Faculty Bibliography

Dental caries are treated by the surgical removal of infected tissue where the biological mineral, hydroxyapatite, has been eroded. For early carious lesions, surgical methods have increasingly been replaced by minimally invasive dentistry protocols to arrest the lesion progression by controlling plaque formation and promoting dentin remineralization. Zinc phosphate mineral deposition in dentinal tubules was studied as a modality for the treatment of dental caries. Extracted permanent human molars, with and without carious lesions, were employed to study the coverage and depth of mineral deposition with in situ mixing of zinc and phosphate salt solutions. Milled hydroxyapatite was employed as a surrogate for dentin in the study of mineral formation in tubules. The mineral composition was identified by X-ray powder diffraction. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed the deposition of zinc phosphate minerals that effectively occlude dentinal tubules by crystallization within dentinal tubules. Mineral deposition was similarly observed at the site of a carious lesion, which highlights the feasibility of zinc phosphate deposition for the treatment of dental caries.

Bone tissue has the capacity to regenerate under healthy conditions, but complex cases like critically sized defects hinder natural bone regeneration, necessitating surgery, and use of a grafting material for rehabilitation. The field of bone tissue engineering (BTE) has pioneered ways to address such issues utilizing different biomaterials to create a platform for cell migration and tissue formation, leading to improved bone reconstruction. One such approach involves 3D-printed patient-specific scaffolds designed to aid in regeneration of boney defects. This study aimed to develop and characterize 3D printed scaffolds composed of type I collagen augmented with β-tricalcium phosphate (COL/β-TCP). A custom-built direct inkjet write (DIW) printer was used to fabricate β-TCP, COL, and COL/β-TCP scaffolds using synthesized colloidal gels. After chemical crosslinking, the scaffolds were lyophilized and subjected to several characterization techniques, including light microscopy, scanning electron microscopy, and x-ray diffraction to evaluate morphological and chemical properties. In vitro evaluation was performed using human osteoprogenitor cells to assess cytotoxicity and proliferative capacity of the different scaffold types. Characterization results confirmed the presence of β-TCP in the 3D printed COL/β-TCP scaffolds, which exhibited crystals that were attributed to β-TCP due to the presence of calcium and phosphorus, detected through energy dispersive x-ray spectroscopy. In vitro studies showed that the COL/β-TCP scaffolds yielded more favorable results in terms of cell viability and proliferation compared to β-TCP and COL scaffolds. The novel COL/β-TCP scaffold constructs hold promise for improving BTE applications and may offer a superior environment for bone regeneration compared with conventional COL and β-TCP scaffolds.

Collagen, an abundant extracellular matrix protein, has shown hemostatic, chemotactic, and cell adhesive characteristics, making it an attractive choice for the fabrication of tissue engineering scaffolds. The aim of this study was to synthesize a fibrillar colloidal gel from Type 1 bovine collagen, as well as three dimensionally (3D) print scaffolds with engineered pore architectures. 3D-printed scaffolds were also subjected to post-processing through chemical crosslinking (in N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide) and lyophilization. The scaffolds were physicochemically characterized through Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis, Differential Scanning Calorimetry, and mechanical (tensile) testing. In vitro experiments using Presto Blue and Alkaline Phosphatase assays were conducted to assess cellular viability and the scaffolds' ability to promote cellular proliferation and differentiation. Rheological analysis indicated shear thinning capabilities in the collagen gels. Crosslinked and lyophilized 3D-printed scaffolds were thermally stable at 37 °C and did not show signs of denaturation, although crosslinking resulted in poor mechanical strength. PB and ALP assays showed no signs of cytotoxicity as a result of crosslinking. Fibrillar collagen was successfully formulated into a colloidal gel for extrusion through a direct inkjet writing printer. 3D-printed scaffolds promoted cellular attachment and proliferation, making them a promising material for customized, patient-specific tissue regenerative applications.

