Morphology of polysaccharide beads and films for environmental and biomedical applicationsMei Li1, Sarah Ziem2, Gisela Buschle-Diller1

1Department of Polymer and Fiber Engineering, Auburn University, Auburn, AL2University of Applied Sciences, Reutlingen, Germany

Conclusions

Results and Discussion – Bead formation

Project Goals

Biopolymers from renewable resources, such as polysaccharides, offerendless opportunities for creating a toolbox of versatile materials. Beads,gels, fibers and films can be loaded with active compounds or used toabsorb undesirable pollutants. Their surface characteristics and theirporous system, among other factors, play an important role for theirefficiency as environmental or biomedical devices and can be tailored bycomposition and method of synthesis.

References

1. Habibi, Y., Lucia, L. (eds.): Polysaccharide Building Blocks. A Sustainable Approach to theDevelopment of Renewable Biomaterials, Wiley, NY, 2012.2. Mike, R., et al., Nanostructure of Calcium Alginate Aerogels Obtained from MultistepSolvent Exchange Route, Longmuir, 2008, 12547-125523. 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.

Experimental Methods

Alginate with cellulose

Introduction

Wet carrageenan beads and fiber (2% aqueous solution) obtained in 1 M potassium chloride

Results and Discussion – Surface Morphology

Polysaccharides are inexpensive and readily available worldwide fromagricultural and forest biomass[1]. These biopolymers can be formed intohydrogels, beads, films and coatings and even into fibers and show incredibleversatility and potential for environmental and biomedical applications. Theyare used in food, cosmetic and pharmaceutical products as thickeners,emulsifiers, binders, stabilizers and for drug encapsulation/delivery.Depending on the nature of their functional groups, they exhibit excellentsorption capabilities. They can act as sorbents or as reservoirs for release ofcompounds. Especially useful are polysaccharide compounds withpredictable and controlled swelling and discharge behavior.

The goal of the current work is to create a portfolio of polysaccharide beadsand hydrogels with a wide variety of morphologies, porosities and otherproperties useful for filtering, delivering of active compounds, clean-up of oiland chemical spills, and similar applications. Alginate, pectin, chitosan,xanthan, and carrageenan are some of the basic polysaccharides currentlybeing investigated and modified to serve a specific purpose in form of beads,hydrogels or electrospun into nanowebs. Their swelling ratios in water andaqueous solutions of selected drugs or dyes are being studied and theirmechanical properties evaluated in relationship to their composition. Thepotential regeneration and reuse of the sorbent material is also beingconsidered for highest efficiency in their respective application. The focus ofthe work presented here is mainly on product morphology and surfacecharacteristics.In an aqueous environment some of these polysaccharides are polycationic,others polyanionic or neutral depending on the pH value. Alginate, obtainedfrom brown algae and bacteria, for example, is a linear copolymer consistingof (1-4)-linked β-D-mannuronic acid (M) and α-L-guluronic acid (G) residues atdifferent ratios and distribution along the chains.

[1,2]Due to their acidic

functional groups, alginate as well as xanthan can be very useful for bindingof cationic compounds. Carrageenan from red seaweed contains ester-sulfategroups.

[1]Crosslinking of these anionic polysaccharides can be achieved with

positive ions to form films or beads, such as Ca2+

and Zn2+

or composite gelswith a polycation, such as chitosan.

O

O

O

ONa

OH

OHO O

HO

O

ONa

OH

O

O

ONaO

OH

HO

O

O

HO

OONa

OH

O

O

O

ONa

OH

HO

(MMM..)

m

(GGG..)n

(MGMG..)

Alginate sodium

OHO

HO

OH

NH2

OO

HO

NH2

OO

OH OH

HO

NH2

OH

n

Chitosan

OO

HOOH

OO

HO

COOH COOCH3

OH

OO

HOOH

O

COOCH3

............

Pectin segment

O

CH2OH

OH

OH

OH

O

O

O

O

CH2OH

OH

OH

CH2OH

OH

OH

OH

n

Starch

Alginate was dissolved in distilled water (2% w/v), pectin at 4 and 5% (w/v),and xanthan at 2% (w/v) at room temperature; carrageenan was stirred into1 M KCl solution at 70˚C. CaCl2, ZnCl2 and zinc acetate (ZnAc) served ascrosslinking agents. Fillers or active compounds for release (drugs, dyes) wereincorporated during the coagulation process. [3,4]

Beads, films or fibers were formed and theirmorphology observed under the scanningelectron microscope (SEM, Zeiss EVO 50). Beaddiameter and size distribution were recordedafter air or freeze drying. Swelling ratios anddifferences in sorption behavior were evaluated.

Wet carrageenan beads and fibers

Polysaccharide solutionAdditional filler, active compound, or drug

Crosslinking agent

Freshly made pectin beads

Beads were formed byadding dissolved polysaccharideinto a crosslinking solution, filmsby using a knife with defineddistance to a glass plate.

Freshly made alginate-based beads

Bead sizes: Composition and formation conditions had a large influence on theaverage diameter of beads and their surface morphology. Beads containing solidfillers, such as starch granules, were clearly bigger than their plain counterparts.All beads were rather large when freshly made, but never regained the samediameter after air or freeze drying. Pectin beads were irregular in shape and hardto crush, while alginate and xanthan formed perfectly round beads. Carrageenanbeads showed the largest variation in bead sizes. They were the least stable of allsamples upon drying.[3-5]

Average diameter (mm) of beads with differing compositions

External and internal surfaces are important factors for the sorptioncapacity of a compound. Extensive studies were conducted using SEM toobserve differences in surface morphology as it relates to compositionand product formation. Pectin beads had smooth surfaces and a compactinternal structure with small pores when air-dried (A), and rough externaland flaky internal surfaces when freeze-dried (B). The addition of xanthanyields beads with cracked surfaces (C).

The surface of films made from xanthan solution differed from those ofthe beads (D). Alginate beads (E, F) were modified by adding solid fillerswhich changed they sorption behavior and impacted their surfacemorphology.

Electrospun fibers from alginate

w/v 1% 3% 5% 10%

2% alginate & starch

1318.62

±129.01514.29

±67.92028.28

±96.52096.51

±72.1

2% alginate & cellulose

1275.91

±69.31446.03

±40.81857.46

±61.22147.49

±65.6

Surface Characteristics of Beads and Films

w/v wet air-dry

5% pectin2% ZnAc

4271.16

±32.41710.16

±3.8

5% pectin 10% ZnAc

3984.94

±21.91786.62

±6.9

Electrospinning of naturalbiopolymers, for example,alginate, can be difficult.[6]

These nanofibers wereelectrospun from glycerolsolution onto a metal targetsprayed with CaCl2 solutionand air-dried.

2.2 % alginate, electrospun 2.2 % alginate, electrospun

Beads form from pectin (5%)and xanthan (2%) in ZnAcsolution (10%); air-dried

Interior of pectin bead(5%) containing 5% ascorbicacid (freeze-dried)

Bead made from pectin(5%), and crosslinked with5% ZnAc solution (air-dried)

A B C

Beads from alginate (2%)and cellulose (10%) in CaCl2solution; air-dried

Beads from alginate (2%)and starch (10%) in CaCl2solution; air-dried

Film made from aqueousxanthan solution (2%) andZnAc (5%); air-dried

D E F