uc u e (Fig. 2c). The heo e ical subs a e
su ace a ea was calcula ed om he g id shape (1.35 mm), he numbe
o p in ed laye s, and he wa e shape. Howe e , elec on mic oscope
images e ealed ha he ac ual su ace a ea was la ge han his
app oxima ion. This disc epancy was a ibu ed o he p esence o
inhomogeneously dis ibu ed sphe ical s uc u es (uni s o ens o mi-
c ome e s) on he g id laye s. These su ace i egula i ies may signi i-
can ly a ec he quali y and p ope ies o subsequen ly p epa ed
coa ings.
Following i ing, he coa ings on he alloy machined shaped ba s
Fig 2. (SEM) Mic os uc u e o he samples a e cleaning: a) he machined w ough od a e mechanical ea men and subsequen cleaning; b) gy oid 5 mm - 3D; c)
dode hick 3D.
A. Knaislo ´
a e al.
Applied Su ace Science Ad ances 29 (2025) 100816
3
p esen ed isola ed c acks (Fig. 3). These c acks did no ha e a nega i e
impac on he p ope ies measu ed. The coa ing a e e y hin, and
pe ec ly copies he su ace o he subs a e, as he mo phology ypical o
g inding is isible. The comme cial hyd oxyapa i e pa icles, wi h pa -
icle sizes in he mic ome e ange, and he sil e pa icles, wi h pa icle
sizes in he nanome e ange o bo h concen a ions, we e dis ibu ed
ela i ely homogeneously h oughou he coa ing su ace.
Following i ing, he coa ings on he 3D-p in ed gy oid alloy
exhibi ed signi ican ly mo e c acking han hose on he machined od
subs a es (Fig. 4). This inc eased c acking is likely due o he i egula
su ace o he gy oid, which hinde ed uni o m coa ing low du ing
wi hd awal, compa ed o he smoo he od samples. The p esence o a
pla e/doughnu s uc u e in he lowe pa o he gy oid sample u he
con ibu ed o une en sol low du ing wi hd awal. Howe e , all coa ings
accu a ely eplica ed he dissec ed su ace o he gy oid, wi h no sig-
ni ican al e a ion o i s dimensions, indica ing op imal sol iscosi y. The
dis ibu ion o comme cial hyd oxyapa i e pa icles wi hin he coa ings
was ela i ely uni o m. Con e sely, a close examina ion e ealed an
une en dis ibu ion o sil e pa icles in bo h concen a ion cases. The
hickness o he basic coa ing (T, Fig. 4a) was low because small and
la ge beads o he o iginal gy oid su ace we e s ill isible a e coa ing.
The coa ings wi h Ag and HA (TAN04HA, TAN06HA) exhibi ed a
signi ican ly g ea e hickness, as hese coa ings co e ed mos o he
gy oid su ace ea u es (Fig. 4b, 4c).
Coa ings o he basic T sol applied o he 3D dode hick subs a e
showed c acking (Fig. 5). This is p obably due o he i egula su ace o
he bead g id and he wa e , which esul ed in complex coa ing low
du ing he ex ac ion p ocess. While c acks we e p esen , he coa ing
emained adhe ed and p ecisely eplica ed he highly s uc u ed su ace.
The coa ing hickness was isually es ima ed o be in he ange o 350 o
400 nm.
Despi e pe ec ly eplica ing he subs a e’s complex su ace, he
coa ing con aining Ag and HA exhibi ed an i egula dis ibu ion o
nano-sized sil e (Ag) and mic o-sized hyd oxyapa i e (HA) pa icles
(Fig. 6). The s uc u ed su ace limi ed he abili y o achie e a homo-
geneous pa icle dis ibu ion. C acks we e obse ed in he coa ing
(TAN04HA); howe e , hey did no nega i ely impac i s quali y o
p ope ies. The coa ing demons a ed excellen adhesion o he
subs a e.
Func ionally, he TAN06HA coa ing was compa able o he
TAN04HA coa ing, di e ing only in i s highe Ag concen a ion.
