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Morphology of polysaccharide beads and films for environmental and biomedical applications
Mei Li1, Sarah Ziem2, Gisela Buschle-Diller1
1Department of Polymer and Fiber Engineering, Auburn University, Auburn, AL
2University of Applied Sciences, Reutlingen, Germany
Introduction
Experimental Methods
Results and Discussion – Surface Morphology
Polysaccharides are inexpensive and readily available worldwide from
Additional
filler,
active
agricultural and forest biomass[1]. These biopolymers can be formed into Polysaccharide solution
compound, or drug
hydrogels, beads, films and coatings and even into fibers and show incredible
Beads
were
formed
bywith cellulose
Alginate
versatility and potential for environmental and biomedical applications. They
adding dissolved polysaccharide
are used in food, cosmetic and pharmaceutical products as thickeners,
into a crosslinking solution, films
emulsifiers, binders, stabilizers and for drug encapsulation/delivery.
by using a knife with defined Freshly made pectin beads
Depending on the nature of their functional groups, they exhibit excellent
distance to a glass plate.
sorption capabilities. They can act as sorbents or as reservoirs for release of
compounds. Especially useful are polysaccharide compounds with
Crosslinking agent
predictable and controlled swelling and discharge behavior.
External and internal surfaces are important factors for the sorption
capacity of a compound. Extensive studies were conducted using SEM to
observe differences in surface morphology as it relates to composition
and product formation. Pectin beads had smooth surfaces and a compact
internal structure with small pores when air-dried (A), and rough external
and flaky internal surfaces when freeze-dried (B). The addition of xanthan
yields beads with cracked surfaces (C).
B
A
C
Project Goals
The goal of the current work is to create a portfolio of polysaccharide beads
and hydrogels with a wide variety of morphologies, porosities and other
properties useful for filtering, delivering of active compounds, clean-up of oil
and chemical spills, and similar applications. Alginate, pectin, chitosan,
xanthan, and carrageenan are some of the basic polysaccharides currently
being investigated and modified to serve a specific purpose in form of beads,
hydrogels or electrospun into nanowebs. Their swelling ratios in water and
aqueous solutions of selected drugs or dyes are being studied and their
mechanical properties evaluated in relationship to their composition. The
potential regeneration and reuse of the sorbent material is also being
considered for highest efficiency in their respective application. The focus of
the work presented here is mainly on product morphology and surface
characteristics.
In an aqueous environment some of these polysaccharides are polycationic,
others polyanionic or neutral depending on the pH value. Alginate, obtained
from brown algae and bacteria, for example, is a linear copolymer consisting
of (1-4)-linked β-D-mannuronic acid (M) and α-L-guluronic acid (G) residues at
[1,2]
different ratios and distribution along the chains.
Due to their acidic
functional groups, alginate as well as xanthan can be very useful for binding
of cationic compounds. Carrageenan from red seaweed contains ester-sulfate
[1]
groups. Crosslinking of these anionic polysaccharides can be achieved with
2+
2+
positive ions to form films or beads, such as Ca and Zn or composite gels
with a polycation, such as chitosan.
HO
O
OH
O
O
ONa
ONa
ONa
HO
O
O
HO
O
OH
O
OH
O
(MMM..)
HO (GGG..)
OH
O
HO
HO
O
O
HO
OH
O
O
HO
OH
CH2 OH
CH2 OH
CH2OH
O
O
O
OH
OH
O
OH
O
Starch
OH
n
Bead sizes: Composition and formation conditions had a large influence on the
average diameter of beads and their surface morphology. Beads containing solid
fillers, such as starch granules, were clearly bigger than their plain counterparts.
All beads were rather large when freshly made, but never regained the same
diameter after air or freeze drying. Pectin beads were irregular in shape and hard
to crush, while alginate and xanthan formed perfectly round beads. Carrageenan
beads showed the largest variation in bead sizes. They were the least stable of all
samples upon drying.[3-5]
w/v
2% alginate &
starch
1%
1318.62
±129.0
3%
1514.29
±67.9
5%
2028.28
±96.5
10%
2096.51
±72.1
w/v
5% pectin
2% ZnAc
wet
4271.16
±32.4
air-dry
1710.16
±3.8
2% alginate &
cellulose
1275.91
±69.3
1446.03
±40.8
1857.46
±61.2
2147.49
±65.6
5% pectin
10% ZnAc
3984.94
±21.9
1786.62
±6.9
Electrospun fibers from alginate
Pectin segment
......
