Resea ch a icle
Enabling low molecula weigh elec ospinning h ough bina y solu ions o
polyme blends
Vic o M. Pe ez-Puyana
a
, Albe o Rome o
a
, An onio Gue e o
a
, Lo enzo Mo oni
b
,
Paul A. Wie inga
b
,
*
a
Depa amen o de Ingenie ía Química, Uni e sidad de Se illa, Facul ad de Química, Se illa 41012, Spain
b
Depa men o Complex Tissue Regene a ion, MERLN Ins i u e o Technology-Inspi ed Regene a i e Medicine, Maas ich Uni e si y, Maas ich 6200 MD, he
Ne he lands
ARTICLE INFO
Keywo ds:
PCL
Gela in
Elec ospinning
Bina y solu ion, Nano ibe s
ABSTRACT
The o ma ion o nano ib ous memb anes ia elec ospinning is ypically es ic ed o high molecula weigh
polyme s in an app op ia e sol en , co ela ed wi h he necessa y o ma ion o polyme chain en anglemen s ha
a e needed o achie e success ul p oduc ion o elec ospun ibe s. The p esen wo k ex ends he elec ospinning
o low molecula weigh polyme s by in es iga ing he elec ospinning o a bina y solu ion sys em consis ing o
wo di e en low molecula weigh polyme s, using as a model sys em polycap olac one (PCL) and gela in in
di e en a ios. The iscosi ies o he polyme solu ions we e cha ac e ized as a p oxy o polyme chain
en anglemen and he esul ing ibe s we e mo phologically cha ac e ized by SEM imaging and u he assessed
wa e con ac angle and molecula composi ion o de e mine he impac and homogenei y o he bina y mix u es.
We ound ha uni a y solu ions o ei he PCL o gela in ailed o gene a e p ope ibe s despi e indica ions o
chain en anglemen . In con as , bina y solu ions o low molecula weigh PCL and gela in gene a ed di e en
ibe quali y and size dis ibu ions, depending on he a io used, wi h di ec co ela ions be ween ibe p ope ies
and he PCL:Gela in a io. I was disco e ed ha he a io o PCL o gela ion was mos p edic i e o success ul
ibe gene a ion, wi h e ec i e elec ospinning occu ing only o a de ine in e media e ange o high blend
a ios while bo h low and high blended bina y solu ions esul ed in poo ibe p oduc ion. Ou s udy con i med
ha his beha io was independen om absolu e polyme concen a ion, indica ing a unique in e ac ion be-
ween hese bina y species which exis s only unde speci ic a io concen a ions and indica es p omising new
a enues o p ocess low molecula weigh polyme s solu ions.
1. In oduc ion
The elec ospinning echnique is a p ocess ha can p oduce
nonwo en ib ous memb anes comp ised o ibe s wi h diame e s
anging om nanome e s o mic ome e s [1]. Thus, hese memb anes
p esen in e es ing p ope ies, such as mode a e po osi y and high spe-
ci ic a ea. Du ing elec ospinning, a polyme ic solu ion is pumped
h ough a me allic spinne e and a high ol age is applied be ween he
spinne e and a su ace, called collec o , ha is held a ixed dis ance
way. The esul ing elec ic ield elec os a ically ex udes he polyme
solu ion om he spinne e , o ming a je o polyme solu ion ha
a els om he spinne e o he collec o . Unde op imum condi ions,
he je unde goes high speed chao ic whipping which inc eases e apo-
a ion a e o he sol en , o ming solid ibe s ha a e e en ually
deposi ed on o he collec o o c ea e a ib ous memb ane [2]. The ibe
o ma ion and he p ope ies o he memb anes depend on he co ec
e olu ion o he polyme je du ing he elec ospinning p ocess.
Fibe o ma ion is an in e play be ween p ocessing pa ame e s,
en i onmen al condi ions and polyme solu ion p ope ies. P ocessing
pa ame e s can be adjus ed o ensu e s able je o ma ion and o une he
ibe diame e [3]. In his sense, se e al au ho s ha e e alua ed he
in luence o he di e en p ocessing pa ame e s ( ol age, humidi y,
wo king dis ance, e c.) on he elec ospinning p ocess [4–7]. En i on-
men al condi ions ha e been s udied in e ms o hei in luence on he
e apo a ion a e o he sol en and he subsequen e ec s on ibe o -
ma ion [8,9]. Bu polyme solu ion is a c i ical aspec in e ms o su ace
ension, conduc i i y o iscosi y. The la e is used as an indica ion o
he deg ee o chain en anglemen . I chain en anglemen is insu icien ,
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (P.A. Wie inga).
Con en s lis s a ailable a ScienceDi ec
Nex Ma e ials
jou nal homepage: www.sciencedi ec .com/jou nal/nex -ma e ials
h ps://doi.o g/10.1016/j.nxma e.2024.100306
Recei ed 1 May 2024; Recei ed in e ised o m 18 June 2024; Accep ed 4 July 2024
Nex Ma e ials 6 (2025) 100306
A ailable online 30 July 2024
2949-8228/© 2024 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY-NC license ( h p://c ea i ecommons.o g/licenses/by-
nc/4.0/ ).
he je canno be con inuously main ained and he p ocess ansi ions
om elec ospinning o elec osp aying whe e he je b eaks up in o
d ople s ha quickly dispe se as a esul o columbic o ces and deposi
on o he collec o as polyme mic osphe es [10].
