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Synthesis and characterization of PIL/pNIPAAm hybrid hydrogels

  • Sylvia Pfensig EMAIL logo , Daniela Arbeiter , Klaus-Peter Schmitz , Niels Grabow , Thomas Eickner and Sabine Illner
Published/Copyright: September 30, 2016
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Current Directions in Biomedical Engineering
From the journal Current Directions in Biomedical Engineering Volume 2 Issue 1

Abstract

In this study, varying amounts of NIPAAm and an ionic liquid (IL), namely 1-vinyl-3-isopropylimidazolium bromide ([ViPrIm]+[Br]−), have been used to synthesize hybrid hydrogels by radical emulsion polymerization. Amounts of 70/30%, 50/50%, 30/70%, 15/85% and 5/95% (wt/wt) of PIL/pNIPAAm were used to produce hybrid hydrogels as well as the parental hydrogels. The adhesive strength was investigated and evaluated for mechanical characterization. Thermal properties of resulting hydrogels have been investigated using differential scanning calorimetry (DSC) in a default heating temperature range (heating rate 10 K min−1). The presence of poly ionic liquids (PIL) in the polymer matrix leads to a moved LCST (lower critical solution temperature) to a higher temperature range for certain hybrid hydrogels PIL/pNIPAAm. While pNIPAAm exhibits an LCST at 33.9 ± 0.3°C, PIL/pNIPAAm 5/95% and PIL/pNIPAAm 15/85% were found to have LCSTs at 37.6 ± 0.9°C and 52 ± 2°C, respectively. This could be used for controlled drug release that goes along with increasing body temperature in response to an implantation caused infection.

Keywords: hydrogel; LCST; N-vinylimidazolium; pNIPAAm; polymeric ionic liquids

1 Introduction

Hydrogels, as a separate class of polymers, are three-dimensional linked structures. They build a network of covalent and non-covalent interactions, gaining considerably in volume in the presence of water.

Biomaterials used as biocompatible coatings for implants have to support tissue integration and should offer antibacterial properties at once. Hydrogels as coatings for biomedical implants are similar to human tissue and often exhibit very good biocompatibility [1]. Furthermore, hydrogels offer inclusion and transportation of drugs [2]. The characterization of stimuli-responsive hydrogels, with an enhanced swelling behaviour responding to a change in environmental variables like temperature or pH, allows further applications, e.g. for controlled drug release [3]. Disadvantages of hydrogels are weak mechanical properties, but amazingly the toughness and fatigue resistance can be improved by crosslinking copolymerization [4].

In this study, we report first the copolymerization of the ionic liquid (IL) [ViPrIm]+[Br]− with NIPAAm. Whereas pNIPAAm is the best investigated thermo-responsive hydrogel with an LCST transition at 32°C [5], [6], the N-vinylimidazolium based IL [ViPrIm]+[Br]− is a less researched attractive co-monomer in biomedical applications.

Ionic liquids are classified as organic salts and existent in liquid texture at temperatures lower than 100°C without the presence of water. Specific properties can be set by structural modification [7]. By free radical polymerization of e.g. reactive vinyl groups in the presence of a crosslinker and a strong oxidizing agent stable parental and hybrid hydrogel with a defined shape can be successfully synthesized. The aim was to generate hybrid hydrogels with varied swelling properties using two different monomers with reactive vinyl and acryl groups for copolymerization. As key parameter for biomedical application the adhesive strength on implant surfaces was investigated on a specially built test setup. To investigate LCST transition as an endothermic process differential scanning calorimetry (DSC) was used.

2 Material and methods

2.1 Synthesis

In a first step, the IL 1-vinyl-3-isopropyl-imidazolium bromide ([ViPrIm]+[Br]−) was prepared following a procedure already described [8].