Sodium glucose cotransporter-2 inhibitors (SGLT2is) promote urinary glucose excretion and decrease plasma glucose levels independent of insulin. Canagliflozin (CANA) is an SGLT2i, which is widely prescribed, to reduce cardiovascular complications, and as a second-line therapy after metformin in the treatment of type 2 diabetes mellitus. Despite the robust metabolic benefits, reductions in bone mineral density (BMD) and cortical fractures were reported for CANA-treated subjects. In collaboration with the National Institute on Aging (NIA)-sponsored Interventions Testing Program (ITP), we tested skeletal integrity of UM-HET3 mice fed control (137 mice) or CANA-containing diet (180 ppm, 156 mice) from 7 to 22 months of age. Micro-computed tomography (micro-CT) revealed that CANA treatment caused significant thinning of the femur mid-diaphyseal cortex in both male and female mice, did not affect trabecular bone architecture in the distal femur or the lumbar vertebra-5 in male mice, but was associated with thinning of the trabeculae at the distal femur in CANA-treated female mice. In male mice, CANA treatment is associated with significant reductions in cortical bone volumetric BMD by micro-CT, and by quantitative backscattered scanning electron microscopy. Raman microspectroscopy, taken at the femur mid-diaphyseal posterior cortex, showed significant reductions in the mineral/matrix ratio and an increased carbonate/phosphate ratio in CANA-treated male mice. These data were supported by thermogravimetric assay (TGA) showing significantly decreased mineral and increased carbonate content in CANA-treated male mice. Finally, the sintered remains of TGA were subjected to X-ray diffraction and showed significantly higher fraction of whitlockite, a calcium orthophosphate mineral, which has higher resorbability than hydroxyapatite. Overall, long-term CANA treatment compromised bone morphology and mineral composition of bones, which likely contribute to increased fracture risk seen with this drug.

BACKGROUND:While autografts to date remain the "gold standard" for bone void fillers, synthetic bone grafts have garnered attention due to their advantages such as ability to be tailored in terms of its physical and chemical properties. Bioactive glass (BG), an inorganic material, has the capacity to form a strong bond with bone by forming a bone-like apatite surface, enhancing osteogenesis. Coupled with three-dimensional printing it is possible to maximize bone regenerative properties of the BG. OBJECTIVE:The objective of this study was to synthesize and characterize 3D printed mesoporous bioactive glass (MBG), BG 45S5, and compare to β-Tricalcium phosphate (β-TCP) based scaffolds; test cell viability and osteogenic differentiation on human osteoprogenitor cells in vitro. METHODS:MBG, BG 45S5, and β-TCP were fabricated into colloidal gel suspensions, tested with a rheometer, and manufactured into scaffolds using a 3D direct-write micro-printer. The materials were characterized in terms of microstructure and composition with Thermogravimetric Analyzer/Differential Scanning Calorimeter (TGA/DSC), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Micro-Computed Tomography (μ-CT), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and Mattauch-Herzog-Inductively Coupled Plasma-Mass Spectrometry (MH-ICP-MS). RESULTS:Scaffolds were tested for cell proliferation and osteogenic differentiation using human osteoprogenitor cells. Osteogenic media was used for differentiation, and immunocytochemistry for osteogenic markers Runx-2, Collagen-I, and Osteocalcin. The cell viability results after 7 days of culture yielded significantly higher (p < 0.05) results in β-TCP scaffolds compared to BG 45S5 and MBG groups. CONCLUSION/CONCLUSIONS:All materials expressed osteogenic markers after 21 days of culture in expansion and osteogenic media.

Bone defects are associated with trauma, congenital disorders, non-unions, or infections following surgical procedures. Defects which are unable to heal spontaneously are categorized as "critical sized" and are commonly treated using bone grafts in an effort to facilitate bone regeneration and stabilization. Grafting materials can be either natural or synthetic, each having their respective advantages and disadvantages. Synthetic bone grafts are favored due to their ability to be tailored to exhibit desired properties and geometric configurations. β-tricalcium phosphate (β-TCP) is a synthetic grafting material that has been widely utilized for regenerative purposes due to its favorable osteoconductive properties. In combination with 3D printing, grafting materials can be further customized with respect to their macro and micro features. One way to customize devices is by using 3D printing and varying the surface area, by varying the internal component measurements. The objective of this study was to compare the effect of porosity and surface area of 3D printed β-TCP scaffolds with different strut diameters and the effect on cell proliferation in vitro. ß-TCP scaffolds were printed using a custom-built 3D direct-write micro printer with syringes equipped with different extrusion tip diameters (fdiameter: 200 µm, 250 µm and 330 µm). After sintering and post processing, scaffolds were subjected to micro-computed tomography (µCT) and a Scanning Electron Microscope (SEM) to evaluate surface area and porosity, respectively. Compressive strength was assessed using a universal testing machine. Cell proliferation was assessed through cellular viability, using human osteoprogenitor cells. The surface area of the scaffolds was found to increase with smaller strut diameters. Statistically significant differences (p<0.05) were detected for cellular proliferation, between the smallest extrusion diameter, 200 μm, and the largest diameter, 330 μm, after 48-, 72-, and 168-hours. No statistical significances were detected (p>0.05) with regards to the mechanical properties between groups. This study demonstrated that a smaller diameter rod yielded a higher surface area resulting in increased levels of cellular proliferation. Therefore, tailoring rod dimensions has the capacity to enhance cellular adhesion and ultimately, proliferation.

