RESEARCH ARTICLE
www.m c-jou nal.de
Fas Visible-Ligh 3D P in ing o Conduc i e PEDOT:PSS
Hyd ogels
Na oa Lopez-La ea, An onela Gallas egui, Luis Lezama, Mi yam C iado-Gonzalez,
Ne ea Casado, and Da id Mece eyes*
Func ional inks o ligh -based 3D p in ing a e ac i ely being sea ched o
being able o exploi all he po en iali ies o addi i e manu ac u ing. He ein, a
as isible-ligh pho opolyme iza ion p ocess is showed o conduc i e
PEDOT:PSS hyd ogels. Fo his pu pose, a new Type II pho oini ia o sys em
(PIS) based on ibofla in (R ), ie hanolamine (TEA), and
poly(3,4-e hylenedioxy hiophene):poly(s y enesul ona e) (PEDOT:PSS) is
in es iga ed o he isible ligh pho opolyme iza ion o ac ylic monome s.
PEDOT:PSS has a dual ole by accele a ing he pho oini ia ion p ocess and
p o iding conduc i i y o he ob ained hyd ogels. Using his PIS, ull
monome con e sion is achie ed in less han 2 min using isible ligh . Fi s ,
he PIS mechanism is s udied, p oposing ha elec on ans e be ween he
iple exci ed s a e o he dye (3R *) and he amine (TEA) is ca alyzed by
PEDOT:PSS. Second, a se ies o poly(2-hyd oxye hyl ac yla e)/PEDOT:PSS
hyd ogels wi h diffe en composi ions a e ob ained by pho opolyme iza ion.
The p esence o PEDOT:PSS nega i ely influences he swelling p ope ies o
hyd ogels, bu significan ly inc eases i s mechanical modulus and elec ical
p ope ies. The new PIS is also es ed o 3D p in ing in a comme cially
a ailable Digi al Ligh P ocessing (DLP) 3D p in e (405 nm wa eleng h),
ob aining high esolu ion and 500 μm hole size conduc i e scaffolds.
N. Lopez-La ea, A. Gallas egui, M. C iado-Gonzalez, N. Casado,
D. Mece eyes
POLYMAT
Uni e si y o he Basque Coun y UPV/EHU
A enida Tolosa 72, Donos ia-San Sebas ian, Guipuzcoa 20018, Spain
E-mail: [email p o ec ed]
L. Lezama
Depa amen o de Química O gánica e Ino gánica
Uni e si y o he Basque Coun y UPV/EHU
Ba io Sa iena s/n, Leioa, Bizkaia 48940, Spain
N. Casado, D. Mece eyes
IKERBASQUE
Basque Founda ion o Science
Plaza Euskadi 5, Bilbao 48009, Spain
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/ma c.202300229
© 2023 The Au ho s. Mac omolecula Rapid Communica ions 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 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.
DOI: 10.1002/ma c.202300229
1. In oduc ion
In he las ew yea s, conduc i e hyd ogels
ha e eme ged as p omising ma e ials o
he nex gene a ion bioelec onic in e aces;
a ificial skin, flexible and implan able bio-
elec onics, and issue enginee ing. This
in e es is due o hei simila i ies o bio-
logical issues and elec ical, mechanical,
and bio unc ional p ope ies.[1–11] How-
e e , i is s ill a challenge o o mula e
hyd ogels wi h high elec ical conduc i i y
wi hou comp omising hei physico-
chemical p ope ies (e.g., s e chabili y
and oughness).[12,13] The mos commonly
used conduc i e polyme s (CPs) o he
syn hesis o conduc i e hyd ogels a e
polyaniline (PANi), polypy ole (PPy) and
poly(3,4-e hylenedioxy hiophene) doped
wi h poly(s y enesul ona e) (PEDOT:PSS),
al hough ce ain ca bon nanoma e ials
such as ca bon nano ubes (CNTs) and
g aphene a e also widely used o he
syn hesis o conduc i e hyd ogels.
