Electrospun antimicrobial poly(lactic acid) foams with nanocellulose for enhanced hydrophilicity and controlled drug release

Elec ospun an imic obial poly(lac ic acid) oams
wi h nanocellulose o enhanced hyd ophilici y and
con olled d ug elease
Dai a Sleinus,
a
Ma ´
ıa Jos´
e Lo a o,
bc
Oska s Pla nieks, *
a
Alisa Sabalina,
a
Se gejs Gaiduko s, *
a
Lou des F anco,
bc
Jo di Puiggal´
ı
bc
and Luis J. del
Valle *
bc
This s udy explo es an ad anced app oach o enhancing he an imic obial efficacy and hyd ophilici y o
poly(lac ic acid) (PLA) scaffolds h ough he s a egic inco po a ion o cellulose nanoc ys als (CNC). The
compa ibili y be ween hese biodeg adable polyme s was in es iga ed o op imize an imic obial agen
elease while p ese ing s uc u al in eg i y. PLA nanocomposi es inco po a ing he an imic obial agen s
cu cumin (Cu ) o polyhexame hylene biguanide (PHMB) we e ab ica ed using h ee dis inc
elec ospinning-based me hodologies. The an ibac e ial p ope ies we e assessed ia a disc diffusion es
agains fi e bac e ial s ains: Esche ichia coli,Esche ichia coli B+, Lac obacillus sali a ius,S ep ococcus
sanguinis, and S ep ococcus mu ans. In addi ion, d ug elease expe imen s we e conduc ed o
de e mine he diffusion kine ics in a simula ed blood se um medium, demons a ing sus ained d ug
elease o up o 98 hou s. PHMB demons a ed po en an ibac e ial ac i i y, while cu cumin p ima ily
exhibi ed bac e ios a ic effec s. The he mal s abili y o he nanocomposi es exhibi ed an inc ease o up
o 41 °C in he maximum deg ada ion empe a u e. The mechanical p ope ies we e assessed o u he
examine he in e ac ions be ween CNC and PLA and he possibili y o eshape he ma e ials o diffe en
deli e y app oaches. The findings unde sco e he c ucial ole o CNC in modula ing he in e ac ion
be ween PLA and an imic obial agen s, making i a p omising candida e o biomedical applica ions
equi ing con olled d ug elease. This s udy p o ides aluable insigh s in o he s uc u al, he mal, and
an ibac e ial pe o mance o CNC–PLA nanocomposi es, es ablishing a s ong ounda ion o he
de elopmen o ad anced biodeg adable ma e ials o d ug deli e y and an imic obial applica ions.
1. In oduc ion
In ecen yea s, biodeg adable ma e ials ha e ga ne ed
conside able in e es due o he g owing awa eness o en i-
onmen al issues. Among hese ma e ials, bio-based alipha ic
polyes e s a e p ominen , known o hei biodeg adabili y,
biocompa ibili y, as well as hei non- oxic cha ac e is ics.
1,2
These ea u es make hem ap o a ange o con empo a y
applica ions, including ood packaging, biomedical suppo s
and o he disposables.
3,4
Specically, poly(lac ic acid) (PLA) no
only offe s hese ad an ages bu also compe es effec i ely wi h
ossil-based al e na i es in e ms o cos and mechanical
p ope ies.
5
Acco ding o ecen ma ke analyses, PLA is
inc easingly a o ed in a ious applica ions due o i s lowe
en i onmen al impac and compa able pe o mance me ics.
6
Elec ospinning has eme ged as a e sa ile echnique o
c aing nano- and mic ob ous scaffolds, p o iding a high
su ace a ea- o- olume a io and adjus able po osi y, which a e
c i ical ea u es o inno a i e uses. Howe e , he applica ion o
PLA-based ma e ials in he biomedical sec o aces challenges,
pa icula ly in augmen ing hei an imic obial efficacy and
hyd ophilici y.
7
These enhancemen s a e essen ial o acili a e
cellula adhesion and p oli e a ion.
8
S udies ha e shown ha
modi ying he su ace p ope ies o PLA can signican ly
imp o e i s in e ac ion wi h biological issues.
8
Fu he mo e,
he in eg a ion o an imic obial unc ionali y in o PLA be s
ex ends hei u ili y beyond he biomedical sphe e.
9
Such
unc ionaliza ion enables he p epa a ion o lms, ma s,
memb anes, e c., ha a e no only use ul in ood packaging bu
also c ucial in wa e pu ica ion p ocesses.
10
Mo eo e , adding
nanopa icles can enhance he p ope ies o elec ospun be s
ela i e o nea PLA be s.
