FRET Sensor-Modified Synthetic Hydrogels for Real-Time Monitoring of Cell-Derived Matrix Metalloproteinase Activity using Fluorescence Lifetime Imaging

Matrix remodeling plays central roles in a range of physiological and pathological processes and is driven predominantly by the activity of matrix metalloproteinases (MMPs), which degrade extracellular matrix (ECM) proteins. Our understanding of how MMPs regulate cell and tissue dynamics is often incomplete as in vivo approaches are lacking and many in vitro strategies cannot provide high-resolution, quantitative measures of enzyme activity in situ within tissue-like 3D microenvironments. Here, we incorporate a Förster resonance energy transfer (FRET) sensor of MMP activity into fully synthetic hydrogels that mimic many properties of the native ECM. We then use fluorescence lifetime imaging to provide a real-time, fluorophore concentration-independent quantification of MMP activity, establishing a highly accurate, readily adaptable platform for studying MMP dynamics in situ. MCF7 human breast cancer cells encapsulated within hydrogels highlight the detection of MMP activity both locally, at the sub-micron level, and within the bulk hydrogel. Our versatile platform may find use in a range of biological studies to explore questions in the dynamics of cancer metastasis, development, and tissue repair by providing high-resolution, quantitative and in situ readouts of local MMP activity within native tissue-like environments.

Glycosaminoglycan-Inspired Biomaterials for the Development of Bioactive Hydrogel Networks

Glycosaminoglycans (GAG) are long, linear polysaccharides that display a wide range of relevant biological roles. Particularly, in the extracellular matrix (ECM) GAG specifically interact with other biological molecules, such as growth factors, protecting them from proteolysis or inhibiting factors. Additionally, ECM GAG are partially responsible for the mechanical stability of tissues due to their capacity to retain high amounts of water, enabling hydration of the ECM and rendering it resistant to compressive forces. In this review, the use of GAG for developing hydrogel networks with improved biological activity and/or mechanical properties is discussed. Greater focus is given to strategies involving the production of hydrogels that are composed of GAG alone or in combination with other materials. Additionally, approaches used to introduce GAG-inspired features in biomaterials of different sources will also be presented.

Adhesive Hydrogels for Maxillofacial Tissue Regeneration Using Minimally Invasive Procedures

Minimally invasive surgical procedures aiming to repair damaged maxillofacial tissues are hampered by its small, complex structures and difficult surgical access. Indeed, while arthroscopic procedures that deliver regenerative materials and/or cells are common in articulating joints such as the knee, there are currently no treatments that surgically place cells, regenerative factors or materials into maxillofacial tissues to foster bone, cartilage or muscle repair. Here, hyaluronic acid (HA)-based hydrogels are developed, which are suitable for use in minimally invasive procedures, that can adhere to the surrounding tissue, and deliver cells and potentially drugs. By modifying HA with both methacrylate (MA) and 3,4-dihydroxyphenylalanine (Dopa) groups using a completely aqueous synthesis route, it is shown that MA-HA-Dopa hydrogels can be applied under aqueous conditions, gel quickly using a standard surgical light, and adhere to tissue. Moreover, upon oxidation of the Dopa, human marrow stromal cells attach to hydrogels and survive when encapsulated within them. These observations show that when incorporated into HA-based hydrogels, Dopa moieties can foster cell and tissue interactions, ensuring surgical placement and potentially enabling delivery/recruitment of regenerative cells. The findings suggest that MA-HA-Dopa hydrogels may find use in minimally invasive procedures to foster maxillofacial tissue repair.

Plasma-induced polymerization as a tool for surface functionalization of polymer scaffolds for bone tissue engineering: an in vitro study

A commonly applied strategy in the field of tissue engineering (TE) is the use of temporary three-dimensional scaffolds for supporting and guiding tissue formation in various in vitro strategies and in vivo regeneration approaches. The interactions of these scaffolds with highly sensitive bioentities such as living cells and tissues primarily occur through the material surface. Hence, surface chemistry and topological features have principal roles in coordinating biological events at the molecular, cellular and tissue levels on timescales ranging from seconds to weeks. However, tailoring the surface properties of scaffolds with a complex shape and architecture remains a challenge in materials science. Commonly applied wet chemical treatments often involve the use of toxic solvents whose oddments in the construct could be fatal in the subsequent application. Aiming to shorten the culture time in vitro (i.e. prior the implantation of the construct), in this work we propose a modification of previously described bone TE scaffolds made from a blend of starch with polycaprolactone (SPCL). The modification method involves surface grafting of sulfonic or phosphonic groups via plasma-induced polymerization of vinyl sulfonic and vinyl phosphonic acid, respectively. We demonstrate herein that the presence of these anionic functional groups can modulate cell adhesion mediated through the adsorbed proteins (from the culture medium). Under the conditions studied, both vitronectin adsorption and osteoblast proliferation and viability increased in the order SPCL << sulfonic-grafted SPCL < phosphonic-grafted SPCL. The results revealed that plasma-induced polymerization is an excellent alternative route, when compared to the commonly used wet chemical treatments, for the surface functionalization of biodevices with complex shape and porosity.