The Bone Glue Gun On Demand 3D Printing for Person - In Situ Printing of Biodegradable Implant for Healing Critical-Sized Bone Defect

By Dr Reza Lankarani , General SurgeonFounder | Surgical Pioneering Newsletter and Podcast Series Editorial Board Member | Genesis Journal of Surgery and MedicineOnline Publication Date:October 17, 2025https://doi.org/10.1016/j.device.2025.100873Summary This study presents a novel, portable in situ 3D-printing platform for the direct fabrication of biodegradable bone implants into critical-sized defects. The technology utilizes a hot-melt extrusion method, modified from a glue gun, to print composites of polycaprolactone (PCL) and hydroxyapatite (HA) without the need for organic solvents or prefabrication. The research demonstrates that by modulating the molecular weight of PCL and the concentration of HA, the mechanical, biological, and degradation properties of the resulting scaffold can be precisely tailored.The study's key findings highlight the system's multifunctionality, including its inherent osteoconductivity and the ability to incorporate antibiotics for localized, sustained anti-infection activity. An in vivo assessment in a rabbit model with a critical-sized femoral defect showed that the in situ printed PCL/HA scaffold significantly improved new bone formation, mechanical stability, and microarchitecture compared to a commercially available bone cement control. The authors conclude that this platform represents a promising, patient-specific therapeutic strategy for bone regeneration, addressing key limitations of conventional treatments such as anatomical mismatch, complexity, and cost.Strengths* Innovative In Situ Printing Technology: The core innovation is a portable, handheld device that allows a clinician to print a customized bone scaffold directly into an irregularly shaped defect. This approach circumvents the need for high-resolution scanning, complex data processing, and costly, time-consuming prefabrication associated with conventional 3D-printed implants.* Biocompatible and Safe Fabrication Method: The use of a solvent-free, low-temperature hot-melt extrusion process is a significant strength. PCL's low melting point (around 60°C) allows for direct application to tissue with minimal risk of thermal damage, a crucial factor for in vivo applicability. The device's temperature can be tuned using a Positive Temperature Coefficient (PTC) chip, with a low-temperature (80°C) version reducing the extruded construct's surface temperature to ~55°C.* Tunable Multifunctionality: The PCL/HA composite system is highly versatile. The study comprehensively demonstrates that scaffold properties can be tailored for specific clinical needs: * Mechanical Properties: Increasing PCL molecular weight and HA concentration enhances compressive strength and elastic modulus, allowing for adaptation to different load-bearing requirements. * Degradation Rate: The inclusion of HA slows the degradation of the PCL matrix, providing sustained structural support during the healing process. * Osteoconductivity: HA incorporation is shown to significantly promote cellular proliferation, osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs), and mineralization in vitro. * Antibacterial Activity: The platform supports the integration of antibiotics (vancomycin, gentamicin), enabling sustained local drug release to prevent post-operative infections, a major cause of implant failure.* Robust In Vivo Validation: The therapeutic efficacy was demonstrated in a clinically relevant critical-sized femoral bone defect model in rabbits. The PCL/HA scaffold (specifically the 50H formulation) not only supported structural integrity but also led to superior new bone formation, quality, and mechanical stability compared to the bone cement control, as quantified by histological and micro-CT analyses.Weaknesses * Sub-Optimal Mechanical and Adhesive Properties: While tunable, the authors explicitly state that both the mechanical strength and the tissue adhesion of the constructs "should be improved" for stable, long-term performance. The addition of HA, while beneficial for strength, was found to decrease adhesive properties.* Lack of Engineered Porosity: The current extrusion method produces a solid construct. The authors suggest that incorporating "porogens" in future work could create an interconnected porous structure, which is critical for enhancing nutrient exchange, cellular waste removal, and ultimately, new bone formation and integration.* Limited Scope of In Vivo Testing: The study was confined to a single type of defect in a small animal model (rabbit). To establish broader clinical applicability, the authors recommend future experiments in large-animal models, infection-based models, and models featuring a variety of anatomical bone defects.* Manual Application and Precision: The pr