Biodegradable Polyurethane Elastomers for Biomedical Applications – Synthesis Methods and Properties

Biodegradable polyurethane elastomers (BioEPUR) are becoming increasingly important as biomaterials because they have excellent chemical, physico-mechanical and biological properties. This review presents the recent developments on BioEPUR and their potential applications in the biomedical and pharmaceutical fields. The aim of this work is to present an overview of the various methods of synthesis and properties of biomedical BioEPUR. Polyurethanes-based aliphatic or cycloaliphatic diisocyanates and polyesters, poly(ester-carbonate)s or copolymers of heterocyclic monomers were discussed.     

Carbohydrate crosslinked biocompatible polyurethanes: Synthesis,characterization, and drug delivery studies

A series of novel polyurethanes (PUs) with carbohydrate crosslinkers was synthesized. The drug loading and release kinetics were studied by using lamotrigine as a model drug. The polymers were designed in such a way that the drug release was tailored by differences in the stoichiometry of polymers. All the PUs were characterized for thermal and morphological properties by using differential scanning calorimetry and thermogravimetric analysis and scanning electron microscope , respectively. The encapsulation of drug inside PU matrix was confirmed via Fourier transform ‐ infrared (FT‐IR) spectra and scanning electron microscope . The kinetics and release mechanisms were observed to be a function of stoichiometric parameters such as type of crosslinker, polyol/crosslinker ratio and polyol/chain extender ratio. All the PUs were observed to be non‐cytotoxic in normal lung cell line L132. The synthesized PUs exhibited good mechanical strength, tunable release rates and biocompatibility that can be utilized in biomedical applications like wound dressing, biomedical implants , and drug delivery carriers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42223.     

Radiopaque polyurethanes with flexible iodine‐containing chain extender

Iodinated polyurethanes (IPUs) with radiopaque property were prepared using poly(oxytetramethylene) glycol, 4,4′‐diphenylmethane diisocyanate, and a novel chain extender. The chain extender, described as N‐(1,3‐dihydroxypropan‐2‐yl)‐2,3,5‐triiodobenzamide, was synthesized in two steps from 2‐aminopropane‐1,3‐diol and 2,3,5‐triiodobenzoic acid with a high yield. A thorough study on the chemical structure, mechanical properties, radiopacity, and physiological properties of the IPUs was conducted. It is revealed that with increasing content of chain extender, the molecular weights of IPUs decreased slightly while the tensile modulus and breaking strength of IPUs increased significantly, illustrating an excellent comprehensive performance. With iodine content high to about 16 wt %, the IPU sample is equal to the aluminum plate with the same thickness in X‐ray radiopacity, meaning that the synthesized polyurethanes are promising as radiopaque materials. The oxidative degradation and cytotoxicity tests illustrated a good performance of stability and biocompatibility for the IPUs. It confirmed that the as‐synthesized IPUs are promising for biomedicine applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42693.     

Enhanced thermal stability of biomedical thermoplastic polyurethane with the addition of cellulose nanocrystals

Freeze‐dried cellulose nanocrystals (CNCs) were dispersed in the thermoplastic polyurethane [Pellethane 2363‐55D (P55D)] by a solvent casting method to fabricate CNC‐reinforced nanocomposites. This study demonstrated that the addition of small amounts (1–5 wt %) of CNCs to P55D increased the thermal degradation temperature while maintaining a similar stiffness, strength, and elongation of the neat P55D. CNC additions to P55D did not alter the glass‐transition temperature, but the onset decomposition temperature was shifted from 286 to 327°C when 1 wt % CNCs was dispersed in the matrix. The higher onset decomposition temperature was attributed to the formation of hydrogen bonds between the hydroxyl groups on the CNC surface and urethane groups in the hard block of P55D. The ultimate tensile strength and strain to failure (ε_f) of the nanocomposites were minimally affected by additions up to 5 wt % CNCs, whereas the elastic modulus was increased by about 70%. The observation that ε_f was unchanged with the addition of up to 5 wt % CNCs suggested that the flow/sliding of the hard blocks and chains were not hindered by the presence of the CNCs during plastic deformation. The ramifications of this study was that CNC additions resulted in wider processing temperatures of P55D for various biomedical devices while maintaining a similar stiffness, strength, and elongation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41970.     

Examination of radio‐opacity enhancing additives in shape memory polyurethane foams

Three microparticle additives, tungsten (W), zirconium oxide (ZrO₂) , and barium sulfate (BaSO₄) were selected to enhance the radio‐opacity in shape memory polymer (SMP) foam biomaterials. The addition of filler causes no significant alterations of glass transition temperatures, density of the materials increases, pore diameter decreases, and total volume recovery decreases from approximately 70 times in unfilled foams to 20 times (4% W and 10% ZrO₂). The addition of W increases time to recovery; ZrO₂ causes little variation in time to shape recovery; BaSO₄ increases the time to recovery. On a 2.00 mean X‐ray density (mean X.D.) scale, a GDC coil standard has a mean X.D. of 0.62 ; 4% W enhances the mean X.D. to 1.89, 10% ZrO₂ to 1.39 and 4% BaSO₄ to 0.74. Radio‐opacity enhancing additives could be used to produce SMP foams with controlled shape memory kinetics, low density , and enhanced X ‐ray opacity for medical materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42054.     