As desc ibed by Colby e al. [11], a polyme solu ion alls in o “ ou
di e en concen a ion egimes: dilu e, semidilu e unen angled, semi-
dilu e en angled, and concen a ed”. Fo elec ospinning, i is he
bounda y be ween he semidilu e unen angled and semidilu e en angled
egimes, commonly known as he en anglemen concen a ion (C
e
),
which is o mos in e es ; his is he poin ha he numbe o polyme
chains in solu ion is su icien ly high o cons ain each o he , hus p o-
ducing en anglemen couplings [12] ha esis he b eakup o he
e ol ing polyme je and p omo e consis en ibe o ma ion [13].
Al hough he en anglemen concen a ion di e s depending on he
wo king sys em, McKee e al. ound ha a concen a ion be ween 2 and
2.5 imes he en anglemen concen a ion is necessa y o achie e
de ec - ee nano ib ous ma s [14]. This has been a gene ally accep ed
guideline and is ollowed by he elec ospinning- esea ch communi y.
The C
e
o a polyme /sol en sys em is o en de e mined by measu ing
he solu ion iscosi y, since his depends on he in e molecula in-
e ac ions in hese polyme solu ions and can se e as a p oxy o he
deg ee o chain en anglemen [15]. The sol en sys em used has a g ea
in luence on iscosi y, due o hei e ec on he dissolu ion and ho-
mogeniza ion o he polyme in solu ion [16]. Simila ly, he polyme
molecula weigh and polyme concen a ion in solu ion ha e a signi -
ican e ec on chain en anglemen wi hin he solu ion, wi h an inc ease
in molecula weigh o concen a ion causing an inc ease in iscosi y
[17]. The e o e, he limi ing concen a ion om which homogeneous
ibe s a e ob ained may di e depending on he polyme o he sol en
used.
In he cu en s udy, we in es iga ed a bina y polyme sys em in a
single sol en , unde he p emise ha in e molecula in e ac ions o wo
dis inc polyme ypes in solu ion can be op imized and co ela ed o an
imp o ed elec ospinning p ocess compa ed o espec i e uni a y
polyme solu ions. F om a wide a ie y o polyme s cu en ly a ailable
o elec ospinning, we selec ed a bina y sys em o PCL and Gela in as
wo dis inc polyme ypes o syn he ic and na u al o igin, espec i ely,
wi h good solubili y in simila sol en s and wi h epo ed applica ions in
issue enginee ing applica ions. Gela in, in pa icula , has been used
ex ensi ely in he elec ospinning o issue enginee ed ib ous cons uc s
as a na u al p o ein polyme ha has high biocompa ibili y compa ed o
syn he ic polyme s [18–20]. Howe e , he elec ospinning o gela in
alone is di icul o ca y ou p ope ly and i o en equi es he use o
o ganic sol en s o achie e app op ia e solu ion iscosi y and he use o
a blended solu ion o syn he ic and na u al polyme s o achie e homo-
geneous ibe s [21–23]. Polycap olac one (PCL) is simila ly a common
syn he ic polyme o elec ospun meshes due o i s sui able mechanical
p ope ies and easy p ocessabili y [24], hough molecula weigh and
polyme concen a ion emain c i ical o nano ibe o ma ion. Consis-
en elec ospinning o PCL has been epo ed when using an a e age
molecula weigh o 45,000 o 80,000 and concen a ions anging om
5 o 20 w % [18,25–28] while no success ul epo s could be ound o
elec ospinning low molecula weigh polycap olac one (LW-PCL,
M
w
=14,000 g/mol). Poo elec ospinning pe o mance is ypically
indica ed by he o ma ion o beads, which is a ibu ed o he low
su ace ension o he polyme solu ion o low molecula weigh o he
dissol ed polyme , which p e en s a con inuous polyme je du ing he
elec ospinning p ocess. Fo low molecula weigh s, in pa icula , i is
sugges ed ha small polyme s chains make i di icul o achie e su i-
cien chain en anglemen o ibe o ma ion e en a high concen a-
ions in solu ion. Ins ead o ibe s, polyme solu ions o his ype o en
esul in he consis en p oduc ion o elec osp ayed mic osphe es,
whe e LW-PCL a e epo ed o p oduce mic osphe es o e a ange o
concen a ions up o 30 % w/ (21.4 mM) [29].
Ou main hypo hesis is ha gela in and LW-PCL, wo polyme s which
canno be success ully elec ospun alone, can be combined o c ea e a
bina y polyme solu ion wi h op imized chain en anglemen and, hus,
success ul elec ospinning. This would lead o nano ibe p oduc ion
using lowe cos polyme s o lowe molecula weigh . The iscosi y o
polyme solu ions wi h a ying concen a ions o LW-PCL and gela in
was measu ed and he elec ospinning ou come o he same polyme
solu ions we e e alua ed using HFIP as sol en , wi h special ocus on
how he addi ion o gela in al e ed ib ous memb ane p oduc ion. To
his end, PCL and PCL:Gela in nano ib ous sca olds we e ab ica ed and
a physicochemical (wa e con ac angle and ene gy dispe si e analysis)
and mic os uc u al cha ac e iza ion (scanning elec on mic oscopy)
we e pe o med. The main no el y o his wo k is he iden i ica ion o an
op imal egime o concen a ions wi hin a bina y sys em, as de ined by
he iscosi y measu emen s and ela i e polyme a ios. This s udy was
ocused on he ole o change he solu ion p ope ies, so all o he pa-
ame e s, such as he p ocessing condi ions, we e main ained cons an .
This s udy p o ides a p oo -o -p inciple o u he explo a ion o p o-
duce ib es wi h lowe cos p ocessing condi ions.
