3D-P in ed Ca ageenan-Based Nanocomposi es o
Fo ce-Sensing Applica ions
Ve a M. Macedo, Nelson Pe ei a, Ca men R. Tubio, Ped o Ma ins, Ca los M. Cos a,*
and Senen xu Lance os-Mendez
1. In oduc ion
A apid echnological e olu ion is aking place linked o he
In e ne o Thing (IoT) concep and he digi aliza ion o he soci-
e y.
[1]
The IoT concep is based on he in e connec ion o physical
and i ual objec s h ough senso s, ac ua o s, and he in e ne .
[2]
The in e connec ion be ween elec onic
de ices allows he con inuous moni o ing,
op imiza ion, and con ol in in elligen ,
dis ibu ed, sel -o ganizing and ene gy-
cons ained ne wo ks,
[2b]
using communi-
ca ion echnologies such as mobile and
wi eless ne wo ks and iden ifica ion by
adio equency, global posi ion sys ems
(GPS), and Blue oo h sys ems,
[2a]
which
c ea e a comple e sys em, ac ing as a
whole. IoT is becoming widesp ead in
a eas including secu i y, sma heal h
sys ems, ag icul u e, anspo , indus y,
and cons uc ion, among o he s.
[2b]
In he indus ial sec o , IoT allows op imi-
za ion o p ocesses, e ec i e p oduc ion imes,
and educed manu ac u ing cos s.
[1]
The me -
i s o he IoT concep s ongly ely on he
imp o emen in ma e ials and manu ac u ing
echniques, ela ed o he Indus y 4.0 pa a-
digm.
[1,2]
Sma ma e ials implemen a ion
has become a co ne s one o he echnological
e olu ion due o hei ac i e ole in imp o ing
ma e ials esponse and in eg a ion.
[3]
Sma ma e ials can be desc ibed as a ma e ial ha senses
en i onmen al changes and esponds, in a p edic able way, o
he espec i e ex e nal s imulus. Depending on he sma
ma e ial g oup, hey eac o di e en s imuli and p o ide a
specific ou pu o ice e sa.
[2a,4]
Ac i e sma ma e ials
g oups include piezoelec ic, piezo esis i e, magne o heological,
V. M. Macedo, C. R. Tubio, S. Lance os-Mendez
BCMa e ials
Basque Cen e o Ma e ials, Applica ions and Nanos uc u es
UPV/EHU Science Pa k
48940 Leioa, Spain
N. Pe ei a, P. Ma ins, C. M. Cos a, S. Lance os-Mendez
Physics Cen e o Minho and Po o Uni e si ies (CF-UM-UP)
Uni e si y o Minho
4710-053 B aga, Po ugal
E-mail: cmscos a@fisica.uminho.p
The ORCID iden ifica ion numbe (s) o he au ho (s) o his a icle
can be ound unde h ps://doi.o g/10.1002/adem.202201806.
© 2023 The Au ho s. Ad anced Enginee ing Ma e ials published by Wiley-
VCH GmbH. This is an open access a icle unde he e ms o he C ea i e
Commons A ibu ion-NonComme cial License, which pe mi s use,
dis ibu ion and ep oduc ion in any medium, p o ided he o iginal
wo k is p ope ly ci ed and is no used o comme cial pu poses.
DOI: 10.1002/adem.202201806
N. Pe ei a
Cen o ALGORITMI
Uni e si y o Minho
Campus de Azu ém, 4800-058 Guima ães, Po ugal
P. Ma ins, C. M. Cos a, S. Lance os-Mendez
Labo a o y o Physics o Ma e ials and Eme gen Technologies (LapMET)
Uni e si y o Minho
4710-057 B aga, Po ugal
C. M. Cos a
Ins i u e o Science and Inno a ion o Bio-Sus ainabili y (IB-S)
Uni e si y o Minho
4710-053 B aga, Po ugal
S. Lance os-Mendez
Ike basque
Basque Founda ion o Science
48009 Bilbao, Spain
Technological de elopmen is leading o an exponen ial g ow h in he imple-
men a ion o senso s and ac ua o s whe e he conce n abou en i onmen al
p oblems is also ocusing on elec onic was e (e-was e), which is composed o
haza dous ma e ials, co esponding o a la ge pa o u ban was e, and has a
s ong en i onmen al impac . The e o e, mo e en i onmen ally iendly elec-
onic componen s a e equi ed, na u al polyme s being a sui able app oach o
sol e o a enua e hose p oblems. This wo k epo s on a bio-based polyme ,
ca ageenan, embedded wi h dielec ic ba ium i ana e (BTO) nanopa icles o
ailo he elec ical esponse. The inclusion o he fille induces sligh modifi-
ca ions in he he mal cha ac e is ics and on he physicochemical p ope ies o
he polyme ma ix. On he o he hand, he mechanical and dielec ic p ope ies
imp o e wi h he addi ion o BTO and a high dielec ic cons an o
ε
013 000 is
ob ained o he composi e wi h 20 w % BTO con en . The inc ease o he
dielec ic cons an is accompanied by a high AC elec ical conduc i i y, leading o
a high-
ε
0–high-loss ma e ial. The 20 w % BTO composi e is used o p oduce a
o ce measu ing senso , due o he highes dielec ic esponse. The unc ional
esponse o he sensing sys em shows good s abili y o e cycling.
