The invention includes a medical hydrogel made from polymerized polysaccharide macromers. The macromers are preferably polysaccharides decorated with polymerizable groups, for example, methacrylates. The macromers may also be made into polymers of at least two macromers polymerized together. These polymers are preferably multi-armed or high-molecular weight and used for medical uses, for example, making coatings on medical devices. Macromers of N-vinylpyrrolidone are also disclosed herein.