## 1 Introduction  
Glass polyalkenoate cements (GPCs) were developed in the early 1970s and are typically used in restorative dentistry for luting and lining applications [1, 2]. They have been candidates for use in skeletal cementation due to their excellent bone-contact biocompatibility, ability to adhere to surgical metals and bone, and lack of volumetric shrinkage and heat evolution [3]. GPCs are composite materials that set via an acid/base reaction between an ion-leachable glass (SiO\({}_{2}\)-AlO\({}_{2}\)-CaO, SiO\({}_{2}\)-AlO\({}_{2}\)-CaF) and a polyalkenoic acid, usually polyacrylic acid (PAA). Upon mixing, an acid-base reaction occurs where metal cations are released from the glass (e.g., Al\({}^{3+}\), Ca\({}^{2+}\)) and form a polyacid salt with carboxylate (COO\({}^{-}\)) groups from the PAA chains. These metal cations cross-link the polyacrylate chains, forming a cement of residual glass particles and a surrounding siliceous hydrogel embedded in a polysalt matrix [4, 5, 6, 7]. GPCs are tailored explicitly for applications in contact with hard biological materials such as tooth enamel and dentin, which consist predominantly of tightly packed hydroxyapatite (HA) crystals that form a microporous structure. When in contact with HA, GPCs can create a direct chemical bond, which is achieved through ionic exchange at the GPC/HA interface [8]. Polyacrylic acid chains can enter the molecular surface of HA, replacing a concentration of calcium and phosphate ions [9]. Due to their therapeutic effects in dentistry, GPCs have been considered for orthopedic applications such as bone cementation and maxillofacial and cranial surgery due to their strong chemical bond to hard tissues [10; 11; 12]. However, the presence of Al\({}^{3+}\) within the glass phase contraindicates the use of GPCs in bone; this can be addressed by modifying the glass composition to include more biocompatible ions such as Sr\({}^{2+}\), Cu\({}^{2+}\), and Zn\({}^{2+}\)[13; 14; 15; 16; 17; 18; 19] in place of Al. Al\({}^{3+}\) release (from the glass phase) in humans is associated with poor local bone mineralization and collagen synthesis, neurotoxicity (one fatal case) [20; 21; 22], and in vitro toxicity, which manifests as mineralization defects when tested in animal models [23]. Despite the Al\({}^{3+}\) concerns, conventional GPCs have been proven to exhibit exceptional biocompatibility in the oral cavity [24]. Modifying their composition is required for use close to physiological fluids. GPCs are highly versatile materials as numerous methods can be utilized to modify their chemistry, which include altering the glass composition, changing the molecular weight of the PAA used, varying the concentration of PAA used during the cement forming process, and modifying the powder-to-liquid ratio (P:L ratio) [25; 26; 27]. Changing any or each of these characteristics will significantly affect the materials' properties, i.e., the setting chemistry, solubility, mechanical properties, and bioactivity. For this work, the glass composition was altered to contain more biocompatible components for use in close contact with physiological fluids. Using bioactive glasses as the glass component for these materials is advantageous, as these materials have been heavily studied and have seen commercial success and use in dentistry, skeletal tissue repair, and wound healing [28; 29; 30; 31; 32; 33; 34]. However, there are specific requirements for GPC formation, as the glass composition needs to incorporate ions capable of forming bonds with the COO\({}^{-}\) groups on the PAA chains. The glass phase developed for this research is a silicate-based glass (SiO\({}_{2}\)-ZnO-CaO). The divalent cations (Ca\({}^{2+}\), Zn\({}^{2+}\)) were incorporated into the glass phase as they are known to be released and form cross-links with the polyacrylic acid, thereby promoting the GPC setting reaction [35]. In addition, these are ions that have a positive therapeutic effect close to growing bone tissue and are known to diffuse between the GPC and host bone tissue.