RESEARCH ARTICLE
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magne oelec ic, shape memo y, elec o heological, ch omic,
sel -healing, and pH-sensi i e ma e ials, among o he s.
[5]
Since hese ma e ials possess a g ea capabili y o espond upon
an ex e nal s imulus, hey a e excellen o sensing applica ions.
Fe oelec ic ce amic–polyme composi es a e examples o
sma ma e ials, since combine he bes o he e oelec ic
ce amic p ope ies (high dielec ic and piezoelec ic coe ficien s,
low dielec ic and mechanical losses and good he mal s abili y)
wi h he ad an ages o he polyme ma ices (low densi y,
flexibili y, excellen in eg abili y and p ocessable by addi i e
manu ac u ing echniques),
[6]
which make i highly sui able
o a la ge a ie y o sensing, elec ic powe and elec onics
sys ems.
[7]
In his a ea, he p oduc ion o senso s based on sma
ma e ials has ypically elied in syn he ic polyme s, as hey
p o ide an e ficien way o achie e he desi ed p ope ies,
h ough hei chemical and s uc u al modifica ion.
Howe e , elec onic equipmen is mass p oduced, leading o a
s ong inc ease o he so-called elec onic was e (e-was e). I
e-was e is no managed p ope ly, i can lead o con amina ion
by oxici y and heal h isks, comp omising he su ounding
communi y.
[8]
E-was e has a po en ial o eco e aluable ma e i-
als as i on, aluminum, coppe , gold, sil e , and a e ea h me als;
ha is why i is globally ecognized as a esou ce o hese
elemen s/ma e ials.
[9]
The ecycling o me als om elec onic
de ices may educe he need o mining i gin ma e ials.
None heless, e-was e collec ion a es and poo ecycling o ine -
ficien end p ocessing o elec ical o elec onic equipmen , and
consequen ly hese aluable esou ces a e was ed.
[9a]
Thus, a di e en s a egy mus be implemen ed. In o de o
achie e mo e sus ainable sma ma e ials and o de elop a he
same ime mo e sus ainable enginee ing p inciples, na u al
polyme s can be used as an al e na i e o syn he ic ones. The
ad an age o na u al polyme s is hei (bio)deg adabili y, non ox-
ici y, and he possibili y, in some cases, o be p ocessed by addi-
i e manu ac u ing wi h wa e as a sol en .
[10]
In elec onic
echnologies, na u al polyme s can acili a e he ecycling p o-
cess due o deg adabili y. They can also lead o less oxic compo-
nen s which a e also biocompa ible, pa icula ly ele an o
wea able senso s.
[10]
The wo main ypes o na u al polyme -
based ma e ials mo e sui able on elec onic applica ions a e poly-
saccha ides (chi osan, aga ose, A abic gum, dex an, hyalu onic
acid, algina e, ca ageenan) and p o eins (albumin, gela ine, soy,
and collagen).
[11]
Ca ageenan is a na u al polyme ha has shown g ea po en-
ial o se e al applica ions, including sma packaging,
[12]
d ug
deli e y,
[13]
and biomedicine.
[14]
Ca ageenan is a na u al
sul a ed and anionic polysaccha ide (ca bohyd a e) ex ac ed
om he mul icellula wall o ce ain species o ed algae sea-
weeds o he Rhodophyceae amily such as Chond us c ispus,
Giga ina, Euchuema, and Hypnea. Ca ageenan exis s in la ge
abundance in na u e a low cos .
[15]
Usually, na u al polysaccha ides a e hyb ids and con ain
epe i i e disaccha ide uni s o se e al ca ageenan ypes
a ached in a single-polyme chain.