OH
OH
O
Surface Characteristics of Beads and Films
COOCH3
O
O
HO
crosslinking agents. Fillers or active compounds for release (drugs, dyes) were
incorporated during the coagulation process. [3,4]
Beads, films or fibers were formed and their
morphology observed under the scanning
electron microscope (SEM, Zeiss EVO 50). Bead
diameter and size distribution were recorded
Results and Discussion
Beaddrying.
formation
after air or–freeze
Swelling ratios and
differences in sorption behavior were evaluated.
Wet carrageenan beads and fibers
NH2
COOCH3
O
HO
OH
OH
n
O
Chitosan
O
O
HO
NH2
COOH
OH
ONa n
OH
NH2
......
(MGMG..)
O
m
OH
Alginate sodium
OH
O
O
ONa
O
HO
O
Wet carrageenan beads and
Alginate
wasaqueous
dissolved
in distilled water (2% w/v), pectin at 4 and 5% (w/v),
fiber (2%
solution)
1M
and obtained
xanthaninat
2%potassium
(w/v) at room temperature; carrageenan was stirred into
1 Mchloride
KCl solution at 70˚C. CaCl2, ZnCl2 and zinc acetate (ZnAc) served as
Average diameter (mm) of beads with differing compositions
OH
O
O
Freshly made alginate-based beads
OH
2.2 % alginate, electrospun
Electrospinning of natural
biopolymers, for example,
alginate, can be difficult.[6]
These
nanofibers
were
electrospun from glycerol
solution onto a metal target
sprayed with CaCl2 solution 2.2 % alginate, electrospun
and air-dried.
Bead made from pectin Interior of pectin bead Beads form from pectin (5%)
(5%), and crosslinked with (5%) containing 5% ascorbic and xanthan (2%) in ZnAc
solution (10%); air-dried
5% ZnAc solution (air-dried) acid (freeze-dried)
The surface of films made from xanthan solution differed from those of
the beads (D). Alginate beads (E, F) were modified by adding solid fillers
which changed they sorption behavior and impacted their surface
morphology.
D
E
F
Film made from aqueous Beads from alginate (2%) Beads from alginate (2%)
xanthan solution (2%) and and starch (10%) in CaCl2 and cellulose (10%) in CaCl2
solution; air-dried
solution; air-dried
ZnAc (5%); air-dried
Conclusions
Biopolymers from renewable resources, such as polysaccharides, offer
endless opportunities for creating a toolbox of versatile materials. Beads,
gels, fibers and films can be loaded with active compounds or used to
absorb undesirable pollutants. Their surface characteristics and their
porous system, among other factors, play an important role for their
efficiency as environmental or biomedical devices and can be tailored by
composition and method of synthesis.
References
1. Habibi, Y., Lucia, L. (eds.): Polysaccharide Building Blocks. A Sustainable Approach to the
Development of Renewable Biomaterials, Wiley, NY, 2012.
2. Mike, R., et al., Nanostructure of Calcium Alginate Aerogels Obtained from Multistep
Solvent Exchange Route, Longmuir, 2008, 12547-12552
3. Li, M., Buschle-Diller, G., Polymeric functionalized beads from alginate for targeted
release of auxin into water, 249th ACS Nat. Meeting & Exposition in Denver, CO, March
22-26, 2015.
4. Ziem, S., Li, M., Buschle-Diller, G., Drug delivery systems based on anionic
polysaccharides, 247th ACS Nat. Meeting & Exposition, Dallas, TX, March 15-19, 2014.
5. Li, M., Buschle-Diller, G. Alginate - a promising polysaccharide for controlled
contaminant removal from waste water, 247th ACS National Meeting & Exposition, Dallas,
TX, March 15-19, 2014.
6. Alongi, R., Skinner, C., Hamilton, S.K., Buschle-Diller, G., Electrospinning of Biopolymer
Network Structures, 247th ACS Nat. Meeting & Exposition, Dallas, TX, March 15-19, 2014.