It is estimated that 1–6% of the adult population have an intracranial aneurysm. Aneurysm coiling is the current preferred treatment method; however, over 20% of coiled aneurysms recur. A novel glass–alginate composite hydrogel has been developed to treat aneurysms, which is designed to completely fill the aneurysm space and prevent aneurysm recurrence. This hydrogel is composed of a polymeric alginate, a novel bioactive glass and glucono-delta-lactone. This novel injectable hydrogel exhibits characteristics suitable for the treatment of cerebral aneurysms. However, poor hydrophilicity of the glass phase results in inhomogeneity and agglomerate formation within the composite, resulting in suboptimal deliverability and strength. This study examines the effect of surface modification of the glass particles using an acid washing technique, designed to increase glass surface hydrophilicity resulting in a homogeneous sample. This study found that acid washing of the glass not only decreased agglomeration and inhomogeneity but also lengthened working times and increased strength of the resultant hydrogel. This lengthened working time, allowed for an increased glass content and, as a result, further increased compressive strength and radiopacity of the resultant hydrogel. Glass particle size analysis revealed that the relative quantity of fine particles was reduced. Surface analysis of the glass particles revealed an increase in hydrophilic silanol groups and increased surface network connectivity. These factors, combined with a decreased surface calcium and an increased surface gallium content, are postulated as the likely reasons for the observed increased strength, working time and hardening time.