[16]
Depending on he numbe
and posi ion o sul a e g oups in he disaccha ide epea ing uni ,
h ee main ypes o ca ageenan can be ound: kappa (κ), io a (ι),
and lambda (λ), whe e i s sul a e con en is 20%, 33%, and 41%
(w/w), espec i ely.
[11,13,15b,17]
Ca ageenan wi h highe le els o sul a ion ends o dec ease
gel s eng h and solubili y empe a u e.
[15b]
This is he eason o
selec ing io a (ι)-ca ageenan o a la ge a ie y o applica ions,
since i s sul a ion is an in e media e alue.
[18]
Ca ageenan is a na u al polyme ha has shown g ea po en-
ial o se e al applica ions, including sma packaging,
[12]
d ug deli e y,
[13]
biomedicine,
[14]
uel cells,
[19]
elec och omic
de ices,
[19]
and solid polyme elec oly es.
[16]
As ep esen a i e
examples, a polyme –sal complex based on ι-ca ageenan and
ammonium b omide (NH
4
B ) has been p oduced by solu ion-
cas ing me hod, leading o a maximum ionic conduc i i y o
1.46 10
5
Scm
1
and an elec ochemical s abili y window o
2.1 V.
[20]
NH
4
NO
3
wi hin ι-ca ageenan has been applied o
elec ochemical de ices
[19]
and solid polyme elec oly es ha e
been de eloped wi h ι-ca ageenan as polyme hos and li hium
chlo ide (LiC) as fille , leading o a high oom empe a u e
conduc i i y o 5.33 10
3
Scm
1
o he 1.0 g ι-ca ageenan:
0.3 g LiCl sample.
[16]
The p ope ies ha d ew a en ion in ca ageenan o be
used as a polyme ma ix o addi i e manu ac u ing echnolo-
gies, in addi ion o i s eco iendly beha io and being soluble
in wa e , we e i s heology and s ong gel p ope ies a e
cooling.
[11,15b,17,21]
Owing he capabili y o c ea e a wa e - e aining hyd ogel,
ι-ca ageenan is sui able o being used in 3D p in ing echni-
ques.
[22]
Ne e heless, despi e hei in e es ing p ope ies, he e
a e also limi a ions in e ms o mechanical and elec ical
p ope ies o some applica ion a eas.
[23]
Thus, in mos na u al
polyme s, nanopa icles a e being used o de elop polyme com-
posi es, allowing o in oduce and/o une specific p ope ies o
he ma e ial by combining hei indi idual p ope ies o polyme
and fille .
[23b]
Ba ium i ana e (BTO, BaTiO
3
) is cha ac e ized by
high dielec ic esponse and ionic conduc i i y cha ac e is ics
and appea s o be a good candida e o nex gene a ion o ma e-
ials wi h high-ε0–high-loss ma e ial, in combina ion wi h
na u al polyme s.
[24]
BTO is a e oelec ic ma e ial, wi h high dielec ic cons an
and spon aneous pola iza ions and low dielec ic losses.
[25]
Despi e i s po en ial in e es o uning polyme ma ix elec ical
esponse, no s udies ha e been epo ed ega ding ca ageenan
composi es wi h BTO nanopa icles, in any o ca ageenan ypes.
The combina ion o ca ageenan/BTO and hei p ocessabili y by
addi i e manu ac u ing, mo e p ecisely by di ec ink w i ing
(DIW), can allow a new gene a ion o elec oac i e ma e ials wi h
educed ma e ial was e du ing p ocessing and imp o ed sus ain-
abili y due o he bio-based o igin o he polyme ma ix.
[26]
In
pa icula , DIW allows o de elop bo h simple and complex cus-
omizable senso designs o imp o e de ice in eg a ion, while
being a scalable, low-cos , sus ainable, and high-accu acy p in -
ing echnology.
[27]
Thus, his wo k p esen s a new composi e o ι-ca ageenan
wi h BTO nanopa icles, p ocesses by 3D p in ing, in o de o
de elop a dielec ic high ε0–high loss ma e ial, op imized o
ouch sensing applica ions.
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2. Expe imen al Sec ion
2.1. Ma e ials
Io a-ca ageenan was pu chased om Al a Aesa . Ul apu e
wa e was ob ained om a Milipo e-Q sys em. Ba ium i ana e
(BTO, BaTiO
3
), wi h 100 nm pa icle size and he su ac an
T i on X-100, we e pu chased om SkySp ing Nanoma e ials
and Sigma-Ald ich, espec i ely.