Among hem, he mos popula con-
duc ing polyme o hese applica ions is
PEDOT:PSS due o i s high conduc i i y,
s abili y, and biocompa ibili y.[14] Howe e , PEDOT:PSS is insol-
uble and in usible, hus, he syn hesis o 3D conduc i e ma e-
ials is s ill a challenge.[15,16] Fo ha eason, addi i e manu ac-
u ing 3D p in ing me hods a e inc easingly being used in o de
o c ea e conduc i e hyd ogels using diffe en ype o echniques
such as inkje p in ing,[17,18] ex usion-based p in ing[19–21] and
ligh -based p in ing.[22–24] Ve y ecen ly, we ha e shown ha
PEDOT can be copolyme ized wi h poly(𝜖-cap olac one) (PCL)
biopolyes e , leading o PEDOT-g-PCL g a copolyme s. This
copolyme shows excellen shea - hinning beha io o be p o-
cessed by ex usion-based p in ing in o de o syn he ize 3D sca -
olds o induce muscle cells (myo ubes) diffe en ia ion.[25] In an-
o he example, we ha e dispe sed PEDOT:PSS in an aqueous ma-
ix o med by inyl esins in o de o pho opolyme ize flexible
and shape-defined conduc i e hyd ogels o applica ion as bio-
elec odes o human elec oca diog aphy (ECG) and elec omyo-
g aphy (EMG) eco dings, showing long- e m ac i i y and en-
hanced de ec ion signals compa ed o comme cial Ag/AgCl med-
ical elec odes o heal h moni o ing.[26] Howe e , hese s a e-
gies o ob ain 3D conduc i e hyd ogels a e s ill a om being
easy and apid me hodologies.
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Scheme 1. Schema ic ep esen a ion o he main eagen s in ol ed in he isible ligh pho opolyme iza ion eac ion.
Ligh -based 3D p in ing encompasses he addi i e manu ac-
u ing me hods wi h he highes esolu ion (be ween 20 and
100 μm).[27] He e, pho oini ia o s ha abso b in he UV ange a e
usually employed o o mula e diffe en conduc i e inks. How-
e e , he use o UV ligh in pho opolyme iza ion p ocesses has
some d awbacks; o example, i can damage use ´s heal h and
can p oduce ozone when he oxygen o he a mosphe e is i -
adia ed wi h UV ligh .[28] Fo ha eason, pho oini ia ing sys-
ems ha can be ac i a ed unde low ligh in ensi y and in he
isible ange (400–700 nm) ha e been esea ched in he e-
cen yea s.[29–33] The use o isible ligh sou ces such as Ligh -
Emi ing Diodes (LEDs) in pho opolyme iza ion p ocesses in-
s ead o UV ligh p o ides a numbe o ad an ages such as
low ene gy consump ion, oom empe a u e ea men , non-
pollu ing, low-cos s, and sol en - ee o mula ions.[28] Addi ion-
ally, ligh pene a ion is limi ed o ≈600 μm in he UV ange,
while using highe wa eleng hs i inc eases up o 2 cm, e idenc-
ing he in e es o polyme izing unde isible ligh .[34] Howe e ,
isible ligh pho oini ia o s a e usually no as enough o be used
in ligh -based 3D p in ing me hods. This happens because UV
ligh and isible ligh pho oini ia o s ha e a diffe en mechanism
o p oduce ac i e adicals.[35] The pho opolyme iza ion eac ions
using isible ligh a e usually p omo ed by Type II pho oini ia o
sys ems (PISs), whe e a sensi ize abso bs pho ons om he is-
ible ligh sou ce and hen i ans e s he ene gy o a co-ini ia o
(hyd ogen dono ) by a hyd ogen abs ac ion eac ion. Du ing his
eac ion, ac i e adical species and sensi ize adicals a e gen-
e a ed, bu only he ac i e adical species ini ia e he ee adi-
cal polyme iza ion.[36–38] Thus, he ini ia ing efficiency o Type II
PISs is slowe han he one o Type I pho oini ia o s, which a e
based on unimolecula o ma ion o adicals. Fu he mo e, Type
II PISs o en equi e he absence o oxygen (a adical polyme iza-
ion inhibi o ), he absence o abso ben addi i es ha could also
abso b isible ligh , and high exposu e imes.[39] The e o e, he
de elopmen o a as isible ligh pho oini ia io sys em (PIS) o
ligh -based 3D p in ing me hods is needed in o de o syn he ize
conduc i e hyd ogels in a as and secu e way.
