Yi Pin Qi

Intrafibrillar Collagen Mineralization Produced by Biomimetic Hierarchical Nanoapatite Assembly

Biomineralization templated by non-collagenous proteins is an example how nature uses nanotechnology to strengthen the load-bearing skeletons of vertebrates.[1–3] Mineralized collagen fibrils are responsible for the second level of hierarchy of bone structure[4] and account for its strength and toughness.[5] Calcium-deficient apatites are deposited in nanocrystalline form at the intrafibrillar and extrafibrillar spaces associated with the collagen fibrillar assembly.[6] Regulation of calcium phosphate phases during biomineralization is believed to exhibit two major characteristics.[7–9] The first is the sequestration of the calcium and phosphate ions into nanoscopic entities known as amorphous calcium phosphate (ACP). The second is the templating of mineral nucleation and growth through noncollagenous extracellular matrix proteins. These protein molecules contain polyanionic domains that are rich in polycarboxylic acid and phosphate function groups that bind to the collagen substrates at specific sites such as the gap zones of the collagen molecular assembly.[1,10] The immobilized proteins contain anionic charge sites wherein calcium binding and apatite nucleation occur at the aforementioned intrafibrillar locations. As a highly ordered manner of intrafibrillar mineralization at the nanoscale is responsible for the biomechanical properties of mineralized collagen,[11] this intricate biological process has inspired scientists to mimic its mechanism for creating mineralized type I collagen scaffolds to repair existing bone defects and/or generate new bone. Here, we demonstrate that the use of two phosphate-based templating analogs of matrix proteins in the presence of a polycarboxylic acid sequestration analog of ACPs results in a highly ordered intrafibrillar nanoapatite assembly that recapitulates the gap and overlap arrangement of collagen molecules within a collagen fibril. Adoption of a dual analog biomimetic strategy provides a means to produce advanced mineralized collagen scaffolds for tissue engineering applications.

Remineralization of artificial dentinal caries lesions by biomimetically modified Mineral Trioxide Aggregate

Fluoride-releasing restorative materials are available for remineralization of enamel and root caries. However, remineralization of dentin is more difficult than remineralization of enamel due to the paucity of apatite seed crystallites along the lesion surface for heterogeneous crystal growth. Extracellular matrix proteins play critical roles in controlling apatite nucleation/growth in collagenous tissues. This study examined the remineralization efficacy of mineral trioxide aggregate (MTA) in phosphate-containing simulated body fluid (SBF) by incorporating polyacrylic acid and sodium tripolyphosphate as biomimetic analogs of matrix proteins for remineralizing caries-like dentin. Artificial caries-like dentin lesions incubated in SBF were remineralized over a 6 week period using MTA alone or MTA containing biomimetic analogs in the absence or presence of dentin adhesive application. Lesion depths and integrated mineral loss were monitored with microcomputed tomography. The ultrastructure of baseline and remineralized lesions was examined by transmission electron microscopy. Dentin remineralization was best achieved using MTA containing biomimetic analogs regardless of whether an adhesive was applied; dentinal tubules within the remineralized dentin were occluded by apatite. It is concluded that the version of MTA employed in this study may be doped with biomimetic analogs for remineralization of unbonded and bonded artificial caries-like lesions in the presence of SBF.

The critical barrier to progress in dentine bonding with the etch-and-rinse technique

OBJECTIVES The lack of durability in resin-dentine bonds led to the use of chlorhexidine as MMP-inhibitor to prevent the degradation of hybrid layers. Biomimetic remineralisation is a concept-proven approach in preventing the degradation of resin-dentine bonds. The purpose of this study is to examine the integrity of aged resin-dentine interfaces created with a nanofiller-containing etch-and-rinse adhesive after the application of these two approaches. METHODS The more established MMP-inhibition approach was examined using a parallel in vivo and in vitro ageing design to facilitate comparison with the biomimetic remineralisation approach using an in vitro ageing design. Specimens bonded without chlorhexidine exhibited extensive degradation of the hybrid layer after 12 months of in vivo ageing. RESULTS Dissolution of nanofillers could be seen within a water-rich zone within the adhesive layer. Although specimens bonded with chlorhexidine exhibited intact hybrid layers, water-rich regions remained in those hybrid layers and degradation of nanofillers occurred within the adhesive layer. Specimens subjected to in vitro biomimetic remineralisation followed by in vitro ageing demonstrated intrafibrillar collagen remineralisation within hybrid layers and deposition of mineral nanocrystals in nanovoids within the adhesive. CONCLUSIONS The impact was realized by understanding the lack of an inherent mechanism to remove water from resin-dentine interfaces as the critical barrier to progress in bonding with the etch-and-rinse technique. The experimental biomimetic remineralisation strategy offers a creative solution for incorporating a progressive hydration mechanism to achieve this goal, which warrants its translation into a clinically applicable technique.

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.

