Physics and chemistry have produced two basic laws of thermodynamics that are obeyed by all forms of matter and energy, including living organisms. The first law is that of conservation of matter and energy, which states that matter and energy cannot be created or destroyed. Matter and energy can be transformed, and energy can be converted from one form into another, but the total of the equivalent amounts of both must always remain constant.
The smallest, thinnest needle is the nano 4mm, 32 gauge needle. By comparison, this needle is thought to be as thin as two strands of hair. The risk of injecting into muscle tissue is very rare when using this needle.
Pen needles. Pen needles are used in conjunction with injection pens to deliver injectable medications into the body. A pen needle consists of a hollow needle which is embedded in a plastic hub and attaches to injection pens. Pen needles come in a variety of needle lengths and diameters and are used by health professionals and patients for injection of a variety of medications.