The goal o his a icle is o p opose a new as isible-ligh
PIS in he p esence o PEDOT:PSS, which allows he p epa-
a ion o 3D conduc ing hyd ogels by ligh -based 3D p in ing
ex ending he ange o conduc ing polyme ma e ials and inks
o addi i e manu ac u ing. The isible-ligh PIS is composed
o Ribofla in (R ) as he sensi ize , commonly known as he
wa e -soluble i amin B2,[40] ie hanolamine (TEA) as he co-
ini ia o , and PEDOT:PSS conduc i e polyme as ca alys , as il-
lus a ed in Scheme 1. This new Type II PIS PEDOT:PSS/R /TEA
was employed in he polyme iza ion o a ious monome s such
as 2-hyd oxye hyl ac yla e (HEA), 4-ac yloyl mo pholine (4-AM)
and ac ylamide (AAm), using a li le amoun o polye hylene
glycol diac yla e (PEGDA Mn 700) as a c oss-linke agen . Us-
ing a isible ligh i adia ion sou ce o 440 nm and powe o
2mWcm
−2, poly(hyd oxye hyl ac yla e) (PHEA) hyd ogels con-
aining PEDOT:PSS we e ob ained in less han 1 min.
2. Resul s and Discussion
In ou p e ious wo k, CNTs we e employed in he PIS sys em.[39]
Su p isingly, he use o PEDOT:PSS ins ead o CNTs in he
Type II PIS makes he pho opolyme iza ion eac ion as e .
Fo ha eason, pho opolyme iza ion eac ion kine ics o di -
e en p e-polyme ic mix u es we e in es iga ed (Table S1, Sup-
po ing In o ma ion). On he one hand, hese p e-polyme ic
mix u es, which need in si u p epa a ion, we e composed o
Monome /PEGDA in a a io o 90/10 (50 w .% o he o al ink
o mula ion), and an aqueous solu ion o diffe en conduc i e
species a 1.3 w .% ( he emaining 50 w .% o he ink). As o
he concen a ion o R and TEA, he co-ini ia o TEA was used
a a concen a ion o 0.2 m and R was used a a concen a ion o
1E-05 m acco ding o Encinas e al., who in es iga ed he poly-
me iza ion a es o 2-hyd oxye hyl me hac yla e (HEMA) pho-
oini ia ed by ibofla in using as co-ini ia o se e al concen a-
ion o diffe en amines ( ie hanolamine, ie hylamine, dibu y-
lamine, and dime hylamine).[41] They ob ained as e kine ics us-
ing TEA as he co-ini ia o and hey conclude ha he pho ochem-
ical efficiency is s ongly dependen on he s uc u al ea u es o
he amines, he e o e, ie hanolamine was chosen as he s an-
da d co-ini ia o . On he o he hand, he kine ics we e ollowed
by Fou ie T ans o m In a ed Spec oscopy (FTIR), i adia ing
wi h isible ligh (440 nm, 2 mW cm−2) he diffe en inks and
ollowing he disappea ance o C=C ou o plane bending ib a-
ion ( inylic peak) o he monome a 990 cm−1(Figu e S1A, Sup-
po ing In o ma ion). LEDs o 440 nm we e used as i adia ion
sou ce as i is he maximum abso p ion wa eleng h o ibofla in,
he molecule ha ac s as sensi ize in he sys em.[40]
Fi s o all, a ious inks con aining diffe en conduc ing
species (PEDOT:PSS, CNTs, polyaniline PANi and poly(3-
hexyl hiophene-2,5-diyl) P3HT) we e analyzed. Resul s e eal
ha when PEDOT:PSS is used, ull con e sion is eached in
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Figu e 1. A) E olu ion o he pho opolyme iza ion eac ion kine ics gi en by % 2-Hyd oxye hyl ac yla e HEA monome con e sion e sus i adia ion
ime (min) o a ious p e-polyme ic mix u es using diffe en PEDOT:PSS concen a ion. B) EPR spec a o PEDOT:PSS 0 and 1.3 w .% inks (con aining
PBN spin ap) a e 60 s o i adia ion.
