Soft Matter Composites Interfacing with Biomolecules, Cells, and Tissues - Bioinspired Approaches for Human-Centric Technologies - page 41

Sodium alginate solutions containing hydrophilic antibacterial agents can be turned
into films or beads which will swell and gelatinize upon contact with, for instance,
hydrated skin wounds. A recent work combined povidone-iodine (PVPI) and
sodium alginate into antimicrobial calcium cross-linked films and beads which
released PVPI in a controlled manner in moist media or in water (Liakos
et al. 2013 ). PVPI is encapsulated in the films forming circular microdomains.
Upon immersion into moist media such as bacteria- or fungi-laden agar or aqueous
media or contaminated water, these films swell, gelatinize, and start releasing the
antimicrobial agent (PVPI) slowly inhibiting the growth. The films also display
antimicrobial and antifungal activity when exposed to agar media heavily popu-
lated by E. coli and Candida albicans fungi as seen in Fig. 2.4 . This was achieved
by natural gelation and swelling of alginate in such media. These alginate films can
also encapsulate hydrophobic antimicrobial agents such as natural essential oils
(EOs) (Liakos et al. 2014 ). The process differs from direct mixing in aqueous
solution in that surfactant stabilized emulsions need to be prepared. Namely,
elicriso italic, chamomile blue, cinnamon, lavender, tea tree, peppermint, eucalyp-
tus, lemongrass, and lemon oils were encapsulated in the films as potential active
substances. Glycerol was used to induce plasticity and surfactants were added to
improve the dispersion of EOs in the sodium alginate matrix.
The topography, chemical composition, mechanical properties, and humidity
resistance of the films were studied. Antimicrobial tests were conducted on films
containing different percentages of EOs against E. coli bacteria and Candida
albicans fungi (Liakos et al. 2014 ). Such diverse types of essential oil-fortified
alginate films can find many applications mainly as disposable wound dressings but
also in food packaging, medical device protection and disinfection, and indoor air
quality improvement applications, to name a few. Not all essential oils encapsulated
in alginic matrices present similar effects against inhibiting bacterial or fungal
growth as exemplified in Fig. 2.5 .
There has been much interest in forming 3-D hydrogel structures from natural
polymers containing large amounts of water but being structurally stable and
functional (antimicrobial and drug releasing). In order to enhance their mechanical
robustness, researchers use physical or chemical cross-linking procedures to create
three-dimensional (3-D) polymeric networks. The most common biopolymer
hydrogels are obtained from alginic acid polymers, chitosan, gelatin, and
ʲ

-cyclodextrin (enzymatically obtained from starch). Due to their high water
content and soft, porous 3-D structure (see Fig. 2.6 ), they can easily simulate in vivo
extracellular matrix (ECM) microenvironment in biomedical applications.
Hydrogels can be applied externally or can be injectable and can carry cells or
drugs into the body in a minimally invasive manner. Hydrogels have also been used
for the creation of 3-D scaffolds for cell culture and transplantation and as carriers
for local release of proteins and drugs (Lee et al. 2013 ; Fonseca et al. 2014 ).
Alginic acid-based natural polymers are linear polysaccharides with homopoly-
meric blocks of (1,4)-linked - L -guluronate that are extracted

from seaweed and shrimp shells (see Fig. 2.7 ). They are widely used in making
various forms of biomedical materials. In general, alginate forms a hydrogel via

ʲ - D -mannuronate and α