Kimia Khoshroo

A current overview of materials and strategies for potential use in maxillofacial tissue regeneration.

Tissue regeneration is rapidly evolving to treat anomalies in the entire human body. The production of biodegradable, customizable scaffolds to achieve this clinical aim is dependent on the interdisciplinary collaboration among clinicians, bioengineers and materials scientists. While bone grafts and varying reconstructive procedures have been traditionally used for maxillofacial defects, the goal of this review is to provide insight on all materials involved in the progressing utilization of the tissue engineering approach to yield successful treatment outcomes for both hard and soft tissues. In vitro and in vivo studies that have demonstrated the restoration of bone and cartilage tissue with different scaffold material types, stem cells and growth factors show promise in regenerative treatment interventions for maxillofacial defects. The repair of the temporomandibular joint (TMJ) disc and mandibular bone were discussed extensively in the report, supported by evidence of regeneration of the same tissue types in different medical capacities. Furthermore, in addition to the thorough explanation of polymeric, ceramic, and composite scaffolds, this review includes the application of biodegradable metallic scaffolds for regeneration of hard tissue. The purpose of compiling all the relevant information in this review is to lay the foundation for future investigation in materials used in scaffold synthesis in the realm of oral and maxillofacial surgery.

Development of 3D PCL microsphere/TiO2 nanotube composite scaffolds for bone tissue engineering

In this research, the three dimensional porous scaffolds made of a polycaprolactone (PCL) microsphere/TiO2 nanotube (TNT) composite was fabricated and evaluated for potential bone substitute applications. We used a microsphere sintering method to produce three dimensional PCL microsphere/TNT composite scaffolds. The mechanical properties of composite scaffolds were regulated by varying parameters, such as sintering time, microsphere diameter range size and PCL/TNT ratio. The obtained results ascertained that the PCL/TNT (0.5wt%) scaffold sintered at 60°C for 90min had the most optimal mechanical properties and an appropriate pore structure for bone tissue engineering applications. The average pore size and total porosity percentage increased after increasing the microsphere diameter range for PCL and PCL/TNT (0.5wt%) scaffolds. The degradation rate was relatively high in PCL/TNT (0.5wt%) composites compared to pure PCL when the samples were placed in the simulated body fluid (SBF) for 6weeks. Also, the compressive strength and modulus of PCL and PCL/TNT (0.5wt%) composite scaffolds decreased during the 6weeks of storage in SBF. MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) assay and alkaline phosphates (ALP) activity results demonstrated that a generally increasing trend in cell viability was observed for PCL/TNT (0.5wt%) scaffold sintered at 60°C for 90min compared to the control group. Eventually, the quantitative RT-PCR data provided the evidence that the PCL scaffold containing TiO2 nanotube constitutes a good substrate for cell differentiation leading to ECM mineralization.

Efficacy of the biomaterials 3 wt%-nanostrontium-hydroxyapatite-enhanced calcium phosphate cement (nanoSr-CPC) and nanoSr-CPC-incorporated simvastatin-loaded poly(lactic-co-glycolic-acid) microspheres in osteogenesis improvement: An explorative multi-phase experimental in vitro/vivo study

AIMS The purpose of this multi-phase explorative in vivo animal/surgical and in vitro multi-test experimental study was to (1) create a 3wt%-nanostrontium hydroxyapatite-enhanced calcium phosphate cement (Sr-HA/CPC) for increasing bone formation and (2) creating a simvastatin-loaded poly(lactic-co-glycolic acid) (SIM-loaded PLGA) microspheres plus CPC composite (SIM-loaded PLGA+nanostrontium-CPC). The third goal was the extensive assessment of multiple in vitro and in vivo characteristics of the above experimental explorative products in vitro and in vivo (animal and surgical studies). METHODS AND RESULTS PERTAINING TO SR-HA/CPC Physical and chemical properties of the prepared Sr-HA/CPC were evaluated. MTT assay and alkaline phosphatase activities, and radiological and histological examinations of Sr-HA/CPC, CPC and negative control were compared. X-ray diffraction (XRD) indicated that crystallinity of the prepared cement increased by increasing the powder-to-liquid ratio. Incorporation of Sr-HA into CPC increased MTT assay (biocompatibility) and ALP activity (P<0.05). Histomorphometry showed greater bone formation after 4weeks, after implantation of Sr-HA/CPC in 10 rats compared to implantations of CPC or empty defects in the same rats (n=30, ANOVA P<0.05). METHODS AND RESULTS PERTAINING TO SIM-LOADED PLGA MICROSPHERES+NANOSTRONTIUM-CPC COMPOSITE: After SEM assessment, the produced composite of microspheres and enhanced CPC were implanted for 8weeks in 10 rabbits, along with positive and negative controls, enhanced CPC, and enhanced CPC plus SIM (n=50). In the control group, only a small amount of bone had been regenerated (localized at the boundary of the defect); whereas, other groups showed new bone formation within and around the materials. A significant difference was found in the osteogenesis induced by the groups sham control (16.96±1.01), bone materials (32.28±4.03), nanostrontium-CPC (24.84±2.6), nanostrontium-CPC-simvastatin (40.12±3.29), and SIM-loaded PLGA+nanostrontium-CPC (44.8±6.45) (ANOVA P<0.001). All the pairwise comparisons were significant (Tukey P<0.01), except that of nanostrontium-CPC-simvastatin and SIM-loaded PLGA+nanostrontium-CPC. This confirmed the efficacy of the SIM-loaded PLGA+nanostrontium-CPC composite, and its superiority over all materials except SIM-containing nanostrontium-CPC.

