Garima Agrawal

Formation of catalytically active gold–polymer microgel hybrids via a controlled in situ reductive process

A newly developed N-vinylcaprolactam/acetoacetoxyethyl methacrylate/acrylic acid based microgel displays in situ reductive reactivity towards HAuCl4, forming hybrid polymer–gold nanostructures at ambient temperature without additional reducing agents. The colloidal gold nanostructure is selectively formed in the core of the microgel and the composite structure is used as a noble metal catalyst, the activity of which can be tuned depending on the size of the formed core. The hybrid particles can easily be isolated after catalysis via centrifugation and re-used with retention of the catalytic activity.

Self-templating amphiphilic polymer precursors for fabricating mesostructured silica particles: a water-based facile and universal method.

A facile and universal approach is reported for the preparation of silica particles of various mesostructures based on the self-assembly of amphiphilic precursor polymers in water and subsequent condensation. Depending on the hydrophilization degree of hyperbranched polyethoxysiloxane, various silica morphologies including mesoporous particles, hollow nanospheres and ultrasmall particles with high application potential are fabricated.

Degradable microgels synthesized using reactive polyvinylalkoxysiloxanes as crosslinkers

In the present work we demonstrate the synthesis of degradable thermo-sensitive poly(N-vinylcaprolactam) microgels via precipitation polymerization using reactive polyvinylalkoxysiloxanes as crosslinkers (Cross-PAOS). These compounds were synthesized by co-condensation of vinyltriethoxysilane and tetraethoxysilane followed by transesterification with poly(ethylene glycol) monomethyl ether (PEG) to increase their water solubility. Experimental results showed that the microgels synthesized using Cross-PAOS exhibited excellent colloidal stability in water. These microgels are thermo-responsive and their size can be tuned depending upon the ratio of vinyl and PEG groups in Cross-PAOS. The size of microgel particles increases with increasing vinyl groups in Cross-PAOS while it decreases with increasing PEG groups. The presence of silicon dioxide in the microgel structure was confirmed by X-ray photoelectron spectroscopy and elemental analysis. Additionally, the microgels prepared in this way contain crosslinking sites which can be degraded under alkaline conditions.

Hydrophobic superparamagnetic FePt nanoparticles in hydrophilic poly(N-vinylcaprolactam) microgels: a new multifunctional hybrid system

We report the synthesis of a new multifunctional colloidal hybrid system consisting of thermoresponsive amphiphilic biocompatible poly(N-vinylcaprolactam) microgels loaded with hydrophobic superparamagnetic FePt nanoparticles (NPs). In the first step, water swellable poly(N-vinylcaprolactam) microgels were mixed with hydrophobically coated sub-10 nm superparamagnetic FePt NPs in a tetrahydrofuran (THF) solution. In the second step, changing the surrounding solvent from THF to water forces the FePt NPs to migrate into the amphiphilic microgels. These new hybrid microgels (i) are colloidally stable in water and their thermo-responsive properties in terms of volume phase transition are retained, (ii) exhibit superparamagnetic characteristics introduced by FePt NPs, (iii) show a drastically reduced cytotoxicity compared to water-soluble FePt NPs of similar size, as known from the literature. This makes the new hybrid microgels suitable e.g. as biocompatible containers for drug delivery or for imaging.

Stimuli-Responsive Microgels and Microgel-Based Systems: Advances in the Exploitation of Microgel Colloidal Properties and Their Interfacial Activity

In this paper, recent developments in the chemical design of functional microgels are summarized. A wide range of available synthetic methods allows the incorporation of various reactive groups, charges, or biological markers inside the microgel network, thus controlling the deformation and swelling degree of the resulting smart microgels. These microgels can respond to various stimuli, such as temperature, pH, light, electric field, etc. and can show unique deformation behavior at the interface. Due to their switchability and interfacial properties, these smart microgels are being extensively explored for various applications, such as antifouling coatings, cell encapsulation, catalysis, controlled drug delivery, and tissue engineering.