1 min. Howe e , when o he conduc ing ma e ials a e employed,
he i adia ion ime o ge 100% con e sion ex ends o 10–12 min
(Figu e S1B, Suppo ing In o ma ion). This beha io can be ex-
plained by he conduc i i y alues o he diffe en CP dispe -
sions ha a e used. Table S2 (Suppo ing In o ma ion) shows he
elec ical conduc i i y o d op-cas ed CP dispe sions. While PE-
DOT:PSS has a conduc i i y alue o 100 mS cm−1, he o he con-
duc i e species (CNTs, PANi and P3HT) ha e conduc i i ies o 3
o de s o magni ude lowe . The e o e, he elec ical conduc i i y
o he CP ha is used seems impo an o he apid pho opoly-
me iza ion kine ics being PEDOT:PSS he one ha shows be e
esul s.
In a nex s ep, pho opolyme iza ion eac ion kine ics we e
analyzed using diffe en monome s (HEA, 4-AM, PEGDA, and
AAm) and PEDOT:PSS. In his case, all inks eached ull con e -
sion in 1 min, excep o 4-AM p e-polyme ic mix u e ha ook
wice as long (2 min) o ge 100% con e sion (Figu e S1C, Sup-
po ing In o ma ion). This can be explained by he ac ha 4-AM
is mo e hyd ophobic han HEA, PEGDA, and AAm monome s.
The e o e, i in e ac s in a less effec i e way wi h he new wa e -
soluble Type II PIS, and hence, kine ics o pho opolyme iza-
ion eac ion a e slowe . Besides, poly(2-hyd oxye hyl ac yla e)
(PHEA) has a lowe glass ansi ion empe a u e (Tg) han he
o he s udied polyme s, so he ob ained hyd ogels could mee
he equi emen o so mechanical p ope ies o bioelec onic
applica ion.[42] Fo ha eason, HEA was chosen as he s anda d
monome o nex expe imen s.
To be e unde s and he ole o PEDOT:PSS in he sys em,
addi ional kine ic s udies we e ca ied ou using as he PIS
only R /TEA, R /PEDOT:PSS and TEA/PEDOT:PSS (Figu e S1D,
Suppo ing In o ma ion). In he case o R /PEDOT:PSS and
TEA/PEDOT:PSS, he polyme iza ion did no occu . Howe e ,
using he con en ional Type II PIS, R /TEA wi hou PEDOT:PSS,
he kine ics we e e y slow, ob aining only a 40% o con e -
sion in 12 min. The e o e, PEDOT:PSS only inc eases up he
pho opolyme iza ion speed when all o he PIS componen s a e
p esen in he sys em and does no ini ia e he pho opolyme -
iza ion eac ion. In o de o confi m ha ibofla in, which maxi-
mum abso bance wa eleng h is 445 nm,[40] is he molecule ha
ini ia e he pho opolyme iza ion and ha PEDOT:PSS, which ab-
so bs in all he isible ange,[43] only speeds up he pho opoly-
me iza ion eac ion, some kine ic measu emen s o PEDOT:PSS
1.3 w .% ink we e pe o med using 525 and 660 nm wa eleng hs
(Figu e S1E, Suppo ing In o ma ion). As expec ed, using g een
and ed-ligh sou ces, pho opolyme iza ion does no occu , con-
fi ming again Type II gene al pho oini ia o mechanism.
Finally, he effec o he PEDOT:PSS concen a ion on he
pho opolyme iza ion eac ion kine ics was s udied. Figu e 1A
shows he kine ics o some p e-polyme ic mix u es employ-
ing 0, 0.25, 0.5, 1.3, 2, and 4 w .% PEDOT:PSS. Resul s e-
eal ha a leas 0.5 w .% PEDOT:PSS is necessa y o accele -
a e he pho opolyme iza ion eac ion. Howe e , when he con-
cen a ion o PEDOT:PSS inc eases up o 4 w .%, he ime o
each a ull con e sion is ex ended om 1 o 4 min. This beha -
io may occu as a esul o a deep cu ing effec . PEDOT:PSS ab-
so bs in he isible ange, he e o e, as he concen a ion o PE-
DOT:PSS inc eases in he sys em, R and PEDOT:PSS compe e
o he abso bance o pho ons and he speed o he pho opoly-
me iza ion slows down. Figu e S2 (Suppo ing In o ma ion)
shows he no malized abso bance o diffe en p e-polyme ic mix-
u es con aining diffe en concen a ions o PEDOT:PSS in he
isible ange.
