Processing Collagen-Hydroxyapatite Composite for Bone Tissue Engineering: A 3D Printing Perspective

Abstract Tissue engineering is an interdisciplinary field combining biology, chemistry, and engineering to create implantable structures that support healing and regeneration. Autografts, tissues taken from a patient’s own body, are commonly used due to their high compatibility and minimal disease transmission risk. However, autografts are limited by the small amount of tissue that can be harvested. Allografts, or transplants from one person to another, provide a more natural alternative to synthetic or metal implants, yet their use is constrained by limited donor availability, high rejection rates, and significant operating costs. Although synthetic polymer, ceramic, and metallic implants have gained popularity due to their affordability and durability, they often lead to chronic pain, restricted movement, and eventual reimplantation because of issues like surface wear and reduced lubrication. Advances in artificial intelligence (AI), machine learning (ML), and 3D printing are opening new possibilities in tissue engineering. Researchers are now exploring natural polymers as an alternative to synthetic materials by focusing on the structural complexities and sustainability of native tissues. For example, type I collagen (Col), the most abundant protein in human connective tissues, shows promise as a replacement for titanium in bone tissue engineering due to its excellent mechanical properties, biocompatibility, and ability to support bone growth (osteogenesis). When combined with hydroxyapatite (HAp), Col-HAp composites can closely mimic the natural organic-inorganic structure of bone, providing both the chemical and physical properties needed to promote tissue healing and regeneration. However, the extraction and processing of collagen pose challenges, as they can degrade its natural properties and complicate the 3D printing of implants. This perspective examines the processing, characterization, and manufacturability of Col, its composites, and other robust biomaterials for bone tissue engineering, aiming to replicate the mechanical behavior of human limbs under both static and dynamic conditions. It also explores how AI and ML can enhance the precision and reproducibility of Col composite printing and enable generative scaffold design to foster vascularization, cell viability, and tissue growth. Finally, this work underscores the advancements in novel and customized 3D bioprinting systems designed to address patient-specific requirements, promote higher cell proliferation, and fabricate complex scaffold structures with improved structural properties.