Alginate Based Polyurethanes a Review of Recent Advances and Perspective 2015 International Journal of Biological Macromolecules

7/25/2019 Alginate Based Polyurethanes a Review of Recent Advances and Perspective 2015 International Journal of Biologic

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378 K.M. Zia et al. / International Journal of Biological Macromolecules 79 (2015) 377387

polymers is their biodegradability, bioactivity, easy availability and

nontoxic nature. With the progress in the research area of chem-

istry, biology, materials and modern sciences, a vast array of novel

synthetic polymeric materials have been introduced from last

ten decades. Synthetic polymers such as nylon, polyethylene and

polyurethanes have transformed daily life, are derived from non-

renewable fossil fuel resources [6]. Petroleum derived synthetic

polymers have been widely used in composites are not readily

biodegradable and resistant to microbial degradation thus accu-

mulated in the environment and become a major source of waste

disposal [7,8]. Another problem is fossil fuel and petroleum prices

volatility that forced to replace commercial synthetic polymers

with natural biodegradable polymers such as polyesters, proteins

and polysaccharides [919]. Sustainability of resources cannot be

achieved if we will continue to use non-renewable resources.

Polyurethanes, from a synthetic class of polymers are receiv-

ing much attention as one of the most biocompatible material.

Due to their easy availability and propensity to modify their

properties, polyurethanes are used for various applications, e.g.

coatings, sealants, adhesives, elastomers, foams, textile finish [20]

and for biomedical applications due to having good biocompati-

bility [21,22]. Use of natural polymers for PUs modification gained

interest as they make them more environmentally green material.

Much research has been conducted on polysaccharides, proteinsand lipids based PUs with their respective applications in different

industrial fields especially for biomedical applications. The struc-

ture of PU results to form a phasesegregatedstructure, whichmake

them available for their use in various ways such as adhesives,

coatings, biomedical materials and elastomers [23,24]. PU elas-

tomers (PUEs) are having the capacityto use in various applications

because they are moldable, injectable and recyclable [25].

Morphological pattern of PUEs have been presented in the

established literature. The effect of the diisocyanate structure and

chain extender (CE) length using ,-alkane diols on the crys-tallinity, surface morphology and thermo-mechanical properties of

PUEs have also been investigated [2628]. Published materials are

also available on the synthesis, characterization and application of

chitin based PUs [2931]. In vitro biocompatibility and cytotoxicityof chitin/1,4-butanediol blends based PUEs have been comprehen-

sively reported [32,33]. Somedocuments areavailable onthe struc-

tural characterizationof chitin-basedPUEs andtheir shape memory

characteristics [34,35]. XRD studies and surface characteristics of

UV-irradiatedand non-irradiatedchitin-basedPUEs have also been

presented elsewhere [3641]. The microstructure of a PU block is

generally known to be composed of differentphases, i.e., it is based

on domains whichhave been built of hard urethane-type segments

and on soft polyol segment [34]. A wide class of materials can be

obtained by controlling variables such as the functionality, chemi-

calcompositionand themolecular weight of thedifferentreactants.

Natural bio-macromolecules serve as basic template for cell

growth, are usually biocompatible, whereas, synthetic polymers

can impart other toxic compounds or impurities that do not allowcell growth. Compared with natural polymers, however, synthetic

polymers have much better thermal and mechanical properties

[42]. The increasing interest in new polymeric material based on

blends of 2 or more natural bio-macromolecules andblends of nat-

ural bio-macromolecules and synthetic polymers can establish a

newform of materialscalled bio-artificialor biosyntheticpolymeric

materials with improved mechanical properties and biocompat-

ibility compared with those of individual polymeric component

[4347].

1.1. Polysaccharides

Bio-macromolecules are diverse and important class of poly-

meric materials formed in nature during the growth cycles of

organisms such as animals, bacteria, green plants and fungi hence

also referred as one of the main class of natural biodegradable

polymers [48]. Bio-macromolecules have potential array of appli-

cations in almost all segments of the economy and can be used as

adhesives, absorbents, lubricants, soil conditions, cosmetics, drug

delivery vehicles, textile, good strength structural materials, etc.

