Rapid rheological screening to identify conditions of biomaterial hydrogelation

Abstract

Hydrogels engineered for biomedical applications consist of numerous components, each of which can affect the material assembly and final mechanical properties. We present methods that rapidly generate rheological libraries to identify regimes of hydrogel assembly in a large composition parameter space. This method conserves both material and time, and leads to critical insight into assembly mechanisms and mechanics, which can then be used for further materials development and optimization.The assembly of precursor molecules and macromolecules into hydrogels, and the resulting material mechanical properties, are principal design factors in the engineering of many biologically active and therapeutic materials. 1 For instance, the gel microstructure and modulus are known to affect the viability and migration of cells 2 and the differentiation of stem cells. 3 Hydrogels intended for such biological applications are typically composed of numerous structural compounds, in addition to soluble and attached epitopes and markers, 2,4,5 each of which can influence, by design or unintentional consequence, the assembly, final material properties, and ultimate material performance. In order to facilitate the design and optimization of therapeutic hydrogel materials over a large parameter space, we apply methods of highthroughput rheological characterization using multiple particle tracking microrheology. This simple, yet powerful approach enables us to rapidly assay compositions for hydrogel formation in a relatively short period of time, while consuming only small quantities of material.In this study, the hydrogelator materials consist of maleimide-functionalized high molecular weight heparin (HMWH, MW = 15 000). 6 Covalent cross-linking occurs by the addition of dithiolized poly(ethylene glycol) (PEG, MW = 10 000).6 Heparin has the unique ability to sequester and stabilize soluble proteins, including growth factors that promote cellular proliferation and differentiation.7 Because of this, heparin hydrogels have recently been engineered to stimulate communication between cells and a surrounding gel matrix,2 behave as stimuli responsive materials,4 ,8 and serve as a three-dimensional matrix for stem cell culture. 5 In general, the high charge and conformational stiffness of many biomolecules, including heparin, may alter the anticipated gelation conditions and rheology. Thus, rapid evaluation of gelation in biomolecular gels provides a valuable tool for the synthesis of materials that mimic the chemical, structural and rheological characteristics of native biological matrices.

Heparin-functionalized polymeric biomaterials in tissue engineering and drug delivery applications

“…Recent advances in mechanical measurements, such as microrheology, could also be brought to bear on these materials, providing a rapid and straightforward method for generating rheological libraries of hydrogelation conditions over a large composition parameter space. Such approaches would be of great value in the identification of hydrogel assembly and efficient optimization of heparin-containing materials for therapeutic applications [129, 130]. The development of a broader range of heparin-based biomaterials, including nanopatterned materials and particle-hydrogel complexes, would also further expand potential applications and impact of these materials.…”

Detection of viscoelasticity in aggregating dilute protein solutions through dynamic light scattering-based optical microrheology

“…Since the short-time or high-frequency response is expected to be highly relevant for dilute samples, this feature becomes increasingly more important. Also, microrheology using tracer particles is now starting to gain increasing popularity as a possible high-throughput methodology for obtaining viscosity for proteins (He et al 2010) and viscoelasticity of other complex fluids (Breedveld and Pine 2003) and biological samples (Schultz et al 2009). Recently, particle tracking-based microrheological methods have been successfully applied to detect the sol-gel transition in proteins and other polymeric and biological systems (Larsen and Furst 2008;Corrigan and Donald 2009b, a).…”

Gelation of Covalently Cross-Linked PEG−Heparin Hydrogels

“…The critical gelation exponent is used to identify the state of each sample, i.e., sol or gel. In each map, a unique “gelation envelope” is measured; the size and location of this region vary with each parameter studied 36. The gelation envelope is compared to the predicted boundaries using Flory–Stockmayer theory.…”