Hydroxyapatite (HAp) polymer composites have gained significant attention due to their applications in bone regeneration and tooth implants. This review examines the synthesis, properties, and applications of Hap, highlighting various manufacturing methods, including wet, dry, hydrothermal, and sol–gel processes. The properties of HAp are influenced by precursor materials and are commonly obtained from natural calcium-rich sources like eggshells, seashells, and fish scales. Composite materials, such as cellulose–hydroxyapatite and gelatin–hydroxyapatite, exhibit promising strength and biocompatibility for bone and tissue replacement. Metallic implants and scaffolds enhance stability, including well-known titanium-based and stainless steel-based implants and ceramic body implants. Biopolymers, like chitosan and alginate, combined with Hap, offer chemical stability and strength for tissue engineering. Collagen, fibrin, and gelatin play crucial roles in mimicking natural bone composition. Various synthesis methods like sol–gel, hydrothermal, and solution casting produce HAp crystals, with potential applications in bone repair and regeneration. Additionally, the use of biowaste materials, like eggshells and snails or seashells, not only supports sustainable HAp production but also reduces environmental impact. This review emphasizes the significance of understanding the properties of calcium–phosphate (Ca-P) compounds and processing methods for scaffold generation, highlighting novel characteristics and mechanisms of biomaterials in bone healing. Comparative studies of these methods in specific applications underscore the versatility and potential of HAp composites in biomedical engineering. Overall, HAp composites offer promising solutions for improving patient outcomes in bone replacement and tissue engineering and advancing medical practices.

During the past decade, there has been a continued increase in the demand for bone defect repair and replacement resulting from long-term illnesses or traumatic incidents. To address these challenges, tissue engineering research has focused on biomedical applications. This field concentrated on the development of suitable materials to enhance biological functionality and bone integration. Toward this aim, it is necessary to develop a proper material that provides good osseointegration and mechanical behavior by combining biopolymers with ceramics, which increase their mechanical stability and mineralization process. Hydroxyapatite (HAp) is synthesized from natural resources owing to its unique properties; for example, it can mimic the composition of bones and teeth of humans and animals. Biopolymers, including chitosan and alginate, combined with HAp, offer good chemical stability and strength required for tissue engineering. Composite biomaterials containing hydroxyapatite could be a potential substitute for artificial synthetic bone grafts. Utilizing various polymers and fabrication methodologies would efficiently customize physicochemical properties and suitable mechanical properties in synergy with biodegradation, thus enhancing their potential in bone regeneration. This review summarizes the commonly used polymers in tissue engineering, emphasizing their advantages and limitations. This paper also highlights recent advances in the production and investigation of HAp-based polymer composites used in biomedical applications.

Polymeric and plastic materials currently have numerous positive impacts due to their unique properties that make them important for various engineering applications. However, sustainability is a vital factor that should be considered, because of environmental issues. Eggshells (ES) are an important way to reduce the impact of nondegradable materials when applied to reinforce different types of polymer matrices, whether natural or synthetic polymers. Therefore, this study is an attempt to explore the potential application of waste eggshell fillers for the first time as a natural reinforcement in polyamide 12 (PA) composites. PA was loaded with three different ratios (3, 5, and 10 wt. %) of eggshell powder. Morphological studies of the PA powder, ES powder, and their composites were carried out by scanning electron microscopy (SEM). Furthermore, differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were performed to study the thermal and chemical properties of the raw materials and the produced composites. The results indicate ES fillers’ potential usage as a reinforcement material to develop the thermal and chemical properties of the PA polymer matrix composites, thereby reducing costs and minimizing the environmental pollution caused by waste eggshells and petroleum-based polymers.

This research investigates the application of electrospinning in the production of CA fibers and examines how two critical parameters influence the morphology and dimensions of the resulting CA products during the spinning process. These factors include the solvent system employed and the concentration of the solution. By analyzing these parameters, the research aims to elucidate their effects on the characteristics of the resultant CA materials following the spinning process. The study employed acetone as a single-solvent system, while acetone–acetic acid (2:1) and acetone-chloroform, N,N-dimethylformamide (DMF) (2:1) were used as mixed-solvent systems at room temperature. For the single-solvent approach, CA was dissolved in acetone at concentrations of (5, 10, 11, 13, and 15 wt%). In the co-solvent systems, CA was dissolved in acetone–DMF (2:1) at concentrations of (5, 10, 15, 16, 18, and 20 wt%), and in acetone-acetic acid (2:1) at concentrations of (5, 10, 15, and 20 wt%). Although DMF and acetic acid could dissolve CA to form clear solutions (at 5 wt%), electrospinning primarily resulted in discrete beads. In contrast, electrospinning CA in acetone produced short, beaded fibers. The optimal results, yielding continuous fibers without beading, were achieved with 10 wt% CA in acetone, 15 wt% CA in acetone/acetic acid (2:1), and 18 wt% CA in acetone/DMF (2:1). The results revealed how various parameters affected the diameter and quality of the fibers, ultimately determining the optimal conditions.

The effects of the oxidation on the micro/nanohardness, density, and microstructure of the silicon nitride–carbon nanotube (Si ₃ N ₄ –CNT) composite were investigated. α‐Si ₃ N ₄ starting powder was oxidized at a temperature of 1000°C for 10 and 20 h and was used to produce composite samples made via hot isostatic pressing (HIP). Density measurements revealed that the 20‐h oxidized α‐Si ₃ N ₄ ‐based composite had higher apparent density than the unoxidized and 10‐h oxidized ones. The micro/nanohardness results proved that this improvement in the density induces changes in the mechanical properties. After the oxidation process and sintering, the microhardness of the composite remained unchanged at 6.525 and 6.49 GPa for the unoxidized and 10‐h oxidized samples, respectively. However, the microhardness was significantly improved, reaching 8.28 GPa for the 20‐h oxidized samples. Similarly, the best nanohardness results were obtained in the 20‐h oxidized samples, significantly surpassing those of the unoxidized and 10‐h oxidized samples. However, some of the scanning electron microscopy images indicate that the CNTs do not disperse or distribute evenly, explaining the large scatter in the nanohardness results. These findings suggest that the 20‐h oxidation process significantly enhanced the micro‐ and nanohardness and density of the Si ₃ N ₄ –CNT composite, potentially improving its overall mechanical performance.