Heonjune Ryou

Effect of biomimetic remineralization on the dynamic nanomechanical properties of dentin hybrid layers.

The mineral and organic phases of mineralized dentin contribute co-operatively to its strength and toughness. This study tested the null hypothesis that there is no difference in nano-dynamic mechanical behavior (complex modulus-E*; loss modulus-E′′; storage modulus-E′; in GPa) of dentin hybrid layers (baseline: E*, 3.86 ± 0.24; E′′, 0.23 ± 0.05; E′, 3.85 ± 0.24) created by an etch-and-rinse adhesive in the presence or absence of biomimetic remineralization after in vitro aging. Using scanning probe microscopy and nano-dynamic mechanical analysis, we demonstrated that biomimetic remineralization restored the nano-dynamic mechanical behavior of heavily remineralized, resin-sparse regions of dentin hybrid layers (E*, 19.73 ± 3.85; E′′, 8.75 ± 3.97; E′, 16.02 ± 2.58) to those of the mineralized dentin base (E*, 19.20 ± 2.42; E′′, 6.57 ± 1.96; E′, 17.39 ± 2.0) [p > 0.05]. Conversely, those resin-sparse, water-rich regions degraded in the absence of biomimetic remineralization, with significant decline [p < 0.05] in their complex and storage moduli (E*, 0.83 ± 0.35; E′′, 0.88 ± 0.24; E′, 0.62 ± 0.32). Intrafibrillar apatite deposition preserves the integrity of resin-sparse regions of hybrid layers by restoring their nanomechanical properties to those exhibited by mineralized dentin.

Quaternary ammonium silane-functionalized, methacrylate resin composition with antimicrobial activities and self-repair potential.

The design of antimicrobial polymers to address healthcare issues and minimize environmental problems is an important endeavor with both fundamental and practical implications. Quaternary ammonium silane-functionalized methacrylate (QAMS) represents an example of antimicrobial macromonomers synthesized by a sol-gel chemical route; these compounds possess flexible Si-O-Si bonds. In present work, a partially hydrolyzed QAMS co-polymerized with 2,2-[4(2-hydroxy 3-methacryloxypropoxy)-phenyl]propane is introduced. This methacrylate resin was shown to possess desirable mechanical properties with both a high degree of conversion and minimal polymerization shrinkage. The kill-on-contact microbiocidal activities of this resin were demonstrated using single-species biofilms of Streptococcus mutans (ATCC 36558), Actinomyces naeslundii (ATCC 12104) and Candida albicans (ATCC 90028). Improved mechanical properties after hydration provided the proof-of-concept that QAMS-incorporated resin exhibits self-repair potential via water-induced condensation of organic modified silicate (ormosil) phases within the polymerized resin matrix.

Infiltration of Silica Inside Fibrillar Collagen

Diatoms frustules are created under the control of biomolecules (silaffins, silacidins and long-chain polyamines) at close to physiologic conditions.[1–4] The mechanism of biosilica formation was traditionally based on the ability of zwitterionic water-soluble proteins to create macromolecular assemblies for silica polymerization.[5–7] Recent discoveries of water-insoluble collagen matrices within certain sponge biosilica spicules[8], chitin-based scaffolds in sponge and diatom biosilica formations[9,10], as well as cingulins within diatom girdle bands[4], revive the use of insoluble biomimetic organic templates for morphogenesis of non-porous silica structures. The use of fibrillar collagen as templates for biosilica synthesis was unsuccessful in the past as only extrafibrillar silica deposition was observed.[11,12] Intrafibrillar mineralization of collagen has important implications from a biophysical perspective.[13] Here, we report a collagen biosilicification scheme based on fusion of stabilized polysilicic acid into a fluidic precursor phase upon their infiltration into polyamine-enriched collagen. The latter serves as a template and catalyst for polymerization of the precursor phase into silica that faithfully reproduces the collagen tertiary architecture. Our findings provide a new concept in biosilica materials synthesis which does not require phosphate supplements.