Modified Glass Ionomer Cement with "Remove on Demand" Properties: An In Vitro Study

Objectives: To investigate the influence of different temperatures on the compressive strength of glass ionomer cement (GIC) modified by the addition of silica-coated wax capsules; Material and Methods: Commercially-available GIC was modified by adding 10% silica-coated wax capsules. Test blocks were fabricated from pure cement (control) and modified cement (test), and stored in distilled water (37 °C/23 h). The compressive strength was determined using a universal testing machine under different temperatures (37 °C, 50 °C, and 60 °C). The maximum load to failure was recorded for each group. Fractured surfaces of selected test blocks were observed by scanning electron microscopy (SEM); Results: For the control group, the average compressive strength was 96.8 ± 11.8, 94.3 ± 5.7 and 72.5 ± 5.7 MPa for the temperatures 37 °C, 50 °C and 60 °C respectively. The test group reported compressive strength of 64.8 ± 5.4, 47.1 ± 5.4 and 33.4 ± 3.6 MPa at 37 °C, 50 °C and 60 °C, respectively. This represented a decrease of 28% in compressive strength with the increase in temperature from 37 °C to 50 °C and 45% from the 37 °C to the 60 °C group; Conclusion: GIC modified with 10% silica-coated wax capsules and temperature application show a distinct effect on the compressive strength of GIC. Considerable compressive strength reduction was detected if the temperature was above the melting temperature of the wax core.

Calcium phosphate/microgel composites for 3D powderbed printing of ceramic materials

Abstract Composites of microgels and calcium phosphates are promising as drug delivery systems and basic components for bone substitute implants. In this study, we synthesized novel composite materials consisting of pure β-tricalcium phosphate and stimuli-responsive poly(N-vinylcaprolactam-co-acetoacetoxyethyl methacrylate-co-vinylimidazole) microgels. The chemical composition, thermal properties and morphology for obtained composites were extensively characterized by Fourier transform infrared, X-ray photoelectron spectroscopy, IGAsorp moisture sorption analyzer, thermogravimetric analysis, granulometric analysis, ESEM, energy dispersive X-ray spectroscopy and TEM. Mechanical properties of the composites were evaluated by ball-on-three-balls test to determine the biaxial strength. Furthermore, initial 3D powderbed-based printing tests were conducted with spray-dried composites and diluted 2-propanol as a binder to evaluate a new binding concept for β-tricalcium phosphate-based granulates. The printed ceramic bodies were characterized before and after a sintering step by ESEM. The hypothesis that the microgels act as polymer adhesive agents by efficient chemical interactions with the β-tricalcium phosphate particles was confirmed. The obtained composites can be used for the development of new scaffolds.

Wettability and contact angle of polymeric biomaterials

The wettability of biomaterials is a prerequisite property for ensuring desired biological response. The measurements of wettability represent essential scientific evaluation of properties for biomaterials. Most commonly used techniques to quantify wettability of polymeric biomaterials surfaces are contact angle measurements. This chapter highlights the fundamental concepts of wettability and contact angle, which play crucial roles in determining the surface properties of polymeric materials. The first section provides a brief overview of various techniques that are commonly used to measure contact angles, including the conventional telescope-goniometer method, Wilhelmy balance method, and the more recently developed drop shape analysis method. In addition, recent advancement of numerous methods for tuning the wettability properties of polymeric biomaterials for various biomedical applications has been discussed in detail.

Functional Microgels: Recent Advances in Their Biomedical Applications

Here, a spotlight is shown on aqueous microgel particles which exhibit a great potential for various biomedical applications such as drug delivery, cell imaging, and tissue engineering. Herein, different synthetic methods to develop microgels with desirable functionality and properties along with degradable strategies to ensure their renal clearance are briefly presented. A special focus is given on the ability of microgels to respond to various stimuli such as temperature, pH, redox potential, magnetic field, light, etc., which helps not only to adjust their physical and chemical properties, and degradability on demand, but also the release of encapsulated bioactive molecules and thus making them suitable for drug delivery. Furthermore, recent developments in using the functional microgels for cell imaging and tissue regeneration are reviewed. The results reviewed here encourage the development of a new class of microgels which are able to intelligently perform in a complex biological environment. Finally, various challenges and possibilities are discussed in order to achieve their successful clinical use in future.

NMR, FT-IR and raman characterization of biomaterials

Abstract Polymeric biomaterials are leading class of materials whose utilization has increased substantively in last few decades toward therapeutic applications. The characterizations of such biomaterials are of paramount importance to understand the structure and chemistry for exploiting the full biomimetic potential. There are several advanced characterization techniques available for the structural characterization of the biomaterials. In this chapter, we will elaborate an overview of the most commonly used spectroscopic characterization techniques such as nuclear magnetic resonance, Fourier transform infrared, and Raman, along with a brief description of their importance, principles, and recent advances in various biomaterials characterization.