Problem set 2 Solution BE462J/3.962J Spring 2003 Issued y 4 Due: Day 5 (20 pts total) 1. (4 pts) An early study in the development of peptide-presenting biomaterials showed that polymer surfaces bearing RGD peptides at a density equivalent to -10 peptides per each cell was sufficient to promote cell attachment, spreading and subsequent cell growth. In contrast, when whole fibronectin protein was adsorbed to polymer surfaces, it was found that many more copies of the intact protein were needed per unit area to obtain similar responses from cells. Explain this result How should the binding of cell integrin receptors to a short RGD peptide compare with binding to native fibronectin? These experiments were discussed in the reading assignment: Two factors leading to the need for more copies of FN adsorbed to a surface vs RGd are denaturation of the protein on adsorption (binding sites are destroyed by unfolding) and masking of binding sites, e.g. the RGD site of FN arranged face down'on the substrate where receptors cannot access it. This result is striking since short peptides taken from adhesion proteins typically show much lower affinities(by up to 100-fold for their receptors than the intact whole protein, due to the presentation of additional residues that are spatially local to the binding site but distant along the folded length of the protein chain and the relative immobilization of the binding sequence in the optimal configuration within the protein 2.(3 pts) In the article by Schense et al. Figures 1 and 2 show that different adhesion peptides incorporated into a natural biopolymer matrix (a fibrin fiber network) induce different degrees of neurite outgrowth from neuronal cells, even when conjugated to the matrix at the same total densities. Provide 2 physico-chemical reasons to explain how different peptides can provide different responses Each peptide may target a different integrin receptor on the cell, and different integrins may be expressed at different total densities on the cell surface. Second, each peptide may be bound with a different affinity even if it binds the same integrin-together, these two factors allow different peptides to provide very different results 3.3 pts)Compare and contrast the erosion characteristics expected for a device to be used in vivo that is fabricated from a polyesteramide vs the characteristics of the same device fabricated using a polyanhydride Polyesteramides are degradable by proteolytic enzymes in addition to being sensitive to hydrolysis This enzymatic sensitivity will cause both the polyesteramide and the polyanhydride device to undergo surface erosion if suitable enzymes are present at the implant site 4. Design of an artificial artery (10 pts)Shown below is a simplified schematic of the structure of an artery. The two primary features of an artery are the endothelial cell lining on the interior lumen of the vessel (contacting blood flow) and the smooth muscle cell layer surrounding the vessel, which 1 of 3Problem Set 2 Solution BE.462J/3.962J Spring 2003 Issued: Day 4 Due: Day 5 (20 pts total) 1. (4 pts) An early study in the development of peptide-presenting biomaterials showed that polymer surfaces bearing RGD peptides at a density equivalent to ~105 peptides per each cell was sufficient to promote cell attachment, spreading, and subsequent cell growth. In contrast, when whole fibronectin protein was adsorbed to polymer surfaces, it was found that many more copies of the intact protein were needed per unit area to obtain similar responses from cells. Explain this result. How should the binding of cell integrin receptors to a short RGD peptide compare with binding to native fibronectin? These experiments were discussed in the reading assignment: Two factors leading to the need for more copies of FN adsorbed to a surface vs. RGD are denaturation of the protein on adsorption (binding sites are destroyed by unfolding) and masking of binding sites, e.g. the RGD site of FN arranged 'face down' on the substrate where receptors cannot access it. This result is striking since short peptides taken from adhesion proteins typically show much lower affinities (by up to 100-fold) for their receptors than the intact whole protein, due to the presentation of additional residues that are spatially local to the binding site but distant along the folded length of the protein chain and the relative immobilization of the binding sequence in the optimal configuration within the protein backbone. 2. (3 pts) In the article by Schense et al., Figures 1 and 2 show that different adhesion peptides incorporated into a natural biopolymer matrix (a fibrin fiber network) induce different degrees of neurite outgrowth from neuronal cells, even when conjugated to the matrix at the same total densities. Provide 2 physico-chemical reasons to explain how different peptides can provide different responses. Each peptide may target a different integrin receptor on the cell, and different integrins may be expressed at different total densities on the cell surface. Second, each peptide may be bound with a different affinity even if it binds the same integrin- together, these two factors allow different peptides to provide very different results. 3. (3 pts) Compare and contrast the erosion characteristics expected for a device to be used in vivo that is fabricated from a polyesteramide vs. the characteristics of the same device fabricated using a polyanhydride. Polyesteramides are degradable by proteolytic enzymes in addition to being sensitive to hydrolysis. This enzymatic sensitivity will cause both the polyesteramide and the polyanhydride device to undergo surface erosion if suitable enzymes are present at the implant site. 4. Design of an artificial artery. (10 pts) Shown below is a simplified schematic of the structure of an artery .The two primary features of an artery are the endothelial cell lining on the interior lumen of the vessel (contacting blood flow) and the smooth muscle cell layer surrounding the vessel, which BE.462J/3.962J PS 1 1 of 3