11
Cellulose nanoc ys als (CNC) ha e
e i ed a en ion due o hei in insic p ope ies, such as
a
Ins i u e o Chemis y and Chemical Technology, Facul y o Na u al Sciences and
Technology, Riga Technical Uni e si y, P. Valdena 3, LV-1048, Riga, La ia. E-mail:
[email p o ec ed]
b
Depa amen d'Enginye ia Qu´
ımica, Escola d'Enginye ia de Ba celona Es (EEBE),
Uni e si a Poli `
ecnica de Ca alunya –Ba celona Tech (UPC, ), A . Edua d
Ma is any 10–14, Ba celona 08019, Spain. E-mail: luis.ja ie .del. [email protected]
c
Ba celona Resea ch Cen e in Mul iscale Science and Enginee ing, Uni e si a
Poli `
ecnica de Ca alunya, Ba celonaTech (UPC), A . Edua d Ma is any, 16,
Ba celona 08019, Spain
Ci e his: RSC Ad .,2025,15,6753
Recei ed 5 h Decembe 2024
Accep ed 24 h Feb ua y 2025
DOI: 10.1039/d4 a08580a
sc.li/ sc-ad ances
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su ace a ea, hyd ophilic affini y, nanoscale dimension, excel-
len exu al igidi y and mechanical p ope ies, and
biodeg adabili y.
12,13
The inco po a ion o nanocellulose in o PLA o enhance he
s uc u al, mechanical, and he mal p ope ies o elec ospun
be s has been well epo ed in he li e a u e.
14–16
Howe e ,
esea ch on he s a egic in eg a ion o CNC in o PLA nano-
be s o imp o e d ug elease kine ics and an imic obial
ac i i y emains ela i ely limi ed. Zhou e al. de eloped elec-
ospun bio-nanocomposi e scaffolds using maleic anhyd ide
(MAH)-g aed PLA ein o ced wi h CNC.
17
The addi ion o
CNCs signican ly imp o ed mechanical p ope ies, he mal
s abili y, and deg ada ion esis ance, while su ace g aing
wi h MAH enhanced in e acial adhesion be ween CNCs and
PLA, leading o a mo e uni o m and ne be s uc u e. The
op imized scaffold wi h 5 w % CNCs exhibi ed supe io ensile
s eng h, con olled deg ada ion, and high biocompa ibili y
wi h human adipose-de i ed mesenchymal s em cells (hASCs).
Wu e al. in es iga ed he use o CNC and polye hylene glycol
(PEG) as bi unc ional ein o cing and compa ibilizing agen s in
elec ospun PLA nanobe s o con olled long- e m d ug
elease.
18
The addi ion o CNC/PEG imp o ed he nanobe s'
mechanical p ope ies, hyd ophilici y, and he mal s abili y
while enabling high d ug loading efficiency (up o 98%) and
sus ained d ug elease o e 1032 hou s. Cheng e al. epo ed
elec ospun poly(3-hyd oxybu y a e-co-3-hyd oxy ale a e)
(PHBV) nanob ous memb anes o biomedical applica ions by
inco po a ing CNC.
19
The addi ion o CNCs signican ly
imp o ed he memb anes' mechanical s eng h, he mal
s abili y, and hyd ophilici y, leading o enhanced cy ocompa i-
bili y and p olonged d ug elease. The op imized memb anes
demons a ed sus ained d ug elease o o e 540 hou s. Sal-
mani e al. p epa ed PLA and poly(3-cap olac one) (PCL) mac-
opo ous scaffolds o bone issue enginee ing by inco po a ing
CNC and a PCL–PEG–PCL iblock copolyme .
20
The CNC ac s as
a s abilize , p e en ing PCL d ople coalescence, while he i-
block copolyme imp o es miscibili y be ween PLA and PCL by
educing in e acial ension, leading o be e po e uni o mi y,
inc eased wa e abso p ion, and imp o ed mechanical s abili y.
The op imized scaffold con aining 10% iblock copolyme and
1.0% CNC exhibi ed high biocompa ibili y, enhanced os eo-
genic diffe en ia ion o human mesenchymal s em cells
(hMSCs), and he highes calcium deposi ion, making i
a p omising ma e ial o bone egene a ion applica ions.
Mohammadalinejhad e al. epo ed PLA nanocomposi e lms
ein o ced wi h sil e nanopa icle (AgNP)-deco a ed cellulose-
based nanobe s o imp o e hei mechanical s eng h,
ba ie p ope ies, and an imic obial effec i eness o ac i e
ood packaging applica ions.
21
The s udy e alua ed h ee
diffe en nanobe s: cellulose nanobe s (CNF), chi osan
nanobe s (CHNF), and lignocellulose nanobe s (LCNF).
Among hese, LCNF was ound o be he mos compa ible wi h
he PLA ma ix, leading o supe io mechanical s abili y,
educed wa e apo pe meabili y, and con olled elease o
AgNPs, which p olonged he an imic obial effec . Howe e ,
CNF-AgNPs ended o agg ega e wi hin he PLA ma ix, educing
hei o e all effec i eness.
