Suitability of Gelatin Methacrylate and Hydroxyapatite Hydrogels for 3D-Bioprinted Bone Tissue

BACKGROUND

Complex bone defects are challenging to treat. Autografting is the gold standard for regenerating bone defects; however, its limitations include donor-site morbidity and increased surgical complexity. Advancements in 3D bioprinting (3DBP) offer a promising alternative for viable bone grafts. In this experiment, gels composed of varying levels of gelatin methacrylate (GelMA) and hydroxyapatite (HA) and gelatin concentrations are explored. The objective was to increase the hydroxyapatite content and find the upper limit before the printability was compromised and determine its effect on the mechanical properties and cell viability.

METHODS

Design of Experiments (DoE) was used to design 13 hydrogel bioinks of various GelMA/HA concentrations. These bioinks were assessed in terms of their pipettability and equilibrium modulus. An optimal bioink was designed using the DoE data to produce the greatest stiffness while still being pipettable. Three bioinks, one with the DoE-designed maximal stiffness, one with the experimentally defined maximal stiffness, and a literature-based control, were then printed using a 3D bioprinter and assessed for print fidelity. The resulting hydrogels were combined with human bone-marrow-derived mesenchymal stromal cells (hMSCs) and evaluated for cell viability.

RESULTS

The DoE ANOVA analysis indicated that the augmented three-level factorial design model used was a good fit (p < 0.0001). Using the model, DoE correctly predicted that a composite hydrogel consisting of 12.3% GelMA, 15.7% HA, and 2% gelatin would produce the maximum equilibrium modulus while still being pipettable. The hydrogel with the most optimal print fidelity was 10% GelMA, 2% HA, and 5% gelatin. There were no significant differences in the cell viability within the hydrogels from day 2 to day 7 (p > 0.05). There was, however, a significantly lower cell viability in the gel composed of 12.3% GelMA, 15.7% HA, and 2% gelatin compared to the other gels with a lower HA concentration (p < 0.05), showing that a higher HA content or print pressure may be cytotoxic within hydrogels.

CONCLUSIONS

Extrusion-based 3DBP offers significant advantages for bone-tissue implants due to its high customizability. This study demonstrates that it is possible to create printable bone-like grafts from GelMA and HA with an increased HA content, favorable mechanical properties (145 kPa), and a greater than 80% cell viability.

EFFECTS OF MOUTHING AND INTERLOCUTOR PRESENCE ON MOVEMENTS OF VISIBLE VS. NON-VISIBLE ARTICULATORS

Speakers take into account what information a conversation partner requires in a given context in order to best understand an utterance. Despite growing evidence showing that movements of visible articulators such as the lips are augmented in mouthed speech relative to vocalized speech, little to date has been done comparing this effect in visible vs. non-visible articulators. In addition, no studies have examined whether interlocutor engagement differentially impacts these. Building on a basic present/not-present design, we investigated whether presence of audible speech information and/or an interlocutor affect the movements of the lips and the tongue. Participants were asked to a) speak or b) mouth three target syllables in interlocutor-present and interlocutor-not-present conditions, while lip and tongue movements were recorded using video and ultrasound imaging. Results show that lip protrusion was greater in mouthed conditions compared to vocalized ones and tongue movements were either attenuated (/wa/) or unaffected (/ri/, /ra/) by these same conditions, indicating differential effects for the visible and non-visible articulators in the absence of an auditory signal. A significant interaction between the social engagement and vocalizing conditions in reference to lip aperture showed that participants produced smaller lip apertures when vocalizing alone, as compared to when in the presence of an interlocutor. However, measures of lip protrusion failed to find an effect of social engagement. We conclude that speakers make use of both auditory and visual modalities in the presence of an interlocutor, and that when acoustic information is unavailable, compensatory increases are made in the visual domain. Our findings shed new light on the multimodal nature of speech, and pose new questions about differential adaptations made by visible and non-visible articulators in different speech conditions.

Systematic study on the chemical stability of the prodrug antitumor agent carzelesin (U-80,244)

The chemical stability of the novel anticancer agent carzelesin in aqueous buffer/acetonitrile (1:1, v/v) mixtures has been investigated utilizing a stability-indicating reversed-phase high-performance liquid chromatographic assay. The degradation kinetics of carzelesin has been studied as a function of pH, buffer composition, ionic strength, and temperature. Degradation of carzelesin follows (pseudo-) first-order kinetics. A pH-rate profile, using rate constants extrapolated to zero buffer concentration, was constructed demonstrating that carzelesin is most stable in the pH region 1-4. The degradation rate of carzelesin was not significantly affected by buffer components and by the ionic strength. In addition to the formation of the degradation products U-76,073, U-76,074, and aniline in alkaline medium and in acetate buffer solution, another degradation product was formed in acetate buffer solution. In perchloric acid buffer solution (pH* < 3), U-76,073 and U-76,074 could not be detected as degradation products.