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The Standards Coordinating Body for Gene, Cell, and Regenerative Medicines and Cell-Based Drug Discovery (SCB) supports the development and commercialization of regenerative medicine products by identifying and addressing industry-wide challenges through standards. Through extensive stakeholder engagement, the implementation of rapid microbial testing methods (RMTMs) was identified as a high-priority need that must be addressed to facilitate more timely release of products. Since 2017, SCB has coordinated efforts to develop standards for this area through surveys, weekly meetings, workshops, leadership in working groups and participation in standards development organizations. This article describes the results of these efforts and discusses the current landscape of RMTMs for regenerative medicine products. Based on discussions with stakeholders across the field, an overview of traditional culture-based methods and limitations, alternative microbial testing technologies and current challenges, fit-for-purpose rapid microbial testing and case studies, risk-based strategies for selection of novel rapid microbial test methods and ongoing standards efforts for rapid microbial testing are captured here. To this end, SCB is facilitating several initiatives to address challenges associated with rapid microbial testing for regenerative medicine products. Two documentary standards are under development: an International Organization for Standardization standard to provide the framework for a risk-based approach to selecting fit-for-purpose assays primarily intended for cell and gene therapy products and an ASTM standard guide focused on sampling methods for microbial testing methods in tissue-engineered medical products. Working with the National Institute of Standards and Technology, SCB expects to facilitate the process of developing publicly available microbial materials for inter-laboratory testing. These studies will help collect the data necessary to facilitate validation of novel rapid methods. Finally, SCB has been working to increase awareness of, dialog about and participation in efforts to develop standards in the regenerative medicine field. [ABSTRACT FROM AUTHOR]

The emergence of cell-based therapeutics has increased the need for high-quality, robust and validated measurements for cell characterization. Cell count, being one of the most fundamental measures for cell-based therapeutics, now requires increased levels of measurement confidence. The National Institute of Standards and Technology (NIST) and the US Food and Drug Administration (FDA) jointly hosted a workshop focused on cell counting in April 2017 entitled “NIST-FDA Cell Counting Workshop: Sharing Practices in Cell Counting Measurements.” The focus of the workshop was on approaches for selecting, designing and validating cell counting methods and overcoming gaps in obtaining sufficient measurement assurance for cell counting. Key workshop discussion points, representing approximately 50 subject matter experts from industry, academia and government agencies, are summarized here. A key conclusion is the need to design the most appropriate cell counting method, including control/measurement assurance strategies, for a specific counting purposes. There remains a need for documentary standards for streamlining the process to develop, qualify and validate cell counting measurements as well as community-driven efforts to develop new or improved biological and non-biological reference materials. [ABSTRACT FROM AUTHOR]

The article reflects on the need of defining quality attributes to enable measurement assurance for cell therapy products and highlights definition of critical quality attributes (CQA) as per the U.S. Food and Drug Administration.

Abstract: Cells are known to sense and respond to the physical properties of their environment and those of tissue scaffolds. Optimizing these cell–material interactions is critical in tissue engineering. In this work, a simple and inexpensive combinatorial platform was developed to rapidly screen three-dimensional (3D) tissue scaffolds and was applied to screen the effect of scaffold properties for tissue engineering of bone. Differentiation of osteoblasts was examined in poly(ethylene glycol) hydrogel gradients spanning a 30-fold range in compressive modulus (≈10 kPa to ≈300 kPa). Results demonstrate that material properties (gel stiffness) of scaffolds can be leveraged to induce cell differentiation in 3D culture as an alternative to biochemical cues such as soluble supplements, immobilized biomolecules and vectors, which are often expensive, labile and potentially carcinogenic. Gel moduli of ≈225 kPa and higher enhanced osteogenesis. Furthermore, it is proposed that material-induced cell differentiation can be modulated to engineer seamless tissue interfaces between mineralized bone tissue and softer tissues such as ligaments and tendons. This work presents a combinatorial method to screen biological response to 3D hydrogel scaffolds that more closely mimics the 3D environment experienced by cells in vivo. [Copyright &y& Elsevier]

