Bioprinting can be defined as 3D patterning of living cells and other biologics by filling and assembling them using a computer-aided layer-by-layer deposition approach to fabricate living tissue and organ analogs for tissue engineering. The presence of cells within the ink to use a 'bio-ink' presents the potential to print 3D structures that can be implanted or printed into damaged/diseased bone tissue to promote highly controlled cell-based regeneration and remineralization of bone. In this study, it was shown for the first time that chitosan solution and its composite with nanostructured bone-like hydroxyapatite (HA) can be mixed with cells and printed successfully. MC3T3-E1 pre-osteoblast cell laden chitosan and chitosan-HA hydrogels, which were printed with the use of an extruder-based bioprinter, were characterized by comparing these hydrogels to alginate and alginate-HA hydrogels. Rheological analysis showed that all groups had viscoelastic properties. It was also shown that under simulated physiological conditions, chitosan and chitosan-HA hydrogels were stable. Also, the viscosity values of the bio-solutions were in an applicable range to be used in 3D bio-printers. Cell viability and proliferation analyses documented that after printing with bio-solutions, cells continued to be viable in all groups. It was observed that cells printed within chitosan-HA composite hydrogel had peak expression levels for early and late stages osteogenic markers. It was concluded that cells within chitosan and chitosan-HA hydrogels had mineralized and differentiated osteogenically after 21 days of culture. It was also discovered that chitosan is superior to alginate, which is the most widely used solution preferred in bioprinting systems, in terms of cell proliferation and differentiation. Thus, applicability and printability of chitosan as a bio-printing solution were clearly demonstrated. Furthermore, it was proven that the presence of bone-like nanostructured HA in alginate and chitosan hydrogels improved cell viability, proliferation and osteogenic differentiation.

Methacrylated gelatin (Gel-MA) is a commonly used biomaterial in bioprinting applications. The Gel-MA synthesis procedure is inadequate and needs to be improved, particularly from the point of optimization and efficacy. We report a significantly faster (by 5 min) and effective method to controllably synthesize Gel-MA using microwave energy (Mw at 1000 W power) with ≥90% degree of methacrylation (DM) even with the use of a very low concentration of methacrylic anhydride (MA). Rheological and mechanical analyses indicated that Gel-MA synthesized by Mw-assisted methacrylation enabled the formation of hydrogels that are more elastic and stronger and have a lower degradation rate (∼27% at 35 days) than Gel-MA synthesized by the conventional method. The viscosity values of the Gel-MA bioink were in the range applicable for use in 3D bioprinters. Additionally, Mw-assisted methacrylated Gel-MA hydrogels that have mechanically superior properties significantly enhanced the viability, attachment, proliferation, alkaline phosphatase (ALP) activity, mineral deposition, and mRNA expression levels of osteogenic genes of MC3T3-E1 preosteoblastic cells.

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Nowadays, scientists focus on the development of tissue-specific and personalized bio-ink that can be used in 3D bioprinting technologies. Platelet-rich plasma (PRP) is a person-specific source that is used as a therapeutic adjunct for the treatment of cartilage damage because it offers a cocktail of growth factors that are necessary for wound healing and tissue regeneration. However, PRP treatments in the clinic are not satisfactory and require upgrading, especially the point of maintaining bioactivity. In this study, we presented PRP as a photo-activated and photo-crosslinkable bio-ink in terms of tissue-specific structures for the first time. We achieved long-term and constant rate growth factor release and bioactivity protection of PRP with satisfactory mechanical characteristics. Photo-crosslinked PRP hydrogel was enabled by the addition of microwave-induced methacrylated gelatin (Gel-MA), which is connected to platelets in PRP via integrin receptors in its structure and chemically cross-linked upon UV irradiation (300–500 nm). Photo-activation of PRP was realized by a polychromatic light source in the near-infrared region (PAC, 600–1200 nm). Our results showed that Gel-MA/PRP hydrogels with the desired mechanical properties (low degradation rate and high mechanical strength) released growth factors at a constant rate for the long-term by the periodic PAC application. In vitro cell culture studies (viability, proliferation, morphology, histology, immunochemistry, biochemistry, gene expression analyses) proved that proliferation and differentiation of the ATDC5 cells increased in the periodically light-applied Gel-MA/PRP hydrogel without any external chemical agents.

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The aim of this study was to develop a 17β-estradiol (E2)-releasing scaffold-nanoparticle system in order to promote osteogenic differentiation of rat adipose tissue-derived mesenchymal stem cells (AdMSCs) for bone tissue regeneration. E2-loaded poly(lactide-co-glycolide) (PLGA) nanoparticles with a diameter of ∼240 nm were produced via an emulsion-diffusion-evaporation method. Because of its higher encapsulation efficiency (54%), PLGA, which has a 65:35 composition, was chosen for the preparation of nanoparticles. Chitosan-hydroxyapatite (HA) scaffolds in macroporous structures with interconnected pores were prepared by combining microwave irradiation and gas-foaming techniques. PLGA nanoparticles were loaded onto scaffolds in 2 ways: via embedding after scaffold fabrication and during fabrication. While 100% of the loaded E2 was released during 55 days from scaffolds loaded by embedding, a controlled release behavior of E2 was observed over 135 days in scaffolds loaded during manufacture. The results of cell culture studies indicated that the controlled delivery of E2 from PLGA nanoparticles loaded on chitosan-HA scaffolds had a significant effect on the osteogenic differentiation of AdMSCs.

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Objective The aim of this study was to evaluate the effect of relatively novel approach of application of polychromatic light waves on flap survival of experimental musculocutaneous flap model and to investigate efficacy of this modality as a delay procedure to increase vascularization of zone 4 of transverse rectus abdominis musculocutaneous (TRAM) flap. Methods Twenty‐one Wistar rats were randomized and divided into 3 experimental groups (n = 7 each). In group 1 (control group), after being raised, the TRAM flap was sutured back to its bed without any further intervention. In group 2 (delay group), photobiomodulation (PBM) was applied for 7 days as a delay procedure, before elevation of the flap. In group 3 (PBM group), the TRAM flap was elevated, and PBM was administered immediately after the flap was sutured back to its bed for therapeutic purpose. PBM was applied in 48 hours interval from 10 cm. distance to the whole abdominal wall both in groups 2 and 3 for one week. After 7 days of postoperative follow‐up, as the demarcation of necrosis of the skin paddle was obvious, skin flap survival was further evaluated by macroscopic, histological and microangiographic analysis. Results The mean percentage of skin flap necrosis was 56.17 ± 23.68 for group 1, 30.92 ± 17.46 for group 2 and 22.73 ± 12.98 for group 3 PBM receiving groups 2 and 3 revealed less necrosis when compared to control group and this difference was statistically significant. Vascularization in zone 4 of PBM applied groups 2 and 3 was higher compared to group 1 (P = 0.001). Acute inflammation in zone 4 of group 1 was significantly higher compared to groups 2 and 3 (P = 0.025). Similarly, evaluation of zone 1 of the flaps reveled more inflammation and less vascularization among the samples of the control group (P = 0.006 and P = 0.007, respectively). Comparison of PBM receiving two groups did not demonstrate further difference in means of vascularization and inflammation density (P = 0.259). Conclusion Application of PBM in polychromatic fashion enhances skin flap survival in experimental TRAM flap model both on preoperative basis as a delay procedure or as a therapeutic approach. Lasers Surg. 51:538–549, 2019. © 2019 Wiley Periodicals, Inc.