[6]. Polysaccharides are the mostabundant organic materials found

in nature and are present in all living organisms where they carry

out one or more of their diverse functions [49]. In comparison

with other biopolymers, these molecules are characterizedby their

chemical diversity, presence of large number of functional groups,

strong hydrophilicity and their rigidity [50]. Polysaccharides are

ubiquitous can be classified as either homo-polysaccharides or

hetero-polysaccharide and found in algae (e.g. alginate), plants

(e.g. starch, cellulose, glucomannan, pectin, guar gum), microbes

(e.g. dextran, xanthan gum), and animals (chitosan, chondroitin)

[5153].

Polysaccharides have some special characteristics which are not

available in other natural polymers which includes; water solubil-

ity, flow behavior, gelling potential and/or surface and interfacial

properties depending upon the difference in monosaccharide com-

position and linkage type [54]. Polysaccharides have been used

for decades in various industrial applications, e.g. pharmaceut-

icals, biomaterials, foodstuff and nutrition, and biofuels, growingunderstanding and deeper investigations of the importance of

Fig. 1. (a)Cations form of calciumalginate, (b)gel formationof calcium alginate in

solution [86].

Fig. 2. Alginate based impression material for dental applications [87].


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K.M. Zia et al. / International Journal of Biological Macromolecules 79 (2015) 377387 379

Table 1

Different techniques for the synthesis and characterization of various alginate-based materials and their prospective applications in various fields.

Sr. No Name Techniques used for

characterization

Potential applications Reference

1. Sodium alginate/poly(vinyl alcohol) alloy FT-IR, SEM, DSC, TGA Membrane for separation of dimethyl

formamide/water mixtures

[97]

2. PVAalginate FT-IR, SEM Wound dressing membrane [98]

3. PVAalginate FT-IR, EDAX For phosphate removal [99]

4. PVAalginate Potentiometric Kinetic

parameters

Hydrolysis of pineapple waste [100]

5. PVAalginate SEM, diffusion,

coefficients, stability

tests (pH)

As a matrix for yeast immobilization [101]

6. PVAalginate EDX, FT-IR Matrix for immobilization of invertase [102]

7. PVAAlginate FESM, EDX Encapsulation of Fe2O3magnetic beads forphotocatalytic reduction of Cr(VI)

[103]

8. PVAalginate SEM Effective removal of N,N-dimethyl formamide

from industrial effluents

[104]

9. MgAl LDHalginate/polyvinyl alcohol XRD, FESEM For water remediation [105]

10. [A336][Mtba]/PVAalginate FTIR, SEM, TGA For removal of divalent mercury from aqueous

solutions

[106]

11. Naalg/PVA composite FT-IR, SEM Nano-filtration and/or desalination [107]

12. Maghemite PVAalginate Beads FESEM, XRD, FT-IR,

XPS, EDX

Cesium removal from radioactive waste water [108]

13. PVAalginatesulfate FESEMEDX, HPLC Matrix for enzyme immobilization [109]

14. Glutaraldehyde/sodium

alginatepoly(vinyl alcohol)

SEM For PV dehydration of isopropanol [110]

15. Aluminum-rich z eolite b eta i ncorporated

sodium alginate

FT-IR, S EM, U TM Employed f or P V dehydration, e sterification

reactions.

[111]

16. Sodium alginate/poly(vinyl alcohol) FT-IR, XRD, SEM For drug (diclofenac sodium) delivery systems [112]

17. poly(vinyl alcohol)/sodium alginate XRD, TGA, DSC A good candidate for alkaline direct methanol fuel

cells applications

[113]

18. CelluloseAlginate IC, SEM, EWC, GC Improved ethanol production [114]

19. Carboxymethyl c ellulosesodium a lginate FT-IR, X RD, D TA, S EM For s eparation o f benzenecyclohexane m ixtures [115]

20. NCCalginate FT-IR, SEM, XRD, DSC,

TGA

Biodegradable films [116]

21. Chitosanalginate (CS/ALG) DLS, SEM, FT-IR Potential use for oral insulin delivery [117]

22. Alginate/chitosan/PLA-H SEM, GPC, Mercury

porosimetry

Scaffolds for VEGF controlled release [118]

23. Poly(acrylic a cid-Co-hydroxyethyl

methacrylate) sodium alginate

FTIR, SEM, XRD,

DTATGA

Foradsorption of twoimportant synthetic dyes, i.e.

