• Preserve the ultra-slim 15 mL purple-and-silver click-pen silhouette
• Use a small stainless rollerball rather than a dropper, pump, spray, or brush
• Calibrate click dose, flow rate, seal integrity, and rollerball movement
• Keep viscosity low enough for even roll-on delivery without leakage
• Develop a fast-drying, non-oily scalp feel suitable for use at the hairline or part
• Perform package leakage, drop, clogging, corrosion, and repeated-actuation testing
• Avoid drug-growth claims unless the formula and market pathway support them