We de eloped and sys ema ically compa ed h ee dis inc
ab ica ion me hods o inco po a ing an imic obial agen s—
cu cumin (Cu ) and polyhexame hylene biguanide (PHMB)—
wi hin he elec ospun PLA ma e ials. The inco po a ion o CNC
was s a egically designed o acili a e con olled d ug elease
and op imize an ibac e ial pe o mance. This wo k supple-
men s p e ious s udies by u he explo ing compa ibili y and
in e ac ions o CNC and PLA as nanobe s uc u e- o ming
ma e ials. We show CNC's pi o al ole in modula ing he
diffusion o ac i e compounds. Mo eo e , d ug elease expe i-
men s con m ha CNC p omo es apid diffusion, pa icula ly
when applied as a coa ing. In addi ion, he esea ch p o ides
a comp ehensi e s uc u al, he mal, and mechanical cha ac-
e iza ion o he de eloped sys ems. The ndings lay a s ong
ounda ion o u he ad ancemen s in bioac i e PLA-based
ma e ials and open new a enues o hei p ac ical imple-
men a ion in an imic obial disposables, wound d essings, and
heal hca e applica ions.
2. Ma e ials and me hods
2.1. Ma e ials
Quali a i e l e pape wi h low ash g ade was ob ained om
Scha lau (Scha lab, Spain) and used as sou ce o CNC. Poly-
lac ic acid (PLA) wi h g ade Ingeo™2002D (Na u eWo ks LLC)
was selec ed as polyme ma ix. The selec ed PLA g ade is
amo phous and is designed o ex usion and he mo o ming
p ocessing, aimed a po en ial applica ions in dai y con aine s,
u ensils, anspa en ood con aine s, blis e packaging, and
cold d ink cups. Chemical eagen s we e secu ed om a ious
supplie s' sul u ic acid (95–98%) om Honeywell, ace one
(syn hesis g ade) was ob ained om Sigma Ald ich, chlo o o m
(99.9%, anhyd ous) om Scha lau (Scha lab, Spain). Cu cumin
(Cu ) was pu chased om Sigma-Ald ich. Polyhexame hylene
biguanide (PHMB) was pu chased om Sha on Labo a o ies
L d, Lu ia–Be ani (LB) b o h om Fishe , and Bac o Aga om
Bec on Dickinson. Nalidixic acid (NA) 30 mg suscep ibili y es
discs we e pu chased om Fishe Scien ic.
2.2. CNC p epa a ion
10 g o sh edded l e pape was mixed wi h 91 ml o 66% w/w
sul u ic acid wa e solu ion using a magne ic s i e a
empe a u e o 25 °C. Ae 3 hou s, 187 ml o 50% w/w sul u ic
acid wa e solu ion was added and s i ed o ew minu es o
homogenize he mix u e. Immedia ely ae wa d, he suspen-
sion was subjec ed o a  s s age o cen i uga ion a 23 °C
using a So all RC 5B Plus cen i uge o en minu es a
5000 pm. The CNC laye was sepa a ed and dilu ed wi h chilled
wa e o app oxima ely ou imes i s ini ial olume and le o
24 hou s. Excess wa e was decan ed ollowed by a second
cen i uga ion s age consis ing o h ee p ocesses a 5000 pm
o 10 min each (23 °C). The CNC laye was collec ed a he end
o cen i uga ion and dialyzed o wo weeks un il he pH was
neu alized. Ae dialysis, he w % o CNC in he suspension
was calcula ed by aking a known, small amoun o he
suspension and de e mining he CNC mass ae o en and
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acuum d ying. Fig. 1 shows he p epa ed CNC AFM opog-
aphy, indica ing ha he CNC pa icle diame e is 13 ±8nm
and he leng h is 235 ±71 nm.
2.3. P epa a ion o PLA be s by elec ospinning me hod
4 g o PLA we e dissol ed in 40 mL 25% / ace one/chlo o o m
solu ion. This solu ion was used o e e ence PLA be p epa-
a ion. Two solu ions wi h an imic obial agen we e p epa ed
(cu cumin o PHMB). The concen a ion o an imic obial
agen s was 1% w/w ela i e o PLA. The solu ions we e elec o-
spun o p epa e PLA be s using a GENEQ Inc. de ice. The
solu ion was placed in a 10 ml sy inge, wi h he needle ip (inne
diame e =0.84 mm) posi ioned 15.0 cm om a oil-co e ed
su ace used as a collec o . The applied elec ic ol age was 15
kV. The eed a e was xed a 10 ml h
−1
.
