Introduction: The gold standard for bone and skin grafts remains the autograft as it provides a scaffold containing the biological cues required for the regeneration of healthy tissue without eliciting an immune response[1]. Autografts, however, require a second surgery for harvesting the tissue, which increases patient morbidity, and is not an option for elderly, pediatric and severely burnt patients. Allografts provide an ideal scaffold but come with high risk for disease transmission and immune rejection[2]. Polymer scaffolds have been developed as alternatives for bone and skin grafts, but the scaffold surfaces are often hydrophobic and lack specific functional groups that promote cell adhesion and growth[2],[3]. To improve polymer scaffolds, we can employ surface modification to control the response of the body to the implant and prevent immune responses, infection, and displacement after surgery from poor integration in the body.
Materials and Methods: We developed a platform to attach chemical groups, such as phosphonates and amino groups, to the surface of polymers using diazonium chemistry[4]. We confirmed each modification with X-ray photoelectron, Raman, and Fourier Transform Infrared spectroscopy and cultured osteoblasts, chondrocytes, cancer-cells, and fibroblasts on both modified and non-modified surfaces to study the effect of each chemical group on cell adhesion and growth. We then measured cell viability and metabolic activity to test the biocompatibility of the modified surfaces.
Results and Discussion: We attached phosphonate and amino groups to poly(D,L-lactic acid) (PDLLA) surfaces to improve the performance of PDLLA bone tissue engineering scaffolds. The phosphonate and amino groups homogeneously attached to both the inner and outer surfaces of the scaffold as a result of the diazonium reaction without damaging the PDLLA backbone. Both osteoblasts and chondrocytes were cultured on the modified and non-modified surfaces, and the phosphonate-modified PDLLA promoted not only increased hydroxyapatite deposition but also improved cell viability and metabolic activity. Amino modifications, instead, did not favor osteoblast adhesion on PDLLA[4]. We obtained similar results with phosphonate groups on poly(etheretherketone) (PEEK) (Figure 1). Finally we tested phosphonate, amino, carboxylic and hydroxyl groups on polystyrene and showed that all the groups strongly improved the adhesion of salivary gland cancer cells, making these substrates equivalent to those commercially modified for cell culture (Figure 2).
Conclusion: We present a simple, nondestructive method for modifying the surface of polymeric materials for tissue engineering. This diazonium-based technique is biocompatible and can be easily adapted to attach any chemical groups to polymer surfaces. To expand the platform, we are now investigating the effect of carboxylic acid, hydroxyl, amino, and phosphonate groups on both polystyrene and poly(lactic-co-glycolic acid) (PLGA) on other cancerous cell lines, chondrocytes, osteoblasts and fibroblasts. We expect that different cell lines will react differently to the various chemical groups, thus showing the possibility of modulating cell-surface interactions with this technique.
Natural Sciences and Engineering Research Council of Canada (NSERC) “Discovery” program; “Nouveaux chercheurs” program from Fonds de recherche du Québec - Nature et technologies (FQRNT); Canada Research Chair program
References:
[1] P.V. Giannoudis et al (2005) Bone substitutes: an update, Injury 36: S20-S27
[2] L. Alrubaiy and K.K. Al-Rubaiy (2009) Skin substitutes: a brief review of types and clinical applications, Oman Medical Journal 24: 1-3
[3] R. Vasita et al (2008) Improved biomaterials for tissue engineering applications: surface modification of polymers, Current Topics in Medicinal Chemistry 8: 341-353
[4] H. Mahjoubi et al (2014) Surface modification of poly(D,L-lactic acid) scaffolds for orthopedic applications: a biocompatible, nondestructive route via diazonium chemistry, ACS Applied Material Interfaces 6: 9975-9987