Abstract: Dimethacrylate polymers and composites are seeing increased usage in orthopedics. As these applications require the material to integrate with the surrounding tissues, direct contact cytotoxicity assays should be used to assess the biocompatibility. This study utilized a combinatorial testing platform to evaluate the cell response to dimethacrylate composites with a variety of properties on a single sample. MC3T3-E1 pre-osteoblasts were cultured directly on composites with varying filler content, filler type, degree of conversion (DC), and surface topography. Cell viability, density, and area depended on an interplay of the material properties, with low DC causing a reduction in cell area but having minimal effect on cell viability, high filler content causing an increase in cell density, and filler content/type altering the surface roughness as a function of DC. The combinatorial testing platform successfully quantified the effects of numerous material properties on several aspects of the osteoblast response. [Copyright &y& Elsevier]

Abstract: We have explored the use of X-ray microcomputed tomography (μCT) for assessing cell adhesion and proliferation in polymer scaffolds. Common methods for examining cells in scaffolds include fluorescence microscopy and soluble assays for cell components such as enzymes, protein or DNA. Fluorescence microscopy is generally qualitative and cannot visualize the scaffold interior. Soluble assays quantitatively measure cell number but do not yield information on cell spatial distribution. Herein, the ability of μCT to detect cells in scaffolds was compared with fluorescence microscopy and a soluble DNA assay. Comparisons were performed using polymer scaffolds that were seeded with cells at different densities and cultured for different times. The results showed that fluorescence microscopy had better resolution than μCT and that the soluble DNA assay was approximately 5× more sensitive than μCT under the conditions tested. However, μCT was able to image through opaque scaffolds to yield quantitative 3D imaging and analysis via a single, non-invasive modality. Quantitative μCT analysis of cell penetration into scaffolds was demonstrated. Further, quantitative μCT volume analysis required that the cell density in the scaffolds be greater than 1 million cells per mL indicating that μCT is best suited for quantifying cells at relatively high density during culture in scaffolds. In sum, the results demonstrate the benefits and limitations of using μCT for 3D imaging and analysis of cell adhesion and proliferation in polymer scaffolds. [Copyright &y& Elsevier]

Abstract: Objectives: The main objective of this study was to assess the feasibility of using X-ray microcomputed tomography (μCT) as a viable technique for accurate measurements of composite volumetric changes due to polymerization. Methods: μCT, a non-destructive 3D imaging technique that measures the intensity of content at each voxel, was used to determine the volume of experimental and commercial polymeric dental composites before and after photopolymerization. The experimental composites consisted of various mass ratios of 2,2-bis(4-(2-hydroxy-3-methacryloxypropoxy)-phenyl]propane (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) filled with various amounts of barium boroaluminosilicate glass and fumed amorphous silica. Polymerization shrinkage was determined using μCT and shrinkage calculated based on density measurements. Results: μCT was successfully used to calculate volumetric shrinkage of dental composites. Results agreed well with shrinkage obtained via density measurements of the same sample. The addition of radio opaque filler was necessary to achieve sufficient contrast between the sample and background. Appropriate image analysis procedures were needed to obtain the volumes of sample specimens. Significance: μCT enables the characterization of polymerization shrinkage under clinically relevant conditions. In particular, the sample geometry and the physical state (liquid or solid) are flexible. The current test allowed multiple samples to be measured at the same time. In addition, the ability to accurately measure the size and shape of the object will allow multiple properties to be determined simultaneously. [Copyright &y& Elsevier]

Abstract: The effects of co-monomer composition and irradiation time in a model two-component dimethacrylate dental resin blend were evaluated using combinatorial methods to determine the degree of methacrylate conversion and resulting mechanical properties. 2-Dimensional gradient samples varying in monomer composition and light exposure time were fabricated. The conversion was measured using near infrared spectroscopy (NIR) and the mechanical properties (i.e., hardness and elastic modulus) were determined using nanoindentation via the continuous stiffness method. An excellent correlation was observed between the reaction conversion and mechanical properties for the cross-linked networks. The methacrylate conversion ranged from 40% to 85% and the mechanical properties increased over two orders of magnitude over this conversion range. The ultimate reaction conversion and mechanical properties depended on both the co-monomer composition and cure time. [Copyright &y& Elsevier]

Cure kinetics and network properties of hydrogels prepared by the reaction of chitosan and a water-soluble blocked diisocyanate cross-linker have been measured using swelling experiments and rheometry. The gel time measured by two different rheological methods, the rate equivalence of the change in modulus as a function of reaction time (G′G″ crossover) and the critical gel via the Winter–Chambon approach, are comparable. The reaction rate increased with increased temperature following the Arrhenius behavior, from which apparent activation energies can be determined. The network moduli can be tailored by adjusting the ratio of chitosan to cross-linker or the solution concentration. This allows for the formation of processable chemically cross-linked chitosan hydrogels with controlled kinetics and mechanical properties. [Copyright &y& Elsevier]