2. Ma e ials and me hods
2.1. Ma e ials
Gela in p o ein (gela in ype B, 80–120 g Bloom) was supplied by
Henan Boom Gela in Co. L d (China). Gela in is mainly composed o
p o ein (ca 98 w %) and mino componen s, such as ash, lipids and
mois u e. Ve y low molecula weigh poly(
ε
-cap olac one) (LW PCL,
M
w
=14,000 g/mol) and 1,1,1,3,3,3-hexa luo o-2-p opanol (HFIP) we e
pu chased om Sigma Ald ich (Ge many).
2.2. Elec ospinning p ocess
PCL and gela in in di e en concen a ions we e mixed oge he
di ec ly in HFIP a oom empe a u e by s i ing o ca 24 h on a mag-
ne ic s i e ollowing he di e en a ios e alua ed. The selec ion o he
sol en was based on he op imiza ion o he elec ospinning p ocess
since HFIP dissol e bo h PCL and gela in p o ein. Once he solu ions
we e p epa ed, he elec ospinning p ocess was ca ied ou using a
Fluidna ek LE-100 equipmen (Bioinicia). Memb anes wi h PCL and
gela in in di e en a ios we e p ocessed ollowing he same p ocessing
condi ions used in p e ious s udies [30]: 14 kV o ol age, 0.4 mL/h o
low a e and 14 cm as he needle-collec o dis ance. The sys ems p o-
cessed wi h di e en p opo ions o PCL and gela in a e shown in
Table 1.
The ma s ob ained we e cha ac e ized by analysing he mean ibe
size and he ibe size dis ibu ion measu ed om SEM imaging. In
addi ion, he con ac angle and he N con en (wi h EDAX) we e also
e alua ed. The p e ious polyme ic solu ions we e cha ac e ised by
means o hei iscosi y.
Table 1
Sys ems p ocessed wi h di e en PCL:Gela in a ios modi ying he PCL o gela in
concen a ion.
Ra io PCL
Concen a ion
Gela in
Concen a ion
To al polyme
Concen a ion
Nomencla u e
3:1 12 w/ % 4 w/ % 16 w/ % 12/4
4:1 16 w/ % 20 w/ % 16/4
5:1 20 w/ % 24 w/ % 20/4
6:1 24 w/ % 28 w/ % 24/4
8:1 32 w/ % 36 w/ % 32/4
6:1* 6 w/ % 38 w/ % 32/6
5:1* 6.4 w/ % 38.4 w/ % 32/6.4
4:1* 8 w/ % 40 w/ % 32/8
3:1* 10.7 w/ % 42.7 w/ % 32/10.7
V.M. Pe ez-Puyana e al. Nex Ma e ials 6 (2025) 100306
2
2.3. Cha ac e iza ion s udies
2.3.1. Fibe mo phology cha ac e iza ion
2.3.1.1. Scanning elec on mic oscopy (SEM). Mic oscopy examina ion
o sca olds was assessed wi h a XL 30 (Philips XL Se ies) a an accel-
e a ion ol age o 10 kV, a spo size o 3 and a wo king dis ance o
10 mm. The samples we e co e ed wi h an Au ilm in a high- esolu ion
spu e coa e . ImageJ (a digi al p ocessing so wa e) was used o
analyze he mean ibe size and he po osi y. The ibe size dis ibu ion
was also ob ained o he di e en sys ems p oduced. Fu he mo e, he
a io o hei s anda d de ia ion o hei mean was calcula ed o de e -
mine he uni o mi y o he sys ems (Eq. 1):
Uni o mi y(%) = (1−s anda d de ia ion
mean ibe diame e )⋅100 (1)
The pa ame e “uni o mi y”has been de ined o e alua e he ho-
mogenei y o he memb anes since i allows compa ing he s anda d
de ia ion and mean ibe diame e o he ibe size dis ibu ion ob-
ained. In his sense, an inc ease in uni o mi y implies a dec ease in he
s anda d de ia ion, which ep esen s a lowe a iabili y o ibe size
ob ained.
2.3.1.2. Ene gy dispe si e x- ays spec oscopy (EDAX). The composi ion
o he elec ospun memb anes was e alua ed using he ene gy dispe si e
spec oscopy capabili y o he SEM equipmen (EDAX Si(Li) de ec o ).
An accele a ion ol age o 20 kV, a spo size o 3 and a wo king dis ance
o 10 mm we e he pa ame e s selec ed.
2.3.2. Wa e con ac angle (WCA)
The hyd ophobici y and we abili y o he sca olds we e analyzed by
measu ing he wa e con ac angle (WCA) wi h he sessile d op me hod
(d ople s wi h an app oxima e olume o 5
μ
L). WCA alues we e ob-
ained as he a e age be ween he igh /le sides alues o he deionized
wa e d ople s. The equipmen used was a D op Shape Analyze (K üss).
2.3.3. Viscosi y
A glass capilla y Ubbelohde iscosime e (VWR, The Ne he lands)
was used o measu e he iscosi y o he PCL:Gela in solu ions. The
empe a u e was main ained a 20±2ºC o all he measu emen s. The
speci ic iscosi y was ob ained using he ollowing equa ion [31] (Eq. 2):
Speci ic Viscosi y =
η
−
η
0
η
0
(2)
Whe e
η
is he iscosi y o he solu ion (Pa⋅s) and
η
0is he iscosi y o he
sol en used (1.65 mPa⋅s a 20 ◦C o HFIP).
2.4. S a is ical analysis
Each measu emen was pe o med, a leas , in iplica e. S a is ical
analyses we e ca ied ou wi h - es s and one way analysis o a iance
(p <0.05) using PASW S a is ics o Windows (Ve sion 18: SPSS, Chi-
cago, IL). S anda d de ia ions we e ob ained o selec ed pa ame e s.