2.2. Sample P epa a ion
BTO nanopa icles in di e en fille con en s (nea ca ageenan
sample, 0, 1, 5, 10, 20 and 40 w %) we e dispe sed o 3 h in a
mix u e o ul apu e wa e wi h he su ac an i on X-100
(0.01 w %), p e iously homogenized in an ul asound ba h
(ATU, model no. ATM40-3LCD, 50 W) o 1 h o p omo e
BTO nanopa icles dispe sion. Fu he , 3 w % o ca ageenan
was added in o he solu ion and s i ed o ano he 3 h a
150 pm. The main s eps o he composi e o ca ageenan/
BTO nanopa icle p oduc ion a e desc ibed in Figu e 1a.
2.3. P in ing P ocess
The p oduced gel was in oduced in o he sy inge and, in o de o
emo e he bubbles, he sy inge was isola ed wi h pa afilm in
bo h edges (so ha he gel does no leak) and placed in o a cen-
i uge (MRC Lab) o 15 min a 2500 pm. The sy inge wi h ee
bubbles gel was placed in he biop in e (Single Head 3D
Biop in e - 3D Cul u es Tissue Sc ibe, 10 mL nozzle) and, a e
an op imiza ion p ocedu e, he ollowing pa ame e s we e used
o he p in ing p ocess: needle o 0.41 mm, space line o 0.51, o
a oid o e lay o lines on he same plane, 30 mm s
1
p in ing
speed, and 0.008 ex usion mul iplie . Then a 3D o m was
p in ed, which esul ed in o a film, due he cu ing p ocess
and wa e e apo a ion, wi h final hickness o 80 μm.
Figu e 1b desc ibes he main p in ing s eps.
2.4. Samples Cha ac e iza ion
The mo phology o he composi es was analyzed ia scanning
elec on mic oscopy (SEM) using a Ca l Zeiss EVO-40 equipped
wi h an ene gy-dispe si e spec oscopy (EDS) de ec o .
To e alua e he polyme s uc u e and possible in e ace
bonding be ween polyme and fille , Fou ie - ans o m in a ed
spec oscopy (FTIR) was pe o med in a Jasco FT/IR-4100 sys-
em. Measu emen s we e pe o med a oom empe a u e, in
he a enua ed o al eflec ion (ATR) mode, be ween 600 and
4000 cm
1
, using 64 scans a a esolu ion o 4 cm
1
.
The mal p ope ies o he sample we e e alua ed by di e en-
ial scanning calo ime y (DSC) using a Me le Toledo DSC 822e
appa a us equipped wi h a sample obo unde ni ogen flow o
20 mL min
1
. The scans we e ca ied ou om 20 o 150 °C a a
hea ing a e o 10 °C min
1
. The samples we e weighed and com-
pac ed in an aluminum c ucible, wi h a small hole on he op.
Figu e 1. Schema ic ep esen a ion o he expe imen al s eps o a) composi e solu ion p epa a ion and o he b) p in ing p ocess.
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The mog a ime ic analysis (TGA) measu emen s we e
pe o med in a TGA/SDTA 851e Me e Toledo appa a us.
The samples we e hea ed om 30 o 600 °C, a a a e o
10 °C min
1
, wi h a ni ogen flow a e o 50 mL min
1
.
The oom- empe a u e mechanical p ope ies o he compo-
si es we e e alua ed unde ensile s ess a a cons an de o ma-
ion o 50 μms
1
wi h a load cell o 200 N in a Linkam Scien ific
Ins umen s TST 360. Samples we e p epa ed in ec angula
shape wi h dimensions o 20 mm 10 mm 80 μm. The esul s
we e p o ided as he a e age o fi e specimens.
Dielec ic measu emen s we e pe o med, in samples wi h he
same hickness (80 μm) and elec ode a ea, by ob aining he
capaci y, C, and he dielec ic losses, an δ, using a Quad ech
1920 induc ance–capaci ance– esis ance (LCR) p ecision me e ,
a oom empe a u e, in he 20 Hz–1 MHz equency ange and
wi h an applied ol age o 0.5 V. In each composi e, ci cula gold
elec odes o 5 mm diame e we e deposi ed in bo h sides in a
magne on spu e ing SC502 spu e coa e . The eal pa o
he dielec ic unc ion (ε0), an δ, and he eal pa o he elec ical
conduc i i y (σ0) we e de e mined h ough he ollowing
equa ions
ε0¼C:d
ε0:A(1)
an δ¼ε00
ε0(2)
and
σ0ðωÞ¼ε0ωε00 ðωÞ(3)
whe e Cis he measu ed capaci ance, ε
0
is he pe mi i i y o ee
space, Ais he elec ode a ea (m
2
), dis he hickness o samples
(m), and ω¼2π is he angula equency.