Congo redand methylViolet from water

[119]

24. Sodium a lginatepoly(N-isopropyl

acrylamide)

FT-IR, TGA For PV dehydration of ethanol [120]

25. PLGA/chitosan cellulose alginate Rheometery,

sonication. FESEM,FT-IR, DSC, TGA

An emulsion stabilizer in synthesisof

biodegradable polymers.

[121]

26. PLGA-alg-RGD MP. XPS, SEM Delivery system for vaccination [122]

27. Chitosanpoly (caprolactone)/alginate SEM For controlled delivering of VEGF [123]

28. Chitosanalginate Sonication, SEM. FT-IR,

DSC

Drug delivery [124]

29. Chitosanalginate Nanogels for vaccine delivery [125]

30. Alginatechitosan FT-IR, Optical

microscopy

A novel fiber forwound care application [126]

31. Chitosanalginate SEM, optical

microscopy

Used in thepreparation of Pickering emulsion as

potent carriers in biomedical area

[127]

32. Carboxymethyl chitosanalginate SEM Site selective protein delivery in intestine [128]

33. Chitosan/alginate nano-layered PET film SEM, DSC, TGA, water

contact angles

For preparation of multilayer films

Coating biomedical appliances or multilayer edible

coatings

[129]

34. Alginate/HPMC Improved in vitro release of BSA [130]

35. Alginate-G-poly(sodium a crylate) a nd p oly

(vinyl pyrrolidone)

SEM, FT-IR Potential candidate for drug delivery systems and

water manageable materials

[131]

36. Alginate/chitosan/titanium ATRFTIR, XPS, SEM,

XRD, DTA

Potential applications in tissue engineering

scaffolds field

[132]

37. Minocycline loaded

chitosan/alginate/titanium

XPS, SEM Inhibit biofilm formation [133]

38. Carboxymethyl c hitosan/organic

rectorite/alginate

FT-IR, F ESEM, X RD Antimicrobial a ctivity f or fi brous m ats [134]

39. Alginate/alginate-resistant starch FT-IR, XRD, DSC, SEM As a controlled release carrier for the food grade

peptide, nisin.

[135]

40. Cellulosealginate FESEM, XRD High potential to be used as high

Strength packaging materials.

[34]

41. Aluminum sulfatealginate As coagulant for wastewater treatment [136]

42. Starchcalcium alginate DSC, FT-IR, SEM For encapsulation of antioxidants [137]

43. Alginatestarch Bacterial encapsulation [138]

44. Starchalginate FT-IR For agrochemical delivery system [139]

45. Alginatesago starch-Ag-NP TGA, SEM, TEM Potential and economical wound dressing material. [140]

46. Iron/montmorillonite/alginate ICP-MS, FT-IR Photo-Fenton catalysts for water

Disinfection

[141]


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Table 1 (Continued)

Sr. No Name Techniques used for

characterization

Potential applications Reference

47. Alginate-graft-poly(ethylene glycol) SEM, NMR Encapsulation and intracellular delivery of a

bioactive growth factor

[142]

48. Calcium phosphatesodium alginate FT-IR, XRD, SEM,

ICP-OES

Drug delivery carriers [143]

49. Sodium alginate/heteropolyacid

H14[Nap5w30o110 ] (HPA)

FTIR, SEM, TGA, DSC,

UTM and contact angle

measurements

Membranes for pervaporation

Dehydration of ethanol

[144]