3. Resul s and discussion
3.1. Uni a y PCL and gela in solu ions: elec ospinning and iscosi y
As men ioned abo e, p e ious epo s ha e co ela ed he ou comes
o he elec ospinning p ocess o he polyme solu ion p ope ies, spe-
ci ically solu ion iscosi y and polyme concen a ion. These wo pa-
ame e s a e in e connec ed, ob aining a co ela ion wi h he minimum
concen a ion needed o achie e a sui able solu ion iscosi y o ca y ou
he elec ospinning p ocess p ope ly. This is achie ed hanks o he
en anglemen be ween he polyme chains, which a ou s he
elec ospinning p ocess.
I has been con i med ha ibe s canno be consis en ly gene a ed
om uni a y solu ions p oduced wi h PCL (supplemen a y ma e ial) o
gela in [30] by elec ospinning. To co ela e his o iscosi y, uni a y
solu ions o PCL and gela in we e i s s udied in a speci ic sol en (HFIP
in his case). Fig. 1A shows he e olu ion o he iscosi y o PCL solu-
ions by inc easing i s concen a ion. Two di e en egions can be
highligh ed by a change in he slope ( om 4.95 o 10.35). The i s e-
gion ends when he o al polyme concen a ion is 20 w/ %, s a ing a
new egion in which he in luence o he concen a ion o e he iscosi y
exhibi s a highe slope. Conside ing he s udy conduc ed by Colby e al.
[11], hese wo egions obse ed co espond o he semidilu e unen-
angled and en angled egimes, wi h he c osso e poin a 20 w/ % as
he en anglemen concen a ion (Ce).
As expec ed, he iscosi y o uni a y solu ions o gela in was also
obse ed o inc ease wi h inc easing p o ein concen a ions (Fig. 1B).
Simila ly, he esul s show an ini ial linea egion up o a concen a ion
o 8 % w/ (wi h a slope o 0.061), wi h a sha p inc ease in iscosi y a
10.7 % w/ (wi h a slope o 1.39). This sudden inc ease sugges s gela in
molecules s a o inc ease hei in e ac ion wi h each o he , indica i e
o inc eased en anglemen .
Despi e hese indica ions o an inc ease in en anglemen , he elec-
ospinning ou come o bo h solu ions emains poo . The elec o-
spinning o LW-PCL esul s in mic osphe es a all concen a ions, bo h
abo e and below he 20 %w/ ansi ion (Figu e S1). Simila ly, ou
p e ious inding o gela in-only s udies ound ha he elec ospinning
p ocess could no be pe o med p ope ly [30]. This beha io can be
explained by he low en anglemen o he polyme chains despi e he
inc easing gela in concen a ion and subsequen inc ease in iscosi y
(Fig. 1B). This low en anglemen is a possible consequence o a low
molecula weigh , which is known o con ibu e o bead o ma ion since
he elec ospinning p ocess canno be ca ied ou con inuously.
Howe e , in con as o bo h uni a y solu ions, which ailed o
gene a e ibe s, we obse ed ha combina ions o LW-PCL and gela in in
di e en a ios we e success ully elec ospun unde ce ain condi ions.
3.2. In luence o he PCL: gela in a io wi h inc easing PCL concen a ion
3.2.1. Viscosi y measu emen s
To be e unde s and his phenomenon, we u he s udied his bi-
na y sys em whe eby he gela in concen a ion was held cons an and
he amoun o LW-PCL was sys ema ically a ied. The e o e, di e en
PCL concen a ions (12, 16, 20, 24 and 32 w/ %) we e combined wi h a
cons an amoun o gela in (4 w/ %) and he measu ed iscosi y o
hese mix u es measu ed, in o de o co ela e and p edic possible
elec ospinning ou comes o hese solu ions (labelled as a io o PCL/
Gela in, speci ically 12/4, 16/4, 20/4, 24/4 and 32/4).
Fig. 2 shows he e olu ion o he speci ic iscosi y o he sys ems
p oduced wi h a 4 % w/ o gela in and inc easing concen a ions o
PCL ( om 12 % o 32 % w/ ), wi h an ini ial slope o 2.49 om 12 % o
16 % w/ ha inc eases o 13.57 om 16 % o 32 % w/ . This de ines
wo well-di e en ia ed egions, whe e he i s egion ( om 12 % o
16 %) co esponds o he semidilu e unen angled egime and he second
egion co ela es o a semidilu e en angled egime; abo e he concen-
a ion o 16 %w/ PCL, chains s a o en angle and, as a consequence,
he iscosi y o he solu ions ma kedly inc eases. The e o e, he com-
bina ion o 16 % o PCL and 4 % o gela in (12/4 PCL:Gela in a io) can
be conside ed he en anglemen concen a ion (Ce, wi h a 20 % o o al
polyme concen a ion). Acco ding o Kong and Ziegle [32], he spin-
ning o good ibe s equi es ha he solu ion concen a ion be 1.2–2.0
imes he en anglemen concen a ion. O he di e en alues s udied, a
PCL:Gela in a io be ween 20/4 and 24/4, o a o al polyme concen-
a ion o 24 % and 28 % w/ , espec i ely, should ep esen he s a o
good ibe o ma ion since he polyme concen a ion is 1.25 and 1.50
imes he en anglemen concen a ion.
V.M. Pe ez-Puyana e al. Nex Ma e ials 6 (2025) 100306
3
3.2.2. Mic os uc u al e alua ion
SEM imaging o he e olu ion o he PCL-based memb anes gene -
a ed wi h a cons an amoun o gela in (4 %w/ ) and inc easing con-
cen a ions o LW PCL (12, 16, 20, 24 and 32 %w/ ) is shown in Fig. 3.