[28]
3. Resul s and Discussion
3.1. Mo phological Analysis
The su ace mo phology o he samples was analyzed using he
ep esen a i e SEM images p esen ed in Figu e 2.
Fo nea ca ageenan (Figu e 2a), a homogeneous fla su ace
wi h low oughness is ob ained. The addi ion o he fille s
(Figu e 2b–d) leads o oughe su ace due o bo h he p esence
o he fille s and, in pa icula , o he numbe o well-dis ibu ed
agglome a es ha inc ease wi h inc easing fille con en , being
pa icula ly e idenced o he sample wi h 40 w % BTO con en .
EDS images om Figu e 2e–g confi m his ac by he iden ifi-
ca ion o he dis ibu ion o ba ium in he samples (p esen ed in
blue) co esponding o he nanopa icles loca ion.
3.2. Physical–Chemical, The mal, and Mechanical P ope ies
FTIR-ATR spec a o nea ca ageenan and BTO/ca ageenan
composi es wi h di e en BTO con en s a e shown in Figu e 3a.
Fo nea ca ageenan, he ypical ib a ion bands a 805,
845, 905, 930, and 1070 cm
1
a e obse ed, ha co espond o
he C─O─SO
3
bonds o 3,6-anyhyd ogalac ose in C2, C4,
and C6 o he galac ose uni y and he C─O bond o 3,
6-anyhyd ogalac se, espec i ely.
[20]
Fu he , he abso p ion
bands o galac ose g oups and S═O bond o sulpha e es e s we e
de ec ed a 970–975 and 1240–1260 cm
1
, espec i ely. The C═O
asymme ic s e ch/N–H de o ma ion and he OH/NH s e ch-
ing a e iden ified a 1635 and 3400 cm
1
, espec i ely.
[29]
No
significan a ia ions a e obse ed in he spec a, independen
o he fille con en compa ed o he FTIR spec a o BTO nano-
pa icles, indica ing ha he e a e no new bonds o s ong in e -
ac ions be ween he fille and he polyme ma ix.
The DSC measu emen s (Figu e 3b) e eal ha he endo he -
mic peak co esponding o he in insic wa e emo al and glass
ansi ion empe a u e o he polyme dec eases wi h inc easing
BTO con en , anging om app oxima ely 100 °C o he p is ine
polyme
[19,30]
o 80 °C o he composi e wi h 40 w %.
F om TGA analysis (Figu e 3c), he fi s mass loss, ela ed o
wa e e apo a ion,
[31]
occu ed a empe a u es a ound 25–100 °C.
The mass loss dec eases wi h dec easing BTO con en , being pa -
icula ly e iden o he 40 w % BTO con en sample. I can be
associa ed o he mois u e encapsula ed in he polyme ma ix.
The highe mass loss was eached a 200–250 and 300 °C,
which is ela ed o he ca ageenan polyme ic backbone
deg ada ion.
[32]
A he end o he es (600 °C), he amoun o
composi es mass de ec ed is ound o be di ec ly p opo ional
o he fille con en .
Figu e 3d shows he s ess–s ain cu es ob ained by
mechanical es s in he ensile mode o all samples. I is
obse ed he ypical mechanical esponse o he ca ageenan
polyme
[33]
and ha he addi ion o he BTO con en imp o es
he mechanical p ope ies, he BTO nanopa icles ac as a
mechanical ein o cemen , as well as he obse ed educed
amoun o wa e which inc eases he s i ness.
[34]
This beha io
is de ec ed o all fille con en s, e en he smalles ones. The
composi es o 20 and 40 w % BTO con en seem o ha e an
iden ical mechanical beha io (Figu e 3d). Young’smodulus
was de e mined by he angen me hod in he elas ic egion
[35]
(inse o Figu e 3d), whe e he samples wi h 10 w % BTO
con en showed highe Young’sModulus,yields eng h,and
ul ima e/ up u e s eng h p obably due o be e dispe sion
o he BTO nanopa icles.
The inco po a ion o fille s in o a polyme ma ix ypically
enhances i s mechanical s eng h ( igidi y, ha dness, ac u e
oughness, among o he s) due he high su ace a ea- o- olume
a io o he fille s, which imp o es he in e ac ion be ween bo h
ma ix and fille and is di ec ly influenced by he fille ’s size,
shape and dis ibu ion, concen a ion, and specific in e ac ion
wi h he ma ix.
