Glutaraldehyde is a chemical crucial to many applications.  In the health care industry, it is used as a 1% or 2% aqueous solution activated by an alkaline buffer such as sodium bicarbonate. The activated solution is used in the chemical disinfection of instruments such as bronchoscopes, dental equipment, and other clinical instruments. Disinfection requires immersion of the instrument in a glutaraldehyde solution.  Aqueous solutions of glutaraldehyde of 10-50% are used for the treatment of water in cooling towers, air washers, and  water recirculating systems to prevent corrosion and microbial build-up. The solution is at 50-100 ppm glutaraldehyde in treated water.  In off-shore operations, a 15-50% aqueous concentrate is added to well injection sea water to prevent the growth of sulfate-reducing bacteria that contribute to metal corrosion.  In the pulp & paper industry, aqueous solutions at 10-50% are used to reduce or inhibit the growth of micro-organisms in pulp slurries administered by automatic dosing equipment to give 50-100 ppm glutaraldehyde in the pulp stock.

Thus, it is not per se so dangerous, but the permissible exposure limit for glutaraldehyde established by the Occupational Safety and Health Administration is 0.8 mg/m^3 (0.2 ppm) based on the irritant effects to the eyes, nose, and throat (OSHA, 1989).  Although it is an excellent cross-linking agent for polysaccharides, the diacetal linkages that it forms are NOT permanent and are therefore subject to hydrolysis.  It can be used in cosmetics at concentrations of up to 0.1% in Europe.  It can be used in both rinse-off or non-rinse off cosmetic products.  For non-rinse off cosmetics (face cream, all purpose cream, body creams, antiperspirants, hairstyling gels), the mean total of use was 20.3g of product/day assuming that the person used all types extensively.  The estimate for average use was 10.8 g/day.  In the final analysis, the answer is not so clear and depends on the use, national health guidelines, and exposure limits.

I would say every biomaterials has its own characteristic bio physical and chemical properties that makes it stand out. And the percentage of glut should be investigated according to that biomaterials before carrying out further tests. 

It all varies from material to material ideally a very small percentage is good enoughl Depend upon the application. 

The use of cross-linker depends on the biopolymer you are using. Glutaraldehyde cross-linking has been controversial for chitosan, where genipin works much better. But referring to the first answer in this discussion chain, glutaraldehyde has been used in several other applications. And moreover, the amount of glutaraldehyde used for biomedical applications like polymer formulations in drug delivery is very less and could be regarded as almost safe.