These s a ing solu ions ha e ela i e a ios o PCL o gela in o 3:1, 4:1,
5:1, 6:1, and 8:1, labelled espec i ely as 12/4, 16/4, 20/4, 24/4 and
32/4 o cla i y he polyme con en pe condi ion. The lowes a io (12/
4) showed a combina ion o ibe s and beads on i s s uc u e. Howe e ,
he inc ease in he a io lead o he homogeniza ion o he sys em wi h
he disappea ance o he beads and he o ma ion o consis en ibe s.
This imp o emen is mainly obse ed o he 16/4 and 20/4 a io, which
co espond wi h he op imal ange ound in he iscosi y measu emen s
shown in he p e ious sec ion. In e es ingly, when he a io is highe
han 20/4 (24/4 and 32/4), he SEM images showed again he o ma ion
o sphe oids in he s uc u e.
F om he SEM images, he dis ibu ion o sizes o he elemen s (ei he
ibe s o beads) p esen in he s uc u e we e analysed and plo ed in
Fig. 3. A shi in he p o ile can be seen, om a wide dis ibu ion
obse ed o he sys em wi h a 12/4 (due o he p esence o bo h ibe s
and beads) o a na ow dis ibu ion owa ds a cen al alue (a ound
0.5 µm) o he 20/4 sys em and a e u n o a wide dis ibu ion when
he a io is highe a 24/4 and 32/4, which gi es ise o a sys em wi h
mo e he e ogeneous ibe sizes and he e-eme gence o sphe oid
o ma ion.
To be e assess he e ec o he PCL:Gela in a io, we quan i ied
ibe uni o mi y (Fig. 3) as unc ion o ibe and bead size (Table 2) o
each o he mixed PCL:Gela in sys ems. This clea ly shows an op imal
egion, whe e uni o mi y inc eases o a maximum be ween PCL:Gela in
a ios o 16/4 and 24/4, e lec ing an inc ease in he sys em homoge-
nei y and a educ ion in bead o ma ion. Howe e , mo ing away om
ha op imal egion encou ages he appea ance o beads esul s in a
dec ease in he mean ibe size. The p oli e ollows a end o an in e ed
second polynomial, eaching he maximum alue a a a io o 20/4 ha
coincides wi h he disappea ance o he beads in i s s uc u e and a
na owed dis ibu ion o ibe diame e s.
O e all, wi h he ansi ion om a semidilu e unen angled o a
semidilu e en angled polyme solu ion we obse ed he expec ed shi
om poo quali y elec ospun ibe gene a ion, deno ed by bead o -
ma ion and a b oad ange o ibe diame e s, o he p oduc ion o
consis en , homogeneous ibe s. In e es ingly, as he polyme concen-
a ion con inued o inc ease, we obse ed a e u n o poo ibe o -
ma ion. This inding is inconsis en wi h cu en heo y which apply o
elec ospinning o uni a y polyme solu ions and sugges s o he unde -
lying mechanisms a e in ol ed when conside ing a semidilu e en angled
bina y polyme sys em.
3.3. In luence o he PCL: gela in a io wi h inc easing gela in
concen a ion
We wan ed o explo e he impo ance o main aining a speci ic PCL:
Gela in a io, i espec i e o he absolu e concen a ions o iscosi y. We
s a ed om an ini ial PCL and gela in concen a ion o 32 % and 4 %,
Fig. 1. E olu ion o he speci ic iscosi y o uni a y sys ems as a unc ion o he (A) PCL concen a ion and (B) Gela in concen a ion.
Fig. 2. (A) E olu ion o he speci ic iscosi y o bina y sys ems PCL:Gela in as a unc ion o he PCL concen a ion. (B) E olu ion o he speci ic iscosi y o bina y
sys ems PCL:Gela in as a unc ion o he PCL concen a ion wi h a dashed egion in which he spinning p ocess canno be ca ied ou p ope ly. SEM images o he
di e en bina y sys ems ha e also been included (scale ba : 10 µm).
V.M. Pe ez-Puyana e al. Nex Ma e ials 6 (2025) 100306
4
espec i ely, o a PCL:Gela in a io o 32/4 in an HFIP sol en ; in
ela i e e ms, his has a a io o 8:1. This cons i u ed semidilu e
en angled polyme solu ion ha , despi e su icien ly high iscosi y, was
al eady shown o ha e poo ibe o ma ion and ex ensi e mic osphe e
p oduc ion. To be e unde s and he ansi ion om beaded ibe s o
consis en ibe s, we held he PCL concen a ion cons an his highe
alue o 32 % w/ and sys ema ically inc eased he quan i y o gela in
wi h concen a ion o 4.0, 6.0, 6.4, 8.0 and 10.7 w/ %, he eby
achie ing he same ela i e a ios o 8:1, 6:1, 5:1, 4:1, and 3:1 (in e e se
o de ); o dis inguish hese solu ions om he p e ious condi ions, he
ela i e a ios include an as e isk ‘*’when men ioned and he condi ions
a e labelled wi h he absolu e a io o PCL o gela in, speci ically 32/
10.7, 32/8, 32/6.4, 32/6 and 32/4. In addi ion, a polyme solu ion o
32 % PCL wi h no gela in was also included o assess he impac o
adding gela in. SEM images and ibe /bead size dis ibu ions o hese
sys ems a e shown in Fig. 4.
