alginate based polyurethanes a review of recent advances and perspective 2015 international journal...
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7/25/2019 Alginate Based Polyurethanes a Review of Recent Advances and Perspective 2015 International Journal of Biologic
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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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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.
-
7/25/2019 Alginate Based Polyurethanes a Review of Recent Advances and Perspective 2015 International Journal of Biologic
9/11
K.M. Zia et al. / International Journal of Biological Macromolecules 79 (2015) 377387 385
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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