On the fatigue behavior of resin-dentin bonds after degradation by biofilm

The durability of resin-dentin bonds is a growing concern in the placement of composite restorations. Most reported evaluations concerning the mechanical behavior of the bonded interface are conducted using static loading to failure only. They also do not account for the acid production of biofilms, which is one of the most common contributors to interfacial failures in vivo. In this investigation resin-dentin bonded interface specimens were exposed to S. mutans for 14 days and then subjected to quasi-static or cyclic four-point flexure to failure. Control specimens (without biofilm) were evaluated after aging for one and fourteen days. While no significant difference in flexure strength resulted from the duration of water aging (66.2 MPa vs. 56.9 MPa), biofilm exposure caused a significant reduction in strength (29.3 MPa; p ≤ 0.000). After water aging for one and fourteen days the apparent endurance limits were 13.0 MPa and 13.1 MPa, respectively. Biofilm treatment caused a significant (p ≤ 0.001) reduction in fatigue resistance of the interface, and the endurance limit was reduced to 9.9 MPa. Fatigue failure of the control specimens initiated within the resin composite adjacent to the interface, whereas failure of the biofilm treated specimens initiated within the hybrid layer and appeared attributed to the localized demineralization of dentin. Biofilm degradation is an important consideration in assessing the durability of resin-dentin bonds.

Biomimetic Analogs for Collagen Biomineralization

Inability of chemical phosphorylation of sodium trimetaphosphate to induce intrafibrillar mineralization of type I collagen may be due to the failure to incorporate a biomimetic analog to stabilize amorphous calcium phosphates (ACP) as nanoprecursors. This study investigated adsorption/desorption characteristics of hydrolyzed and pH-adjusted sodium trimetaphosphate (HPA-Na3P3O9) to collagen. Based on those results, a 5-minute treatment time with 2.8 wt% HPA-Na3P3O9 was used in a single-layer reconstituted collagen model to confirm that both the ACP-stabilization analog and matrix phosphoprotein analog must be present for intrafibrillar mineralization. The results of that model were further validated by complete remineralization of phosphoric-acid-etched dentin treated with the matrix phosphoprotein analog and lined with a remineralizing lining composite, and with the ACP-stabilization analog supplied in simulated body fluid. An understanding of the basic processes involved in intrafibrillar mineralization of reconstituted collagen fibrils facilitates the design of novel tissue engineering materials for hard tissue repair and regeneration.

Fatigue of the resin–dentin interface: A new approach for evaluating the durability of dentin bonds

UNLABELLED There are concerns regarding the longevity of resin composite restorations and the clinical relevance of in vitro bond strength testing to the durability of dentin bonds in vivo. OBJECTIVE The objectives of this investigation were to: (1) develop a new method of experimental evaluation for quantifying the durability of dentin bonds, (2) apply this method to characterize the interfacial strength of a selected commercial system under both monotonic and cyclic loading, and (3) distinguish mechanisms contributing to the interface degradation and failure. METHODS A new method for fatigue testing the resin-dentin interface was developed based on a four-point flexure arrangement that includes two identical bonded interfaces. Cyclic loading of specimens comprised of coronal dentin bonded to a commercial resin composite and controls of resin composite was performed to failure within a hydrated environment. Scanning electron microscopy and nanoscopic dynamic mechanical analysis were used to evaluate failure mechanisms. RESULTS The fatigue strength of the resin-dentin interface was significantly lower (p≤0.0001) than that of the resin composite and reported for dentin over the entire finite life regime. Defined at 1×10(7) cycles, the apparent endurance limit of the resin-dentin interface was 13MPa, in comparison to 48MPa and 44MPa for the resin composite and dentin, respectively. The ratio of fully reversed endurance limit to ultimate strength of the interface (0.26) was the lowest of the three materials. SIGNIFICANCE The proposed approach for characterizing the fatigue strength of resin-dentin bonds may offer new insights concerning durability of the bonded interface.

Fatigue of the resin-enamel bonded interface and the mechanisms of failure.