The sys ems composed o only PCL p esen ed a s uc u e mainly
o med by beads. In e es ingly, he addi ion o gela in o a cons an
concen a ion o PCL (32 %) ollowed he same end as was p e iously
obse ed. The mo phology o elec ospun deposi ion e ol ed om
he e ogeneous ibe s wi h bead o ma ion (sys em 32/4) o homoge-
neous ibe s o in e media e a ios (32/6, 32/6.4 and 32/8), ollowed
again by beads and small ibe s (sys em 32/10.7). Bead o ma ion was
la ges o he 32/4 a io, while bo h highes and lowes a ios also
displayed a dec ease in he size o he ibe s gene a ed. An analysis o
ibe uni o mi y shows he same in e ed second o de polynomial end
o his 32 % PCL-based bina y sys em (Fig. 5), whe e he 32/10.7 and
32/4 PCL:Gela in a ios led o less han 40 % uni o mi y ha e lec s he
eme gence o sphe oids. Con e sely, uni o mi y and ibe diame e in-
c ease o he in e media e a ios (shown in Fig. 5).
Fig. 3. SEM images (scale ba : 10 µm) and ibe /bead size dis ibu ions o he memb anes gene a ed wi h mixed PCL:Gela in sys ems wi h di e en a ios: 12 %+4 %
(12/4, a io 3:1), 16 %+4 % (16/4, a io 4:1), 20 %+4 % (20/4, a io 5:1), 24 %+4 % (24/4, a io 6:1) and 32 %+4 % (32/4, a io 8:1).
Table 2
Mean ibe and beads diame e s o memb anes p ocessed wi h di e en PCL and
gela in pe cen ages and PCL:Gela in a ios: 12 %+4 % (12/4), 16 %+4 % (16/
4), 20 %+4 % (20/4), 24 %+4 % (24/4), 32 %+4 % (32/4), 32 %+6 % (32/6),
32 %+6.4 % (32/6.4), 32 %+8 % (32/8) and 32 %+10.7 % (32/10.7).
SYSTEM Nomencla u e Ra io Fibe Size
(nm)
Beads Size
(nm)
PCL (12 %) +Gela in
(4 %)
12/4 3:1 288 ±86 807 ±223
PCL (16 %) +Gela in
(4 %)
16/4 4:1 485 ±170 -
PCL (20 %) +Gela in
(4 %)
20/4 5:1 415 ±91 -
PCL (24 %) +Gela in
(4 %)
24/4 6:1 443 ±95 874 ±176
PCL (32 %) +Gela in
(4 %)
32/4 8:1 308 ±100 1.160 ±450
PCL (32 %) +Gela in
(6 %)
32/6 6:1* 590 ±218 -
PCL (32 %) +Gela in
(6.4 %)
32/6.4 5:1* 357 ±93 -
PCL (32 %) +Gela in
(8 %)
32/8 4:1* 724 ±376 -
PCL (32 %) +Gela in
(10.7 %)
32/10.7 3:1* 290 ±107 1.299 ±328
V.M. Pe ez-Puyana e al. Nex Ma e ials 6 (2025) 100306
5
Fig. 4. SEM images (scale ba : 10 µm) and ibe /bead size dis ibu ions o he memb anes gene a ed wi h mixed PCL:Gela in sys ems wi h di e en a ios: 32 %+4 %
(32/4, a io 8:1), 32 %+6 % (32/6, a io 6:1*), 32 %+6.4 % (32/6.4, a io 5:1*), 32 %+8 % (32/8, a io 4:1*) and 32 %+10.7 % (32/10.7, a io 3:1*).
Fig. 5. SEM images and ibe /bead size dis ibu ions o he memb anes gene a ed wi h mixed PCL:Gela in sys ems wi h di e en PCL:Gela in a io: (A) 12 %+4 %
(12/4), 16 %+4 % (16/4), 20 %+4 % (20/4), 24 %+4 % (24/4), 32 %+4 % (32/4); (B) 32 %+10.7 % (32/10.7), 32 %+8 % (32/8), 32 %+6.4 % (32/6.4), 32 %+
6 % (32/6) and 32 %+4 % (32/4).
V.M. Pe ez-Puyana e al. Nex Ma e ials 6 (2025) 100306
6
Simila o he PCL:Gela in (4 %) sys ems, hese esul s o he PCL
(32 %):Gela in sys ems a e pa ly consis en wi h he p oposed expla-
na ion ega ding polyme concen a ion and chain en anglemen as i
pe ains o he elec ospinning p ocess. As he polyme solu ion ansi-
ions om a lowe concen a ion (e.g. 4 % gela in) o highe concen-
a ion (wi h gela in concen a ions be ween 6 % and 8 %),
he e ogeneous ibe s gi e way o he p oduc ion o homogeneous ibe s
wi h no beads. Howe e , om his concen a ion on, homogenei y is los
again, and beaded memb anes a e ob ained, wi h he subsequen
dec ease in uni o mi y. One possibili y is ha he o e all high iscosi y
o he solu ion, when bo h PCL and gela in concen a ions a e high,
p e en s a consis en elec ospinning je and, he e o e, inc easing he
he e ogenei y o he esul ing memb anes. Al e na i ely, ano he
possible eason is a change in miscibili y o he wo polyme s as he
ela i e concen a ions inc ease; his has been p e iously epo ed o
o he na u al-syn he ic polyme solu ion blends [33,34]. Wi h such a
dec ease in polyme miscibili y and subsequen polyme phase sepa a-
ion, i would be expec ed ha less in e -species polyme chain in e -
ac ion would occu , consequen ly esul ing in poo elec ospinning
ou comes, and ha he e would be a consis en inhomogeneous polyme
species dis ibu ion wi hin he deposi ed ibe s.
