In vitro evaluation of a new polymethylmethacrylate cement reinforced with hydroxyapatite

The nature of the orthopedic implant surface affects the interaction between cells and subsequent bone formation. The bone/cement interface in cement-held prostheses is considered to be the main cause of fracture leading to implant revision. It is thought that the introduction of a bioactive phase, such as hydroxyapatite (HA), to cement may permit a stronger implant by encouraging direct bone apposition rather than encapsulation of the implant by fibrous tissue. Thus, a poly(methylmethacrylate) (PMMA) cement incorporating 17.5% HA by weight has been investigated. In this study, in order to analyze the interaction at the cellular level, the in vitro biological response of the HA/PMMA to a similar PMMA without HA incorporation has been studied. Primary human osteoblast-like cells (HOB) were used as they are a model of the cell type the cements might encounter in vivo. Cell proliferation and growth were assessed by measurement of total cellular DNA and tritiated thymidine ([3H]-TdR) incorporation. Alkaline phosphatase (ALP) production was measured as an indicator of HOB phenotype upon the cements. The results showed that HA/PMMA was a better substrate for HOB cells, resulting in increased proliferation and ALP activity. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that HOB cells cultured on the HA-filled PMMA preferentially anchored to HA particles exposed at the cement surface, with a close intimacy observed between HA and HOB cells.