[36]
In his way, he mechanical p ope ies o
ne ca ageenan a e imp o ed (Figu e 3b, inse o he Young
modulus) o he composi es up o 10 w % BTO con en . Fo
fille concen a ions abo e 10 w % BTO, he e is a dec ease in
mechanical p ope ies, as la ge fille concen a ions lead o fille
agglome a es (Figu e 2), ac ing as de ec s unde mechanical
de o ma ion.
3.3. Dielec ic Beha io
Figu e 4a shows he eal (ε0) pa o he dielec ic cons an o
nea ca ageenan and BTO/ca ageenan composi es a oom
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empe a u e, as a unc ion o equency. F om Figu e 4a, i is
obse ed ha ε0dec eases wi h inc easing equency, indepen-
den o he BTO con en , co esponding o slow dipola
mobili y.
[28]
A high dielec ic esponse is obse ed o nea ca ageenan,
(Figu e 4a) due o he high hyd ogen bonds, pola g oups,
and wa e con en , con ibu ing bo h o he dielec ic esponse
(Figu e 4a) and o conduc i i y (Figu e 4b).
I is obse ed ha ε0inc eases wi h inc easing BTO con en
due o he inc eased mobile cha ge ca ie s and in e acial cha ge
con ibu ions o he Maxwell–Wagne –Silla s (MWS) e ec .
[28]
This e ec is obse ed in Figu e 4c o ε0as a unc ion o
BTO con en a 10 kHz.
Figu e 4b shows he AC elec ical conduc i i y, σ0, alue as a
unc ion o equency calcula ed om Equa ion (3) o all sam-
ples, showing ha σ’inc eases wi h inc easing equency, due o
he inc eased cha ge ca ie mobili y in localized s a es. In addi-
ion, i is no iced ha he AC conduc i i y inc eases wi h BTO
con en , as he inclusion o he fille s inc eases he in e acial
and wa e e ec s.
[37]
Figu e 4c shows he ε0o he samples a 10 kHz as a unc ion
o BTO con en a oom empe a u e. A linea beha io o ε0is
obse ed as a unc ion o fille con en up o fille con en o 20 w
% and a dec ease o he dielec ic esponse is obse ed o he
40 w % BTO samples, due o he la ge fille agg ega es, ha
educe he wa e e ec . The highes dielec ic cons an o
BTO/ca ageenan composi es is 13 000 o he sample wi h
20 w % BTO con en .
Thus, i is e ified ha ε0inc eases wi h inc easing BTO
con en due in e acial and space cha ge pola iza ion, he
composi e wi h 20 w % BTO wi h he la ges dielec ic esponse
a 10 kHz.
Figu e 2. Su ace SEM images o nea ca ageenan a) and he composi es wi h di e en BTO con en s: b) 1 w %, c) 10 w %, and d) 40 w % o BTO. EDS
mapping images o Ba (Ba ium, blue) o samples wi h e) 1 w % o BTO, ) 10 w % o BTO, and g) 40 w % o BTO.
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3.4. Fo ce Senso De elopmen and Func ional Response
Figu e 5 shows he schema ic ep esen a ion o he senso (a), i s
wo king p inciple (b), and he ac ual image (c).
A o ce senso has been de eloped wi h he BTO/ca ageenan
composi e wi h 20 w % o BTO conside ing i s high dielec ic
alue. The sample was placed be ween wo conduc i e
PET/ITO films wi h a PET sepa a o . The geome y o he de el-
oped senso allows he measu emen o a comp ession o ce
based on a 200 μm ai gap, c ea ed by he sepa a o and he
BTO/ca ageenan composi e wi h 20 w % o BTO. The gap
educes i s size wi h he p essu e, which changes he dis ance
be ween he wo elec odes, changing he elec ical esponse
o he senso , measu ed as a capaci y signal.
The esul s o Figu e 6a show he capaci y alue o he sample
a a equency o 1 kHz while applying a o ce om 0 o 10 N
(0–55 kPa) a 1 N s
1
.
Figu e 6a,b shows he no malized capaci y a ia ion unde
cyclic applied o ce o 80 and 70 (de ail) cycles, espec i ely.
Figu e 6c shows he sensi i i y o he sample.
I is shown ha he o ce senso p esen s good epea abili y
o o e 80 cycles. Figu e 6c shows ha he sample p esen s
good linea i y un il he 30 kPa ange, wi h a sensi i i y o
0.0667 kPa
1
( he sensi i i y is defined as S=(ΔC/C
0
)/p,
1000 1500 2000 2500 3000 3500 4000
BTO
(a)
40w .%BTO
1w .%BTO
T ansmi ance / a. u.