3.4. Physicochemical e alua ion
Di ec ly measu ing he beha iou o a bina y polyme solu ion du -
ing elec ospinning is a challenge gi en he dynamic na u e o he p o-
cess, including he con inual e apo a ion o sol en , subsequen apid
changes in polyme concen a ion, and high-speed e olu ion o luidic
je du ing p ocessing. To look o e idence o polyme phase sepa a ion
in he esul ing ibe , wa e con ac angle (WCA) and EDAX measu e-
men s we e used o assess ibe p ope ies as indica o s o inhomoge-
neous ibe composi ion. These wo echniques p o ide an indica ion o
he su ace composi ion o he ibe s, whe ein we expec ed homoge-
neous ibe s o ha e a change in WCA and EDAX eadou ha is di ec ly
p opo ional o he changes in polyme concen a ion. In con as , we
an icipa ed any inhomogenei y in he ibe su ace composi ion,
esul ing om phase sepa a ion and a subsequen unde - o o e -
ep esen a ion o one polyme species e sus he o he on he ibe
su ace, would p esen as a nonlinea ela ionship wi h espec o
polyme composi ion.
As can be obse ed in Fig. 6A and 6B, he alue o he con ac angle
inc eased when he a io be ween he polyme s was highe , due o he
p esence o he hyd ophobic polyme (PCL) in a highe concen a ion
compa ed o he concen a ion o gela in, which is he hyd ophilic
polyme o he mix u e. Fo ha eason, he con ac angle a ied (almos
doubled) compa ing he alues ob ained o he sys ems wi h he lowes
(a ound 40º, a io 12/4) and he highes (a ound 75º, a io 32/4) a io
be ween PCL and gela in. Mo eo e , an e olu ion owa ds a mo e hy-
d ophilic sys em ook place when he concen a ion o gela in was
inc eased, swi ching om ca 70º(32/4 sys em) o ca 40º(32/10.7 sys-
em). Fu he mo e, simila con ac angle alues we e ob ained o he
sys ems p ocessed wi h a simila PCL:Gela in a io.
Pe o ming a linea eg ession o he con ac angle measu emen s
wi h espec o he PCL:Gela in a ios om 12/4–32/4 and om 32/
4–32/10.7, i was possible o de e mine a clea linea end (Fig. 5A and
5B) ha esul ed in he ollowing equa ion (Eqs. 3 and 4, espec i ely):
WCA =6.68⋅[PCL :Gela in Ra io] + 20.28 (3)
WCA =6.91⋅[PCL :Gela in Ra io] + 36.03 (4)
This con i ms expec a ions ha an inc ease in he a io be ween PCL
and gela in p oduces an inc ease in he con ac angle, since he sys em
ob ained is mo e hyd ophobic due o he g ea e p esence o PCL.
Fu he , acco ding o i pa ame e s o di e en co ela ions shown in
Table 3, a linea end was obse ed, which achie ed an imp o ed i (an
inc ease in R
2
alue) when he ou e mos a ios (12/4 and 32/4) we e
excluded. Since he o e all dis ibu ion o ma e ial deposi ion is he
same o all samples, his imp o ed i can e lec he change in ibe
mo phology (beads o ibe s) bu can also indica e an imp o ed homo-
genei y in ibe composi ion o in e media e PCL:Gela in a ios.
To u he in es iga e he co ela ion be ween he homogenei y o
ibe composi ion and ini ial polyme solu ion a io, he ela ion be-
ween PCL and gela in was assessed ia EDAX analysis o he elec ospun
ibe s, whe e he % amoun o ni ogen pe uni a ea was used as a
me ic o p o ein dis ibu ion wi hin he ibe s uc u e (Table S1). The
ni ogen p esen in he su ace ob ained om he EDAX p o iles, shown
in Fig. 5A and 5B, shows an ob ious co ela ion be ween N con en and
he changing a ios be ween he wo polyme s. The esul s shown
Fig. 6. (A) Co ela ion be ween he WCA and N con en wi h he PCL:Gela in a io and (B) ela ion be ween he uni o mi y and mean ibe size o he memb anes
p ocessed wi h di e en PCL:Gela in a io: 12 %+4 % (12/4), 16 %+4 % (16/4), 20 %+4 % (20/4), 24 %+4 % (24/4), 32 %+4 % (32/4), 32 %+6 % (32/6), 32 %+
6.4 % (32/6.4), 32 %+8 % (32/8) and 32 %+10.7 % (32/10.7).
Table 3
R
2
alues o he di e en co ela ions o Con ac Angle and Ni ogen con en o
memb anes p ocessed wi h di e en PCL and gela in pe cen ages and PCL:
Gela in a ios: 12 %+4 % (12/4), 16 %+4 % (16/4), 20 %+4 % (20/4), 24 %+
4 % (24/4), 32 %+4 % (32/4), 32 %+6 % (32/6), 32 %+6.4 % (32/6.4),
32 %+8 % (32/8) and 32 %+10.7 % (32/10.7).