Many ac o s could be con ibu ing o he impo an inc ease
in he polyme iza ion a e using he PEDOT:PSS/R /TEA PIS.
On he one hand, as known o R /TEA Type II pho oini ia o sys-
em, he e is an elec on ans e be ween he iple exci ed s a e
o he dye (3R *) and he amine (TEA) ollowed by a as p o on
abs ac ion.[39] In his way, ac i e amino adicals (R•) a e o med
and chain eac ion s a s (Scheme 2A). On he o he hand, we
hypo hesize ha PEDOT:PSS conduc ing polyme , whose s uc-
u e is al eady oxidized, could ca alyze his elec on ans e be-
ween 3R * and TEA (Scheme 2B), hus inc easing he eac ion
speed.[14,44] I is wo h no ing ha PEDOT:PSS only ac s as elec-
on conduc o in he mechanism, and i emains wi h he same
edox s uc u e a e pho opolyme iza ion, gi ing blue colo o
he final hyd ogel.[45] Ano he conside a ion o bea in mind is
ha PEDOT:PSS mus be also well dispe sed in he aqueous p e-
polyme ic mix u e in o de o be in close con ac wi h R and TEA.
I is well known ha PEDOT:PSS swells in aqueous media, and as
R and TEA a e solubilized in he aqueous solu ion, he in e ac-
ion be ween he PEDOT:PSS su ace and all PIS componen s is
high enough o speed up he pho opolyme iza ion eac ion.[46–48]
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Scheme 2. Visible ligh pho oini ia o mechanism o inyl polyme iza ion employing A) he known Type II pho oini ia o sys em R /TEA and B) he
p oposed pa hs when PEDOT:PSS in e ene in he p ocess.
This closeness would a oid diffusional s eps and he possible in-
hibi ion o oxygen in he sys em.
To cla i y he ole o PEDOT:PSS in he pho opolyme iza-
ion mechanism, elec on pa amagne ic esonance (EPR) ex-
pe imen s we e ca ied ou . Fi s o all, he EPR spec um o
PEDOT:PSS 0.5 w .% aqueous solu ion was eco ded, as PE-
DOT:PSS i sel gi es a single iso opic signal a g =2.0030 (see
Figu e S3A, Suppo ing In o ma ion). Then, he spec a o wo
p e-polyme ic solu ions (PEDOT:PSS 0 w .% and PEDOT:PSS
1.3 w .%) con aining N- e -bu yl-𝛼-phenylni one (PBN) spin
ap we e eco ded a diffe en i adia ion imes a oom em-
pe a u e. These wo samples we e compa ed a 60 s o i adia-
ion ime, and i can be seen ha he EPR signal o PEDOT:PSS
con aining sample is mo e in ense (see Figu e 1B). The obse ed
spec a could be well fi ed wi h g =2.0058 and AN=16.5 G (see
Figu e S3B, Suppo ing In o ma ion), in good ag eemen wi h
wha is expec ed o a ni one adical, he in ensi y o he lines
being quan i a i ely ela ed o he numbe o adicals ha he
pho opolyme iza ion sys em is c ea ing. The e o e, i is demon-
s a ed ha he p esence o PEDOT:PSS in he Type II PIS accel-
e a es he adical gene a ion eac ion. Mo eo e , he c ea ion o
adicals in he PEDOT:PSS con aining sample was also ollowed
by EPR. Figu e S4 (Suppo ing In o ma ion) shows he EPR spec-
a o he sample a diffe en i adia ion imes (0, 30, and 60 s),
and i can be seen ha he in ensi y o he signal inc eases wi h
ime. These expe imen s confi m he p oposed mechanism in
Scheme 2, whe e PEDOT:PSS ca alysis he elec on ans e be-
ween 3R * and TEA, a o ing he c ea ion o ac i e adicals o
ini ia e he polyme iza ion.
The e o e, as he p esence o PEDOT:PSS clea ly influences
he kine ics o he sys em, PHEA hyd ogels we e syn he ized
wi h 0, 0.5, 1.3, and 2 w .% PEDOT:PSS ( he mos apid o mu-
la ions, see Figu e S5, Suppo ing In o ma ion) in o de o de-
e mine how he elec ochemical and mechanical p ope ies o
hyd ogels change wi h PEDOT:PSS concen a ion. I is e y im-
po an o s udy hese p ope ies as he conduc i e hyd ogels a e
po en ial ma e ials o applica ion in bioelec onics, whe e good
elec ical conduc i i y is needed o biosensing and so mechan-
ical p ope ies a e needed o mimic human issue.