2.4. Foam and lm p epa a ion
Elec ospun be memb anes we e cu in o smalle pieces and
dispe sed in wa e ( a io 1 : 20 w/w) using T 18 Ul a-Tu ax®
(IKA) se a 10 000 pm o 15 min. Ae wa ds, CNC wa e
suspension (1.78 w %) was added o PLA be suspension and
he weigh a io 1 : 100 (CNC : PLA), wi h excep ion o
PLA_2CNC, which used 2 : 100 a io. In addi ion, some samples
we e coa ed wi h mix o CNC and an imic obial agen s (Cu o
PHMB) wi h xed mass 1% w/w ela i e o PLA. Ae epea ed
homogeniza ion, he suspension was eeze-d ied using Lyo-
Ques (Telsa ) de ice. The eeze-d ying yielded sample oams
(Fig. 3a).
In addi ion, a composi ion wi h a 10 : 100 weigh a io
(CNC : PLA) was p epa ed o illus a e he CNC coa ing on he
nanobe su aces, as shown in Fig. 2a–c. The size o pu e PLA
nanobe s was examined by SEM (Fig. 2d and e), and he co -
esponding his og am is p esen ed in Fig. 2 . The mean diam-
e e o he PLA be s which was es ima ed by a e aging he
measu emen s o 100 be s om he ma anges om app ox-
ima ely 2.17 ±0.5 mm.
Selec ed samples we e co e ed wi h Teon lms and
aluminum oils and comp ession molded be ween wo ho
pla es o 30 s a 160 °C. Resul an p essed lms had a hickness
o a ound 0.15 mm (Fig. 3b). Full lis o samples is p esen ed in
Table 1 and he concen a ion o an imic obial agen s we e 1%
w/w ela i e o PLA, independen o addi ion me hod (in he
be s o as coa ing).
Fig. 1 AFM opog aphy image o CNC.
Fig. 2 SEM mic og aphs o elec ospun PLA fibe s: (a) PLA fibe s coa ed wi h CNC a a 10 : 100 (CNC : PLA) weigh a io; (b) highe magnifica ion
o a single coa ed PLA fibe , wi h a yellow inse highligh ing a CNC bundle; (c) u he enla gemen o he highligh ed egion, e ealing he CNC
s uc u e; (d) pu e elec ospun PLA fibe s and (e) hei magnifica ion; ( ) diame e dis ibu ion his og am, whe e AD deno es he a e age fibe
diame e , SD he s anda d de ia ion, and N he numbe o fibe s measu ed. As e isks (*) in (a) ma k egions wi h no able CNC concen a ions.
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2.5 Me hods
A omic o ce mic oscopy (AFM) opog aphy measu emen s we e
ob ained wi h Smena by NT-MDT (Russia). The samples we e
p epa ed on he silicon subs a e and es ed in he semicon ac
mode ( apping mode) using HA_NC (ETALON) ip. The samples
we e p oduced by e apo a ing wa e om d ople o CNC
suspension wi h a concen a ion o 0.002 w %. The diame e
was de i ed om opog aphic heigh measu emen s, enabling
he de e mina ion o a co ec ion ac o o accoun o he
appa en wid h in oduced by he measu emen ip. This
co ec ion was subsequen ly applied o he leng h
measu emen s.
Scanning elec on mic oscopy (SEM) was employed o
examine he mo phology o samples. Mic og aphs we e ob-
ained wi h a Phenom XL Desk op SEM ins umen . Samples
we e moun ed on a double-sided adhesi e ca bon disc and we e
spu e -coa ed wi h a hin laye o ca bon o p e en sample
cha ging p oblems using a K950X Tu bo E apo a o .
A DSC-1 (Me le Toledo) analyze was used o pe o m
diffe en ial scanning calo ime y (DSC) analysis on he samples.
Unde ni ogen pu ge, samples in aluminum pans weighing
abou 10 mg we e hea ed o 200 °C, held he e o 5 minu es,
cooled o 25 °C, held he e o 5 minu es, and hen hea ed o
200 °C once mo e. The hea ing/cooling a e was cons an 10 °
C min
−1
.
Fou ie ans o m in a ed spec oscopy (FTIR) in a enua ed
o al eec ance mode was used o he sample in es iga ion
wi h a Nicole 6700 (The mo Scien ic, Ge many) de ice. A
esolu ion o 4 cm
−1
in he 800–4000 cm
−1
egion was used o
pe o m six een measu emen s wi h a measu emen e o o
1%. The a e age spec um is displayed.
The he mal s abili y was examined using he mog a ime ic
analysis (TGA) wi h TG50 equipmen (Me le Toledo) in
acco dance wi h ASTM D3850 s anda d. The samples we e
hea ed a a a e o 10 °C min
−1
in an ai a mosphe e be ween 25
and 700 °C.
Dynamic mechanical analysis (DMA) was pe o med in
a ension mode using a DMA/SDTA861e (Me le Toledo).