Development of chitosan/gelatin/keratin composite containing hydrocortisone sodium succinate as a buccal mucoadhesive patch to treat desquamative gingivitis

Abstract The aim of this research was to develop chitosan/gelatin/keratin composite containing hydrocortisone sodium succinate as a buccal mucoadhesive patch to treat desquamative gingivitis, which was fabricated through an environmental friendly process. Mucoadhesive films increase the advantage of higher efficiency and drug localization in the affected region. In this research, mucoadhesive films, for the release of hydrocortisone sodium succinate, were prepared using different ratios of chitosan, gelatin and keratin. In the first step, chitosan and gelatin proportions were optimized after evaluating the mechanical properties, swelling capacity, water uptake, stability, and biodegradation of the films. Then, keratin was added at different percentages to the optimum composite of chitosan and gelatin together with the drug. The results of surface pH showed that none of the samples were harmful to the buccal cavity. FTIR analysis confirmed the influence of keratin on the structure of the composite. The presence of a higher amount of keratin in the composite films resulted in high mechanical, mucoadhesive properties and stability, low water uptake and biodegradation in phosphate buffer saline (pH = 7.4) containing 104 U/ml lysozyme. The release profile of the films ascertained that keratin is a rate controller in the release of the hydrocortisone sodium succinate. Finally, chitosan/gelatin/keratin composite containing hydrocortisone sodium succinate can be employed in dental applications.

3D printed TCP-based scaffold incorporating VEGF-loaded PLGA microspheres for craniofacial tissue engineering

OBJECTIVE Vascularization is a critical process during bone regeneration/repair and the lack of tissue vascularization is recognized as a major challenge in applying bone tissue engineering methods for cranial and maxillofacial surgeries. The aim of our study is to fabricate a vascular endothelial growth factor (VEGF)-loaded gelatin/alginate/β-TCP composite scaffold by 3D printing method using a computer-assisted design (CAD) model. METHODS The paste, composed of (VEGF-loaded PLGA)-containing gelatin/alginate/β-TCP in water, was loaded into standard Nordson cartridges and promptly employed for printing the scaffolds. Rheological characterization of various gelatin/alginate/β-TCP formulations led to an optimized paste as a printable bioink at room temperature. RESULTS The in vitro release kinetics of the loaded VEGF revealed that the designed scaffolds fulfill the bioavailability of VEGF required for vascularization in the early stages of tissue regeneration. The results were confirmed by two times increment of proliferation of human umbilical vein endothelial cells (HUVECs) seeded on the scaffolds after 10 days. The compressive modulus of the scaffolds, 98±11MPa, was found to be in the range of cancellous bone suggesting their potential application for craniofacial tissue engineering. Osteoblast culture on the scaffolds showed that the construct supports cell viability, adhesion and proliferation. It was found that the ALP activity increased over 50% using VEGF-loaded scaffolds after 2 weeks of culture. SIGNIFICANCE The 3D printed gelatin/alginate/β-TCP scaffold with slow releasing of VEGF can be considered as a potential candidate for regeneration of craniofacial defects.

Surface modification of dental implants

Abstract Dental implant surface advancement techniques have been developing rapidly to facilitate osseointegration and bone formation on the implant surface and to enhance the predictability of accelerated implant therapy. Surface modifications have been proven effective on capitalizing the features of titanium that make it the material of choice in dental implantology. Some of these features include wettability, surface area, and osteogenic potential. The following chapter is a brief review of commercial methods of surface modification processing and demonstrates the advantages and disadvantages of each, noting potential for improvement when applicable. Prospective studies in surface modification of implants attempt to address problems in conventional implant treatment, from promoting soft-tissue adherence and antimicrobial properties to induction of osteogenic processes. Overall, prospective trends indicate a shift in the focus to increase the success rate in compromised patients, such as those suffering from osteoporosis, as well as improving soft-tissue integration onto the implant surface to reduce the risk of development of periimplant disease. Surface roughness continues to be optimized, with prospects of configuration at a nanoscale.

