Osteoconductive scaffolds based on bioactive polysaccharides for the proliferation of human derived dental pulp stem cells

Bone tissue damages can derive from diseases such as osteogenesis imperfecta, osteoarthritis, osteomyelitis, and osteoporosis, or from traumatic injury, orthopaedic surgeries and primary tumour resection (Porter et al. 2009 Biotechnol Progress). In particular, non-critical bone defects and voids represent a hot spot for mechanical stresses that can cause fractures, thus it is necessary to accelerate their healing (Jawad et al. 2013 J Orthop Res). Moreover, spinal fusion, maxillary sinus floor elevation, guided bone regeneration, represent other clinical cases in which it is necessary to provide substitutes for bone tissue regeneration. (Mardas et al. 2010 Clin Oral Impl Res) The use of synthetic bone substitutes reduces surgical procedures and the risk of infection or immunogenicity, and decreases the risk of disease transmission (Mottaghitalab et al 2015 J Control Rel; Porter et al. 2009 Biotechnol Progress). Moreover, synthetic scaffolds can be loaded with bioactive molecules or cells before implantation. Polysaccharides offer the opportunity to prepare biocompatible bone substitutes with specific morphological and biological characteristics, such as high interconnectivity and enhanced cell adhesion, which could mimic properly the bone tissue and support and enhance bone healing (Woodruff et al. 2010 Prog Polym Sci; Ward et al. 2010 Oral Dis) In this work, tridimensional scaffolds based on alginate, hydroxyapatite (HAp) and derivatives of chitosan were prepared and characterized. The scaffolds were obtained through freeze casting of alginate/HAp hydrogels. Morphological characterization, obtained by means of micro-computed tomography, revealed that scaffold porosity and interconnectivity are compatible with the requirements for the bone tissue regeneration (Turco et al. 2009 Biomacromolecules). Moreover, the physical-chemical stability displayed by the scaffolds makes them suitable for supporting cell adhesion, colonization and growth. Another important aspect hereby taken in account was the introduction of the chitosan derivatives that showed bioactive properties such as increased osteoblasts proliferation and ALP activity, and increased bone-implant contact in the case of thermosets functionalized with this polysaccharide (Marsich et al. 2013 Acta Biomater). The scaffolds presented in this work were successfully used for the growth and the differentiation of human derived dentin pulp stem cells (hDPSCs). Flow cyotofluorimetry proved that hDPSCs harvested in our laboratory can be maintained in culture with an undifferentiated phenotype and that can be differentiated in osteoblasts under proper stimuli, as demonstrated by enzymatic and biochemical assays. Overall, the combination of hDPSCs and polysaccharide based bioactive scaffolds, represents an effective strategy for the preparation of osteoconductive and osteoinductive cell-loaded biomaterials for the treatment of bone defects and for the clinical practice in oral surgery.