BB-04: Stimuli sensitive soft materials and hydrogels. I
1:30pm - 3:30pm
Session Chair: Andre R. Studart, ETH Zürich Session Chair: Terry Steele, Nanyang Technological University
1:30pm - 2:00pm Invited
Tough Non-Swellable Hydrogels for Cell Encapsulation
University of Warwick, United Kingdom
Tailoring the characteristics of a material to meet the needs of a biological environment is a key goal in material science. Hydrogels, with their high water content and synthetic flexibility, are promising candidates to achieve this goal. The controlled ability to tune and pre-define these materials allows for the synthesis of unique hydrogels for specific requirements e.g. a particular biological environment or to elicit a desired cellular response. Recently, the nucleophilic thiol-yne click reaction has been demonstrated as an attractive route for the synthesis of bio-materials.
The synthesis of a range of robust, tuneable hydrogel materials has been undertaken utilising the nucleophilic thiol-yne click reaction, while maintaining a high water content (ca. 90%). Remarkably, optimization of the molecular weight and geometry of the poly(ethylene glycol) (PEG) precursors allow access to strong materials (up to 2.4 MPa) with a range of storage moduli. Moreover, these hydrogels can be tuned to specific requirements by a simple precursor blending process leading to a range of materials with intermediate stiffness, controlled swelling and high cell compatibility, without modifying the chemistry used and with minimal changes to the hydrogel structure.
2:00pm - 2:30pm Invited
Strength of Soft Polymer Networks
ESPCI ParisTech, France
Soft polymer networks are broadly interesting for engineering applications (elastomers) and also for biomedical applications (typically hydrogels). They are generally made by connecting together flexible polymer chains by permanent or dynamic chemical bonds and they can be highly swollen (gels) or fully dry (elastomers above their Tg). Both gels and elastomers share some important properties such as reversible but non-linear elasticity up to large deformations, modulus controlled by entropic elasticity and strength controlled by the architecture of the network. Recently much progress has been made also in the understanding of what controls the mechanical strength of such networks and it has become clear that creating sacrificial bonds inside the material to enhance energy dissipation is an effective strategy. Two synthetic methods have been broadly used: creating sacrificial bonds not by bond strength but by architecture with interpenetrated networks, and creating weak and strong bonds in the same network. We will discuss how these strategies can lead to an improvement of the mechanical strength of the network and how to optimize it in view of recent results.
2:30pm - 2:45pm Oral
Drug Eluting Chitosan/Tamarind Seed Polysaccharide Hydrogels with Herbal Extracts for Diabetic Wound Healing
Department of Biotechnology and Medical Engineering, National Institute of Technology, Rourkela, India
The number of people with diabetes is increasing steadily for the past 3 decades and caused 1.5 million deaths worldwide in 2012. In diabetic patients, an elevated blood sugar level decreases the blood flow by narrowing the blood vessels and reduces the oxygen and nutrients supply leading to impaired wound healing. The existing therapies and interventions for diabetic wound healing are unsatisfactory, thus, a new wound dressing that meets the requirements of rapid wound healing is needed. Various natural and synthetic polymers have been used to develop ideal wound dressing hydrogels depending on the type of wound. In the present work, suitable wound dressing hydrogels were prepared with chitosan (CS)/tamarind seed polysaccharide (TSP) composites using freezing-thawing method. Natural herbal extract such as papaya leaf, henna leaf and orange peel extracts were incorporated in CS/TSP hydrogels and its wound healing properties were evaluated. The synthesized hydrogels were characterized using scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and Fourier transform infra-red (FT-IR) spectroscopy techniques. The drug release kinetics, mechanical strength, in-vitro swelling studies, water vapor transmission rate (WVTR), gel fraction test, hemolysis and antibacterial tests were carried out to study its wound dressing characteristics. All the hydrogels showed better wound healing properties in comparison to the CS/TSP hydrogels. The antimicrobial activity of the herbal extracts resulted in a larger zone of inhibition against both, gram positive and gram negative bacteria. The WVTR of the hydrogels was found to be in a range of 2020-2700 g/m2/day indicating that the hydrogels can maintain a moist environment for exuding wound which would enhance epithelial cell migration during the healing process. From this study, it is evident that CS/TSP hydrogels with the addition of natural herbal extracts could be used as a potential wound dressing material.