Rec angula samples (8.5 ×4.0 ×0.15 mm) we e p econdi-
ioned in 40% ela i e humidi y (RH) a oom empe a u e (22 °
C) o 24 h. The expe imen used a empe a u e ange o −70 o
+100 °C, 5 N o applied o ce, an elonga ion o 10 mm, 1 Hz
equency, and a hea ing a e o 3 °C min
−1
.
A Tinius Olsen ype 25ST (USA) uni e sal es ing machine
was used o measu e he ensile cha ac e is ics. The p e-
condi ioning o ec angula samples (5.0 ×1.0 ×0.015 cm) was
done in he same way as o DMA. A 5 kN load cell was
employed, and he es ing c osshead speed was se a 1.0
mm min
−1
. Fo e e y sample, en measu emen s we e ca ied
ou unde ambien condi ions (22 °C, RH 40%).
An imic obial ac i i y assay was pe o med wi h disc diffu-
sion es o e LB aga , se up wi h  e bac e ia usually used in
labo a o y se ings, such as Esche ichia coli biolm-nega i e
CECT 101 (E. coli), Esche ichia coli biolm-posi i e (B+) CECT
434 (E. coli B+), Ligilac obacillus sali a ius CECT 4063 (L. sali-
a ius), S ep ococcus mu ans CECT 479 (S. mu ans), and S ep-
ococcus sanguinis CECT 480 (S. sanguinis). The bac e ia we e
cul u ed in Lu ia–Be ani (LB) b o h o 24 h and hen an
inoculum 0.5 o he McFa land scale was p epa ed. Finally,
bac e ia we e seeded by exhaus ion on LB aga pla es. Visual
e alua ion was pe o med daily o 5 days o moni o possible
changes in g ow h. 10 mg o oam sample was used o p epa e
Table 1 Samples abb e ia ions and composi ion
Sample abb e ia ion Fo m Fibe composi ions Fibe coa ing
PLA Film PLA —
PLA_CNC Film PLA CNC
PLA_2CNC Film PLA 2 ×CNC
PLA(C) Foam PLA CNC
PLA_Cu Foam PLA + Cu CNC
PLA_PHMB Foam PLA + PHMB CNC
PLA(C)Cu Foam PLA CNC + Cu
PLA(C)PHMB Foam PLA CNC + PHMB
Fig. 3 Samples (a) PLA(C)Cu and (b) PLA_CNC.
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each comp ession molded pelle (2- on p essu e, 2 min, 25 °C).
To demons a e bac e ial sensi i i y, a comme cial nalidixic
acid (NA) disc loaded wi h 30 mg o he an ibio ic was used as
a con ol (Bec on Dickinson and Co., BD BBL).
Release expe imen s we e made wi h samples weighing
a ound 15 mg. Each sample was incuba ed a 37 °C in a o a o y
shake a 80 pm in a 2 mL mic o ube lled wi h 1 mL o he
elease medium o 1 week. Specically, a phospha e buffe
saline (PBS) supplemen ed wi h 70% e hanol was used (PBS :
E OH, 30 : 70 ). A p ede e mined ime in e als, he mic o-
ube was cen i uged a 5000g o 5 min, and he supe na an
was collec ed, and 1 mL o esh medium was added o he
mic o ube o con inue he d ug elease. Finally, samples we e
dissol ed in 200 mL o chlo o o m and ex ac ed wi h e hanol o
cu cumin and wa e o PHMB o eco e he occluded d ug.
D ug concen a ions we e de e mined by UV spec oscopy using
a Shimadzu 3600 spec ome e . All d ug elease expe imen s
we e ca ied ou using h ee eplica es, and he esul s we e
a e aged.
3. Resul s and discussion
3.1. Spec oscopy
Fig. 4 p esen s he FTIR spec a o p epa ed PLA-based lm and
oam samples. The cha ac e is ic peaks o PLA a e iden ied a
2997 and 2939 cm
−1
, co esponding o he asymme ical and
symme ical s e ching o he C–H bonds.
22
The peak a
1743 cm
−1
indica es he s e ching o he ca bonyl C]O bond
om he es e linkage.
23
Addi ionally, he bending o –CH
3
is
obse ed a 1452 cm
−1
, while he asymme ical and symme -
ical bending o –CH a e p esen a 1382 and 1356 cm
−1
,
espec i ely.
22
P ominen peaks a 1180 and 1080 cm
−1
a e
a ibu ed o he asymme ical s e ching o he C–O bond in
he es e .
24
The PLA_Cu sample exhibi s addi ional peaks; no ably, he
bands a 1512 and 1628 cm
−1
a e a ibu ed o a oma ic ing
C]C s e ching.