Abstract: Nanofiber scaffolds are effective for tissue engineering since they emulate the fibrous nanostructure of native extracellular matrix (ECM). Although electrospinning has been the most common approach for fabricating nanofiber scaffolds, airbrushing approaches have also been advanced for making nanofibers. For airbrushing, compressed gas is used to blow polymer solution through a small nozzle which shears the polymer solution into fibers. Our goals were 1) to assess the versatility of airbrushing, 2) to compare the properties of airbrushed and electrospun nanofiber scaffolds and 3) to test the ability of airbrushed nanofibers to support stem cell differentiation. The results demonstrated that airbrushing could produce nanofibers from a wide range of polymers and onto a wide range of targets. Airbrushing was safer, 10-fold faster, 100-fold less expensive to set-up and able to deposit nanofibers onto a broader range of targets than electrospinning. Airbrushing yielded nanofibers that formed loosely packed bundles of aligned nanofibers, while electrospinning produced un-aligned, single nanofibers that were tightly packed and highly entangled. Airbrushed nanofiber mats had larger pores, higher porosity and lower modulus than electrospun mats, results that were likely caused by the differences in morphology (nanofiber packing and entanglement). Airbrushed nanofiber scaffolds fabricated from 4 different polymers were each able to support osteogenic differentiation of primary human bone marrow stromal cells (hBMSCs). Finally, the differences in airbrushed versus electrospun nanofiber morphology caused differences in hBMSC shape where cells had a smaller spread area and a smaller volume on airbrushed nanofiber scaffolds. These results highlight the advantages and disadvantages of airbrushing versus electrospinning nanofiber scaffolds and demonstrate that airbrushed nanofiber scaffolds can support stem cell differentiation. [Copyright &y& Elsevier]

Abstract: Proliferation and differentiation of cells are known to be influenced by the physical properties of the extracellular environment. Previous studies examining biophysics underlying cell response to matrix stiffness utilized a two-dimensional (2D) culture format, which is not representative of the three-dimensional (3D) tissue environment in vivo. We report on the effect of 3D matrix modulus on human bone marrow stromal cell (hBMSC) differentiation. hBMSCs underwent osteogenic differentiation in poly(ethylene glycol) hydrogels of all modulus (300-fold modulus range, from 0.2 kPa to 59 kPa) in the absence of osteogenic differentiation supplements. This osteogenic differentiation was modulus-dependent and was enhanced in stiffer gels. Osteogenesis in these matrices required integrin-protein ligation since osteogenesis was inhibited by soluble Arginine-Glycine-Aspartate-Serine peptide, which blocks integrin receptors. Immunostained images revealed lack of well-defined actin filaments and microtubules in the encapsulated cells. Disruption of mechanosensing elements downstream of integrin binding that have been identified from 2D culture such as actin filaments, myosin II contraction, and RhoA kinase did not abrogate hBMSC material-driven osteogenic differentiation in 3D. These data show that increased hydrogel modulus enhanced osteogenic differentiation of hBMSCs in 3D scaffolds but that hBMSCs did not use the same mechanosensing pathways that have been identified in 2D culture. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: The objectives of this study were to (1) demonstrate X-ray micro-computed tomography (μCT) as a viable method for determining the polymerization shrinkage and microleakage on the same sample accurately and non-destructively, and (2) investigate the effect of sample geometry (e.g., C-factor and volume) on polymerization shrinkage and microleakage. Methods: Composites placed in a series of model cavities of controlled C-factors and volumes were imaged using μCT to determine their precise location and volume before and after photopolymerization. Shrinkage was calculated by comparing the volume of composites before and after polymerization and leakage was predicted based on gap formation between composites and cavity walls as a function of position. Dye penetration experiments were used to validate μCT results. Results: The degree of conversion (DC) of composites measured using FTIR microspectroscopy in reflectance mode was nearly identical for composites filled in all model cavity geometries. The shrinkage of composites calculated based on μCT results was statistically identical regardless of sample geometry. Microleakage, on the other hand, was highly dependent on the C-factor as well as the composite volume, with higher C-factors and larger volumes leading to a greater probability of microleakage. Spatial distribution of microleakage determined by μCT agreed well with results determined by dye penetration. Significance: μCT has proven to be a powerful technique in quantifying polymerization shrinkage and corresponding microleakage for clinically relevant cavity geometries. [Copyright &y& Elsevier]