Wa enumbe / cm
-1
C-O-C
O=S=O
-O-SO
C-O
C-H
O-H
0w .%BTO
5w .%BTO
10w .%BTO
20w .%BTO
20 40 60 80 100 120 140
endo
(b)
Hea Flow / W.g
-1
Tempe a u e / ºC
80 ºC
89 ºC
100 ºC
99 ºC
102 ºC
40w .% BTO
20 w .% BTO
10 w .% BTO
5 w .% BTO
1 w .% BTO
0w .% BTO 105 ºC
100 200 300 400 500 600
20
30
40
50
60
70
80
90
100
(c)
Weigh / %
Tempe a u e / ºC
0 w .% BTO
1 w .% BTO
5 w .% BTO
10 w .% BTO
20 w .% BTO
40 w .% BTO
0 4 8 1216202428
0
10
20
30
40
50
60
(d)
S ess / MPa
S ain / %
0 w .% BTO
1 w .% BTO
5 w .% BTO
10 w .% BTO
20 w .% BTO
40 w .% BTO
Figu e 3. a) FTIR-ATR spec a, b) DSC scans, c) TGA he mog ams, and d) s ess–s ain mechanical cu es (inse : Young’s modulus as a unc ion o
BTO con en in he composi es) o nea ca ageenan and BTO/ca ageenan composi es con aining di e en BTO con en s.
10
2
10
3
10
4
10
5
10
6
10
2
10
3
10
4
10
5
(a)
/ Hz 10
2
10
3
10
4
10
5
10
6
/ Hz
0w .% BTO
1w .% BTO
5w .% BTO
10w .% BTO
20w .% BTO
40w .% BTO
1E-3
0,01
0,1
(b)
0w .% BTO
1w .% BTO
5w .% BTO
10w .% BTO
20w .% BTO
40w .% BTO
' / S.m
-1
010203040
4000
6000
8000
10000
12000
14000
(c)
w .% o BTO
10kHz
Figu e 4. a) ε0and b) σ0 o nea ca ageenan and BTO/ca ageenan nanocomposi es. c) Va ia ion o he dielec ic cons an as a unc ion o BTO con en
a 10 kHz.
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whe e Cand C
0
deno e he capaci y wi h and wi hou applied
p essu e, and pdesigna es he applied p essu e), he signal s a -
ing o sa u a e o highe comp ession o ces.
Once cha ac e ized, he de eloped o ce senso was connec ed
o an elec onic ci cui based on a mic ocon olle A duino Uno
(Figu e 7a,b). The ci cui sends a con inuous signal a 1 kHz o
one o he elec odes o he senso and eads he alue on he
o he elec ode ha is connec ed o he mic ocon olle
analog– o-digi al con e e (ADC). A digi al Bu e wo h low-pass
fil e wi h a cu equency o 10 Hz was implemen ed in he
mic ocon olle fi mwa e, in o de o fil e he high- equency
signal, while lea ing he signal om he p essu e e en .
Figu e 7c shows he da a ecei ed by he mic ocon olle ADC
ha was sen o a g aphical use in e ace (GUI) c ea ed in QT
C ea o , whe e he da a can be isualized in eal ime (see sup-
plemen a y ideo). The esul s show good co ela ion wi h he
p e ious es s using he LCR me e . The senso can de ec a fin-
ge p essu e and quan i y an inc ease o dec ease in p essu e. In
Figu e 5. a) Schema ic diag am o he senso , b) senso wo king p inciple, and c) pic u e o he ab ica ed o ce/ ouch senso .
-10
0
10
20
30
40
50
60
P essu e / kPa
0 500 1000 1500 2000 2500 3000 3500 4000 4500
-0,5
0,0
0,5
1,0
1,5
2,0
2,5
3,0 P essu e
C/C
0
Time / s
C/C0
-10
0
10
20
30
40
50
60
P essu e / kPa
500 550 600 650 700 750
-0,5
0,0
0,5
1,0
1,5
2,0
2,5
(b)
(a)
P essu e
C/C
0
Time / s
C/C
0
0 102030405060
-0,5
0,0
0,5
1,0
1,5
2,0
2,5
3,0
(c)
C/C0
P essu e / kPa
Mean+ SD
Fi
Figu e 6. a) BTO/ca ageenan composi e wi h 20 w % o BTO unde 80 cycles o comp ession wi h a ying p essu e om 0 o 55 kPa. b) Magnifica ion
a ea o he cycles ( ec angle in a)) and c) sensi i i y o he sample.