Figu e 2A p esen s he swelling beha io in wa e e sus ime,
an impo an ea u e o hyd ogels ha desc ibes hei abili y o
e ain wa e . I can be no ed ha he maximum wa e up ake
capaci y o he hyd ogels is achie ed in 2 h. Mo eo e , as PE-
DOT:PSS concen a ion inc eases in he polyme ic ma ix, he
swelling a io dec eases con inuously, om 362 ±10% o PE-
DOT:PSS 0 w .% hyd ogel o 236 ±12% o PEDOT:PSS 2 w .%.
These esul s a e expec ed due o he addi ion o PEDOT:PSS
hyd ophobic addi i e in he PHEA hyd ogel s uc u e. O e all,
diffe en swelling alues can be achie ed changing he concen-
a ion o PEDOT:PSS, which can be ad an ageous o diffe en
applica ions such as sensing o cell cul u e.[49–51]
In e es ingly, he elec ical conduc i i y o PHEA/PEDOT:PSS
hyd ogels was measu ed by he 4-Poin P obe me hod, and e-
sul s a e shown in Figu e 2B. Ob iously, as he PEDOT:PSS
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Figu e 2. A) Swelling cu es in wa e , B) Elec ical conduc i i y in d ied/swollen s a e and C) Cyclic ol ammog ams o e a glassy ca bon elec ode in
0.1 m NaCl aqueous solu ion a 20 mV s−1o PHEA hyd ogels con aining 0, 0.5, 1.3, and 2 w .% PEDOT:PSS. D) Lab-made elec ical ci cui o conduc
he elec ical cu en om he ba e y o he LED ( ed), passing h ough he PHEA hyd ogel con aining 1.3 w .% PEDOT:PSS (blue).
concen a ion inc eases, so does he conduc i i y, as obse ed in
o he ela ed wo ks,[22,52–54] eaching 0.1 S cm−1 o he hyd ogel
con aining 2 w .% PEDOT:PSS, simila alue as he comme cial
PEDOT:PSS (He aeus PH1000). Conduc i i y o hyd ogels was
also measu ed in hei swollen s a e. In his case, he conduc i -
i y alue dec eases almos one o de o magni ude o all samples
compa ing wi h hei d ied s a e. I is wo h no ing ha he hy-
d ogel wi hou PEDOT:PSS used as con ol only shows low con-
duc i i y alues in i s swollen s a e due o he ionic conduc i i y
and i does no show elec ical conduc i i y in i s d y s a e, as ex-
pec ed, p o ing he key ole o PEDOT:PSS in he hyd ogels o
conduc i e pu poses.
The elec oac i e beha io o hyd ogels was also es ed by
cyclic ol amme y in 0.1 m NaCl aqueous solu ion (Figu e 2C;
Figu e S6, Suppo ing In o ma ion). Only he cyclic ol ammo-
g ams (CV) o he hyd ogels con aining 1.3 and 2 w .% PE-
DOT:PSS show a capaci i e beha io , wi h a b oad anodic peak
be ween 0.2 and 0.4 V and a b oad ca hodic peak a 0.1 V, no
obse ed in he case o hyd ogels con aining 0 and 0.5 w .%
PEDOT:PSS (Figu e 2C). These esul s can be compa ed wi h
he elec ical conduc i i y measu emen s when hyd ogels a e
swollen, whose endency is he same. Mo eo e , he CVs o PE-
DOT:PSS 1.3 w .% hyd ogel a diffe en scan a es show a p opo -
ional inc ease o he anodic and ca hodic cu en s wi h he scan
a e, which means ha he edox p ocesses a e no limi ed by di -
usion and he whole hyd ogel is in ol ed in he elec o-chemical
p ocesses (Figu e S6, Suppo ing In o ma ion).
As a isual p oo -o -concep o hyd ogel´s elec ical p ope ies,
a lab-made elec ical ci cui ha inco po a es he syn he ized hy-
d ogel was buil (see Figu e 2D). The hyd ogel is able o ans-
e he elec ical cu en om he ba e y o he LED swi ching
i on.
