The invention is related to a scraping tool that can be assembled and replaced for scraper blade quickly. The distal end may be embedded in bone with the proximal end exposed. The model is then applied in an inversion process to generate predicted values of an electric charge at the spinneret output and an electric field between the spinneret and electrode required to fabricate a selected fiber mat design. The general formula preferably has a glycine unit, a histidine unit, a lysine unit, an aspartic acid unit, or an N-methylglycine unit.