Hybrid hydrogels have been synthesized by using varying amounts of N-isopropylacrylamide (NIPAAm) and [ViPrIm]+[Br]−. Defined masses were mixed and dissolved in distilled water. Constant amounts of N,N′-methylene-bisacrylamide (MBAA) as crosslinker, ammonium peroxidesulfate (APS) as initiator and tetramethylethylenediamine (TEMED) as catalyst were added subsequently for radical polymerization into optional shapes.

Figure 1 illustrates the amounts of basic raw materials for synthesis of hybrid hydrogels PIL/pNIPAAm. The materials and chemicals have been purchased from Sigma-Aldrich (St Louis, MO, USA) and used as received.

Figure 1: Amounts of components for synthesis of hydrogels PIL and pNIPAAm and hybrid hydrogels PIL/pNIPAAm 1/2/3/4/5.
Figure 1:

Amounts of components for synthesis of hydrogels PIL and pNIPAAm and hybrid hydrogels PIL/pNIPAAm 1/2/3/4/5.

2.2 Characterization of adhesive strength

To simulate the connection of hydrogels to the surface of cardiovascular implants, a determination of their adhesive strength was established in dependence on DIN SPEC 91063:2011-07.

Parental hydrogels of PIL and pNIPAAm and hybrid hydrogels PIL/pNIPAAm 1/2/3 have been manufactured by casting the solution into a mold (Figure 2), where the gel polymerized for approximately 10–20 min covered by a glass plate. The stainless steel surface of the appliance wasn’t biofunctionalyzed before and no coupling agents or adhesives were used.

Figure 2: Appliance of stainless steel to determine the adhesive strength of hydrogels.
Figure 2:

Appliance of stainless steel to determine the adhesive strength of hydrogels.

The sticky tape was removed and the free flap was fixed between the upper clamping jaws, while the appliance itself was placed between the lower clamping jaws of the tensile testing machine Zwick/Roell BT1-FR2.5TN.D14 (Zwick, Ulm, Germany). The sample was peeled off of the rail for at least 50 mm under uniaxial strain with a testing speed of 20 mm min−1. To evaluate the test results the peel off strength (σA) is calculated as the difference of the measured peel off force (FAb) and the sample width (b0):

(1)σA=FAb/b0

2.3 Thermal characterization

Differential scanning calorimetry was used for investigation of the basic raw materials NIPAAm and [ViPrIm]+[Br]− and to compare thermal properties of parental hydrogels pNIPAAm and PIL with those of developed hybrid hydrogels PIL/pNIPAAm. The thermo-behaviour of all samples was monitored on a DSC1 STARe System (Mettler-Toledo, Gießen, Germany).

In a first instance, the melting temperature of NIPAAm and [ViPrIm]+[Br]− was investigated. For each material a sample of approximately 5–10 mg was placed on aluminium DSC plates and sealed. Surrounded by nitrogen the samples were heated from 20°C to 200°C at 10 K min−1.

Furthermore, three samples of parental hydrogels PIL and pNIPAAm and hybrid hydrogels PIL/pNIPAAm 1/2/3/4/5 have been analysed, respectively. Samples of approximately 5–10 mg were exempted of excessive water after swelling in PBS buffer solution (pH 7.38) for 24 h and weighed on a microscale before DSC measurement. Placed on aluminium plates and sealed as well, thermal scans of the samples were conducted at 10 K min−1 to determine their LCST values as an endothermic peak during a process of heating from 0°C to 80°C.

3 Results

3.1 Adhesive strength

A test to determine the adhesive strength was executed for parental hydrogels PIL and pNIPAAm and for hybrid hydrogels PIL/pNIPAAm 1/2/3.

PIL and PIL/pNIPAAm 1 hydrogels couldn’t be peeled off without multiple cracks from the very first. For pNIPAAm, PIL/pNIPAAm 2 and PIL/pNIPAAm 3 it was feasible to peel off the hydrogels completely without a crack. The peel off strength (σA) of those hydrogels was lower than the tensile strength. The following Table 1 represents the calculated peel off strength (σA) of hydrogels.