Bone defects are often linked to congenital disorders, high impact traumas, tumors or oncological resections. Potential treatment options include autografts, allografts, or synthetic grafts, such as bioactive ceramic-based materials which have been successfully utilized in an effort to regenerate bone. β-tricalcium phosphate (β-TCP), is a commonly utilized bioactive ceramic for regenerative purposes with favorable osteoconductive properties. Alternatively, Synthetic Bone Mineral (SBM) has been previously utilized in in vivo experiments as a supplement for bone loss treatment. As a potential alternative to β-TCP, it is also a bioactive ceramic, which consists of a carbonate hydroxyapatite with ionic substitutions such as F^−, Zn²⁺ and Mg²⁺. The objective of this work was to characterize the physiochemical properties of the colloidal gel obtained from a formulation of SBM and compare the properties directly to β-TCP. Mechanical properties were evaluated for both materials in bulk, using Biaxial Flexural Strength tests. Scanning electron microscopy and micro-computed tomography were utilized to explore the structure of the bulk material and the three dimensionally (3D) printed scaffolds. Inductive coupled plasma (ICP), X-ray diffraction (XRD), and Fourier transform infrared spectrometry (FT-IR), were utilized to determine the calcium-phosphorous ratio (Ca:P), quantitative analysis of crystalline phases, and functional groups, respectively. Thermogravimetric analysis (TGA) was used to quantify the weight percent of water, organic components, carbonate and mineral in the SBM colloidal gel. Flexural strength of SBM discs sintered at 700°C were statistically analogous to β-TCP sintered at 900°C. The Ca:P ratio of the sintered SBM was found to be 1.47 ± 0.04, statistically different from β-TCP sintered at higher temperatures. The carbonate content of the SBM was determined to be ~2.8% ± 0.9. The novel SBM colloidal gel has hence been characterized chemically and physically for its potential use in 3D printing grafts to repair critical sized bone defects.

Osteopenia and osteoporosis affect over 40 million US adults 50 years and older. Both diseases are strongly influenced by estrogen and nutritional-mineral deficiencies. This study investigates the efficacy of orally delivered synthetic-bone-mineral (SBM), a newly developed calcium phosphate based biomaterial, on reversing bone loss induced by these two critical deficiencies. Thirty 3-month-old female rats were randomly allocated to either control-sham surgery on normal diet; or one of the four experimental groups: Sham surgery on a low mineral diet (LMD), ovariectomized (OVX) on LMD, OVX on LMD with SBM with/without fluoride (F). The rats were sacrificed after 6 months, at 9-month-old. After 6 months, although all groups lost bone mineral density relative to controls, the supplemented OVX rats showed higher bone mineral density than their unsupplemented counterparts. The 2 SBM supplemented groups improved bone loading capacity by 28.1 and 35.4% compared to the OVX LMD group. Bones from supplemented rats exhibited higher inorganic/organic ratios. The addition of F did not have a significant influence on bone loss. Our findings suggest that SBM supplement is effective in maintaining bone health and offsetting the deleterious effects of estrogen and/or mineral deficiencies on bone density, microarchitecture, and strength.

AIM/OBJECTIVE:Die silicone materials are used to build chairside composite restorations. The purpose of this study was to compare the flowability, dimension accuracy, and tear strength of four elastomeric die materials. MATERIAL AND METHODS/METHODS:Materials were divided into four groups: Mach-2 (M2), Scan Die (SD), GrandioSO Inlay System (GIS), and Impregum-F (IM). Flowability analysis was carried out using the shark fin test (SFT). For dimension accuracy, impressions were taken from a premolar Class I preparation and an elastomeric model was cast. Composite resin restorations were built and positioned into the premolar for gap measurement. The mean gap length was divided into three levels: acceptable (A), not acceptable (NA), and misfit (M). For tear strength, strip specimens were made with a V-shaped notch (n = 6). The specimens were tested in a universal machine until tear. All data were analyzed statistically with a confidence interval of 95%. RESULTS:GIS showed the lowest flowability values, with no differences between IM, M2, and SD. For dimension accuracy, IM showed 100% 'A' gap values, followed by M2 (80%), SD (60%), and GIS (60%). For tear strength, IM showed the highest values, followed by M2, GIS, and SD. CONCLUSIONS:M2, SD, and IM had similar flowability, while GIS had the lowest. IM presented higher tear strength than M2, followed by GIS and SD. IM showed the highest degrees of acceptable gap filling, followed by M2.