50. Alginate/collagen-I SEM Enhance wound healing properties [145]

51. Alginatethiol-terminated peptides UV-VS, 1 H NMR Potential application for tissue engineering [146]

52. Sodium alginatePNIPAM IR, NMR, SEM For biomedical applications [147]

53. Alginate/polyethyleneimine

and biaxially oriented poly(lactic acid)

UV-VIS, FESEM, AFM Promising alternative to non-biodegradable

synthetic food

Packaging materials

[148]

54. Prosopis Juliflora

Carbon/Ca/alginate

FT-IR, S EM For t he a dsorptive r emoval o f aniline

Blue dye (AB dye)

[149]

55. Hyaluronic acid/sodium

alginate

SEM, FT-IR,Water

contact angle

For pervaporation dehydration of ethanolwater

mixtures

[150]

56. Sodium alginatepolyacrylamide FTIR, NMR SEM,

DTATGA, XRD, PZC

For drug delivery systems [151]

57. AgNPsalginate FT-IR, SEM Treatment process for antibacterial finishing and

textiles.

[152]

58. Sodium alginate/superabsorbent polymer FT-IR, TGA, SEM Effective recycling of textile dyes from textile

effluents

[153]

59. Ag/alginate UVvis, FESEM For tissue engineering scaffolds, soft tissue

implants, antimicrobial wound dressings

[154]

60. B-cyclodextrin/acrylic a cid/sodium

alginate

FT-IR, S EM, N MR As a n agricultural w ater r etention a gent i n saline

soil

[155]

61. Polycaprolactone (PCL)/alginate FT-IR, SEM For biomedical applications [156]

62. Alginic a cid/metal coordinated

carboxylated alginic acid

FTIR, EDAX, SEM For deflouridation process [157]

63. Alginatezirconium FTIR, XRD, SEM, EDAX For deflouridation of water [158]

64. Alginatelignin SEM, Micro-CT Scaffolds for tissue engineering [159]

65. Halloysite/alginate EDX, FT-IR, FESEM, TGA Applications including bioprocessing and tissue

engineering.

[160]

66. Methacrylated alginate/PEG Bioadhesive for clinical use in biomedical

applications

[161]

67. AlginatePEGAc SEM Novel muco adhesive material for controlled drug

release

[162]

68. Calcium phosphate/alginate optical microscopy,

ESEM, TEM, SEM, FT-IR

For protein imprinting [163]

69. Alginate/HNT AFM, TEM, FTIR, XRD,

TGA

Great potential forapplicationsin tissue

engineering.

[164]

70. Znoalginate XRD, XPS Controlled environment for antimicrobial activity [165]

71. Alginatesilicate SEM For decolorization of the azo dye, reactive Red 22 [166]

72. A lginatechitosanpoly(lactic-co-glycolic

acid)

SEM For protein delivery system [167]

73. Alginate-glass ceramics SEM, EDAX, AFM, FTIR,

XRD

Useful for periodontal tissue regeneration [168]

74. Alginate/polyacrylamide SEM Promising biomaterial for cartilage tissue [169]

75. Alginategelatin SEM, FT-IR, XRD, DSC,

PALS

Membranes for enhancement of diffusion and

sorption

[170]

polysaccharides in life science are driving the development of

polysaccharides for novel (bio-molecular) applications [5561].

1.2. Reasons for choosing alginates and polyurethanes

Alginates have a potential array of commercial applications, as

they are widely used in the food and textile industries as thick-

eners, stabilizers, gel-formers, film-formers, etc. [62]. Due to the

abundance of algae in water bodies, there is a large amount of algi-

nate material present in nature with its excellent biocompatibility,

biodegradability, non-toxicity, chelating ability and relatively low

cost [63,64]. Hence, there is significant additional potential to

design sustainable biomaterials based on alginates. Alginate can be

easily modified in any form such as microspheres, microcapsules,

sponges,hydrogels, foams, elastomers, fibers, etc.This property can

increase the applications of alginate in various fields such as tis-

sue engineering and drug delivery [65]. Significant research has

been conducted on application of alginate as a bone tissue engi-

neering material [6669], therapeutic cell entrapment [7073],

nanoparticlesof alginates for drugdeliverysystems andfor enzyme

immobilization [74]. Notable amount of research article has been

published covering different aspects of alginates. Further PU has

shown excellent characteristic regarding biocompatibility with the

body cells. Following study has clearly demonstrates the poten-tial of PU regarding its use without any cytotoxicity. In one of the

reported method, preparation of regenerated silk fibroin solution

(SF) Cocoons ofB. mori silkworm was degummed 3 times in 0.5%

(w/v) Na2CO3 solution at 98100C for 30min, rinsing with dis-

tilled water to separate proteins and waxes [75].