Al hough local c acks we e p esen , pa icula ly a ound he HA beads
and pa icles, he coa ing accu a ely eplica ed he g id’s s uc u ed
su ace wi hou dimensional changes (Fig. 7). An une en dis ibu ion o
sil e nanopa icles was obse ed. The coa ing exhibi ed high adhesion
o he subs a e.
C oss-sec ional analysis was pe o med o examine he mic os uc-
u e o dode hick (Fig. 8). To assess whe he he iscosi y o he sols (T,
TAN04HA, and TAN06HA) acili a ed hei pene a ion h ough he
sca old la ice o he pla e du ing coa ing unde cons an s i ing, he
coa ed subs a es we e sec ioned and isually cha ac e ized pos - i ing.
E alua ion o bo h op ical mic oscopy (OM) images and scanning elec-
on mic oscopy (SEM) de ails e ealed ha he coa ings p ecisely
eplica ed he in ica e inne su ace o he la ice, hus con i ming he
pene a ion o all sols o he pla e. Hyd oxyapa i e (HA) pa icles and
sil e (Ag) pa icles we e obse ed wi hin he TAN04HA and TAN06HA
coa ings inside he coa ed sca olds (Fig. 8b, 8c). In e es ingly, he
coa ings showed li le e idence o c acking wi hin he subs a es.
Ne e heless, he concen a ion and dis ibu ion o he inco po a ed
elemen s (mic o-HA, nano-Ag) wi hin he la ice ca i ies equi e u he
in es iga ion.
The mic os uc u e o he sol-gel-coa ed i anium and Ti6Al4V alloy
samples exhibi ed dis inc cha ac e is ics depending on he subs a e
geome y and coa ing composi ion. Un [35] ound h ough ex ensi e
expe imen al esea ch ha he composi ion o he sol, dip-coa ing con-
di ions and he mal ea men can signi ican ly a ec he p ope ies o
sol-gel coa ings. The s i ness disc epancy (be e bonding) be ween he
implan and he bone issue can be add essed by making po ous
Fig 3. (SEM) Mic os uc u e o he machined w ough od a e i ing: a) T coa ing; b) TAN04HA coa ing; c) TAN06HA coa ing.
A. Knaislo ´
a e al.
Applied Su ace Science Ad ances 29 (2025) 100816
4
ma e ials. In addi ion, he gene a ed po es could imp o e bone ing ow h
owa ds he in e io o he implan (wi h an op imal po e size) [36–38].
The machined w ough Ti6Al4V alloy od displayed a ela i ely
uni o m and smoo h su ace a e mechanical g inding and ul asonic
cleaning. Following sol-gel coa ing and he mal ea men , he coa ings
demons a ed good adhesion wi h minimal c acking, ensu ing homo-
geneous co e age. Hyd oxyapa i e (HA) and sil e (Ag) pa icles we e
e enly dis ibu ed ac oss he su ace, and no signi ican delamina ion
was obse ed. Sol pene a ion was op imal, esul ing in a s able and
adhe en coa ing.
In con as , he 3D-p in ed gy oid s uc u es p esen ed g ea e
challenges in achie ing homogeneous coa ings due o hei complex
geome y [39]. Al hough he coa ings adhe ed well o he subs a e,
signi ican c acking was obse ed, likely due o une en sol low o e he
in ica e su ace du ing dip-coa ing and subsequen he mal expansion
s esses. Howe e , he coa ings main ained good adhesion, and hei
bioac i e and an ibac e ial unc ionali ies we e e ained. The sil e
nanopa icle dis ibu ion was less uni o m compa ed o he od samples,
which could in luence he localized an ibac e ial pe o mance. The
gy oid s uc u es, wi h hei highly po ous a chi ec u e, p o ided an
inc eased su ace a ea, po en ially enhancing in e ac ions wi h biolog-
ical en i onmen s [40].
