Interaction of acid glycosaminoglycans (mucopolysaccharides) with hydroxyapatite

Interplay of Hydrogel Composition and Geometry on Human Mesenchymal Stem Cell Osteogenesis

Microgels are emerging as an outstanding platform for tissue regeneration because they overcome issues associated with conventional bulk/macroscopic hydrogels such as limited cell-cell contact and cell communication and low diffusion rates. Owing to the enhanced mass transfer and injectability via a minimally invasive procedure, these microgels are becoming a promising approach for bone regeneration applications. Nevertheless, there still remains a huge gap between the understanding of how the hydrogel matrix composition can influence cell response and overall tissue formation when switching from bulk formats to microgel format, which is often neglected or rarely studied. Here, we fabricated polyethylene glycol-based microgels and bulk hydrogels incorporating gelatin and hyaluronic acid (HA), either individually or together, and assessed the impact of both hydrogel composition and format upon the osteogenic differentiation of encapsulated human bone marrow-derived mesenchymal stem cells (hBMSCs). Osteogenesis was significantly greater in microgels than bulk hydrogels for both gelatin alone (Gel) and gelatin HA composite (Gel:HA) hydrogels, as determined by the expression of Runt-related transcription factor (Runx2) and alkaline phosphatase (ALP) genes and mineral deposition. Interestingly, Gel and Gel:HA hydrogels behaved differently between bulk and microgel format. In bulk format, overall osteogenic outcomes were better in Gel:HA hydrogels, but in microgel format, while the level of osteogenic gene expression was equivalent between both compositions, the degree of mineralization was reduced in Gel:HA microgels. Investigation into the affinity of hydroxyapatite for the different matrix compositions indicated that the decreased mineralization of Gel:HA microgels was likely due to a low affinity of hydroxyapatite to bind to HA and support mineral deposition, which has a greater impact on microgels than bulk hydrogels. Together, these findings suggest that both hydrogel composition and format can determine the success of tissue formation and that there is a complex interplay of these two factors on both cell behavior and matrix deposition. This has important implications for tissue engineering, showing that hydrogel composition and geometry must be evaluated together when optimizing conditions for cell differentiation and tissue formation.

Viscosities of mixtures of hyaluronic acids with different molecular weights and their effects on enzymatic activities of lysozyme and peroxidase

OBJECTIVES

To investigate the viscosity values of mixtures of hyaluronic acids with different molecular weights and the effects of these mixtures on the enzymatic activities of lysozyme and peroxidase.

MATERIALS AND METHODS

Mixtures of high molecular weight (1 or 2 MDa) and low molecular weight (10 or 100 kDa) hyaluronic acids at different concentrations were used for viscosity measurements. Hyaluronic acid mixtures showing viscosity values similar to those of human whole saliva were used for enzyme experiments in solution and on hydroxyapatite surface. Hen egg-white lysozyme, bovine lactoperoxidase, and human whole saliva were used as enzyme sources. Lysozyme activity was measured by hydrolysis of fluorescein-labeled Micrococcus lysodeikticus. Peroxidase activity was measured by oxidation of fluorogenic 2',7'-dichlorofluorescein to fluorescing 2',7'-dichlorofluorescein.

RESULTS

The mixtures of 1 MDa (0.5 mg/mL) or 2 MDa (0.2 mg/mL) hyaluronic acid with 10 kDa (2.0 mg/mL) or 100 kDa (0.1 mg/mL) hyaluronic acid had viscosity values similar to those of human whole saliva at shear rates, reflecting normal oral functions. Compared with single molecular weight hyaluronic acids, these mixtures showed viscosity values more similar to those of human whole saliva. The mixtures inhibited lysozyme and peroxidase activities on the hydroxyapatite surfaces; however, the degree of inhibition did not differ from that of hyaluronic acid of 1 or 2 MDa only.

CONCLUSIONS

Compared with single molecular weight hyaluronic acids, hyaluronic acid mixtures showed viscosity values more similar to those of human whole saliva, without additional inhibitory effects on lysozyme and peroxidase activities.

CLINICAL RELEVANCE

Hyaluronic acid mixtures offer distinct advantages for the development of saliva substitutes.