2. Alginate: an overview

Inthe very first,alginatewas reportedby the British chemistE. C.

C. Stanfordin 1881. Alginatean anionicand hydrophilicpolysaccha-

ride is one of the most abundant biosynthesized natural materials

thatis derived primarilyfrom twosources,marineplants,i.e. brown

sea weed (40% of dry matter) and bacteria. Commercially, algi-

nates species are derived primarily from brown algae, included


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Fig. 3. Chemical procedure forsynthesis of PU(I) and PU-g-CaA (II) [113,178].

Laminaria hyperborea, Ascophyllum nodosum and Macrocystis

pyrifera. Alginates isolated from bacteria such as Azotobacterand

Pseudomonasspecies are usually not economicallyfeasible for com-

mercial applications and limited to small-scale research studies

[76,77].

In structural presentation, alginate contains linear blocks of

(14)-linked -d-mannuronic acid (M) and -l-guluronic acid(G)monomers. Typically, the blocks are composedof three different

forms of polymer segments: consecutive G residues, consecutive M

residues and alternating MG residues. The copolymer composition,

sequence and molecular weights vary with the source and species

that produce the copolymer, also reflected in their properties. Vis-

cosity depends upon molecular size, the affinity for cations and

gel forming properties are mostly related to the block structure ofguluronic acidresidue.The contentsof G-blocksmainlycontributed

to gel strength and stability [67,71,7883].

Alginates have four reactive sites for contribution in a chemical

reaction including carboxylic acid and hydroxyl functional groups,

and two relatively not sustainable bonds, i.e. 14 glycosidic

and internal glycolic bonds. The characteristics, e.g., hydrophilic-

ity, solubility, and chemical and biological properties of alginate

derivativesmay be modified by creatingnew functional groups into

the alginate backbone [84]. Carboxyl groups and hydroxyl groups

laterallyon the backbone of the alginate enable remarkably several

modification approaches to enhance or tailor the properties suchas

physicochemical, biological, mechanical, and other desired proper-

ties [85]. Sodiumalginate is water soluble andwhen it trickled into

a solution containing Ca

2+

ions, each Ca

2+

ion knocks away the two

Na+ ions. Thealginate molecule containsloadsof OH group that can

be coordinated to cations (Fig. 1a).

Whenalginate is coordinated to Na+, its a very flexible chainand

when Na+ is replaced by Ca2+ however, each Ca2+ ion (black dots in

Fig. 1b) coordinates to two alginate chains, linking them together.

The flexible chains become less flexible andform a huge network

a gel within seconds after the alginate mixture is dripped into the

water bath with the Ca2+ ions [86]. Due to its hydrophilic nature,

alginate takes a good impression (Fig. 2) in a moist environment

and can use as dental material [87].

2.1. Applications, development and limitations

Alginate forms a solid gelundermild handlingconditions whichallows it to be used for entrapping cells into beads and shapes [88].

Interestingly, cell encapsulation of some types of alginate beads

may actually enhance cell survival and growth. In addition, algi-

nate has been explored for use in liver, nerve, heart, and cartilage

tissue engineering [8993]. Pharmaceutical, food (as additive) and

technical applications (such as in print paste for the textile indus-

try) are quantitative hand the market for alginates. Alginate beads

immobilized on PU matrix increasethe degradation of O-phthalates

by enhancing the activity of Bacillus sp. cells. Widely used phtha-

late is a plasticizer used in resins causing serious terrorism threats

formulation intended to environment [94].

