Bioglas

Bioglass, or bioactive glass, is a family of silica-based glasses designed to interact positively with biological tissues. Unlike inert implants, these materials form a chemical bond with bone and sometimes soft tissue by surface reactions that lead to the formation of a hydroxycarbonate apatite layer. Bioglass is used as bone graft substitutes and as coatings for metal implants to promote osseointegration.

Composition and types: The most widely cited composition is known as 45S5 bioglass, containing about 45% SiO2, 24.5% Na2O, 24.5% CaO and 6% P2O5 by weight. Variants adjust silica content or include other oxides (e.g., B2O3, MgO, SrO) to tailor degradation rate, mechanical properties, and biological response.

Mechanism of action: On immersion in body fluids, the glass surface undergoes ion exchange, forming a silica-rich outer layer and releasing ions such as Na+ and Ca2+. These reactions promote precipitation of calcium phosphate and ultimately hydroxycarbonate apatite, which bonds to bone. The process enables chemical bonding and osteoconduction.

Applications and forms: Bioglasses are used as particulate bone graft substitutes, scaffolds for tissue engineering, and coatings for metallic implants. They can be processed as granules, monolithic glasses, fibers, or composite materials and are used in dentistry as well.

History and considerations: Bioglass originated from research in the 1960s–1970s showing that certain glasses bond to bone. While they offer advantages such as osteoconductivity and ion release that can stimulate healing, they are brittle and may have slower mechanical performance under load compared with metals or dense ceramics, and their resorption rates must be matched to tissue regeneration.