A New Hydrolysis-Dependent Thermosensitive Copolymer Does Not Inhibit Human Osteoblast Survival or Mineralization

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Authors: Goltzer O, Pauken C, Overstreet D, McLaren A, McLemore R.
Banner Good Samaritan Medical Center, Phoenix, AZ and Arizona State University, Tempe, AZ

Title: A New Hydrolysis-Dependent Thermosensitive Copolymer Does Not Inhibit Human Osteoblast Survival or Mineralization

Background: Current methods of treating orthopaedic infections local antimicrobial delivery. PMMA based drug delivery systems are important for temporary structural function but PMMA is often not used in the final reconstruction. In contrast, in situ forming antimicrobial delivery hydrogels can be used in dead space and implant host interfaces when PMMA is not used. We have previously developed a viscous, water-rich gel based on a thermosensitive copolymer called PNDJ for local drug delivery. Local cytotoxicity from copolymer degradation products is currently unknown.

Hypothesis/Purpose: Do PNDJ degradation products inhibit human osteoblast cell survival and mineralization?

Methods: Human osteoblasts were seeded at 8000 cells/cm2 and grown until confluent in Osteoblast Growth Media supplemented with ascorbic acid, dexamethasone, and gentamicin. Mineralization in the confluent osteoblastic cultures was induced by the addition of beta-glycerophosphate. These cultures were exposed to varying weight-percent concentrations of PNDJ degradation products (0wt%, 1wt%, 2wt%, 4wt%, and 8wt%). The media was changed every 48-72 hours. At three weeks, the cells were fixed with 3.7% formalin and stained with Alizarin Red, which identified mineralized calcium deposits as red spots. Osteoblast survival and mineralization was visualized on polarized light microscopy.

Results: Human osteoblasts grew in expected numbers and normal morphology at all concentrations of PNDJ degradation byproducts. Mineralization was observed at all concentrations of PNDJ degradation products (Fig 1).

Discussion: It has been previously demonstrated that PNDJ hydrogel serves as an excellent drug delivery vehicle. It is viscoelastic and can be used where PMMA is not, has sustained antimicrobial release, and degrades over 2-6 weeks. These studies show that human osteoblasts survive and mineralize in vitro in the presence of up to 8 wt% of PNDJ hydrogel degradation products which is higher concentration than expected in vivo. Subsequent studies are needed to evaluate the biocompatibility of this polymer in vivo.

A New Hydrolysis-Dependent Thermosensitive Copolymer Does Not Inhibit Human Osteoblast Survival or Mineralization