The durability of adhesive bonds to enamel and dentin and the mechanisms of degradation caused by cyclic loading are important to the survival of composite restorations. In this study a novel method of evaluation was used to determine the strength of resin-enamel bonded interfaces under oth static and cyclic loading, and to identify the mechanisms of failure. Specimens with twin interfaces of enamel bonded to commercial resin composite were loaded in monotonic and cyclic 4-point flexure to failure within a hydrated environment. Results for the resin-enamel interface were compared with those for the resin composite (control) and values reported for resin-dentin adhesive bonds. Under both modes of loading the strength of the resin-enamel interface was significantly (p≤0.0001) lower than that of the resin composite and the resin-dentin bonded interface. Fatigue failure of the interface occurred predominantly by fracture of enamel, adjacent to the interface, and not due to adhesive failures. In the absence of water aging or acid production of biofilms, the durability of adhesive bonds to enamel is lower than that achieved in dentin bonding.

Multiphase Intrafibrillar Mineralization of Collagen

In the past, the two major biomineralization motifs, biosilicification and biocalcification, have been considered as two discrete processes. However, there is increasing evidece suggesting existence of an inextricable relationship between biosilica and calcium-based biominerals.[1] Recent discovery of a unique silica–chitin–aragonite biocomposite in one genus of Demosponges (Verongida) further introduces a novel mechanism of multiphase hierarchical biomineralization.[2] Considerable efforts have been devoted to the development of silica/calcium-based organic-inorganic hybrids;[3-5] however none of these techniques could demonstrate the composite nature of their natural counterparts. Here, we report a biomineralization scheme that results in intrafibrillar mineralization of collagen with hierarchically-arranged, silica-apatite multiphase minerals via a bottom-up, biomimetic strategy. The mineralization mechanism involves precipitation and crystal growth of polymer-induced amorphous calcium phosphate precursors within the intrafibrillar spaces of hierarchicallysilicified collagen. Silicified collagen-templated intrafibrillar apatite formation provides a model for the formation of multiphase-mineralized skeleton in invertebrates, and also results in a biocomposite with increased fatigue resistance and resilience, due to the interpenetrating arrangement of amorphous silica, collagen and crystalline apatite, as well as enhanced bioactivity, biocompatibility and bone defect restoring potential caused by the presence of those multiphase components.[1,6,7]

Subtleties of biomineralisation revealed by manipulation of the eggshell membrane

Biocalcification of collagen matrices with calcium phosphate and biosilicification of diatom frustules with amorphous silica are two discrete processes that have intrigued biologists and materials scientists for decades. Recent advancements in the understanding of the mechanisms involved in these two biomineralisation processes have resulted in the use of biomimetic strategies to replicate these processes separately using polyanionic, polycationic or zwitterionic analogues of extracellular matrix proteins to stabilise amorphous mineral precursor phases. To date, there is a lack of a universal model that enables the subtleties of these two apparently dissimilar biomineralisation processes to be studied together. Here, we utilise the eggshell membrane as a universal model for differential biomimetic calcification and silicification. By manipulating the eggshell membrane to render it permeable to stabilised mineral precursors, it is possible to introduce nanostructured calcium phosphate or silica into eggshell membrane fibre cores or mantles. We provide a model for infiltrating the two compartmental niches of a biopolymer membrane with different intrafibre minerals to obtain materials with potentially improved structure-property relationships.

Importance of age on the dynamic mechanical behavior of intertubular and peritubular dentin.

An experimental evaluation of human coronal dentin was performed using nanoscopic dynamic mechanical analysis (nanoDMA). The primary objectives were to quantify any unique changes in mechanical behavior of intertubular and peritubular dentin with age, and to evaluate the microstructure and mechanical behavior of the mineral deposited within the lumens. Specimens of coronal dentin were evaluated by nanoDMA using single indents and in scanning mode via scanning probe microscopy. Results showed that there were no significant differences in the storage modulus or complex modulus between the two age groups (18-25 versus 54-83 yrs) for either the intertubular or peritubular tissue. However, there were significant differences in the dampening behavior between the young and old dentin, as represented in the loss modulus and tanδ responses. For both the intertubular and peritubular components, the capacity for dampening was significantly lower in the old group. Scanning based nanoDMA showed that the tubules of old dentin exhibit a gradient in elastic behavior, with decrease in elastic modulus from the cuff to the center of tubules filled with newly deposited mineral.