Synthesis and characterization of biodegradable polyurethanes with unsaturated carbon bonds based on poly(propylene fumarate)

The segmented polyurethanes synthesized from biodegradable polyesters are very promising and widely applicable because of their excellent physiochemical properties. Poly(propylene fumarate) (PPF), a kind of linear aliphatic unsaturated and biodegradable polyesters, has been well recognized in biomedical applications. Herein novel polyurethanes (PPFUs) were synthesized based on the PPF‐diol, diisocyanates such as 1,6‐diisocyanatohexane, l ‐lysine diisocyanate, and dicyclohexylmethane diisocyanate, and chain extenders such as 1,4‐butylene glycol and l ‐lysine methyl ester hydrochloride (Lys‐OMe·2HCl). By varying the types of diisocyanates, and chain extenders, and the proportion of hard segments, the PPFUs with tailored properties such as mechanical strength and degradation rate were easily obtained. The synthesized PPFUs had an amorphous structure and slight phase separation with strong hydrogen bonding between the soft segments and the hard segments. The elongation of PPFU elastomers reached over 400% with a slow deformation‐recovery ability. The PPFUs were more sensitive to alkaline (5 M, NaOH) hydrolysis than acid (2 M, HCl) and oxidative (30 vol.%, H₂O₂) erosion. The tensile strength, deformation‐recovery ability, and glass transition temperature of the PPFUs were improved with the increase of hard segment proportion, while the degradation rate was opposite because of the faster degradation of the soft segments. In vitro culture of smooth muscle cells in the extractant of the PPFUs or on the PPFUs film surface revealed low cytotoxicity and good cytocompatibility in terms of cell viability, adhesion, and proliferation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42065.     

Modification of narrow‐spectrum peptidomimetic polyurethanes with fatty acid chains confers broad‐spectrum antibacterial activity

Each year, thousands of patients die from antimicrobial‐resistant bacterial infections that fail to respond to conventional antibiotic treatment. Antimicrobial polymers are a promising new method of combating antibiotic‐resistant bacterial infections. We have previously reported the synthesis of a series of narrow‐spectrum peptidomimetic antimicrobial polyurethanes that are effective against Gram‐negative bacteria, such as Escherichia coli; however, these polymers are not effective against Gram‐positive bacteria, such as Staphylococcus aureus. With the aim of understanding the correlation between chemical structure and antibacterial activity, we have subsequently developed three structural variants of these antimicrobial polyurethanes using post‐polymerization modification with decanoic acid and oleic acid. Our results show that such modifications converted the narrow‐spectrum antibacterial activity of these polymers into broad‐spectrum activity against Gram‐positive species such as S. aureus, however, also increasing their toxicity to mammalian cells. Mechanistic studies of bacterial membrane disruption illustrate the differences in antibacterial action between the various polymers. The results demonstrate the challenge of balancing antimicrobial activity and mammalian cell compatibility in the design of antimicrobial polymer compositions. © 2019 Society of Chemical Industry     

Carbon nanotubes‐filled thermoplastic polyurethane–urea and carboxylated acrylonitrile butadiene rubber blend nanocomposites

This article reports the preparation and characterization of multiwalled carbon nanotubes (MWCNTs)‐filled thermoplastic polyurethane–urea (TPUU) and carboxylated acrylonitrile butadiene rubber (XNBR) blend nanocomposites. The dispersion of the MWCNTs was carried out using a laboratory two roll mill. Three different loadings, that is, 1, 3, and 5 wt % of the MWCNTs were used. The electron microscopy image analysis proves that the MWCNTs are evenly dispersed along the shear flow direction. Through incorporation of the nanotubes in the blend, the tensile modulus was increased from 9.90 ± 0.5 to 45.30 ± 0.3 MPa, and the tensile strength at break was increased from 25.4 ± 2.5 to 33.0 ± 1.5 MPa. The wide angle X‐ray scattering result showed that the TPUU:XNBR blends were arranged in layered structures. These structures are formed through chemical reactions of ? NH group from urethane and urea with the carboxylic group on XNBR. Furthermore, even at a very low loading, the high degree of nanotubes dispersion results in a significant increase in the electrical percolation threshold. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40341.     

Effect of diisocyanate on pyridine containing shape memory polyurethanes based on N,N‐bis(2‐hydroxylethyl)isonicotinamide

This article demonstrates a comparative investigation about the effect of diisocyanate on pyridine containing shape memory polyurethanes (Py‐SMPUs), which are synthesized with N,N‐bis(2‐hydroxylethyl)isonicotinamide (BINA) and four different diisocyanates: 1,6‐hexanediisocyante (HDI), isophorone diisocyanate (IPDI), methylene diphenyl diisocyanate (MDI), and tolylene diisocyanate (TDI). Results show that all BINA–SMPU systems have amorphous reversible phase. Comparatively, the MDI–BINA and TDI–BINA systems show higher T_g; and the HDI–BINA and IPDI–BINA systems show better thermal stability. In addition, the HDI–BINA and the IPDI–BINA systems exhibit good thermal‐induced shape memory effect and good moisture‐sensitive shape memory effect due to their better moisture absorption properties. Particularly, the HDI–BINA system has better response speed and better shape recovery. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40721.     

Synthesis and characterization of polyurethane foam matrices for the support of granular adsorbent materials

Polyurethane foams with different formulations were synthesized and characterized for use as supporting matrices of granular solid adsorbents. The open cell content, specific gravity, thermal stability, and hydrophobicity were determined and related to the formulation composition. The synthesized foams had open cell contents of 88.1–98.5% and specific gravity values of 120–28 kg m^?3. The thermal stability of the prepared foams was influenced mainly by the water content and the type of isocyanate used. The hydrophobicity was assessed by an analysis of the water adsorption isotherms determined on selected foams, and a correlation between these results and the formulation of the foams was attempted. Two types of activated carbons were supported in a polyurethane matrix. The adsorption characteristics evaluated before and after the supporting procedure, by nitrogen adsorption, revealed that there was only a moderate surface area reduction of 15–20%. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2045–2053, 2004