Abstract: The effect of blending two silk proteins, regenerated Bombyx mori fibroin and synthetic spidroin containing RGD, on silk film material structure (β-sheet content) and properties (solubility), as well as on biological response (osteoblast adhesion, proliferation and differentiation) was investigated. Although the elasticity and strength of silks make them attractive candidates for bone, ligament, and cartilage tissue engineering applications, silk proteins generally lack bioactive peptides for enhancing cell functions. Thus, a synthetic spider silk, spidroin, containing two RGD cell adhesive sequences (RGD-spidroin) was engineered. RGD-spidroin was blended with different ratios of fibroin and spun coat into films on glass coverslips. β-Sheet formation, contact angle, surface topography and RGD surface presentation were characterized and correlated with cell behavior. We found that the amount of β-sheet formation was directly related to the RGD-spidroin content of the blends after annealing, with the pure RGD-spidroin demonstrating the highest amount of β-sheet content. The increased β-sheet content improved film stability under culture conditions. A new visualization technique demonstrated that the RGD presentation on the film surface was affected by both the RGD-spidroin content and annealing conditions. It was determined that 10mass% RGD-spidroin was necessary to improve film stability and to achieve osteoblast attachment and differentiation. [Copyright &y& Elsevier]

Abstract: Objectives: The increased usage of composite dental restorations underscores the need for continued improvements in material properties. Well-controlled sample fabrication and reproducible methods to quantify and compare material properties will accelerate material design and optimization. Our objectives were to fabricate samples encompassing a range of processing parameters and develop techniques that systematically quantify multiple properties of these samples, thus reducing sample-to-sample variation while concurrently testing numerous processing conditions. Methods: Gradient samples were prepared to evaluate the effects of composition and irradiation time. Comonomer ratio of 2,2-bis[p-2′-hydroxy-3′-methacryloxypropoxy]-phenyl]propane (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) was varied discretely, and irradiation time was varied continuously across each composition. Degree of conversion was measured using infrared spectroscopy, mechanical properties were evaluated using nanoindentation, and cell viability and density were quantified using fluorescence microscopy. Results: Higher BisGMA contents increased elastic moduli while higher TEGDMA contents increased conversions. Cell response depended only on irradiation time and not composition, with conversions of at least 52% and 60% required for unaffected viability and cell density, respectively. A single composition–irradiation combination to achieve all of the ‘best’ properties (highest conversion, highest elastic modulus, lack of cytotoxicity) was not identified, illustrating the necessity of testing all combinations for multiple relevant properties. Significance: Simultaneously screening composition and conversion increased the experimental throughput and allowed for the quantification of chemical, mechanical, and biological properties in a controlled, reproducible fashion. This 2D gradient approach is useful for optimizing compositions and processing parameters to achieve the desired combination of properties. [Copyright &y& Elsevier]

Abstract: Gas-separation membranes composed of polyethers such as poly(ethylene glycol)diacrylate (PEGda) or poly(propylene glycol)diacrylate (PPGda) exhibit high CO2 solubility selectivity, which makes them attractive for use in H2 and air purification. In this work, we investigate the factors governing CO2 and H2 transport in mixed polyether matrices. Addition of semicrystalline poly(ethylene oxide)s to amorphous PEGda lowers the net CO2 permeability and CO2/H2 selectivity due to crystal formation. Gas permeation through the amorphous fraction, however, remains unaffected, confirming the existence of a molecular weight limit below which the entire membrane participates in gas transport. The permeabilities of CO2 and H2, as well as their activation energy of permeation, in miscible PEGda/PPGda blends follow the linear rule of mixtures over the temperature range explored. Incorporation of amine moieties employed in liquid membranes into either the PEGda matrix during crosslinking or the PEG backbone generally reduces CO2/H2 selectivity but occasionally improves CO2 permeability. [Copyright &y& Elsevier]

The development of standards for the field of regenerative medicine has been noted as a high priority by several road-mapping activities. Additionally, the U.S. Congress recognizes the importance of standards in the 21st Century Cure Act. Standards will help to accelerate and streamline cell and gene therapy product development, ensure the quality and consistency of processes and products, and facilitate their regulatory approval. Although there is general agreement for the need of additional standards for regenerative medicine products, a shared understanding of standards is required for real progress toward the development of standards to advance regenerative medicine. Here, we describe the roles of standards in regenerative medicine as well as the process for standards development and the interactions of different entities in the standards development process. Highlighted are recent coordinated efforts between the U.S. Food and Drug Administration and the National Institute of Standards and Technology to facilitate standards development and foster science that underpins standards development. [ABSTRACT FROM AUTHOR]

