Commonly used medical equipment includes scalpels, forceps, scissors, clamps, and retractors. Examples of such instruments include scalpels, hypodermic needles, and artificial pacemakers. Alternatives to scalpels in surgical applications include electrocautery and lasers. Knives and scalpels fill a variety of needs, including cutting board or scraping off mistakes. Double-edged scalpels are referred to as "lancets". Surgical scalpels consist of two parts, a blade and a handle. Harmonic scalpels or lasers have also been used. Metallurgy was a technique that allowed the use of saws and scalpels. Obsidian scalpels may currently be purchased for surgical use on research animals. He invented skin scrapers for this purpose and these were the original scalpels. Historically, the preferred material for surgical scalpels was silver. Scalpels and Japanese samurai swords are perhaps the most well-known examples of such tools. Laser scalpels are used for ablation in both hard- and soft-tissue surgeries. There are essentially two kinds of disposable safety scalpels offered by various manufacturers. Scalpels may be single-use disposable or re-usable.