25
The weigh a io o d ugs and CNC o PLA is
ela i ely small, making i challenging o loca e p onounced
peaks, such as hose in he PLA_Cu sample, due o he sensi-
i i y o he de ice. Some peak shis, obse able in he C]O
and C–O bands, can be a ibu ed o diffe en chain a ange-
men s (c ys alliza ion p ocess) o PLA o oams and lms (PLA
and PLA_2CNC). Al hough he selec ed PLA g ade is amo -
phous, he in e ac ions o sol en s and molecula chains can
al e he s uc u e du ing elec ospinning compa ed o
comp ession molding.
26
Fo he oam samples, a sligh p es-
ence o wa e is no ed by he hyd oxyl (O–H) s e ching a
3338 cm
−1
, which is no obse ed in he lms due o he addi-
ional hea ing du ing he comp ession molding s age.
3.2. The mal p ope ies
Fig. 5 shows he he mal deg ada ion o PLA lms and oams.
Table 2 p o ides an o e iew o he he mal s abili y pa ame-
e s: T
5%
, ep esen ing he empe a u e co esponding o 5%
weigh loss (which also ma ks he onse o deg ada ion); T
max
,
indica ing he empe a u e a which he ma e ial unde goes he
mos signican weigh loss; and he cha yield a 700 °C. The
 s de i a i e cu es (DTG) show only one decomposi ion s age
bu wi h a no able shiin he deg ada ion peak (T
max
) o
a highe empe a u e (up o 41 °C) compa ed o nea PLA, which
exhibi ed a maximum deg ada ion empe a u e o 358 °C. This
shi o highe empe a u es is a ibu ed o CNC coa ing ac ing
as a p o ec i e laye o PLA oxida ion and subsequen deg a-
da ion in he a mosphe ic condi ions. Fig. 5a shows ha ini ial
deg ada ion s a s abo e 300 °C. Composi ions con aining Cu
exhibi ed sligh ly as e deg ada ion han o he samples,
whe eas comp ession-molded lms wi h CNC demons a ed
Fig. 4 FTIR spec a o he samples wi h cha ac e is ic peaks.
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he highes he mal deg ada ion esis ance. The nal deg ada-
ion s ep o PLA_Cu is sligh ly diffe en om o he composi-
ions and can be explained wi h cha o ma ion on he su ace
o he sample, which sligh ly delays he deg ada ion p ocess.
O e all, i is e iden ha he inco po a ion o CNC enhances
he mal s abili y. Mo eo e , cha yield was obse ed exclusi ely
in samples con aining CNC, indica ing ha CNC-de i ed cha
con ibu es o enhanced he mal s abili y.
DSC was used o analyze he he mal p ope ies o PLA and
PLA/CNC composi e lms. Fig. 6 shows nea PLA and PLA/CNC
cooling and second hea ing scans. Table 2 displays he calo i-
me ic cha ac e is ics (mel ing empe a u e (T
m
), cold c ys al-
liza ion empe a u e (T
cc
), mel ing en halpy (DH
m
), and glass
ansi ion empe a u e (T
g
) o he samples.
The cooling scans showed PLA glass ansi ion empe a u e
a abou 57 °C o nea PLA and i s composi es. Also, exo he mic
c ys alliza ion peaks o nea PLA and PLC/CNC composi es
we e no obse ed du ing cooling. PLA c ys alliza ion is ela-
i ely slow wi hou nuclea ing lle s. In addi ion, he manu-
ac u e species ha he used PLA g ade is amo phous.
The cold c ys alliza ion p ocess is cha ac e is ic o PLA, wi h
T
cc
occu ing a app oxima ely 98 °C. The addi ion o 1 w %
CNC inc eased T
cc
by abou 30 °C, whe eas 2 w % CNC led o
a smalle inc ease o only 9 °C. Li e a u e epo s indica e ha
CNC p omo es nuclea ion bu gene ally educes he c ys alli-
za ion a e as i s concen a ion inc eases.
27,28
A highe CNC
con en may lead o he o ma ion o la ge agg ega es, which
a e less effec i e in p omo ing nuclea ion.
The T
m
o nea PLA is app oxima ely 156 °C, wi h a T
g
o
abou 64 °C. Adding 1 w % CNC had no signican effec on
hese alues. Howe e , a highe CNC concen a ions, bo h T
g
and T
m
dec eased sligh ly—by abou 5 °C and 2 °C, espec i ely.
This educ ion in he mal ansi ions is a ibu ed o weakened
in e molecula bonding be ween PLA chains. CNC agg ega ion
a he in e ace dis up s PLA chain in e ac ions and inc eases
in e molecula spacing, enhancing chain mobili y.