The p esence o PEDOT:PSS also affec ed he mechanical
p ope ies o he PHEA hyd ogels, as obse ed in Figu e 3A
and Figu e S7 (Suppo ing In o ma ion). I can be seen ha
s o age modulus (G´) and loss modulus (G″) do no in e sec
be ween hem, which means ha he hyd ogels beha e like a
solid in all he equency ange. Mo eo e , he s o age modulus
(G´) inc eases om 9.3E +04 Pa o 8.1E +05 Pa (a 1 Hz e-
quency and 25 °C), ob aining a ha de ma e ial as he concen a-
ion o PEDOT:PSS inc eases in he polyme ma ix. Figu e 3B
shows he s ess-s ain cu es o he syn he ized ma e ials wi h
Type V p obe shape (Figu e 3C) ob ained om he ensile es
expe imen . As he PEDOT:PSS quan i y inc eases in he sys-
em, he Young´s Modulus also inc eases om 0.24 ±0.03 o
1.52 ±0.40 MPa, o PEDOT:PSS 0 and 2 w .% ma ixes, espec-
i ely (Figu e S8, Suppo ing In o ma ion). In he same way, he
elonga ion a b eak dec eases om 34 ±2 o23±5% wi h he
addi ion o PEDOT:PSS in he ma ix. E en hough he inco -
po a ion o PEDOT:PSS makes he hyd ogels o be ha de , he
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Figu e 3. A) Ma ix cha ac e iza ion by dynamic mechanical analysis (DMA) and B) S ess−s ain cu es o syn he ized ma e ials con aining 0, 0.5, 1.3,
and 2 w .% PEDOT:PSS. C) Rep esen a i e pic u e o he 1.3 w .% PEDOT:PSS hyd ogel wi h a Type V p obe shape be o e he ensile es analysis.
Figu e 4. A) Rep esen a i e scheme o he 3D p in e sys em and a pic u e o he 3D p in ed honeycomb hyd ogel. B) SEM images o he p in ed
honeycomb hyd ogel.
ma e ials a e s ill flexible o some biological applica ions such
as biosensing.[55]
Finally, he new PIS based on PEDOT:PSS/R /TEA was
es ed o 3D p in ing o p o e ha he new Type II PIS
is compa able o o he epo ed me hods,[56,57] employing he
PEDOT:PSS 1.3 w .% p e-polyme ic mix u e (using HEA as
monome ) and a comme cially a ailable DLP (Digi al Ligh P o-
cessing) 3D p in e , Any Cubic Pho on Mono X 6K model (wa e-
leng h =405 nm and powe =2mWcm
−2). Al hough ibofla in
can abso b also a 405 nm, he mos efficien p in abili ies a e
ob ained wi h blue ligh , o which new isible ligh 3D p in e s
a e being de eloped in o de o maximize he efficiency o Type
II PIS like he one explo ed he e, o pho opolyme ize in a secu e
way and no damaging he use ´s heal h.[58] These ypes o 3D
p in e s no only need a as and highly efficien PIS o ini ia e
he polyme iza ion wi hou needing he deoxygena ion s ep, bu
also he iscosi y o he ink mus be low enough so i can un
h ough he a . The inks o DLP 3D p in ing gene ally equi e
a iscosi y lowe han 20 Pa.s a a shea a e o 10 o 100 s−1 o be
easily p ocessed.[59,60] Figu e S9 (Suppo ing In o ma ion) shows
he iscosi y o diffe en p e-polyme ic solu ions con aining a i-
ous amoun s o PEDOT:PSS, om 0 o 2 w .%. I can be app eci-
a ed ha as he concen a ion o PEDOT:PSS inc eases in he ink,
he iscosi y also inc eases, bu all o hem mee he equi emen
o be p ocessed by DLP. Figu e 4A shows a schema ic ep esen-
a ion o he employed 3D p in e whe e he ink is deposi ed in
a a , and h ough a laye -by-laye ligh i adia ion in he Z axis,
he p e-polyme ic solu ion is pho opolyme ized on he pla o m,
hus ob aining a hyd ogel. A laye heigh o 0.15 mm and a laye
exposu e ime o 20 s we e applied as he op imal p in ing condi-
ions. A honeycomb-based hyd ogel was p in ed, wi h an a ea o
6×4 mm and 1 mm hickness. Figu e 4B shows he SEM images
o he shape-defined p in ed scaffolds wi h a hole size o 500 μm.