Objective Resin-based composites are known to elute leachables that include unincorporated starting materials. The objective of this work was to determine the effect of common dental monomers and initiators on Streptococcus mutans biofilm metabolic activity and biomass. Methods S. mutans biofilms were inoculated in the presence of bisphenol A glycerolate dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA), camphorquinone (CQ), and ethyl 4-(dimethylamino)benzoate (4E) at 0.01 μg/mL up to 500 μg/mL, depending on the aqueous solubility of each chemical. Biofilms were evaluated at 4 h and 24 h for pH ( n = 3–8), biomass via crystal violet ( n = 12), metabolic activity via tetrazolium salt ( n = 12), and membrane permeability for selected concentrations via confocal microscopy ( n = 6). Parametric and non-parametric statistics were applied. Results 500 μg/mL TEGDMA reduced 24 h metabolic activity but not biomass, similar to prior results with leachables from undercured BisGMA-TEGDMA polymers. 50 μg/mL BisGMA reduced biofilm biomass and activity, slightly delayed the pH drop, and decreased the number of cells with intact membranes. 100 μg/mL CQ delayed the pH drop and metabolic activity at 4 h but then significantly increased the 24 h metabolic activity. 4E had no effect up to 10 μg/mL. Significance Monomers and initiators that leach from resin composites affect oral bacterial biofilm growth in opposite ways. Leachables, which can be released for extended periods of time, have the potential to alter oral biofilm biomass and activity and should be considered in developing and evaluating new dental materials. [ABSTRACT FROM AUTHOR]

Background aims Cell counting measurements are critical in the research, development and manufacturing of cell-based products, yet determining cell quantity with accuracy and precision remains a challenge. Validating and evaluating a cell counting measurement process can be difficult because of the lack of appropriate reference material. Here we describe an experimental design and statistical analysis approach to evaluate the quality of a cell counting measurement process in the absence of appropriate reference materials or reference methods. Methods The experimental design is based on a dilution series study with replicate samples and observations as well as measurement process controls. The statistical analysis evaluates the precision and proportionality of the cell counting measurement process and can be used to compare the quality of two or more counting methods. As an illustration of this approach, cell counting measurement processes (automated and manual methods) were compared for a human mesenchymal stromal cell (hMSC) preparation. Results For the hMSC preparation investigated, results indicated that the automated method performed better than the manual counting methods in terms of precision and proportionality. Discussion By conducting well controlled dilution series experimental designs coupled with appropriate statistical analysis, quantitative indicators of repeatability and proportionality can be calculated to provide an assessment of cell counting measurement quality. This approach does not rely on the use of a reference material or comparison to "gold standard" methods known to have limited assurance of accuracy and precision. The approach presented here may help the selection, optimization, and/or validation of a cell counting measurement process. [ABSTRACT FROM AUTHOR]

Objective Recurrent caries at the margins is a primary reason for restoration failure. The objectives of this study were to develop bonding agent with the double benefits of antibacterial and remineralizing capabilities, to investigate the effects of NACP filler level and solution pH on Ca and P ion release from adhesive, and to examine the antibacterial and dentin bond properties. Methods Nanoparticles of amorphous calcium phosphate (NACP) and a quaternary ammonium monomer (dimethylaminododecyl methacrylate, DMADDM) were synthesized. Scotchbond Multi-Purpose (SBMP) primer and adhesive served as control. DMADDM was incorporated into primer and adhesive at 5% by mass. NACP was incorporated into adhesive at filler mass fractions of 10%, 20%, 30% and 40%. A dental plaque microcosm biofilm model was used to test the antibacterial bonding agents. Calcium (Ca) and phosphate (P) ion releases from the cured adhesive samples were measured vs. filler level and solution pH of 7, 5.5 and 4. Results Adding 5% DMADDM and 10-40% NACP into bonding agent, and water-aging for 28 days, did not affect dentin bond strength, compared to SBMP control at 1 day (p>0.1). Adding DMADDM into bonding agent substantially decreased the biofilm metabolic activity and lactic acid production. Total microorganisms, total streptococci, and mutans streptococci were greatly reduced for bonding agents containing DMADDM. Increasing NACP filler level from 10% to 40% in adhesive increased the Ca and P ion release by an order of magnitude. Decreasing solution pH from 7 to 4 increased the ion release from adhesive by 6-10 folds. Significance Bonding agents containing antibacterial DMADDM and remineralizer NACP were formulated to have Ca and P ion release, which increased with NACP filler level from 10% to 40% in adhesive. NACP adhesive was "smart" and dramatically increased the ion release at cariogenic pH 4, when these ions would be most-needed to inhibit caries. Therefore, bonding agent containing DMADDM and NACP may be promising to inhibit biofilms and remineralize tooth lesions thereby increasing the restoration longevity. [ABSTRACT FROM AUTHOR]

