Alendronate-eluting polyglucose-lignol composite (POGLICO): A new biomaterial for fracture fixating implants

Background and purpose —

Due to the known drawbacks of metal implants, new biomaterials for internal fracture fixation are attracting increasing interest, among them poly(lactic-co-glucolic) acids (PLGAs) and the recently developed silk-tenoin derived materials (STDMs). In accordance with the new philosophy of bio-derived biomaterials (BIODERIBIOs), I describe a novel innovative technology for use in fracture fixation.

Patients and methods —

Screws (2 mm dia.) were manufactured from cylindrical bars of polyglucose-lignol composite (POGLICO) in the form of birch toothpicks from the hospital canteen, dip-coated with alendronate (1 mg/mL, n = 6) or saline (n = 6), and inserted in the proximal tibias of rats for 4 weeks. Fixation was evaluated by mechanical pullout testing. POGLICO nails were inserted in the contralateral tibia for microCT and histology.

Results —

All POGLICO implants remained fixed in the bone (p < 0.001) with a mean pullout force of 37 (SD 5.5) N. MicroCT showed that the control nails were surrounded by a thin layer of new bone, while all bisphosphonate-treated implants were surrounded by a thick layer of cancellous bone. Bisphosphonates more than doubled the bone density around the nails (p = 0.004).

Interpretation —

POGLICO is biocompatible, remains in situ, and appears to provide a higher resistance to pullout forces than bulk silk protein. The material is light, strong, and bio-derived. BIODERIBIO-POGLICO can be sterilized by autoclaving, and has a porous surface that can serve for slow release of drugs applied by simple dip-coating, as demonstrated by the effect of the alendronate treatment. As the raw material for the screws is readily available from the toothpick industry, I believe that the possibilities for commercial development of the material for fracture fixation are promising.In order to eliminate the problems associated with metal implants, such as temperature sensitivity (Perrone et al. 2014), the development of non-metal, resorbable implant materials has gained increasing interest. Such materials include polylactic-co-glucolic acids, which are, however, associated with problems of local inflammation due to degradation products (Bostman and Pihlajamaki 2000). For this reason, a new biomaterial—bulk silk-tenoin—has recently been tested for biocompatibility and reported in a high-impact journal (Perrone et al. 2014). This material is claimed to be superior to poly(lactic-co-glucolic) acids in many ways, including biocompatibility, its ability to undergo machining and autoclaving, and its usefulness for elution of drugs (Perrone et al. 2014). In view of these recent advances in the research on bio-derived biomaterials (BIODERIBIO), I have tested another material, namely birch, in much the same way as the silk-derived implants were tested. I found that birch may be equally useful and has advantages over silk from its well-documented use in other fields of construction, its easy availability, and the manufacturing know-how gained through the toothpick industry.Local bisphosphonate treatment has been shown to improve implant fixation in clinical randomized trials of knee prostheses, external fixation pins, and dental implants (Hilding and Aspenberg 2007, Abtahi 2012, Toksvig-Larsen and Aspenberg 2013). I therefore determined whether birch could also act as a carrier of a bisphosphonate.