The high p in ing esolu ion shows he g ea abili y o he new
p oposed PIS o be employed o ligh -based 3D p in ing. Mo e-
o e , he inco po a ion o PEDOT:PSS CP in he final ma e ial
is highly desi able o diffe en applica ions such as issue engi-
nee ing, biosenso s o bioelec onic de ices.
3. Conclusion
In conclusion, a new pho oini ia o sys em based on PE-
DOT:PSS/R /TEA has been de eloped o as isible-ligh pho-
opolyme iza ion o wa e soluble ac ylic monome s in he p es-
ence o PEDOT:PSS. Resul s indica e ha PEDOT:PSS pa ici-
pa es in he pho oini ia ion p ocess, ca alyzing he elec on ans-
e be ween he iple exci ed s a e o he dye (3R *) and he
amine (TEA), inc easing he pho opolyme iza ion eac ion ki-
ne ics. This new PIS allows us o a oid p oblems commonly
p esen in his Type II pho oini ia o sys ems, such as slow
Mac omol. Rapid Commun. 2024,45, 2300229 2300229 (6 o 8) © 2023 The Au ho s. Mac omolecula Rapid Communica ions published by Wiley-VCH GmbH
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polyme iza ions and he p esence o oxygen. As a esul , con-
duc ing PHEA/PEDOT:PSS hyd ogels ha e been syn he ized in
less han 4 min. As he PEDOT:PSS concen a ion inc eases, he
elec ical conduc i i y o hyd ogels enhances up o 0.1 S cm−1
and hey become s iffe , wi h Young´s Modulus om 0.24 o
1.52 MPa. The new PIS was also es ed o 3D p in ing pu poses
in a comme cially a ailable DLP 3D p in e , ob aining a high-
esolu ion honeycomb like s uc u e wi h 500 μm hole size. In
addi ion, he use o isible ligh in he pho opolyme iza ion p o-
cess allows low ene gy consump ion, oom empe a u e ea -
men , non-pollu ing and low cos s compa ing wi h classical UV
pho opolyme iza ion, which could damage use ’s heal h. In ad-
di ion, he use o na u al molecules (such as ibofla in) in he
pho oini ia ion sys em can c ea e mo e sus ainable, eco- iendly
and easy scalable app oaches, as well as wa e -based inks o
biomedical applica ions, while he majo i y o Type I pho oini-
ia o s a e insoluble.[61] Due o he use o isible ligh in his sys-
em, i is possible o use i in nanomedicine; using biocompa i-
ble monome s, i can be explo ed he possibili y o di ec ly pho-
opolyme ize inks and syn he ize hyd ogels inside he in e es ed
issue ( o issue enginee ing applica ions, o example) wi hou
damaging he cell media. As he isible ligh pene a ion/cu ing
dep h can be up o 2 cm, di ec injec ion o he ink in o he hu-
man issue and subsequen pho opolyme iza ion om ou side
can be de elop as a u u e s a egy, whe e he conduc i i y o
PEDOT:PSS can accele a e cell p oli e a ion o diagnosis o dis-
eases can be ob ained by elec oca diog aphy (ECG) eco dings.
Finally, i is wo h no ing ha hese hyd ogels can be e y e sa-
ile as diffe en polyme ma ixes can be used o ob ain he mal,
ligh o e en pH esponsi e ma e ials, apa om he elec ical
conduc i i y ha hey may possess, and in eg a e hem in some
bioelec onic de ices such as o ganic elec ochemical ansis o s
(OECTs).
Suppo ing In o ma ion
Suppo ing In o ma ion is a ailable om he Wiley Online Lib a y o om
he au ho .
Acknowledgemen s
Financial suppo o he Spanish Agencia Es a al de In es igación o he
MINECO h ough p ojec PID2020-119026GB-I00 is acknowledged.
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
Resea ch da a a e no sha ed.
Keywo ds
3D p in ing, conduc ing polyme s, hyd ogels, PEDOT:PSS, Type II pho-
oini ia o sys em, isible-ligh pho opolyme iza ion
Recei ed: Ap il 24, 2023
Re ised: June 1, 2023
Published online: July 2, 2023
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