Table 1:

Peel off strength (σA) of hydrogels PIL/pNIPAAm 2/3 and pNIPAAm as the difference of measured peel off force and sample width (10 mm).

HydrogelMass ratio (wt%)σA (N/10 mm)
PIL/pNIPAAm 250/500.04
PIL/pNIPAAm 330/700.09
pNIPAAm0/1000.11

3.2 Thermal characterization

The heat flow of basic raw materials NIPAAm and [ViPrIm]+[Br]− was studied as a function of increasing temperature to determine the melting temperatures of both materials (Figure 3). Figure 3 illustrates a sharp endothermic melting peak around 50–70°C for NIPAAm. In contrast, [ViPrIm]+[Br]− exhibited a broad melting peak in the range 155–170°C. The maximum of each peak indicated the melting point, respectively.

Figure 3: Heat flow as a function of increasing temperature and melting point (MP), respectively of a sample of NIPAAm (12.45 mg) and [ViPrIm]+[Br]− (16.88 mg) at 10 K min−1 using DSC.
Figure 3:

Heat flow as a function of increasing temperature and melting point (MP), respectively of a sample of NIPAAm (12.45 mg) and [ViPrIm]+[Br]− (16.88 mg) at 10 K min−1 using DSC.

Figure 4 illustrates the heat flow of swollen parental and hybrid hydrogels as a function of increasing temperature in a range 10–80°C. A lower critical solution temperature for pNIPAAm as well as PIL/pNIPAAm 5 and PIL/pNIPAAm 4 was shown.

Figure 4: Heat flow as a function of increasing temperature of the swollen hydrogels at 10 K min−1 using DSC. LCST of pNIPAAm and PIL/pNIPAAm 4/5 is illustrated.
Figure 4:

Heat flow as a function of increasing temperature of the swollen hydrogels at 10 K min−1 using DSC. LCST of pNIPAAm and PIL/pNIPAAm 4/5 is illustrated.

While the hybrid hydrogels PIL/pNIPAAm 5 and PIL/pNIPAAm 4 exhibited broad LCST transitions (35–44°C and 40–60°C), pNIPAAm showed its relatively sharp characteristically LCST around 34°C. In Table 2, a review of LCST of investigated hydrogels is given (n = 3). The hydrogels PIL and PIL/pNIPAAm 1/2/3 exhibited a broad and featureless DSC profile within the temperature range.

Furthermore all hybrid hydrogels and PIL exhibited an artefact as a small and sharp exothermic peak around 26°C.

Table 2:

Measured LCST of investigated hydrogels pNIPAAm and PIL/pNIPAAm 4/5 (mean ± SD).

HydrogelMass ratio (wt%)σA (N/10 mm)
PIL/pNIPAAm 415/8552 ± 2
PIL/pNIPAAm 55/9537.6 ± 0.9
pNIPAAm0/10033.9 ± 0.3

4 Discussion

In the presented study hybrid hydrogels of pNIPAAm and PIL were synthesized successfully by adding crosslinker, initiator and catalyst to a solution of the main components.

The adhesive strength of hydrogels to a stainless steel substrate was investigated to simulate the connection of hydrogels to the surface of cardiovascular implants. No peel off strength (σA) could be calculated for PIL and PIL/pNIPAAm 1 hydrogels. The tensile strength was higher than interconnections within the hydrogel matrix so that the hydrogels disintegrated. In a first test, increasing peel off strength was observed for hybrid hydrogels with higher amount of pNIPAAm. To make a clear assessment about the correlation between peel off strength and the behaviour of hydrogels as coatings for implant surfaces, further tests will be necessary.

