When designing biomaterials to degrade naturally, various factors can be controlled to influence their degradation rate and mode. The chemical composition of the biomaterial can determine its susceptibility to degradation; for instance, polymers with ester bonds are more prone to hydrolysis than polymers with amide bonds, while metals with low corrosion resistance, such as iron and magnesium, are more likely to degrade than metals with high corrosion resistance, such as titanium and gold. Additionally, the molecular weight, crystallinity, morphology, and environment of the biomaterial all affect its degradation kinetics. For example, higher molecular weight hyaluronic acid degrades slower than low molecular weight hyaluronic acid; likewise, crystalline poly(lactic acid) degrades slower than amorphous poly(lactic acid). Furthermore, biomaterials with larger surface area have higher degradation rates due to increased contact with degrading agents. In addition, biomaterials with porous or hollow structures have faster degradation rates due to more internal space for water infiltration and mass loss. Finally, biomaterials with higher pH have lower degradation rates due to less hydrolytic activity, while those with higher temperature have higher degradation rates due to more kinetic energy and molecular motion.