2:45pm - 3:00pm Oral
Fabrication of Gelatin Scaffolds Via Two-Photon Polymerization for Biological Applications
1School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore; 2Singapore Centre for 3D Printing, Nanyang Technological University, Singapore
Fabrication of biomaterials with 3D microstructures and sub-diffraction resolution through two-photon direct laser writing has gained tremendous attention in scientific research due to its biological applications. In this work, 3D scaffolds of biopolymer gelatin and initiator rose bengal have been fabricated via two-photon polymerization by using a 780-nm near-infrared femtosecond laser. In-house built setup which includes a femtosecond laser, beam delivery optics, a 3-axis translational piezo stage, and a microscope has been used where gelatin microstructures are formed via two-photon polymerization due to focal cross linking of poly peptide molecules. It will be very interesting to observe how the bacteria cells can affects the morphological behaviour of fabricated gelatin matrix. Moreover, the effect of laser power on the feature size of the fabricated gelatin scaffold through layer-by-layer fabrication controlled by piezo stage, will be of immense interest. Femtosecond-laser-based 3D printing with high resolution and high throughput patterning can be used for cell based interaction studies in the biopolymer matrix.
3:00pm - 3:15pm Oral
Polysaccharide Based Oral Delivery Systems for Site Specific Delivery in Gastro-Intestinal Tract
Kaarunya SAMPATHKUMAR, Say Chye Joachim LOO
School of Materials Science and Engineering, Nanyang Technological University, Singapore
Oral delivery is regarded as the facile method for the administration of active pharmaceutical ingredients (API) and drug carriers. In an initiative towards sustainable nanotechnology, an oral nano delivery system has been developed that is made entirely of food based materials and can also act as a site specific delivery device depending on the stimulus encountered in different parts of the gastro intestinal tract (GIT). The delivery system has been fabricated from food grade polysaccharide materials like chitosan and starch through electrospraying technique without the use of any organic solvents. A model drug doxorubicin has been loaded into the nano carrier to test its efficacy in encapsulation and stimuli based release of the drug. The release kinetics of the drug from the carrier was evaluated in simulated gastric, intestinal and colonic fluid and was found to be triggered both by the enzymes and the pH in each part of the intestinal tract depending on the polysaccharide being used. The toxicity of the nanoparticles on the intestinal epithelial cells was tested and found to be relatively safe for up to 24 hours at a concentration of 0.2 mg/mL with cellular uptake also being observed. The developed nano carrier thus serves as a promising delivery vehicle for targeted delivery to different parts of the GIT with the inherent conditions of the GIT itself acting as the stimulus. In addition, being fabricated from food grade materials, the carrier can be used for both drug and nutraceutical delivery in the pharmaceutical and food industries respectively.
3:15pm - 3:30pm Oral
Interactions Between Rheological and Lap Shear Approaches to Explain the Strength of Electro Cured Bio-adhesive
Manisha SINGH, Terry WJ STEELE
Nanyang Technological University, Singapore
Several explanations have been proposed for the tissue and an adhesive interface phenomenon, the utmost accepted of which are the interpenetration-inter diffusion theory and the wetting-spreading theory (Chickering and Mathiowitz, 1999). The interface strength at breaking can be ascribed to the mechanical hindrance provided by the tissue and adhesive interface, tested by the classical lap shear adhesion test. Also, the occurrence of the above-mentioned phenomenon influences the rheological properties of the interface. Looking at the widespread role of these testing techniques, it appeared interesting to understand whether the strengthening at the bio-adhesive interface was allied with the rheological properties.
In this pioneering work of ours (Ping et al., 2015), a new instant electro-curing adhesive is designed and subsequent experiments are performed to achieve a better understanding of the type and strength of bio-adhesion. In this article, we will describe the result of some of our research in which the correlation between lap shear and rheological parameters of different viscosity grades of the same polymer was investigated at different voltage levels. The adhesion work and various viscoelastic interaction parameters were calculated using the different variables obtained i.e. G', G", Tan delta and the area under the force-displacement curve.
However, the data contents of these two methods (rheological and lap-shear) are dissimilar and complementary to each other. The purpose of this article is not to review the feasibility of in vitro-in vivo interaction of bioadhesion tests but to justify their possible correlation in the preliminary screening of electrocured bio- adhesive polymer. Having said that, the results obtained so far indicate that, a significant correlation was seen when the relationship between ‘’the adhesion work’’ and ‘’the tan delta variation’’ was considered. Also, the similar rank order of bio-adhesiveness has been obtained with rheology and shear adhesion testing.