In vitro evaluation of a new polymethylmethacrylate cement reinforced withhydroxyapatite

The nature of the orthopedic implant surface affects the interaction betwee n cells and subsequent bone formation. The bone/cement interface in cement- held prostheses is considered to be the main cause of fracture leading to i mplant revision. It is thought that the introduction of a bioactive phase, such as hydroxyapatite (HA), to cement may permit a stronger implant by enc ouraging direct bone apposition rather than encapsulation of the implant by fibrous tissue. Thus, a poly(methylmethacrylate) (PMMA) cement incorporati ng 17.5% HA by weight has been investigated. In this study, in order to ana lyze the interaction at the cellular level, the in vitro biological respons e of the HA/PMMA to a similar PMMA without HA incorporation has been studie d. 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 an d growth were assessed by measurement of total cellular DNA and tritiated t hymidine ([H-3]-TdR) incorporation. Alkaline phosphatase (ALP) production w as 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 incr eased proliferation and ALP activity. Scanning electron microscopy (SEM) an d transmission electron microscopy (TEM) showed that HOB cells cultured on the HA-filled PMMA preferentially anchored to HA particles exposed at the c ement surface, with a close intimacy observed between HA and HOB cells. (C) 1999 Kluwer Academic Publishers.