Objectives: The objective of this study was to investigate the effects of dentine primer containing dual antibacterial agents, namely, 12-methacryloyloxydodecylpyridinium bromide (MDPB) and nanoparticles of silver (NAg), on dentine bond strength, dental plaque microcosm biofilm response, and fibroblast cytotoxicity for the first time. Methods: Scotchbond Multi-Purpose (SBMP) was used as the parent bonding agent. Four primers were tested: SBMP primer control (referred to as ''P''), P + 5% MDPB, P + 0.05% NAg, and P + 5% MDPB + 0.05% NAg. Dentine shear bond strengths were measured using extracted human teeth. Biofilms from the mixed saliva of 10 donors were cultured to investigate metabolic activity, colony-forming units (CFU), and lactic acid production. Human fibroblast cytotoxicity of the four primers was tested in vitro. Results: Incorporating MDPB and NAg into primer did not reduce dentine bond strength compared to control ( p > 0.1). SEM revealed well-bonded adhesive-dentine interfaces with numerous resin tags. MDPB or NAg each greatly reduced biofilm viability and acid production, compared to control. Dual agents MDPB + NAg had a much stronger effect than either agent alone ( p < 0.05), increasing inhibition zone size and reducing metabolic activity, CFU and lactic acid by an order of magnitude, compared to control. There was no difference in cytotoxicity between commercial control and antibacterial primers ( p > 0.1). Conclusions: The method of using dual agents MDPB + NAg in the primer yielded potent antibacterial properties. Hence, this method may be promising to combat residual bacteria in tooth cavity and invading bacteria at the margins. The dual agents MDPB + NAg may have wide applicability to other adhesives, composites, sealants and cements to inhibit biofilms and caries. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: Previous studies have developed calcium phosphate and fluoride releasing composites. Other studies have incorporated chlorhexidine (CHX) particles into dental composites. However, CHX has not been incorporated in calcium phosphate and fluoride composites. The objectives of this study were to develop nanocomposites containing amorphous calcium phosphate (ACP) or calcium fluoride (CaF2) nanoparticles and CHX particles, and investigate Streptococcus mutans biofilm formation and lactic acid production for the first time. Methods: Chlorhexidine was frozen via liquid nitrogen and ground to obtain a particle size of 0.62μm. Four nanocomposites were fabricated with fillers of: nano ACP; nano ACP+10% CHX; nano CaF2; nano CaF2 +10% CHX. Three commercial materials were tested as controls: a resin-modified glass ionomer, and two composites. S. mutans live/dead assay, colony-forming unit (CFU) counts, biofilm metabolic activity, and lactic acid were measured. Results: Adding CHX fillers to ACP and CaF2 nanocomposites greatly increased their antimicrobial capability. ACP and CaF2 nanocomposites with CHX that were inoculated with S. mutans had a growth medium pH>6.5 after 3 d, while the control commercial composites had a cariogenic pH of 4.2. Nanocomposites with CHX reduced the biofilm metabolic activity by 10–20 folds and reduced the acid production, compared to the controls. CFU on nanocomposites with CHX were three orders of magnitude less than that on commercial composite. Mechanical properties of nanocomposites with CHX matched a commercial composite without fluoride. Significance: The novel calcium phosphate and fluoride nanocomposites could be rendered antibacterial with CHX to greatly reduce biofilm formation, acid production, CFU and metabolic activity. The antimicrobial and remineralizing nanocomposites with good mechanical properties may be promising for a wide range of tooth restorations with anti-caries capabilities. [Copyright &y& Elsevier]