The 3D-p in ed dode hick s uc u es p esen ed an e en mo e in i-
ca e su ace mo phology, composed o o e lapping g id laye s and
embedded beads. The coa ings on hese s uc u es exhibi ed localized
c acking, pa icula ly a ound he beads, bu main ained excellen
adhesion. The sol e ec i ely pene a ed h ough he sca old o he
unde lying pla e, indica ing ha he iscosi y was op imized o such
geome ies. The mic o-HA and nano-Ag addi i es we e dis ibu ed
h oughou he su ace, al hough achie ing homogenei y was
Fig 4. (SEM) Mic os uc u e o he Ti6Al4V gy oid 3D a e i ing: a) T coa ing; b) TAN04HA coa ing; c) TAN06HA coa ing.
Fig 5. (SEM) Mic os uc u e o he Ti dode hick 3D wi h T coa ing a e i ing.
A. Knaislo ´
a e al.
Applied Su ace Science Ad ances 29 (2025) 100816
5
challenging. C oss-sec ional analysis con i med ha he coa ings suc-
cess ully pene a ed he la ice, e ec i ely co e ing he complex in e -
nal su aces. In e es ingly, ewe c acks we e obse ed wi hin he inne
egions o he dode hick sca olds, sugges ing ha su ace cu a u e and
con ined geome ies in luenced s ess dis ibu ion du ing he mal
ea men .
The s udy demons a ed ha sol-gel coa ings e ec i ely con o med
o di e en i anium-based subs a es, bu subs a e geome y signi i-
can ly impac ed coa ing homogenei y and in eg i y. While smoo h su -
aces such as he machined od acili a ed uni o m coa ings wi h
minimal de ec s, complex 3D-p in ed s uc u es, especially gy oid and
dode hick designs, equi ed ca e ul op imiza ion o sol iscosi y and
deposi ion echniques o minimize c acking. Fu u e wo k should ocus
on e ining coa ing applica ion me hods, po en ially inco po a ing
mul i-s ep laye ing o modi ied d ying p o ocols o enhance coa ing
uni o mi y and mechanical s abili y ac oss highly s uc u ed su aces.
The phase composi ion o he TAN04HA, TAN06HA coa ings on od,
gy oid and dode hick a e i ing is showed on Fig. 9. The di ac og ams
o he coa ings a e i ing need o be iewed om wo angles. Fi s , om
he ma e ial poin o iew, i is ob ious ha he in ensi y o he peak o
he basic i anium phase is g ea ly in luenced by he shape o he sub-
s a e. The peaks a e mos in ense o he od, hen o he gy oid, and
he smalles peak belongs o he dode hick. Second, om he composi-
ion o he coa ings poin o iew, i is ob ious ha he phase o com-
me cial hyd oxyapa i e (HA) was de ec ed mainly o he od and
gy oid. Bu he in ensi y is e y small compa ed o he in ensi y o i-
anium. I was again con i med ha he shape o he subs a e also in-
luences he de ec ion o comme cial hyd oxyapa i e and sil e . In bo h
ypes o coa ings, nei he hyd oxyapa i e no sil e was de ec ed on he
dode hick. Mo eo e , i is ob ious om he SEM images ha he pa i-
cles in bo h ypes o coa ings co e he en i e su ace o he s uc u ed
dode hick subs a e.
3.2. P ope ies o he p epa ed samples
3.2.1. Adhesion es
The coa ings on he alloy samples o he machined w ough od
showed e y good adhesion, e alua ed acco ding o he classi ica ion
able as g ade 5B (possibly e en 4B). A e isual cha ac e iza ion, i was
ound ha pa icles o comme cial hyd oxyapa i e and sil e ( o bo h
concen a ions) emained ixed in he coa ings a e he ape was peeled
o (Fig. 10). E en some o he adhesi e om he ape emained on he
sample a e i was o n o .
