Bioprinting, an advanced additive manufacturing technology, enables the fabrication of complex, viable three-dimensional (3D) tissues using bioinks composed of biomaterials and cells. This technology has transformative applications in regenerative medicine, drug screening, disease modeling, and biohybrid robotics. In particular, in situ bioprinting has emerged as a promising approach for directly repairing damaged tissues or organs at the defect site. Unlike traditional 3D bioprinting, which is confined to flat surfaces and require complex equipment, in situ techniques accommodate irregular geometries, dynamic environments and simple apparatus, offering greater versatility for clinical applications. In situ bioprinting via hand-held devices prioritize flexibility, portability, and real-time adaptability while allowing clinicians to directly deposit bioinks in anatomically complex areas, making them cost-effective, accessible, and suitable for diverse environments, including field surgeries. This review explores the principles, advancements, and comparative advantages of robotic and hand-held in situ bioprinting, emphasizing their clinical relevance. While robotic systems excel in precision and scalability, hand-held bioprinters offer unparalleled flexibility, affordability, and ease of use, making them a valuable tool for personalized and minimally invasive tissue engineering. Future research should focus on improving biosafety, aseptic properties, and bioink formulations to optimize these technologies for widespread clinical adoption.

The parathyroid glands are localized at the back of the thyroid glands in the cervical region and are responsible for regulation of the calcium level in the blood, through specialized cells that sense Ca²⁺ and secrete parathyroid hormone (PTH) in response to a decline in its serum level. PTH stimulates the skeleton, kidneys and intestines and controls the level of Ca²⁺ through specialized activities. Iatrogenic removal of the parathyroid gland, as well as damage to its vascular integrity during cauterization are some of the common complications of thyroid surgery. Therefore, regeneration and/or replacement of malfunctioning parathyroid tissue is required. Tissue engineering is an emerging and promising field for patients with organ failure with recent pioneering clinical applications. The success of tissue engineering strategy depends on the use of proper cells, bioactive factors that stimulate the activities of these cells and scaffolds that are produced to recapitulate the tissue structure and support the function of the engineered tissues. 3D printing is a developing strategy for the production of these scaffolds by providing a delicate control over their structure and properties. In this study, human primary parathyroid cells were successfully isolated and their viability and ability to secrete PTH upon stimulation with different levels of Ca²⁺ were shown in vitro. These cells were then seeded onto 3D printed alginate scaffolds and 3D bioprinted within alginate bioink, and cell viability as well as the ability to secrete PTH upon stimulation were also demonstrated. Therefore, functional hormone-active parathyroid tissue substitute was engineered in vitro through 3D printed hydrogels and autologous cells.

Background and Objectives: Hypocalcemia due to hypoparathyroidism (HypoPTH) is the most common complication following thyroid surgery, typically resulting from iatrogenic removal, tissue damage, or compromised vascularization of the parathyroid glands. Patients with persistent HypoPTH are at risk for long-term complications such as osteoporosis, cardiac dysfunction, and renal impairment. Lifelong regulation of calcium levels is therefore essential to prevent morbidity and mortality associated with these complications. In this study, we aimed to evaluate the functional engraftment efficacy of 3D bioprinted human parathyroid tissue constructs in a xenograft model in vivo. Materials and Methods: Primary cells obtained from freshly excised human parathyroid tissue specimens were isolated and 3D bioprinted using alginate-based bioink. The bioprinted tissue constructs were implanted into CD1 athymic mice. Histopathological evaluation of the grafted constructs was performed at different time points. In addition, surface calcium-sensing receptor (CaSR) expression was assessed by immunofluorescence as an indicator of functional parathyroid tissue engraftment. Results: The presence of CaSR on parathyroid cells within the 3D-printed scaffolds confirmed the persistence of functional parathyroid cells following implantation. In tissue samples obtained during the first, second, and third weeks after implantation, CaSR positivity was consistently observed in the parathyroid cells. However, at the three-month follow-up, the pores within the scaffolds were found to be filled with calcified material and replaced by fibrotic tissue. At this stage, the absence of parathyroid hormone (PTH) expression indicated a loss of functional activity in the grafted biomaterial. Conclusions: Human primary parathyroid cells were successfully isolated, and a functional, hormone-active parathyroid tissue substitute was developed ex vivo using 3D-bioprinted hydrogel scaffolds combined with autologous cells. Although short-term functional engraftment was achieved, long-term graft viability and hormonal activity were limited due to scaffold degradation and fibrosis. These findings indicate the necessity for further improvement in scaffold biocompatibility to enhance the therapeutic potential of 3D-bioprinted parathyroid tissue constructs for in vivo applications.

Honey is known to be a natural food product with antibacterial and wound-healing properties. Among its different types, some attributed more with medical applications including Manuka honey. In this study, some wound healing-related parameters were systematically investigated on two different types of Turkish honey (Chestnut and Anzer), in comparison with Manuka honey. Chestnut honey had considerable amount of hydrogen peroxide (5 μg/mL) whereas Manuka and Anzer honey did not contain any. Additionally, Chestnut honey had the highest acidity among all tested samples (24.50 meq/kg), as well as higher antioxidant activity (IC50 ; 2.45 mg/ml) than those of Anzer (13.02 mg/ml) and Manuka honey (6.27 mg/ml). It was also demonstrated that Chestnut honey displayed a considerable antimicrobial activity against selected pathogens. On the other hand, in the scratch assay performed as a model for the wound healing process, Anzer honey induced the highest cell proliferation corresponding to almost total wound closure for all concentrations tested. Overall, the results showed that the Turkish Chestnut and Anzer honey samples had distinguished characteristics for wound healing that is comparable to Manuka honey, and therefore are both promising candidates for use in clinical applications.

Effective skeletal muscle tissue engineering relies on the control over the scaffold architecture for providing the muscle cells with required directionality, together with mechanical property match with the surrounding tissue. Although recent advances in 3D printing fulfills the first requirement, the available synthetic polymers are either too rigid or show unfavorable surface and degradation profiles for the latter. In addition, natural polymers that are generally used as hydrogels, lack the required mechanical stability to withstand the forces exerted during muscle contraction. Therefore, one of the most important challenges in the 3D printing of soft and elastic tissues such as skeletal muscle is the limitation of the availability of elastic, durable and biodegradable biomaterials. Herein, we have synthesized novel, biocompatible and biodegradable, elastomeric, segmented polyurethane and polyurethane-urea (TPU) copolymers which are amenable for extrusion 3D printing and show high elasticity, low rigidity, controlled biodegradability and improved wettability, compared to conventional polycaprolactone (PCL) and PCL based TPUs. The degradation profile of the 3D printed TPU scaffold was in line with the potential tissue integration and scaffold replacement process. Even though TPU attracts macrophages in 2D configuration, its 3D printed form showed limited activated macrophage adhesion and induced muscle-like structure formation by C2C12 mouse myoblasts in vitro, while resulting in a significant increase in muscle regeneration in vivo in a tibialis anterior defect in a rat model. Effective muscle regeneration was confirmed with histopathological assessment as well as gait analysis and micro-CT evaluation. These results demonstrate that matching the tissue properties for a given application via use of tailor-made polymers can substantially contribute to the regenerative outcomes of 3D printed tissue engineering scaffolds.