Introduction: In this in-vitro study, we designed a 3D printed composite of zinc oxide (ZnO) nanoparticles (NPs) with photocatalytic activities encapsulated within hydrogel (alginate) constructs, for antibacterial purposes applicable towards wound healing. We primarily sought to confirm the mechanical properties and cell compatibility of these ZnO NP infused scaffolds. Methods: The antibacterial property of the ZnO NPs was confirmed by hydroxyl radical generation using ultraviolet (U.V.) photocatalysis. Titanium dioxide (TiO₂), a well-known antibacterial compound, was used as a positive control (1% w/v) for the ZnO NP-based alginate constructs and their antibacterial efficacies compared. Among the ZnO group, 3D printed gels containing 0.5% and 1% w/v of ZnO were analyzed and compared with manually casted samples via SEM, swelling evaluation, and rheological analysis. Envisioning an in-vivo application for the 3D printed ZnO NP-based alginates, we studied their antibacterial properties by bacterial broth testing, cytocompatibility via live/dead assay, and moisture retention capabilities utilizing a humidity sensor. Results: 3D printed constructs revealed significantly greater pore sizes and enhanced structural stability compared to manually casted samples. For all samples, the addition of ZnO or TiO₂ resulted in significantly stiffer gels in comparison with the alginate control. Bacterial resistance testing on Staphylococcus epidermidis indicated the addition of ZnO NPs to the gels decreased bacterial growth when compared to the alginate only gels. Cell viability of STO-fibroblasts was not adversely affected by the addition of ZnO NPs to the alginate gels. Furthermore, the addition of increasing doses of ZnO NPs to the alginate demonstrated increased humidity retention in gels. Discussion: The customization of 3D printed alginates containing antibacterial ZnO NPs leads to an alternative that allows accessible mobility of molecular exchange required for improving chronic wound healing. This scaffold can provide a cost-effective and durable antibacterial treatment option.

Alginate is a hydrogel commonly used for cell culture by ionically crosslinking in the presence of divalent Ca²⁺ ions. However these alginate gels are mechanically unstable, not permitting their use as scaffolds to engineer robust biological bone, breast, cardiac or tumor tissues. This issue can be addressed via encapsulation of multi-walled carbon nanotubes (MWCNT) serving as a reinforcing phase while being dispersed in a continuous phase of alginate. We hypothesized that adding functionalized MWCNT to alginate, would yield composite gels with distinctively different mechanical, physical and biological characteristics in comparison to alginate alone. Resultant MWCNT-alginate gels were porous, and showed significantly less degradation after 14 days compared to alginate alone. In vitro cell-studies showed enhanced HeLa cell adhesion and proliferation on the MWCNT-alginate compared to alginate. The extent of cell proliferation was greater when cultured atop 1 and 3 mg/ml MWCNT-alginate; although all MWCNT-alginates lead to enhanced cell cluster formation compared to alginate alone. Among all the MWCNT-alginates, the 1 mg/ml gels showed significantly greater stiffness compared to all other cases. These results provide an important basis for the development of the MWCNT-alginates as novel substrates for cell culture applications, cell therapy and tissue engineering.

In this study, a hybrid system consisting of 3D printed polycaprolactone (PCL) filled with hydrogel was developed as an application for reconstruction of long bone defects, which are innately difficult to repair due to large missing segments of bone. A 3D printed gyroid scaffold of PCL allowed a larger amount of hydrogel to be loaded within the scaffolds as compared to 3D printed mesh and honeycomb scaffolds of similar volumes and strut thicknesses. The hydrogel was a mixture of alginate, gelatin, and nano-hydroxyapatite, infiltrated with human mesenchymal stem cells (hMSC) to enhance the osteoconductivity and biocompatibility of the system. Adhesion and viability of hMSC in the PCL/hydrogel system confirmed its cytocompatibility. Biomineralization tests in simulated body fluid (SBF) showed the nucleation and growth of apatite crystals, which confirmed the bioactivity of the PCL/hydrogel system. Moreover, dissolution studies, in SBF revealed a sustained dissolution of the hydrogel with time. Overall, the present study provides a new approach in bone tissue engineering to repair bone defects with a bioactive hybrid system consisting of a polymeric scaffold, hydrogel, and hMSC.