29
3.3. The momechanical and mechanical analysis
The beha io o s o age modulus (E0) and loss modulus (E00 )as
a unc ion o empe a u e o PLA and PLA/CNC nano-
composi es con aining 1% and 2% w % o CNC a e shown in
Fig. 7. Du ing comp ession molding o oams, CNC om he
oam su aces dispe ses in o he PLA ma ix. PLA_CNC and
PLA_2CNC illus a e he dispe sion o CNC and i s inuence on
mechanical p ope ies. In he glassy s a e (Fig. 7a), PLA_CNC
demons a es an inc eased s o age modulus. Howe e ,
PLA_2CNC exhibi s p ope ies simila o nea PLA, likely due o
Fig. 5 TGA cu es: (a) he empe a u e e olu ion o weigh loss and (b) i s fi s de i a i e.
Table 2 The mal p ope ies o PLA and PLA/CNC composi es
Samples T
m
,°C DH
m
,Jg
−1
T
g
,°C T
cc
,°C T
5%
,°C T
max
, °C Cha
700
,%
PLA 156.2 5.68 57.6
a
99.2 313 358 0
63.8
b
PLA_CNC 156.5 9.85 57.7
a
126.6 355 398 0.7
63.6
b
PLA_2CNC 154.3 15.54 57.9
a
104.6 361 397 0.9
59.6
b
PLA_Cu —— ——337 375 0.8
PLA_PHMB —— ——344 388 0.6
PLA(C)Cu —— ——336 399 0.4
PLA(C)PHMB —— ——337 384 0.2
a
T
g
om he cooling scans.
b
T
g
om he hea ing scans.
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he o ma ion o CNC agglome a es, which diminish ein-
o cemen efficiency. Nea PLA shows a sligh ly delayed glass
ansi ion, esul ing in highe s o age modulus alues be ween
60 and 80 °C. The sha pe ansi ion obse ed in samples wi h
CNC sugges s ha CNC dis up s in e molecula bonding
be ween PLA chains. Simila ly, he loss modulus peak (Fig. 7b)
indica es a educ ion in glass ansi ion empe a u e by up o 2 °
C in CNC-con aining samples compa ed o nea PLA (62 °C).
The ep esen a i e s ess–s ain cu es o he nea PLA and
PLA/CNC nanocomposi e lms a e p esen ed in Fig. 8a. All
cu es show ailu e sho ly ae he elas ic egion, wi h
minimal plas ic de o ma ion. The a e age alues o elas ic
modulus (E), ensile s eng h (s), and elonga ion a b eak (3) a e
p o ided in Fig. 8b–d. The elas ic modulus o nea PLA was
1.19 GPa. The addi ion o 1 w % and 2 w % o he cellulose lle
o he PLA ma ix caused a sligh dec ease in E alues o
1.09 GPa and 0.96 GPa, espec i ely. The educ ion in he elas ic
modulus can be a ibu ed o he poo dis ibu ion o nanolle .
PLA's ensile s eng h (s) g adually dec eases ae inco po-
a ing CNCs. The s o nea PLA was 44.37 MPa, while PLA_CNC
and PLA_2CNC demons a ed a dec ease in s alues o 1.11- and
1.36- old, espec i ely. The educ ion in he ensile s eng h can
be a ibu ed o he agglome a es o he CNC wi hin he
composi e s uc u e, which esul ed in local s ess concen a-
ions. The PLA achie ed an elonga ion a b eak o abou 6.2%.
S ain a b eak (3) is i ually unchanged o PLA_CNC
compa ed o PLA. The PLA_2CNC composi e, which con ained
2 w % o CNC, saw a no able d op o 4.09%.
The dec ease in mechanical p ope ies and oughness o
composi es could be associa ed wi h an agg ega ion o nano-
lle s. CNC agglome a ion can ac as s ess concen a o s,
p omo ing de ec p opaga ion. These de ec s can g ow o sizes
mo e signican han he c i ical c ack size, esul ing in lm
ailu e.
30
3.4. An ibac e ial p ope ies
The disc diffusion es , shown in Fig. 9, was used o e alua e he
effec i eness o he an ibac e ial agen s (Cu and PHMB)
diffusion om he composi e s uc u e agains  e selec ed
bac e ia s ains. The pla es we e e alua ed e e y day o 5 days,
bu no changes we e obse ed om he  s day o e alua ion.
The lm sample p epa a ion ou e was no es ed due o poo
CNC dispe sion and esul ing he e ogenei y. Du ing incuba-
ion, he an ibac e ial agen s diffuse adially ou wa d om he
discs h ough he aga . I he an ibac e ial agen is effec i e, i
will inhibi bac e ial g ow h, c ea ing a clea , ci cula a ea
Fig. 6 DSC (a) cooling and (b) second hea ing scans o nea PLA and PLA/CNC composi es.
Fig. 7 (a) S o age modulus (E0) and (b) loss modulus (E00 ) o PLA/CNC samples.
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Fig. 8 (a) S ain–s eng h cu es, (b) elas ic modulus (E), (c) ensile s eng h (s), and (d) elonga ion a b eak (3) o PLA and PLA/CNC films.