* Central Growth Factor Loaded Depots in Bone Tissue Engineering Scaffolds for Enhanced Cell Attraction

Tissue engineering, the application of stem and progenitor cells in combination with an engineered extracellular matrix, is a promising strategy for bone regeneration. However, its success is limited by the lack of vascularization after implantation. The concept of in situ tissue engineering envisages the recruitment of cells necessary for tissue regeneration from the host environment foregoing ex vivo cell seeding of the scaffold. In this study, we developed a novel scaffold system for enhanced cell attraction, which is based on biomimetic mineralized collagen scaffolds equipped with a central biopolymer depot loaded with chemotactic agents. In humid milieu, as after implantation, the signaling factors are expected to slowly diffuse out of the central depot forming a gradient that stimulates directed cell migration toward the scaffold center. Heparin, hyaluronic acid, and alginate have been shown to be capable of depot formation. By using vascular endothelial growth factor (VEGF) as model factor, it was demonstrated that the release kinetics can be adjusted by varying the depot composition. While alginate and hyaluronic acid are able to reduce the initial burst and prolong the release of VEGF, the addition of heparin led to a much stronger retention that resulted in an almost linear release over 28 days. The biological activity of released VEGF was proven for all variants using an endothelial cell proliferation assay. Furthermore, migration experiments with endothelial cells revealed a relationship between the degree of VEGF retention and migration distance: cells invaded deepest in scaffolds containing a heparin-based depot indicating that the formation of a steep gradient is crucial for cell attraction. In conclusion, this novel in situ tissue engineering approach, specifically designed to recruit and accommodate endogenous cells upon implantation, appeared highly promising to stimulate cell invasion, which in turn would promote vascularization and finally new bone formation.

A randomized controlled clinical study of the effect of daily intake of Ascophyllum nodosum alga on calculus, plaque, and gingivitis

OBJECTIVE

The aim of this study is to evaluate, in a randomized controlled cross-over study, the effect of daily intake of the alga Ascophyllum nodosum on supragingival calculus, plaque formation, and gingival health over a 6-month period.

MATERIAL AND METHODS

Sixty-one adults with moderate to heavy calculus formation since their last yearly recall visit participated. In a randomized order over two 6-month periods, they swallowed two capsules daily, comprising a total of 500 mg dried marine alga powder (Ascophyllum nodosum, ProDen PlaqueOff®) or two negative control tablets. During the study, the participants maintained their regular oral habits. Their teeth were professionally cleaned at the start of each period and after the 6-month registrations. A wash out period of 1 month separated the two 6-month periods. Supragingival calculus (Volpe Manhold), gingivitis (Löe and Silness), gingival bleeding (Ainamo and Bay), and plaque (Quigley-Hein) were registered at screening and at the end of the two periods. Differences in oral health between the test and control periods were analyzed using a paired t test and Wilcoxon signed rank test.

RESULTS

Fifty-five participants completed the study. After the alga intake, the mean calculus reduction was 52% compared to the control (p < 0.0001). Fifty-two participants showed less calculus formation in the alga group than in the control group. Plaque (p = 0.008) and gingival bleeding (p = 0.02) were also significantly less in the alga group. However, no significant difference was found between the groups for gingivitis (p = 0.13).

CONCLUSIONS

The alga intake significantly reduced the formation of supragingival calculus and plaque and occurrence of gingival bleeding. The alga has a systemic effect on oral health.

CLINICAL RELEVANCE

Daily intake of the alga Ascophyllum nodosum as an adjunct to customary oral hygiene showed a major reduction of supragingival calculus formation and reduced plaque formation. In addition, the calculus in the alga group was characterized by a more porous and less solid structure and was easier to remove than the calculus in the control group.

Design of a Novel 3D Printed Bioactive Nanocomposite Scaffold for Improved Osteochondral Regeneration

Chronic and acute osteochondral defects as a result of osteoarthritis and trauma present a common and serious clinical problem due to the tissue's inherent complexity and poor regenerative capacity. In addition, cells within the osteochondral tissue are in intimate contact with a 3D nanostructured extracellular matrix composed of numerous bioactive organic and inorganic components. As an emerging manufacturing technique, 3D printing offers great precision and control over the microarchitecture, shape and composition of tissue scaffolds. Therefore, the objective of this study is to develop a biomimetic 3D printed nanocomposite scaffold with integrated differentiation cues for improved osteochondral tissue regeneration. Through the combination of novel nano-inks composed of organic and inorganic bioactive factors and advanced 3D printing, we have successfully fabricated a series of novel constructs which closely mimic the native 3D extracellular environment with hierarchical nanoroughness, microstructure and spatiotemporal bioactive cues. Our results illustrate several key characteristics of the 3D printed nanocomposite scaffold to include improved mechanical properties as well as excellent cytocompatibility for enhanced human bone marrow-derived mesenchymal stem cell adhesion, proliferation, and osteochondral differentiation in vitro. The present work further illustrates the effectiveness of the scaffolds developed here as a promising and highly tunable platform for osteochondral tissue regeneration.