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Abstract

Sir: On reading the queries on the original article, we would like to clarify certain facts. It has been clearly stated that the control material was a siloxane-integrated poly(carbonate-urea)urethane and not polydimethylsiloxane or silicone. This has been reported on page 1654, the last four lines of polymer synthesis, for your reference. As the biocompatibility characteristics of silicone, including its potential to form significant capsular contracture in certain cases, are well described, we decided that using a siloxane-integrated poly(carbonate-urea)urethane (PCU) counterpart to polyhedral oligomeric silsesquioxane (POSS)-PCU is a more suitable control. Regarding the attenuated total reflectance (ATR)–Fourier transform infrared (FTIR) spectra, it has been well documented in the literature that silsesquioxanes show a characteristic peak at approximately 1100 cm–1, and this absorbance is clearly evident in our POSS-modified PCU. As is shown on page 1655, the higher than expected intensity of the Si-O-Si peak from the POSS-PCU is attributable to a high POSS surface effect, which has been discussed in an earlier published work of ours.1 This surface effect enhances the biological biocompatibility properties of the POSS-PCU. Furthermore, our studies on AFM and FTIR on increasing concentrations of POSS show2 an increasing peak at 1108 cm–1. In contrast, if bulk FTIR spectra are performed, a significant reduction of this signal would be identified. The before-and-after implantation ATR-FTIR results for the control show a distinct change in surface chemistry, which would imply some sort of surface degradation. The exact mechanism for this is not clear, but initial interpretation would imply a reduction of Si-O-Si at the surface of the control after implantation. This could also be caused by some phase separation of the siloxane soft segments and a reduction in integrity of the polymer. This may be explained by the fact that polydimethylsiloxane-modified polyurethanes are known to be problematic in terms of phase incompatibility. Next, the polyurethane component of this nanocomposite is a specifically designed polycarbonate-urea based urethane, the ATR-FTIR spectra of which is illustrated in an earlier work.3 Based on the references of the letter, it would suggest that the author was using ester- and ether-based conventional polyurethanes as comparison, which is incorrect. As regards “silicone-osis,” it was a contentious diagnosis at the time of our submission, but in the 3 years since our work, the weight of evidence has shifted against a systemic manifestation of silicone. With the advantage of hindsight, it would thus be very convenient to comment. However, the point we tried to make in making that statement is that silicone has its attendant disadvantages, the main one being capsular contracture. POSS-PCU would possibly provide us with a better solution. Ruben Y. Kannan, M.D. Henryk J. Salacinski, Ph.D. Biomaterials and Tissue Engineering Centre Academic Division of Surgery and Interventional Sciences University College London London, United Kingdom Jalal-edin Ghanavi, M.D. Nanomedicine Research Centre Shaheed Beheshti University of Medical Sciences Tehran, Iran Ashish Narula, Ph.D. Department of Histopathology Royal Free Hampstead NHS Trust London, United Kingdom Marianne Odlyha, Ph.D. Department of Materials Chemistry Birkbeck College, University of London London, United Kingdom Habiballah Peirovi, M.D. Nanomedicine Research Centre Shaheed Beheshti University of Medical Sciences Tehran, Iran Peter E. Butler, M.D. Department of Plastic and Reconstructive Surgery Royal Free Hampstead NHS Trust London, United Kingdom Alexander M. Seifalian, Ph.D. Biomaterials and Tissue Engineering Centre Academic Division of Surgery and Interventional Sciences University College London London, United Kingdom