Coa ings on he machined w ough Ti6Al4V alloy od demons a ed
ou s anding adhesion, wi h minimal pa icle de achmen obse ed in
he ape es . This s ong adhesion can be a ibu ed o he od’s ela-
i ely smoo h su ace, which acili a ed uni o m coa ing deposi ion and
s ong in e acial bonding du ing he mal ea men . Milella [41] p e-
pa ed i anium sol-gel coa ings con aining HA and ound c acks on hei
su ace a e i ing. The c acks do no in luence he mechanical and
adhesi e p ope ies (by ensile es ) o he coa ing. In con as , he
3D-p in ed gy oid and dode hick s uc u es main ained good adhesion,
al hough some su ace i egula i ies and c acks we e p esen . The
coa ings adhe ed well e en o he highly po ous and in ica e la ice
s uc u es, indica ing hei po en ial o biomedical applica ions. How-
e e , he gy oid and dode hick samples exhibi ed mo e p onounced
c acking, likely due o in e nal s esses in oduced du ing d ying and
i ing by hei complex geome ies.
Fig 6. (SEM) Mic os uc u e o he Ti dode hick 3D wi h TAN04HA coa ing a e i ing.
Fig 7. (SEM) Mic os uc u e o he Ti dode hick 3D wi h TAN06HA coa ing a e i ing.
A. Knaislo ´
a e al.
Applied Su ace Science Ad ances 29 (2025) 100816
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3.2.2. Bioac i i y es
The alloy coa ings con aining comme cial hyd oxyapa i e
(TAN04HA, TAN06HA) showed excellen bioac i e p ope ies, wi h a
isually de ec ed hick laye o p ecipi a ed bone hyd oxyapa i e (HAp)
a e he in i o es (Fig. 11b, 11c). The hyd oxyapa i e globules,
composed o pla e-like nanoc ys als, g ew and clus e ed wi h inc easing
exposu e ime in SBF. The laye c acked as a esul o d ying (du ing
p epa a ion o SEM measu emen s), which allowed o a ough es i-
ma ion o he laye hickness in he mic ome e ange. I is impo an o
conside ha , in i o, he laye would no be ai -exposed, sugges ing ha
Fig. 8. (SEM) Mic os uc u e o Ti - dode hick (3D p in ing; g id: 1.35) – c oss sec ion: a) T coa ing a e i ing; b) TAN04HA coa ing a e i ing; c) TAN06HA
coa ing a e i ing.
Fig. 9. XRD pa e ns o he TAN04HA, TAN06HA coa ings on od, gy oid and dode hick a e i ing.
A. Knaislo ´
a e al.
Applied Su ace Science Ad ances 29 (2025) 100816
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he c acking was induced by labo a o y measu emen s. In compa ison,
he T coa ing (wi hou HA and Ag addi i es) exhibi ed e y low bioac-
i i y, indica ed by he p ecipi a ion o isola ed, e y small HAp globules
on he coa ing su ace (Fig. 11a).
The coa ings on he 3D gy oid beha ed consis en ly wi h he coa ings
on he machined w ough od (Fig. 12). Ac oss all coa ing ypes, su ace
images showed ha he laye o p ecipi a ed hyd oxyapa i e ai h ully
eplica ed he i ed coa ing, e en wi h c acking p esen . The nanopla e-
like globules p esen ed a consis en s uc u e, wi h sizes in he mic o-
me e ange. The ou e and inne spaces o he gy oid demons a ed
uni o m beha io h oughou he es , wi h no localized changes in
beha io de ec ed, despi e he sample’s complex geome y.
Dode hick wi h coa ing T (base coa ing wi hou addi i es) showed
no changes a e 21 days o exposu e in simula ed body luid (SBF) so-
lu ion (Fig. 13). The coa ing’s su ace displayed no changes in
mo phology o composi ion, and no phases o p ecipi a es we e
de ec ed. This coa ing did no demons a e bioac i e p ope ies
ollowing in i o es ing.
The TAN04HA coa ing on dode hick, con aining lowe sil e (Ag)
and comme cial hyd oxyapa i e (HA) con en , showed excellen bioac-
i e p ope ies (Fig. 14). A he conclusion o he 21-day in i o es , a
isually de ec ed laye o p ecipi a ed hyd oxyapa i e (HAp) was
obse ed, composed o globules o pla ele -shaped nanoc ys als. This
laye expe ienced c acking due o d ying, a p ocedu e necessa y o SEM
measu emen s.
