Bone cements with tailored solubility from intermediate oxide-containing glasses and branched polycarboxylates

• Applicants: Professorin Dr. Delia Brauer; Professor Dr. Felix H. Schacher
• Subject Area: Biomaterials
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 271153954

Bone cements are used as bone fillers (eg. in vertebro- or kyphoplasty) or for anchoring implants (eg. hip implants) into the bone. Current materials include acrylic (eg. poly(methyl methacrylate, PMMA) or calcium phosphate (CaP) cements. Both have several drawbacks, however, such as exothermic setting reaction (damaging the surrounding tissue), lack of chemical bonding to bone (adhesion by mechanical interlocking only) and absence of bioactivity (encapsulation in fibrous tissue rather than bonding to bone) for PMMA cements, or poor mechanical properties (allowing for use in non-load bearing applications only) for CaP cements. In addition, particularly for bone filler applications, the use of resorbable materials would be of great interest, as it allows for bone regeneration rather than bone replacement. While CaP cements can be resorbable depending on their composition, PMMA cements are long-term stable. Glass ionomer cements (which set by a neutralisation reaction between an acid-degradable glass and a polymeric acid) are routinely used in dentistry, show excellent mechanical properties and form chemical bonds with hard tissue (teeth and bone) or surgical metals. However, the release of aluminium ions from these cements limits their use in orthopaedics, and the development of Al-free alternatives has so far failed because of poor understanding of the glass acid degradation mechanism as well as a need for suitable polycarboxylates allowing for the formation of mechanically stable but resorbable cements.The aim of this project is the synthesis and characterization of novel bone cements based on Al-free, acid-degradable glasses and branched, partly resorbable polycarboxylates suitable for use in non-load bearing (and potentially also load bearing) applications according to their mechanical properties (compressive strength, Young's modulus, adhesion to metal and bone). This will be realized via the synthesis of intermediate oxide (predominantly MgO)-containing Al-free glasses and investigations concerning their solubility under relevant pH conditions (pH 1-8). Particular emphasis will be put on gaining in-depth understanding on the relationship between glass composition, structure, and solubility in order to predict and tailor glass stability under relevant pH conditions. Regarding the polymeric component of the targeted bone cements, we synthesize novel, highly branched polycarboxylates using free radical polymerization techniques. We will control the amount of carboxylic acid groups by different ratios of methacrylic/itaconic acid as (co-)monomers, whereas the degree of branching and the inter-chain distance can be controlled by varying type and amount of a suitable crosslinker. Furthermore, we will synthesize a degradable crosslinker based on glycolic acid to provide bone cements with a controlled degradation profile under physiological conditions. The latter will pave the way towards fully resorbable bone cements.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Anja Träger