Fig. 9 Aga diffusion es images a 24 hou s o composi e samples: (a) E. coli B+, (b) L. sali a ius, (c) E. coli, (d) S. mu ans, and (e) S. sanguinis.
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a ound he disc known as he “zone o inhibi ion o halo o
inhibi ion”. The concen a ion o he an ibac e ial agen is
di ec ly p opo ional o he a ea o he halo. Nalidixic acid (NA),
as a b oad-spec um an ibio ic, was used as a posi i e con ol o
demons a e bac e ial sensi i i y. I can be clea ly seen ha
sample PLA(C)PHMB o ms a isible con inuing zone o inhi-
bi ion in all es ed bac e ial media. Sample PLA(C)Cu exhibi s
good diffusion o Cu , as indica ed by he dis inc o ange
colo a ion, al hough i did no inhibi bac e ial g ow h.
Al hough i is oen indica ed ha cu cumin is an an ibac e ial
agen , i s co ec ac i i y is bac e ios a ic; ha is, e en wi hou
p oducing bac e ial dea h, i can slow bac e ial g ow h. The
esul s clea ly eec hose composi ions ha used a coa ing
app oach and had success ul diffusion o an ibac e ial agen s
compa ed o ones ha in eg a ed hem in o he elec ospun
be s uc u e. The ailu e o PLA_PHMB and PLA_Cu o
elease an imic obial agen s om he s uc u e could be
a ibu ed o he ela i e s abili y and slow biodeg ada ion o
PLA.
31
The long PLA chains wi h s ong in a- and in e molec-
ula bonding signican ly es ic he diffusion p ocess.
Fu he mo e, he inhe en ly hyd ophilic na u e o cellulose,
a ibu ed o i s abundance o hyd oxyl g oups, con as s
sha ply wi h he p edominan ly hyd ophobic molecula s uc-
u e o PLA.
3.5. D ug elease
D ug elease expe imen s we e conduc ed o elucida e he
diffusion kine ics o he d ugs om bo h he be -encapsula ed
and coa ing-encapsula ed o mula ions (Fig. 10). A elease
medium composed o a 3 : 7 ( / ) mix u e o PBS buffe and
e hanol, chosen o i s pola i y o mimic blood se um
32
and i s
sui abili y o spec opho ome ic quan ica ion, was used o
e alua e d ug elease. As shown in Fig. 10a, all encapsula ed
d ugs we e eleased apidly unde hese condi ions. Howe e ,
dis inc diffe ences in he ini ial elease a es we e e iden
(Fig. 10b).
Bo h Cu and PHMB in he coa ing exhibi ed a nea ly
comple e elease wi hin 4 hou s, whe eas Cu encapsula ed in
PLA be s (PLA_Cu ) ollowed a simila end bu a a slowe
a e. The lowes elease a e was obse ed o PHMB encapsu-
la ed in PLA be s (PLA_PHMB). These ndings sugges ha he
hyd oxyl- ich CNC ma ix acili a es apid d ug elease, while
he hyd ophobic PLA ma ix hinde s diffusion. The hyd ophi-
lici y and size o he d ug molecule also play a ole in explaining
he sus ained elease o e 98 hou s o PLA_PHMB.
The elease beha io is u he explained by kine ic
cons an s de i ed om he Higuchi
33,34
and  s -o de
35,36
models, which oge he accoun o he o e all d ug elease
(Table 3). Finally, hese esul s a e consis en wi h he disc
Fig. 10 D ug elease: (a) long- e m elease o Cu and PHMB o e 98 hou s and (b) ini ial elease o he d ugs.
Table 3 Higuchi and fi s -o de elease cons an s using he combined model o d ug elease. k
H
quan ifies he d ug elease a e in he ini ial
phase o deli e y (0–60%) and k
1
eflec s he abili y o each he final equilib ium condi ion (40–100%)
Sample
Higuchi model
a
Fi s -o de model
b
k
H
(h
−0.5
) (%) k
1
(h
−1
) (%)
PLA_PHMB 0.220 98.60 0.343 99.50
PLA-Cu 0.443 99.32 0.584 93.07
PLA(C)PHMB 0.687 99.43 0.809 96.40
PLA(C)Cu 0.656 98.57 0.842 99.91
a
M
M0
¼kH 1=2;0#
M
M0
#0:6:
b
ln1
M
M0¼ak1 ;0:4#
M
M0
#1:0;whe e: k
H
and k
1
ep esen , espec i ely, he Higuchi and he  s -
o de elease cons an ; a is ela ed o he elease in he  s s ep; M
is he d ug pe cen age eleased a ime ; and M
0
is he maximum d ug
pe cen age ha can be eleased in he medium (i.e., he o al amoun o d ug).
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