CORRELATIONS Sys ems R
2
R
2
(wi hou 12/4
sys em)
R
2
(wi hou 12/4 and
32/4 sys ems)
Con ac Angle 12/4–32/4 0.9607 0.9768 0.9839
Ni ogen con en 12/4–32/4 0.8908 0.9809 0.9998
Con ac Angle 32/
10.7–32/4
0.9511 0.9082 0.7992
Ni ogen con en 32/
10.7–32/4
0.9774 0.9871 0.9886
V.M. Pe ez-Puyana e al. Nex Ma e ials 6 (2025) 100306
7
conclude ha he e is a simila dec easing linea end (Eqs. 5 and 6):
Ncon en = − 0.63⋅[PCL :Gela in Ra io] + 5.26 (5)
Ncon en = − 0.70⋅[PCL :Gela in Ra io] + 5.94 (6)
This con i ms ha inc easing he PCL:Gela in a io esul s in a lowe
amoun o p o ein-associa ed ni ogen. Fu he mo e, he analysis o he
di e en co ela ions pe o med (Table 3) showed he simila beha iou
exhibi ed by he con ac angle measu emen s, whe e an inc ease in he
R
2
i ing alue is achie ed when excluding he ou e mos a ios o 12/4
and 32/4. While is i cu en ly no possible o di ec ly con i m he
esponse o he wo polyme species as hey a e subjec ed o a apid
inc ease in concen a ion and simul aneous mechanical o ces du ing
he e apo a ion and whipping phases o he elec ospun polyme je , he
obse ed changes in ibe mo phology and bo h he con ac angle and
e alua ion o ni ogen dis ibu ion p o ide indi ec suppo wi h he
hypo hesis o inhomogenei y in he dis ibu ion o gela in and, hus,
phase sepa a ion wi hin he esul ing ibe s [35].
4. Conclusions
Sui able PCL/Gela in nano ibe memb anes can be ob ained using
low molecula weigh (LW) PCL. The ypical o ma ion o beads du ing
he elec ospinning p ocess using LW PCL can be a oided wi h he
addi ion o gela in, which is homogeneously dis ibu ed in he mem-
b ane. The g ea e hyd ophilici y, he lowe su ace ension and he
inc eased iscosi y o he polyme sys ems leads o imp o e he elec-
ospinning p ocess. Howe e , a u he inc ease in gela in p o ein
concen a ion leads o an inc ease in iscosi y, which could cause
g ea e di icul ies in he elec ospinning p ocess, o could igge phase
sepa a ion wi hin he bina y solu ion. Consequen ly, i would be
con enien o cha ac e ize he solu ion e olu ion du ing he elec o-
spinning p ocess in e ms o iscosi y, su ace ension, and composi ion,
al hough his cu en ly p esen s a challenge due o he dynamic na u e
o his manu ac u ing p ocess.
Di e en co ela ions be ween he PCL:Gela in a io and he
di e en p ope ies measu ed (N con en and con ac angle) we e
es ablished. Linea co ela ions we e ob ained, al hough wi h opposi e
slopes, since he hyd ophobici y o he sys ems inc eases wi h he PCL:
Gela in a io whe eas he N con en dec eases as he a io inc eases. On
he o he hand, he homogenei y o he sys ems was analyzed calcu-
la ing he uni o mi y o he nano ib ous memb anes om he SEM im-
aging. A maximum was ound o he a io wi h he lowes mean ibe
size ( a io 20/4). In ac , highe mean sizes lead o an inc ease in he
he e ogenei y o he sys ems.
The p esen wo k demons a es ha no only he o al polyme
concen a ion a ec s he ibe o ma ion, bu also he a io be ween he
wo polyme s when using a bina y sys em; ini ial indica ions sugges
ha phase sepa a ion may occu o some polyme sys ems as hey
become mo e concen a ed du ing he elec ospinning p ocess, esul ing
in poo en anglemen and ibe uni o mi y. Fo PCL and gela in, he
mos sui able a ios we e ound o be 16/4, 20/4 and 24/4. The use o
bina y solu ions p esen s a new a enue o p ocess low molecula weigh
polyme s ia elec ospinning, whe e low molecula weigh polyme s a e
also ypically mo e economic o p oduce. While a ca ea is he use o
HFIP as a necessa y uni e sal sol en o bo h species o his bina y
sys em, he eby no in line wi h eme ging obliga ions o g een
manu ac u ing p ocesses, i p o ides a case s udy o he de elopmen o
low cos , low molecula weigh polyme species ha a e compa ible
wi h sui able sol en sys ems. In any case, memb anes wi h con ollable
mo phology, s uc u e and p ope ies could be achie ed by adjus ing he
PCL:Gela in a io.
Funding sou ces
This wo k is pa o a esea ch p ojec sponso ed by he “Minis e io
de Economía y Compe i i idad”(MCI/AEI/FEDER, EU) om he Span-
ish Go e nmen (Re . RTI2018-097100-B-C21). The au ho s g a e ully
acknowledge hei inancial suppo . The au ho s also acknowledge he
Uni e si y o Se ille o he VPPI-US p edoc o al g an and Jun a de
Andalucía (Eu opean Social Fund, PAIDI DOCTOR –Con oca o ia
2019–2020, DOC_00586) o he pos doc o al con ac o Vic o M.
Pe ez-Puyana. Pa o his wo k was ca ied ou a he Depa men o
Complex Tissue Regene a ion (Maas ich Uni e si y, MERLN-Ins i u e
o Technology-Inspi ed Regene a i e Medicine) and by inancial sup-
po om he p og am “Es ancias b e es en Espa˜
na y en el ex anje o pa a
bene icia ios de Becas p edoc o ales o PIF de la US y de Becas de la
Fundaci´
on C´
ama a” om he Uni e si y o Se ille. This esea ch p ojec
was made also possible hanks o he Du ch p o ince o Limbu g.
Au ho con ibu ions
The manusc ip was w i en h ough con ibu ions o all au ho s. All
au ho s ha e gi en app o al o he inal e sion o he manusc ip .
Decla a ion o Compe ing In e es
The au ho s decla e ha hey ha e no known compe ing inancial
in e es s o pe sonal ela ionships ha could ha e appea ed o in luence
he wo k epo ed in his pape .
Appendix A. Suppo ing in o ma ion
Supplemen a y da a associa ed wi h his a icle can be ound in he
online e sion a doi:10.1016/j.nxma e.2024.100306.
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