Effects of Calcium Silicate–based Materials on Collagen Matrix Integrity of Mineralized Dentin

INTRODUCTION Calcium silicate-based materials (CSMs) are used in various endodontic procedures. The present study examined whether prolonged contact of mineralized dentin with recently commercialized versions of these materials adversely affects dentin collagen matrix integrity. METHODS Dentin slabs prepared from extracted human third molars (7 × 3 × 0.3 mm) were divided into 3 groups on the basis of the material to which dentin was exposed (MTA Plus, Biodentine, untreated control dentin slabs) and the time period of exposure (24 hours, 1, 2, and 3 months; n = 6). Hydroxyproline assay was performed on each groups supernatant to quantify the collagen extraction amounts of each group per time period. Data were analyzed with two-factor repeated-measures analysis of variance and Holm-Sidak pair-wise comparisons (α = 0.05) to determine the effects of material and aging time on collagen extraction. Dentin slabs from the 3 months of aging group were demineralized for transmission electron microscopy examination of collagen matrix ultrastructural changes. RESULTS Material (P = .002), aging time (P < .001), and their interactions (P = .007) significantly affected the amount of hydroxyproline (pg/mg of mineralized dentin) extracted from mineralized dentin and were significantly correlated by power regression models. Collagen degradation was identified from the surface of dentin slabs that were in direct contact with CSMs. CONCLUSIONS Prolonged contact of mineralized dentin with CSMs has an adverse effect on the integrity of the dentin collagen matrix. However, the amount of collagen extracted was limited to the contact surface. Clinicians can continue to apply CSMs in endodontic procedures; however, caution is advised when these materials are applied to thin dentinal walls.

Effects of an Experimental Calcium Aluminosilicate Cement on the Viability of Murine Odontoblast-like Cells

INTRODUCTION Quick-setting calcium aluminosilicate cement with improved washout resistance is a potential substitute for calcium silicate cements in endodontics. This study examined the effect of an experimental calcium aluminosilicate cement (Quick-Set; Primus Consulting, Bradenton, FL) on the viability of odontoblast-like cells. METHODS The biocompatibility of Quick-Set and white ProRoot MTA (WMTA; Dentsply Tulsa Dental Specialties, Tulsa, OK) cements and their eluents was evaluated using a murine dental papilla-derived odontoblast-like cell line (MDPC-23); 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to examine the effects of the 2 hydraulic cements on mitochondrial metabolic activity. Flow cytometry and confocal laser scanning microscopy were used to identify the effects of the 2 cements on cell death-induced plasma membrane permeability to fluorescent dyes and DNA stains. RESULTS After the first week of immersion in culture medium, Quick-Set and WMTA were more cytotoxic than the Teflon-negative control (P < .05), and the cells exhibited more apoptosis/necrosis than Teflon (P < .05). After the second week of immersion, the 2 cements were as biocompatible as Teflon (P > .05), with cells exhibiting minimal apoptosis/necrosis. Eluents from the set cements at 1:1 dilution were significantly more cytotoxic that eluents at 1:10 or 1:100 dilution (P < .05). CONCLUSIONS Quick-Set and WMTA exhibited similar cytotoxicity profiles. They possess negligible in vitro toxicologic risks after time-dependent elution of toxic components.

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.

Intrafibrillar silicification of collagen scaffolds for sustained release of stem cell homing chemokine in hard tissue regeneration

Traditional bone regeneration strategies relied on supplementation of biomaterials constructs with stem or progenitor cells or growth factors. By contrast, cell homing strategies employ chemokines to mobilize stem or progenitor cells from host bone marrow and tissue niches to injured sites. Although silica‐based biomaterials exhibit osteogenic and angiogenic potentials, they lack cell homing capability. Stromal cell‐derived factor‐1 (SDF‐1) plays a pivotal role in mobilization and homing of stem cells to injured tissues. In this work, we demonstrated that 3‐dimensional collagen scaffolds infiltrated with intrafibrillar silica are biodegradable and highly biocompatible. They exhibit improved compressive stress‐strain responses and toughness over nonsilicified collagen scaffolds. They are osteoconductive and up‐regulate expressions of osteogenesis‐ and angiogenesis‐related genes more significantly than nonsilicified collagen scaffolds. In addition, these scaffolds reversibly bind SDF‐1α for sustained release of this chemokine, which exhibits in vitro cell homing characteristics. When implanted subcutaneously in an in vivo mouse model, SDF‐1α‐loaded silicified collagen scaffolds stimulate the formation of ectopic bone and blood capillaries within the scaffold and abrogate the need for cell seeding or supplementation of osteogenic and angiogenic growth factors. Intrafibrillar‐silicified collagen scaffolds with sustained SDF‐1α release represent a less costly and complex alternative to contemporary cell seeding approaches and provide new therapeutic options for in situ hard tissue regeneration.—Niu, L.‐N., Jiao, K., Qi, Y.‐P., Nikonov, S., Yiu, C. K. Y., Arola, D. D., Gong, S.‐Q., El‐Marakby, A., Carrilho, M. R. O., Hamrick, M. W., Hargreaves, K. M., Diogenes, A., Chen, J.‐H., Pashley, D. H., Tay, F. R. Intrafibrillar silicification of collagen scaffolds for sustained release of stem cell homing chemokine in hard tissue regeneration. FASEB J. 26, 4517–4529 (2012). www.fasebj.org

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.