For thermal characterization, DSC was used determining material properties as the melting point. Furthermore, hydrogels have been investigated on existence of LCST transition. No explicit statement for an artefact that all hydrogels exhibited around 26°C could be made. The thermo-responsive hydrogel pNIPAAm showed a characteristically LCST at 33.9 ± 0.3°C. Hybrid hydrogels with high amounts of NIPAAm exhibited a shifted and broader endothermic peak indicating LCST transition. The hybrid hydrogel PIL/pNIPAAm 5 with an amount of 5% IL and 95% NIPAAm exhibited an LCST at 37.6 ± 0.9°C, while PIL/pNIPAAm 4 with an amount of 15% IL and 85% NIPAAm exhibited an LCST at 52 ± 2°C. Thus, it could be revealed, that LCST of pNIPAAm can be influenced and shifted to higher temperatures by copolymerization with the IL 1-vinyl-3-isopropylimidazolium bromide.

In conclusion, hybrid hydrogels of NIPAAm and [ViPrIm]+[Br]− have been synthesized successfully in different mass ratios with new deviating material properties. Characterization of adhesive strength of parental and hybrid hydrogels exhibited significant differences. Thermal characterization by DSC demonstrated, that LCST of pNIPAAm can be influenced significantly by co-polymerization of NIPAAm with [ViPrIm]+[Br]−. This allows an adjustment of LCST and might be useful for controlled drug release to treat infection after medical implantation that goes along with increasing body temperature.

Built on these findings, a continuative evaluation containing the thermo-responsive swelling behavior and further mechanical characteristics of the hybrid hydrogels will be published.

Acknowledgement

Financial support by the Federal Ministry of Education and Research (BMBF) within RESPONSE “Partnership for Innovation in Implant Technology” is gratefully acknowledged.

Author’s Statement

Research funding: The author state no funding involved. Conflict of interest: Authors state no conflict of interest. Material and Methods: Informed consent: Informed consent is not applicable. Ethical approval: The conducted research is not related to either human or animal use.

References

[1] Buwalda SJ, Boere KWM, Dijkstra PJ, Feijen J, Vermonden T, Hennink WE. Hydrogels in a historical perspective: from simple networks to smart materials. J Control Release. 2014;190:254–73.10.1016/j.jconrel.2014.03.052Search in Google Scholar PubMed

[2] Caló E, Khutoryanskiy VV. Biomedical applications of hydrogels: a review of patents and commercial products. Eur Polym J. 2015;65:252–67.10.1016/j.eurpolymj.2014.11.024Search in Google Scholar

[3] Chung J, Yokoyama M, Aoyagi T, Sakurai Y, Okano T. Effect of molecular architecture of hydrophobically modified poly(N-isopropylacrylamide) on the formation of thermoresponsive core-shell micellar drug carriers. J Control Release. 1998;53:119–30.10.1016/S0168-3659(97)00244-7Search in Google Scholar PubMed

[4] Sun J-Y, Zhao X, Illeperuma WRK, Chaudhuri O, oh KH, Mooney DJ, et al. Highly stretchable and tough hydrogels. Nature. 2012;489:133–6.10.1038/nature11409Search in Google Scholar PubMed PubMed Central

[5] Heskins M, Guillet JE. Solution properties of poly(N-isopropylacrylamide). J Macromol Sci. 1968;A2:1441–55.10.1080/10601326808051910Search in Google Scholar

[6] Schild HG, Tirrel DA. Microcalorimetric detection of lower critical solution temperatures in aqueous polymer solutions. J Phys Chem. 1990;94:4352–6.10.1021/j100373a088Search in Google Scholar

[7] Angell AC, Ansari Y, Zhao Z. Ionic liquids. Past, present and future. Faraday Discuss. 2012;514:9–27.10.1039/C1FD00112DSearch in Google Scholar

[8] Pinaud J, Vignolle J, Gnanou Y, Taton D. Poly(N-heterocyclic-carbene)s and their CO 2 adducts as recyclable polymer-supported organocatalysts for benzoin condensation and transesterification reactions. Macromolecules. 2011;44:1900–8.10.1021/ma1024285Search in Google Scholar

Published Online: 2016-9-30
Published in Print: 2016-9-1

©2016 Sylvia Pfensig et al., licensee De Gruyter.

