Chemical strategies for the presentation and delivery of growth factors

Since the first demonstration of employing growth factors (GFs) to control cell behaviour in vitro, the spatiotemporal availability of GFs in vivo has received continuous attention. In particular, the ability to physically confine the mobility of GFs has been used in various tissue engineering applications e.g. stents, orthopaedic implants, sutures and contact lenses. The lack of control over the mobility of GFs in scaffolds jeopardizes their performance in vivo. In this feature article, an overview is given on how to effectively present GFs on scaffolds. In the first part, non-covalent strategies are described covering interaction motifs that are generic to direct GF immobilization. In the second part, covalent strategies are described emphasizing the introduction of reactive groups in existing biomaterials. The feature article ends with a description of strategies based on the physical entrapment of growth factors

Synthesis, characterization and in vitro toxicity of paramagnetic Au nanorods

Coated Au nanorods are widely known for their absorption in the near infrared1, making them excellent candidates for near infrared imaging and photo thermal therapy2. Furthermore, recent studies have shown that these nanomaterials are excellent candidates for Magnetic Resonance Imaging (MRI) since they can be used as T1 contrast agents when functionalized with Gd3+-containing moieties and as multimodal agents for MR-CT3 and MR-plasmonic4 imaging. In this context, our aim is to explore the possible incorporation of Gd3+ complexes to these nanosystems in order to use them as T1 contrast agents for MRI and, in a more advanced stage, as multimodal imaging agents. Here we describe the synthesis, characterization, properties and in vitro toxicity of paramagnetic nanorods coated, in one step, with combinations of thiol functionalized Gd3+ complexes of a 1,4,7,10-tetraazacyclododecane-1,4,7-tris(acetic acid) (DO3A)-based ligand and polyethylene glycol (PEG). Preliminary results show that these paramagnetic Au nanorods are biocompatible, show T1 contrast at low Gd3+ concentrations and are envisioned to become excellent candidates for multimodal purposes

Reversibly tethering growth factors to surfaces: guiding cell function at the cell-material interface

Development of novel methodologies for tethering growth factors (GFs) to materials is highly desired for the generation of biomaterials with improved tissue repair properties. Progress in the development of biomaterials that incorporate GFs and the in vivo performance of such biomaterials in tissue engineering applications, such as stents, orthopaedic implants, sutures and contact lenses, is still challenged by the required control over the mobility of growth factors in biomaterials. Many of the current methodologies to introduce GFs in biomaterials suffer from a lack of control over the spatiotemporal delivery of GFs. The aim of the work described in this thesis is the functional tethering of GFs to biomaterials using reversible chemical strategies with spatiotemporal control, thus following nature’s paradigm. This work consisted of three parts: a) non-covalent strategies have been used to capture GFs to surfaces by employing nanobodies and peptides. In this part of the research considerable attention has been paid as well to fundamental aspects on controlling protein orientation in densely packed layers; b) reversible covalent chemistry has been used to control the spatiotemporal availability of GFs in the extracellular matrix (ECM) by using hydrolysable siloxane and imine bonds as examples and c) a protein array technology has been introduced to create functional platforms of various shapes and content for studying cell behavior. In summary, the reversibility of the tether has been found to play important roles in the biological activity. The results of the studies demonstrate the advantage of tethers that combine immobilized GFs, such as GF stability or the creation of locally highly concentrated GF reservoirs, with released mobile GFs, such as optimization of orientation for an optimal interaction with cellular receptors. Although such systems are attractive, knowledge about the application of such tethering strategies in vivo is limited and deserves detailed attention in future research and leaves ample room for synthesis. For example, stimuli responsive systems might provide tools for a breakthrough in the tissue engineering field

Orthogonal supramolecular protein assembly on patterned bifunctional surfaces

We report successful and selective dual protein assembly on patterned bifunctional βCD-Ni(ii)NTA surfaces, using red fluorescent protein variants with hexahistidine-tags and teal fluorescent protein variants conjugated with a peptide containing three adamantyl groups. We show that dual protein patterns can only be assembled, when opposing supramolecular interactions have been optimized and nonspecific interactions have been sufficiently suppressed

Hydrolytically Labile Linkers Regulate Release and Activity of Human Bone Morphogenetic Protein-6

Release of growth factors while simultaneously maintaining their full biological activity over a period of days to weeks is an important issue in controlled drug delivery and in tissue engineering. In addition, the selected strategy to immobilize growth factors largely determines their biological activity. Silica surfaces derivatized with glycidyloxy propyl trimethoxysilane and poly(glycidyl methacrylate) brushes yielded epoxide-functionalized surfaces onto which human bone morphogenetic protein-6 (hBMP-6) was immobilized giving stable secondary amine bonds. The biological activity of hBMP-6 was unleashed by hydrolysis of the surface siloxane and ester bonds. We demonstrate that this type of labile bonding strategy can be applied to biomaterial surfaces with relatively simple and biocompatible chemistry, such as siloxane, ester, and imine bonds. Our data indicates that the use of differential hydrolytically labile linkers is a versatile method for functionalization of biomaterials with a variety of growth factors providing control over their biological activity

Hydrolytically Labile Linkers Regulate Release and Activity of Human Bone Morphogenetic Protein‑6

Release of growth factors while simultaneously maintaining their full biological activity over a period of days to weeks is an important issue in controlled drug delivery and in tissue engineering. In addition, the selected strategy to immobilize growth factors largely determines their biological activity. Silica surfaces derivatized with glycidyloxy propyl trimethoxysilane and poly­(glycidyl methacrylate) brushes yielded epoxide-functionalized surfaces onto which human bone morphogenetic protein-6 (hBMP-6) was immobilized giving stable secondary amine bonds. The biological activity of hBMP-6 was unleashed by hydrolysis of the surface siloxane and ester bonds. We demonstrate that this type of labile bonding strategy can be applied to biomaterial surfaces with relatively simple and biocompatible chemistry, such as siloxane, ester, and imine bonds. Our data indicates that the use of differential hydrolytically labile linkers is a versatile method for functionalization of biomaterials with a variety of growth factors providing control over their biological activity