Abstract: Objectives: Calcium and phosphate ion-releasing resin composites are promising for remineralization. However, there has been no report on incorporating antibacterial agents to these composites. The objective of this study was to develop antibacterial and mechanically strong nanocomposites incorporating a quaternary ammonium dimethacrylate (QADM), nanoparticles of silver (NAg), and nanoparticles of amorphous calcium phosphate (NACP). Methods: The QADM, bis(2-methacryloyloxyethyl) dimethylammonium bromide (ionic dimethacrylate-1), was synthesized from 2-(N,N-dimethylamino)ethyl methacrylate and 2-bromoethyl methacrylate. NAg was synthesized by dissolving Ag 2-ethylhexanoate salt in 2-(tert-butylamino)ethyl methacrylate. Mechanical properties were measured in three-point flexure with bars of 2mm×2mm×25mm (n =6). Composite disks (diameter=9mm, thickness=2mm) were inoculated with Streptococcus mutans. The metabolic activity and lactic acid production of biofilms were measured (n =6). Two commercial composites were used as controls. Results: Flexural strength and elastic modulus of NACP+QADM, NACP+NAg, and NACP+QADM+NAg matched those of commercial composites with no antibacterial property (p >0.1). The NACP+QADM+NAg composite decreased the titer counts of adherent S. mutans biofilms by an order of magnitude, compared to the commercial composites (p <0.05). The metabolic activity and lactic acid production of biofilms on NACP+QADM+NAg composite were much less than those on commercial composites (p <0.05). Combining QADM and NAg rendered the nanocomposite more strongly antibacterial than either agent alone (p <0.05). Significance: QADM and NAg were incorporated into calcium phosphate composite for the first time. NACP+QADM+NAg was strongly antibacterial and greatly reduced the titer counts, metabolic activity, and acid production of S. mutans biofilms, while possessing mechanical properties similar to commercial composites. These nanocomposites are promising to have the double benefits of remineralization and antibacterial capabilities to inhibit dental caries. [Copyright &y& Elsevier]

Abstract: Objectives: The widespread incidence of recurrent caries highlights the need for improved dental restorative materials. The objective of this study was to synthesize low viscosity ionic dimethacrylate monomers (IDMAs) that contain quaternary ammoniums groups (antimicrobial functionalities) and are compatible with existing dental dimethacrylate-based monomers. Such monomers have the potential to copolymerize with other methacrylate monomers and produce antibacterial polymers. Methods: Two monomers (IDMA-1 and IDMA-2) were synthesized using the Menschutkin reaction and incorporated at 0–30% (by mass) into a 1:1 (by mass) bisphenol A glycerolate dimethacrylate (BisGMA):triethylene glycol dimethacrylate (TEGDMA) resin. Resin viscosity was quantified using rheology, and polymer degree of conversion (DC) and surface charge density were measured using Fourier transform infrared spectroscopy (FTIR) and fluorescein binding, respectively. Effects of IDMA-1 on initial attachment of Streptococcus mutans and on viability and metabolic activity (via reductase enzymes) of RAW 264.7 macrophage-like cells were quantified. Results: IDMA-1 and IDMA-2 were prepared and characterized. IDMA-1 was miscible with BisGMA:TEGDMA and slightly increased the resin viscosity and DC. As expected, polymeric surface charge density increased with increasing IDMA-1. Incorporation of 10% IDMA-1 into BisGMA:TEGDMA reduced bacterial colonization without affecting viability or metabolic activity of mammalian cells. Increasing IDMA-1 up to 30% had no additional effect on bacterial coverage, but ≥20% IDMA-1 significantly reduced macrophage density, viability, and metabolic activity. Leachables from polymers containing IDMA-1 were not cytotoxic. Significance: The Menschutkin reaction provides a facile, convenient means to synthesize new monomers with quaternary ammonium groups for dental and medical applications. [Copyright &y& Elsevier]

Abstract: Objective: Use X-ray microcomputed tomography (μCT), to test the hypothesis that composite shrinkage and sites of potential leakage in human teeth are non-uniformly distributed and depend on cavity geometry and C-factor. Methods: Two holes of equal volume but different dimensions were drilled into the exposed dentin of extracted human molars. The cavities were filled with composite and teeth were scanned, before and after curing, using μCT. Three-dimensional (3D) reconstructions of the data were prepared and analyzed using image analysis software. Results: 3D reconstructions showed that cavity geometry did not affect the polymerization shrinkage. The shrinkage for all restorations was 2.66±0.59%, and cavity dimensions did not affect the volume lost, either in quantity or location on the sample. Potential leakage sites were identified by gap formations and found to be non-uniformly distributed along the tooth–composite interface. Leakage in regions calculated by μCT was confirmed by visualization of sectioned samples with confocal laser scanning microscopy. Significance: μCT evaluation will add tremendous value as part of a suite of tests to characterize various properties of dental materials. The non-uniform distribution of potential leakage sites about the cavities that was determined by μCT emphasizes the inadequacy of traditional methods of determining leakage, which are capable of analyzing only limited areas. Additionally, μCT evaluation can produce quantitative analyses of shrinkage and leakage, compared to the conventional methods, which are qualitative or semi-quantitative. Finally, experimentally determined shrinkage and leakage of composite in extracted teeth agrees with the results of similar experiments in model cavities, confirming the validity of those models. [Copyright &y& Elsevier]