In some recent studies, the MW of alginates (MW

30,000690,000) and the mole fraction (FM 0.690.86) of man-

nuronate residues present in alginate molecular chains were also


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Fig. 4. Chemical procedure for the synthesis of (a) cationic aqueous PU dispersion [181], (b) anionic aqueous PU dispersion [181], (c) ionic PU dispersion extended with

TBAAlg [182] and (d) non-ionic PU dispersion [182].


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Fig. 5. SEMimages of (a)CaA and(b) PU-g-CaA; (c)XRD pattern of CaA andPU-g-CaA;(d) theinfluenceof reaction temperature on theswellingdegree of PU-g-CaA andCaA

microspheres [178].

identified as key factors relating to the immunological activity of

alginates [95]. Unfortunately, in the literature, some drawbacks

associated with alginates are poor cell adhesion and mechanical

weaknesses have been reported. As a remedy to overcome thesedraw backs, the strength and cell behavior of alginate have been

enhanced by mixing it with other materials, including the natural

polymers agarose and chitosan [93,96]. Alginates based blends,

copolymers and composites havebeen presentedin the established

literature (Table 1).

3. Alginate based polyurethanes

Functionalizationof polyurethanes withnaturalpolymers espe-

cially polysaccharide foundto be a suitable process for biomaterials

development. Alginate-based polyurethanes are perhaps more

interesting options because alginates retain advantages like low

cost, abundance and range of applications [171176].

3.1. PUAlg hydrogel

PUalginate gel compositions are potentialmaterialfor biomed-

ical application and food industry with various constituent ratios

based on an anionic PU (APU) water dispersion (WD) and sodium

alginate (AG) prepared by cross-linking with Ca+ ions. By opti-

mizing the degree of cross-linking, by varying the composition

ratio and Ca2+ quantity, systems with controlled thermo and pH-

sensitivity, swelling ratio, and strength indexes can be obtained. It

is worth to mention that the alginate contents increased the ten-

sile strength of the material films. Mixtures of APU and AG formed

structural non-Newtonian stable systems with higher viscosity in

comparison with initial components in the absence of divalent

cation [174].

The mechanical strength of alginate hydrogel is subject to

biodegradation and swelling [177,178]. Numerous attempts have

been made to control the swelling degree of alginate based mate-

rials by modifying its structure with various methods such asblending, copolymerization, etc. [178]. Because of the crystalline

character of PU, it contains high tensile strength and anti-swelling

property [179]. The PU-grafted Ca+ alginate gel, therefore, can be

synthesized by 2-hydroxyethyl methacrylate (HEMA) and dieth-

ylene glycol (DEG) capped isophrone diisocyanate (IPDI) forming

crystallizing area in the matrix of polysaccharide (Fig. 3). Grafted

PU, side chains may affect the arrangement of alginates which may

formed highly ordered crystalline region, andprovide alginatewith

physical cross-linking points. As a result the thermodynamic prop-

erties such as stability and anti-swelling stability were improved

in PU-g-CaA samples due to intensified intermolecular force [178].

One recent application of PUalginate hydrogels is in molecules

imprinting such as sugars, amino acids and metal ions. For bovine

serum albumin (BSA) imprinting, the PU grafted calcium alginate(PU-g-CaA) hydrogel microspheres were synthesized and charac-

terized. It has been previously confirmed that the grafted PU side

chains have constructed physical cross-linking points and improve

the mechanical and chemical stability of hydrogel [178] which is

therefore expected to be benefited for protein recognition which

is confirmed by the enhanced imprinting efficiency and selective

factors obtained at high grafting ratio. Compared with CaA, PU-g-

CaA MIPs exhibit higher rebindingselectivityand are more capable

of recognizing and separating target protein molecules, having

promising applications as advanced material for chemical sensing

and bio-separation [180]. Preparation of alginate-based PUs had

beena significant challenge because of the final polymers tendency

to the phase separation [174]. Alginate and PU are two incom-

patible polymers with different glass transition temperatures.


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Nevertheless, the development of such methods to improve the

compatibility between the two polymers is a challenge.