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

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https://doi.org/10.1515/cdbme-2016-0004
Keywords for this article
hydrogel; LCST; N-vinylimidazolium; pNIPAAm; polymeric ionic liquids
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BY-NC-ND 4.0

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  58. Application of microwave sensor technology in cardiovascular disease for plaque detection
  59. Artificial blood circulatory and special Ultrasound Doppler probes for detecting and sizing gaseous embolism
  60. Detection of microsleep events in a car driving simulation study using electrocardiographic features
  61. A method to determine the kink resistance of stents and stent delivery systems according to international standards
  62. Comparison of stented bifurcation and straight vessel 3D-simulation with a prior simulated velocity profile inlet
  63. Transient Euler-Lagrange/DEM simulation of stent thrombosis
  64. Automated control of the laser welding process of heart valve scaffolds
  65. Automation of a test bench for accessing the bendability of electrospun vascular grafts
  66. Influence of storage conditions on the release of growth factors in platelet-rich blood derivatives
  67. Cryopreservation of cells using defined serum-free cryoprotective agents
  68. New bioreactor vessel for tissue engineering of human nasal septal chondrocytes
  69. Determination of the membrane hydraulic permeability of MSCs
  70. Climate retainment in carbon dioxide incubators
  71. Multiple factors influencing OR ventilation system effectiveness
  72. Evaluation of an app-based stress protocol
  73. Medication process in Styrian hospitals
  74. Control tower to surgical theater
  75. Development of a skull phantom for the assessment of implant X-ray visibility
  76. Surgical navigation with QR codes
  77. Investigation of the pressure gradient of embolic protection devices
  78. Computer assistance in femoral derotation osteotomy: a bottom-up approach
  79. Automatic depth scanning system for 3D infrared thermography
  80. A service for monitoring the quality of intraoperative cone beam CT images
  81. Resectoscope with an easy to use twist mechanism for improved handling
  82. In vitro simulation of distribution processes following intramuscular injection
  83. Adjusting inkjet printhead parameters to deposit drugs into micro-sized reservoirs
  84. A flexible standalone system with integrated sensor feedback for multi-pad electrode FES of the hand
  85. Smart control for functional electrical stimulation with optimal pulse intensity
  86. Tactile display on the remaining hand for unilateral hand amputees
  87. Effects of sustained electrical stimulation on spasticity assessed by the pendulum test
  88. An improved tracking framework for ultrasound probe localization in image-guided radiosurgery
  89. Improvement of a subviral particle tracker by the use of a LAP-Kalman-algorithm
  90. Learning discriminative classification models for grading anal intraepithelial neoplasia
  91. Regularization of EIT reconstruction based on multi-scales wavelet transforms
  92. Assessing MRI susceptibility artefact through an indicator of image distortion
  93. EyeGuidance – a computer controlled system to guide eye movements
  94. A framework for feedback-based segmentation of 3D image stacks
  95. Doppler optical coherence tomography as a promising tool for detecting fluid in the human middle ear
  96. 3D Local in vivo Environment (LivE) imaging for single cell protein analysis of bone tissue
  97. Inside-Out access strategy using new trans-vascular catheter approach
  98. US/MRI fusion with new optical tracking and marker approach for interventional procedures inside the MRI suite
  99. Impact of different registration methods in MEG source analysis
  100. 3D segmentation of thyroid ultrasound images using active contours
  101. Designing a compact MRI motion phantom
  102. Cerebral cortex classification by conditional random fields applied to intraoperative thermal imaging
  103. Classification of indirect immunofluorescence images using thresholded local binary count features
  104. Analysis of muscle fatigue conditions using time-frequency images and GLCM features
  105. Numerical evaluation of image parameters of ETR-1
  106. Fabrication of a compliant phantom of the human aortic arch for use in Particle Image Velocimetry (PIV) experimentation
  107. Effect of the number of electrodes on the reconstructed lung shape in electrical impedance tomography
  108. Hardware dependencies of GPU-accelerated beamformer performances for microwave breast cancer detection