The TAN06HA coa ing on dode hick, con aining a highe concen-
a ion o sil e (Ag) and he same concen a ion o comme cial hy-
d oxyapa i e (HA) as he TAN04HA coa ing, showed simila beha io o
he TAN04HA coa ing (Fig. 15). A e 21 days o in i o es ing in
simula ed body luid (SBF), he coa ed dode hick sca old su ace was
almos comple ely co e ed wi h a laye o p ecipi a ed hyd oxyapa i e
(HAp). This p ecipi a ed phase was cha ac e ized by globules composed
Fig. 10. (SEM) The adhesion o he coa ings o he machined w ough od a e i ing: a) TAN04HA; b) TAN06HA.
Fig. 11. (SEM) Mic os uc u e o he machined w ough od a e in i o es in SBF: a) T coa ing; b) TAN04HA coa ing; c) TAN06HA coa ing.
A. Knaislo ´
a e al.
Applied Su ace Science Ad ances 29 (2025) 100816
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o pla ele -like nanoc ys als. De ailed SEM analysis e ealed ha he
p ecipi a ed HAp pla ele s g ew di ec ly om he comme cial HA pa -
icles wi hin he TAN06HA coa ing. As he in i o es ing ime inc eased,
he HAp globules (wi h sizes in he mic ome e ange) g ew and in e -
connec ed, o ming a con inuous laye . This laye comple ely co e ed
he o iginal coa ing, illed i ing c acks, and illed oids in he sca old
la ice. A low magni ica ion (x30), SEM images showed ha he
p ecipi a ed hyd oxyapa i e laye pe ec ly eplica ed he mo phology
o he coa ed sca old. The HAp nanopla ele globules exhibi ed he
same s uc u e o bo h ypes o coa ings (TAN04HA, TAN06HA).
The phase composi ion o he TAN04HA, TAN06HA coa ings on od,
gy oid and dode hick a e in i o es is showed on Fig. 16. The analysis
demons a ed he p esence o p ecipi a ed hyd oxyapa i e (HAp) phase
om SBF on he su ace o bo h ypes o coa ings on all ypes o sub-
s a es. Again, he in luence o he subs a e shape on bo h he in ensi y
and shape o he HAp peaks and he de ec ed amoun was e iden . F om
he di ac og ams, i is ob ious a i s glance ha he mos HAp is on
he TAN04HA and TAN06HA coa ings on he gy oid (55 - 65 %) and on
he od (15 - 20 %). XRD analysis o he coa ings on dode hick de ec ed
only ace amoun s o he HAp phase, al hough he SEM images clea ly
show he en i e co e age o his shaped subs a e wi h he new p ecip-
i a ed phase.
Al hough XRD analysis canno dis inguish comme cial hyd oxyapa-
i e om p ecipi a ed hyd oxyapa i e (Ca
10
(PO
4
)
6
(OH)
2
applies o
bo h), by compa ing he peak in ensi ies, hei shapes and he amoun (
%) o he phase o bo h ypes o coa ings TAN04HA and TAN06HA a e
i ing and a e in i o es ing, he di e ence be ween he hyd oxyap-
a i es is ob ious a i s glance.
Using AAS, he concen a ion o Ca
2+
was de e mined, and UV–VIS
was used o measu e he concen a ion o (PO
4
)
3-
ions in SBF solu ions
be o e and a e he 21-day in i o es . Fo bioma e ial p edic i e
es ing, moni o ing changes in he concen a ions and pH o he SBF
Fig. 12. (SEM) Mic os uc u e o he gy oid a e in i o es in SBF: a) T coa ing; b) TAN04HA coa ing; c) TAN06HA coa ing.
Fig. 13. (SEM) Mic os uc u e o Ti - dode hick (3D p in ing; g id: 1.35) wi h T coa ing a e in i o es in SBF: a) a ea; b) de ail.
A. Knaislo ´
a e al.
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9
