(c) A fluorescence image of a gelatin film sequentially patterned with two fluorescent CMPs [CF(GPO)9in green, TAMRA(GPO)9in red]. a corneal tissue. Since the CMP is a chemically and biologically inert peptide which is proven to be an ideal carrier for bioactive molecules, our patterning method provides a radically new tool for immobilizing drugs to natural tissues and for functionalizing scaffolds intended for complex tissue formation. Keywords: hydrogel, microenvironment, spatial control, tissue engineering, triple helix == 1 . Introduction == Native tissues exhibit complex architectural features ranging from micro to millimeter length scale. Such complex features are managed by cells in response to spatio-temporally dynamic microenvironment in the form of soluble cues (e. g., growth factors and hormones), as well as insoluble cues such as cell- and extracellular matrix (ECM)-bound signaling molecules. Controlling the interactions between cells and their microenvironment is crucial intended for guiding cells into formation of complex tissue constructs.[1]Recent advancements in micropatterning technology have enhanced our ability to spatially encode these biochemical signals in the cell microenvironment within biocompatible platforms. Many research groups have reported the use of Glycine photo-activated chemical reactions to pattern biomolecules onto hydrogels comprised of simple synthetic and natural polymers, such as poly(ethylene glycol) (PEG) and agarose.[2-14]Although such simple and inert polymer networks are easy to pattern by photo-chemistry, they are generally not ideal for cell culture because they are not cement adhesive to cells and/or cannot be degraded by cells. This lack of cell-interactive elements in synthetic scaffolds greatly limits the ability of cells to proliferate, migrate and grow into organized structures.[15]Bioactivity of such hydrogels can be improved to some extent by incorporation of basic cell interactive components (commonly derived from ECM), such as cell binding,[9]and matrix metalloproteinase (MMP)-degradable domains.[2]Although these patterned synthetic hydrogels are great systems to recapitulate and investigate the role of spatiotemporal cues in vitro,[16]they are not ideal for engineering complex tissues. Conventional hydrogel patterning techniques use photo-activated reactions to conjugate biomolecules to chemically modified matrices;[2-14, 17]in contrast, in natural tissues, many signaling molecules bind to ECM via non-covalent interactions (e. g., growth factor-ECM binding).[18]This inspired us to seek a natural ECM patterning technique based on non-covalent binding interactions. We envisioned that the non-covalent patterning of natural ECM would maintain the native chemical composition from the ECM and that such a patterning approach will have immediate translational applications in tissue engineering and regenerative medicine. Gelatin is one of the most widely used biocompatible platforms intended for tissue engineering and drug delivery. Gelatin, which is an unfolded collagen denatured by Glycine heat or by fragmentation of protein chains, can be derived from a variety of sources by inexpensive means. Gelatin answer spontaneously forms a transparent hydrogel upon cooling from high temperature, and as a natural ECM protein, it inherently contains cell binding motifs, such as the RGD and GFOGER sequences,[19]as well as protease-cleavable sites, making it an ideal substrate intended for tissue culture. Gelatin is frequently used to coating cell culture plates to improve attachment Glycine of cells, and gelatin hydrogels have been used as scaffolds in delivering chondrocytes and stem cells for osteochondral tissue repair.[20, 21]It is also a popular matrix to deliver various types of growth factors for tissue regeneration in vivo.[22-24] Previously, we discovered that a collagen mimetic peptide (CMP) [sequence: (GPO)n, n = 610, O: hydroxyproline] with strong propensity to fold into collagen-like triple helix can specifically hybridize to unfolded gelatin chains.[25-34]This binding is primarily driven by the triple helical hybridization between monomeric CMPs and the gelatin chains, which is similar to small DNA fragments binding to complimentary DNA strands. To enable photo-triggered gelatin binding, we incorporated a photo-labile nitrobenzyl protective group into the CMP backbone and developed a caged collagen mimetic peptide [sequence: (GPO)4NBGPO(GPO)4, designated asNB(GPO)9, NBG: N-o-nitrobenzyl-glycine] whose folding and gelatin binding are activated by UV light.[31, 35]The caged CMP cannot hybridize to gelatin due to the steric hindrance caused by the NB cage group, yet removal of the cage group by UV light immediately triggers the peptide to hybridize with the gelatin chains(Figure 1).[31] == Determine 1 . == Schematics from the photo-triggered activation of the caged CMP (a) and the experimental setup and process of photo-patterning gelatin films with caged CMPs. The CMP, comprised of GlyProHyp repeats, is an excellent carrier for bioactive molecules.[25]The Glycine Glycine peptide is made Rabbit polyclonal to CDK4 entirely of neutral and hydrophilic amino acids which make them highly inert with respect to protein adsorption and enzymatic degradation. In addition , its simple chemical composition allows for easy modification and conjugation to other peptides and bioactive molecules, and even to inorganic and polymeric nanoparticles.[33, 36]For example , CMPs have been conjugated to growth element mimetics, cell binding motifs, antibody Fab regions, monosaccharides, fatty acids and a number of optical.