  109. Computer assisted assessment of progressing osteoradionecrosis of the jaw for clinical diagnosis and treatment
  110. Evaluation of reconstruction parameters of electrical impedance tomography on aorta detection during saline bolus injection
  111. Evaluation of open-source software for the lung segmentation
  112. Automatic determination of lung features of CF patients in CT scans
  113. Image analysis of self-organized multicellular patterns
  114. Effect of key parameters on synthesis of superparamagnetic nanoparticles (SPIONs)
  115. Radiopacity assessment of neurovascular implants
  116. Development of a desiccant based dielectric for monitoring humidity conditions in miniaturized hermetic implantable packages
  117. Development of an artifact-free aneurysm clip
  118. Enhancing the regeneration of bone defects by alkalizing the peri-implant zone – an in vitro approach
  119. Rapid prototyping of replica knee implants for in vitro testing
  120. Protecting ultra- and hyperhydrophilic implant surfaces in dry state from loss of wettability
  121. Advanced wettability analysis of implant surfaces
  122. Patient-specific hip prostheses designed by surgeons
  123. Plasma treatment on novel carbon fiber reinforced PEEK cages to enhance bioactivity
  124. Wear of a total intervertebral disc prosthesis
  125. Digital health and digital biomarkers – enabling value chains on health data
  126. Usability in the lifecycle of medical software development
  127. Influence of different test gases in a non-destructive 100% quality control system for medical devices
  128. Device development guided by user satisfaction survey on auricular vagus nerve stimulation
  129. Empirical assessment of the time course of innovation in biomedical engineering: first results of a comparative approach
  130. Effect of left atrial hypertrophy on P-wave morphology in a computational model
  131. Simulation of intracardiac electrograms around acute ablation lesions
  132. Parametrization of activation based cardiac electrophysiology models using bidomain model simulations
  133. Assessment of nasal resistance using computational fluid dynamics
  134. Resistance in a non-linear autoregressive model of pulmonary mechanics
  135. Inspiratory and expiratory elastance in a non-linear autoregressive model of pulmonary mechanics
  136. Determination of regional lung function in cystic fibrosis using electrical impedance tomography
  137. Development of parietal bone surrogates for parietal graft lift training
  138. Numerical simulation of mechanically stimulated bone remodelling
  139. Conversion of engineering stresses to Cauchy stresses in tensile and compression tests of thermoplastic polymers
  140. Numerical examinations of simplified spondylodesis models concerning energy absorption in magnetic resonance imaging
  141. Principle study on the signal connection at transabdominal fetal pulse oximetry
  142. Influence of Siluron® insertion on model drug distribution in the simulated vitreous body
  143. Evaluating different approaches to identify a three parameter gas exchange model
  144. Effects of fibrosis on the extracellular potential based on 3D reconstructions from histological sections of heart tissue
  145. From imaging to hemodynamics – how reconstruction kernels influence the blood flow predictions in intracranial aneurysms
  146. Flow optimised design of a novel point-of-care diagnostic device for the detection of disease specific biomarkers
  147. Improved FPGA controlled artificial vascular system for plethysmographic measurements
  148. Minimally spaced electrode positions for multi-functional chest sensors: ECG and respiratory signal estimation
  149. Automated detection of alveolar arches for nasoalveolar molding in cleft lip and palate treatment
  150. Control scheme selection in human-machine- interfaces by analysis of activity signals
  151. Event-based sampling for reducing communication load in realtime human motion analysis by wireless inertial sensor networks
  152. Automatic pairing of inertial sensors to lower limb segments – a plug-and-play approach
  153. Contactless respiratory monitoring system for magnetic resonance imaging applications using a laser range sensor
  154. Interactive monitoring system for visual respiratory biofeedback
  155. Development of a low-cost senor based aid for visually impaired people
  156. Patient assistive system for the shoulder joint
  157. A passive beating heart setup for interventional cardiology training
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