3.2. PUAlg blend

Keeping in view the aim of improving compatibility of two

polymers, aqueous PU dispersion sodium alginate compositions

(PUD/SA) were synthesized. PU dispersions were prepared with

polytetramethylene glycol (PTMG) and isophorone diisocyanate

(IPDI), extended with dimethylol propionic acid (DMPA) (Fig. 4a

and b). Both storage modulus andtan versus temperature showedidentical Tg and other thermal transition for control PUD and

its blends with sodium alginate. The SEM and EDX showed the

presence of alginate and its distribution as agglomerations in

PU matrix. The surface properties including contact angle values

decreased with increasing sodium alginate content that ascribed

increase in the hydrophilicity of the blends. Such transformation

was attributed to the presence of hydrophilic carboxylate, hydroxyl

and ether functional groups attached to the alginate molecules

[171]. Another approach for the preparation of compatible algi-

nate based polyurethane withdesired properties was the synthesis

of novel soluble alginate-based PUs in common aprotic organic

solvent by the reaction of NCO-terminated PU prepolymer and tri-

butyl ammonium alginate (TBA-Alg) for the first time (Fig. 4c).The presence of TBA-Alg into the backbone of PU was revealed

byspecificpeaksof uronicacid residues in 1H NMR. Theionic nature

of PU backbone not only effects on thermal properties of samples,

but also changes the morphology of chemically-bonded alginate.

Both polyether and polyester based non-ionic PUs extended by

TBA-Alg illustrated the distinct alginate, i.e. aggregate-like struc-

tures of alginate into the matrix of PU (Fig. 4d) whereas those

ionomers extended by alginate were appeared as continuous sys-

tems at nanoscale [182].

The PU segment had a very important impact on the morphol-

ogy of gel surface as shown in Fig. 5a and b. The Ca+ alginate

(CaA) hydrogel microspheres possessed coarse surface and big cav-

ity while PU-g-CaA showed a dense and smooth surface. As shown

in Fig. 5c, the CaA exhibits characteristic 2values at 13.1, 25.06

and 39.42, which is due to the stronger hydrogen as well as polar

intramolecular andintermolecular interactions. In thisstudy, sharp

peak observed at 18.46 correspond to PU-g-CaA in-spite of 39.42,

which is attributed to the addition of carbamate groups and ether

bond. Apart from above,PU interferes with the arrangementof CaA

forming highly order crystal region, which indicate that PU was

grafted on to the CaA. The relationship between reaction tempera-

ture and swelling degree of PU-g-CaA is presented in Fig. 5d. It can

be observed that the increase in of reaction temperature results

to first swelling degree decreased and then increased. Such phe-

nomenon is mainly attributed to PU side chains that intense the

intermolecular interaction, forming crystal structure and facilitat-

ing the loss of inner water. Meanwhile, the hydrophobic nature of

PU also resists water from inward diffusion.

3.3. PUAlg elastomer

Modification in the chemical structure of PU to improve the

incompatibility of alginate based PU was previously focused

in researches [181184]. The role of emulsifier on the final

properties of composites containing PUDs and alginates was rel-

atively a new strategy, studied by Daemi et al. [181,182]. Two

different anionic and cationic PUs samples using DMPA and N-

methyldiethanolamine emulsifiers respectively were synthesized.

A series of the alginate-based PUEs were formulated by solution

blending of the PUDs and sodium alginate. The nano-composite

elastomers of cationic PUs and SA showed excellent miscibility,

excellent mechanical properties with high elongation at break and

Fig. 6. Invitrotestof ratfibroblast cell (a)thecellsgrownin cell culture media only,

(b) thecells grown in EGF-loaded AHPtreated media for48 h [185].