Abstract: Current methods to determine debonding/leakage at the tooth–composite interface are qualitative or semi-quantitative. Our previous work introduced a 3D imaging technique to determine and visualize leakage and its distribution at the interface of cavity wall and composite restoration in model cavities. In this study, an automated program was developed to quantify leakage in terms of area and volume. 3D leakage distribution obtained via the image analysis program was shown to have excellent agreement with leakage visualized by dye penetration. The relationship between leakage and various material performance parameters including processability, shrinkage, stress, and shrinkage strain-rate was determined using a series of experimental composites containing different filler contents. Results indicate that the magnitude of leakage correlated well with polymerization stress, confirming the validity of the common approach utilizing polymerization stress to predict bonding durability. 3D imaging and image analysis provide insight to help understand the relations between leakage and material properties. [Copyright &y& Elsevier]

Abstract: We have developed a combinatorial method for determining optimum tissue scaffold composition for several X-ray imaging techniques. X-ray radiography and X-ray microcomputed tomography enable non-invasive imaging of implants in vivo and in vitro. However, highly porous polymeric scaffolds do not always possess sufficient X-ray contrast and are therefore difficult to image with X-ray-based techniques. Incorporation of high radiocontrast atoms, such as iodine, into the polymer structure improves X-ray radiopacity but also affects physicochemical properties and material performance. Thus, we have developed a combinatorial library approach to efficiently determine the minimum amount of contrast agent necessary for X-ray-based imaging. The combinatorial approach is demonstrated in a polymer blend scaffold system where X-ray imaging of poly(desaminotyrosyl-tyrosine ethyl ester carbonate) (pDTEc) scaffolds is improved through a controlled composition variation with an iodinated-pDTEc analog (pI2DTEc). The results show that pDTEc scaffolds must include at least 9%, 16%, 38% or 46% pI2DTEc (by mass) to enable effective imaging by microradiography, dental radiography, dental radiography through 0.75cm of muscle tissue or microcomputed tomography, respectively. Only two scaffold libraries were required to determine these minimum pI2DTEc percentages required for X-ray imaging, which demonstrates the efficiency of this new combinatorial approach for optimizing scaffold formulations. [Copyright &y& Elsevier]

Abstract: Particle spatial dispersion is a crucial characteristic of polymer composite materials and this property is recognized as especially important in nanocomposite materials due to the general tendency of nanoparticles to aggregate under processing conditions. We introduce dispersion metrics along with a specified dispersion scale over which material homogeneity is measured and consider how the dispersion metrics correlate quantitatively with the variation of basic nanocomposite properties. We then address the general problem of quantifying nanoparticle spatial dispersion in model nanocomposites of single-walled carbon nanotubes (SWNTs) dispersed in poly(methyl methacrylate) (PMMA) at a fixed SWNT concentration of 0.5% using a ‘coagulation’ fabrication method. Two methods are utilized to measure dispersion, UV–vis spectroscopy and optical confocal microscopy. Quantitative spatial dispersion levels were obtained through image analysis to obtain a ‘relative dispersion index’ (RDI) representing the uniformity of the dispersion of SWNTs in the samples and through absorbance. We find that the storage modulus, electrical conductivity, and flammability property of the nanocomposites correlate well with the RDI. For the nanocomposites containing the same amount of SWNTs, the relationships between the quantified dispersion levels and physical properties show about four orders of magnitude variation in storage modulus, almost eight orders of magnitude variation in electric conductivity, and about 70% reduction in peak mass loss rate at the highest dispersion level used in this study. The observation of such a profound effect of SWNT dispersion indicates the need for objective dispersion metrics for correlating and understanding how the properties of nanocomposites are determined by the concentration, shape and size of the nanotubes. [Copyright &y& Elsevier]