The Joel Schumacher era of Batman is often known for its campy aesthetic and over-the-top portrayal of villains. Thematically, it serves as a more updated version of the '60s Batman TV show; however, in its more serious moments, there are times where the tone can become more introspective. This is explored in Batman & Robin as Bruce copes with the potential death of Alfred. In contrast, Mr. Freeze will stop at nothing to cure his wife of a similar disease, even stealing diamonds to power his cryo-suit. However, science has shown that if he had studied one crucial aspect of his suit, he could've had more time to cure his wife.
In Batman & Robin, Victor Fries is a scientist studying molecular biology until his wife contracted a disease known as McGregor Syndrome. In his studies to cryogenically freeze her while looking for a cure, an accident causes him to fall into the cryogenic liquid. Instead of dying, his body mutated, turning his skin blue. He also can't survive in average temperatures and wears a cryo-suit powered by diamonds. In the film, he is shown stealing diamonds to keep his suit running at the necessary temperatures, but in reality, he could have simply made his own diamonds in a lab.
Natural diamonds are among the most sought-after rocks for their rarity and value. They can go for thousands of dollars on the market, if not more. As a result, they are often kept under heavy protection when in museums or jewelry stores. However, even though they are one of the most precious gems on the planet, they aren't totally incapable of being recreated. Since the '80s, lab-grown diamonds have changed the industry by creating diamonds that are nearly identical to the real thing, aside from some changes to the nitrogen in the rock.
Mr. Freeze, being that he's an intelligent scientist with enough knowledge on diamonds to extract the necessary elements to power his suit, could have easily made his own had he known he could. In doing so, he could also have given more time to trying to cure his wife rather than working on the next big heist. Even if he were unable to fabricate his own, the value of lab-grown diamonds continues to dwindle, meaning he could easily afford them if he pulled his resources. That said, with lab-grown diamonds seemingly accessible, why wouldn't he try to find or make his own?
Scientifically, one reason could be that the chemical and elemental make-up is not identical to what he needs from a real diamond. For example, nitrogen plays a significant role in creating real diamonds. Coincidentally, nitrogen is also key in creating the incredible frigid, liquid nitrogen. Therefore, in terms of movie science, the smaller amounts of the element would likely make for an incompatible or easily depleted power source.
Batman & Robin's Mr. Freeze is one of the franchise's most intelligent villains, but the film never shows him entertaining the idea of making his own diamonds or at least stealing the material to make his own. He could have cured his wife's disease at an even faster rate had he done so. However, if he did, his separation and need to do crime would be diminished, likely making him an ally rather than an enemy.