## 6 Current Challenges and Future Prospects
### Present Obstacles Faced by AM Technologies
#### 6.2.1 Bioprinting
Alginate-HA scaffolds, when crosslinked with calcium ions, show enhanced mechanical properties and are used in bone regeneration without adverse effects on liver or kidney functions. Hyaluronic acid (HyA) plays a vital role in bone regeneration, particularly in craniofacial and dental applications. HyA-based scaffolds, especially when combined with nano-hydroxyapatite (nHA), promote cellular adhesion and proliferation, offering stability and biocompatibility in tissue engineering. Ceramic materials like HA and tricalcium phosphate (TCP) are widely used in 3D-printed scaffolds due to their robust mechanical properties and ability to support cellular proliferation and bone formation. These materials are suitable for both load-bearing and non-load-bearing applications. Poly (lactic-co-glycolic acid) (PLGA) combined with HA forms a composite scaffold that resembles human bone in structure and function, enhancing mechanical strength and supporting controlled drug release. Chitosan-HA composites are also widely used in bone tissue engineering for their biocompatibility and ability to promote osteoblast cell proliferation. Polyethylene glycol (PEG) and polycaprolactone (PCL) combined with HA form biocompatible scaffolds that show promise in bone regeneration. Gelatin, derived from collagen, has been combined with HA to create scaffolds that support natural regenerative processes, offering significant potential in bone tissue engineering [138]. As 4D printing emerges as a key player in the manufacturing landscape, there is a growing emphasis on making it a robust and energy-efficient process. Groundbreaking applications such as wind turbine blades and smart solar concentrators showcase the transformative potential of 4D printing in real-world settings [139]. These advancements highlight the ability of 4D printing to revolutionize industries by creating smart, adaptive structures that respond to environmental stimuli, making it particularly relevant in the renewable energy sector. In the context of large composite structure manufacturing, specifically for wind turbine blades, 4D printing, when combined with large-scale additive manufacturing (LSAM) processes, enables the creation of complex and massive components more efficiently than traditional methods. LSAM integrates multiple additive manufacturing techniques, such as fused deposition modeling (FDM), continuous fiber reinforcement (CFR), and stereolithography (SLA), which are tailored for creating intricate and large-scale wind turbine structures [140]. These processes allow for rapid production of blade cores, molds, and tail sections, while also improving strength and performance through the incorporation of advanced materials like carbon fiber. Additionally, 4D printing's ability to create adaptive materials that adjust to varying wind conditions can further optimize the performance of wind turbine blades, reducing maintenance needs and enhancing energy efficiency. This convergence of adaptive materials and cutting-edge manufacturing processes offers new possibilities for wind turbine design, making 4D printing a key innovation in the future of sustainable energy. The integration of conductive polymers, for instance, enables structures to exhibit electrical conductivity in response to stimuli, enhancing both safety and operational efficiency by enabling self-monitoring capabilities [141].