Evaluation of the in vitro biodegradation and biological behavior of poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite composite microsphere-sintered scaffold for bone tissue engineering

The objective of this research was to study the degradation and biological characteristics of the three-dimensional porous composite scaffold made of poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite microsphere using sintering method for potential bone tissue engineering. Our previous experimental results demonstrated that poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite composite scaffold with a ratio of 4:1 sintered at 90ºC for 2 h has the greatest mechanical properties and a proper pore structure for bone repair applications. The weight loss percentage of both poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite and poly(lactic-co-glycolic acid) scaffolds demonstrated a monotonic trend with increasing degradation time, that is, the incorporation of nano-fluorhydroxyapatite into polymeric scaffold could lead to weight loss in comparison with that of pure poly(lactic-co-glycolic acid). The pH change for composite scaffolds showed that there was a slight decrease until 2 weeks after immersion in simulated body fluid, followed by a significant increase in the pH of simulated body fluid without a scaffold at the end of immersion time. The mechanical properties of composite scaffold were higher than that of poly(lactic-co-glycolic acid) scaffold at total time of incubation in simulated body fluid; however, it should be noted that the incorporation of nano-fluorhydroxyapatite into composite scaffold leads to decline in the relatively significant mechanical strength and modulus during hydrolytic degradation. In addition, MTT assay and alkaline phosphatase activity results defined that a general trend of increasing cell viability was seen for poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite scaffold sintered by time when compared to control group. Eventually, experimental results exhibited poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite microsphere-sintered scaffold is a promising scaffold for bone repair.

Collagenous matrix supported by a 3D-printed scaffold for osteogenic differentiation of dental pulp cells

OBJECTIVE A systematic characterization of hybrid scaffolds, fabricated based on combinatorial additive manufacturing technique and freeze-drying method, is presented as a new platform for osteoblastic differentiation of dental pulp cells (DPCs). METHODS The scaffolds were consisted of a collagenous matrix embedded in a 3D-printed beta-tricalcium phosphate (β-TCP) as the mineral phase. The developed construct design was intended to achieve mechanical robustness owing to 3D-printed β-TCP scaffold, and biologically active 3D cell culture matrix pertaining to the Collagen extracellular matrix. The β-TCP precursor formulations were investigated for their flow-ability at various temperatures, which optimized for fabrication of 3D printed scaffolds with interconnected porosity. The hybrid constructs were characterized by 3D laser scanning microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and compressive strength testing. RESULTS The in vitro characterization of scaffolds revealed that the hybrid β-TCP/Collagen constructs offer superior DPCs proliferation and alkaline phosphatase (ALP) activity compared to the 3D-printed β-TCP scaffold over three weeks. Moreover, it was found that the incorporation of TCP into the Collagen matrix improves the ALP activity. SIGNIFICANCE The presented results converge to suggest the developed 3D-printed β-TCP/Collagen hybrid constructs as a new platform for osteoblastic differentiation of DPCs for craniomaxillofacial bone regeneration.

3D printed tissue engineered model for bone invasion of oral cancer

Recent advances in three-dimensional printing technology have led to a rapid expansion of its applications in tissue engineering. The present study was designed to develop and characterize an in vitro multi-layered human alveolar bone, based on a 3D printed scaffold, combined with tissue engineered oral mucosal model. The objective was to incorporate oral squamous cell carcinoma (OSCC) cell line spheroids to the 3D model at different anatomical levels to represent different stages of oral cancer. Histological evaluation of the 3D tissue model revealed a tri-layered structure consisting of distinct epithelial, connective tissue, and bone layers; replicating normal oral tissue architecture. The mucosal part showed a well-differentiated stratified oral squamous epithelium similar to that of the native tissue counterpart, as demonstrated by immunohistochemistry for cytokeratin 13 and 14. Histological assessment of the cancerous models demonstrated OSCC spheroids at three depths including supra-epithelial level, sub-epithelial level, and deep in the connective tissue-bone interface. The 3D tissue engineered composite model closely simulated the native oral hard and soft tissues and has the potential to be used as a valuable in vitro model for the investigation of bone invasion of oral cancer and for the evaluation of novel diagnostic or therapeutic approaches to manage OSCC in the future.

Dual Porosity Protein-based Scaffolds with Enhanced Cell Infiltration and Proliferation

Abstract3D dual porosity protein-based scaffolds have been developed using the combination of foaming and freeze-drying. The suggested approach leads to the production of large, highly porous scaffolds with negligible shrinkage and deformation compared to the conventional freeze-drying method. Scanning electron microscopy, standard histological processing and mercury intrusion porosimetry confirmed the formation of a dual network in the form of big primary pores (243 ± 14 µm) embracing smaller secondary pores (42 ± 3 µm) opened onto their surface, resembling a vascular network. High interconnectivity of the pores, confirmed by micro-CT, is shown to improve diffusion kinetics and support a relatively uniform distribution of isolated human dental pulp stem cells within the scaffold compared to conventional scaffolds. Dual network scaffolds indicate more than three times as high cell proliferation capability as conventional scaffolds in 14 days.