How Magnesium Actually Disappears
Magnesium Series Episode 3
The chemistry is not complicated
In contact with extracellular fluid, magnesium undergoes an electrochemical reaction that has been characterized for over a century Mg + 2H2O → Mg(OH)2 + H2. Products are released at the implant–tissue interface.
Mg2+ ions clear through normal renal pathways, since magnesium is already the fourth most abundant cation in the human body.
Magnesium hydroxide gradually converts to phosphate and carbonate, chemistries the periosteum knows well. Nothing foreign is left behind.
What separates early magnesium implants from modern ones
The real problem is hydrogen gas. The field has converged on four levers that work together: rare-earth alloy design (most commonly WE43, Mg-4Y-3RE), surface engineering through plasma electrolytic oxidation (PEO), microstructural control through laser powder bed fusion (LPBF), and treating geometry itself as a corrosion variable rather than an afterthought.
Matching degradation to bone healing
The result of these innovative ideas is a degradation profile that can actually be shaped. The implant stays mechanically intact through roughly the first eight weeks, transfers load gradually to remodeling bone over the following two to six months, and clears progressively over six to twenty-four months.
The specific window shifts with alloy, geometry, surface treatment, and anatomic site, which is why patient-specific design matters. The goal is precision: support until bone takes over.