increased hydrophilicity that may be due to formation of tertiary

ammonium carboxylate salts produced from electrostatic inter-

action between cationic PU and poly-anionic alginate while the

anionic ones were appeared as the relatively incompatible ingre-

dients and their elongation was significantly dropped because of

the immiscibility of the SA and anionic PUs [181]. Alginates and

other natural polysaccharides can be used in different applica-

tions in drug delivery and control release systems as they can

be used as micro and nano encapsulation agents [183,184]. Some

investigation has been reported for drug delivery application of

PUAlg elastomer/hydrogel [185189], in vitro test of rat fibro-

blast cells, the cells grown in cell culture media only and the cells

grown in epidermal growth factor (EGF)-loaded AHP treated media

were studied. The EGF-treated, EGF-loaded alginate hydrogel, andEGF loaded alginate hydrogel polyurethane (AHP) cells were pro-

liferated 2.7, 2.5, and 2.2 times compared with cell only group,

respectively [185]. Fig. 6 shows that AHP treated well group was

much more packed with cells. However, EGF-treated cells were the

most proliferated, hydrogel-treated cells were the next, and AHP-

treated cells were the last order. Regardingthe EGF release profiles

from alginate hydrogel and AHP at four different pH conditions;

the cumulative release increased rapidly with time and reached an

equilibriumvalue aftera certain time. In general, the release behav-

ior of EGF was similar withthat of BSA since bothof these drugs are

protein drug [185]. However, EGFrelease rate from alginate hydro-

gel only and AHP was different. EGF release rate from AHP was

slower than that from alginate hydrogel because of its composite

structure.


9/11


Fig. 7. (a) Schemeof theelementary unit of APU, (b) schematic performance of alginate unit [174].

3.4. PUAlg nanocomposite

Compatible aqueous cationic PUDsodium alginate nanoparti-

cles (CPUD/SA) elastomers were prepared by solution blending of

cationic PUDs based on PTMG and IPDI extended with N-methyl

diethanolamine (MDEA), 1,4-BDO chain extenders and sodium

alginate (SA). Pristine CPUD and its nano-composite elastomers

with SA showed excellent miscibility that arise from different

charges of both anionic alginate and cationic PU and hydrogen

bonding which was supported by DMTA and FTIR results. The

prepared composites indicated two interesting nano-bead (low

molecular weight SA) and nano-rod (higher molecular weight SA)

morphologies in respect of different molecular weights of sodium

alginate samples proved by SEM and EDX. The phase separation of

PU segments decreased resulting in lower elongation and higher

mechanical strength, in thepresence of greater amounts of Na algi-

nate. Moreover, with increasing alginate content in the elastomers,

the thermal stability and hydrophilicity increases because of the

presence of quite thermally stable uronic acid residues and pres-

ence of hydrophilic carboxylate and hydroxyl groups [172]. While

progressing in another study, anionic water based PU (APU) was

formed (Fig. 7) as a result of interaction of an isocyanate precur-

sor on the basis of oligo(oxytetramethylene) glycol (MM1000) and

aliphatic diisocyanate (HMDI) (1:2) with dianhydride of pyromel-

litic acid and dihydrazide of dicarbonic acid in acetone solutionfollowed by carboxylic groups transfer to a salt form and consecu-

tive dispersion in water [174].

In a study [174], the APU and aqueous solution of alginate

(5wt.%) were mixed in various compositions and the sample films

were cast by pouring the compositions on glass substrates, dried

at room temperature for 72h, and then dried at 60C to constant

weight in a vacuum oven. The prepared material was used for var-

ious potential applications.

4. Summary

From the last fewdecades the trend of utilization of polysaccha-

ride in various industrial fields owing to their structural diversity,

biodegradability, biocompatibility, abundance, non-toxicity and

specific bioactive properties is rapidly increasing. The most abun-

dant marine polysaccharide, alginate, with their inherent well

known gelling and stabilizing properties proved to be a poten-

tial candidate for syntheticmodifiedbiomaterials.However certain

limitations associated with this unique polymer can be overcome

either by modification in their structure or blending with other

natural and synthetic polymers. Polyurethanes/alginate hydrogels,

elastomers and nanocomposites systems with novelty in their

propertiesare making thealginates a potent polymer to be explored

further.

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Alginate Based Polyurethanes a Review of Recent Advances and Perspective 2015 International Journal of Biological Macromolecules