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o de o isola e a ouch e en om he hand (p oximi y o he
finge o he elec odes), a polylac ic acid (PLA) od was also used
o es he p essu e de ec ion.
The demons a ed simple-ci cui implemen a ion shows he
e sa ili y o he de eloped senso o ouch/p essu e de ec ion
applica ions. I is he fi s ime ha a o ce senso based on
ca ageenan wi h BTO nanopa icles has been epo ed and i s
beha io is compa able o senso s epo ed in he li e a u e
based on composi es p oduced by syn he ic polyme s such as,
ca bon nano ube/polydime hylsiloxane (PDMS),
[38]
MXene/
poly inylidene fluo ide,
[39]
and BTO wi h PDMS.
[40]
The dielec ic esponse o he BTO/ca ageenan nanocompo-
si es as a o ce senso was demons a ed in a unc ional de ice,
opening new a enues o he de elopmen o en i onmen ally
iendly composi e ma e ials o elec onic applica ions.
4. Conclusion
Ca ageenan-based composi es wi h BTO nanofille s ha e been
de eloped by di ec ink w i ing o o ce-sensing applica ions.
Fu he , he influence o BTO nanofille s con en , up o 40 w %,
on he composi e physical–chemical p ope ies has been also
add essed.
The samples showed a compac mic os uc u e, he BTO
fille being homogeneously dis ibu ed in o he ma ix
and obse ing an inc ease in fille agg ega ion o he samples
wi h la ge nanopa icle con en . The he mal p ope ies
o he samples depend on BTO fille con en , T
g
alues, and
endo he mic peak in ensi y, dec easing wi h inc easing fille
con en .
Mechanical and dielec ic p ope ies we e also a ec ed by he
BTO con en . Mechanically, he bes sample was he one wi h
10 w % o BTO, ac ing as be e mechanical ein o cemen .
Dielec ic p ope ies o he composi es we e gene ally imp o ed
upon BTO addi ion. In pa icula , o he 20 w % BTO con en
sample, he dielec ic cons an was 13 000, showing also an
AC conduc i i y o 0.011 S m
1
a 10 kHz, being he e o e a
high-ε0–high-loss ma e ial.
Wi h espec o senso applica ion, a good epea abili y in he
senso elec ical esponse has been ob ained wi h he 20 w %
BTO sample o o e 80 cycling es s o o ce a ia ion be ween
0 and 10 N. A good linea i y has been ob ained o o ces up o
5 N ange (a ound 86.7 pF N
1
), s a ing o sa u a e a highe
comp ession o ces.
In summa y, he de eloped BTO/ca ageenan composi es
exhibi a sui able sensing esponse, hus allowing o de elop
o ce senso s o sus ainable elec onics.
0102030405060708090100110120
200
300
400
500
600
(c)
Value / a.u.
Time / s
(a) (b)
Figu e 7. a) Pho og aphy o he elec onic ci cui and capaci i e senso , b) schema ic o he elec onic ci cui , and c) da a ecei ed om he elec onic
ci cui when a p essu e e en occu s.
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Acknowledgemen s
The au ho s hank he Fundação pa a a Ciência e Tecnologia (FCT) o
financial suppo unde he amewo k o S a egic Funding g an s
UIDB/04650/2020, UID/FIS/04650/2020, UID/EEA/04436/2020, and
UID/QUI/0686/2020 and unde p ojec s POCI-01-0145-FEDER-028157
and PTDC/FIS-MAC/28157/2017 unded by na ional unds h ough FCT
and by he ERDF h ough he COMPETE2020—P og ama Ope acional
Compe i i idade e In e nacionalização (POCI). The au ho s also hank
he FCT o financial suppo unde g an SFRH/BD/131729/2017
(N.P.) and con ac s unde he S imulus o Scien ific Employmen ,
CEECIND/03975/2017 (P.M.) and 2020.04028.CEECIND (C.M.C.).
Financial suppo om he Basque Go e nmen Indus y Depa men
unde he ELKARTEK p og am is acknowledged. The au ho s hank ech-
nical and human suppo p o ided by SGIke (UPV/EHU/ERDF, EU).
Conflic o In e es
The au ho s decla e no conflic o in e es .
Da a A ailabili y S a emen
The da a ha suppo he findings o his s udy a e a ailable om he
co esponding au ho upon easonable eques .
Keywo ds
ca ageenan, polyme –ma ix composi es, senso s, sma ma e ials
Recei ed: Decembe 13, 2022
Re ised: Feb ua y 22, 2023
Published online: Ma ch 18, 2023
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