The Ability of Biodegradable Thermosensitive Hydrogel Composite Calcium-Silicon-Based Bioactive Bone Cement in Promoting Osteogenesis and Repairing Rabbit Distal Femoral Defects

Biocompatibility and Bone Regeneration by Shape Memory Polymer Scaffolds

Biodegradable, shape memory polymer (SMP) scaffolds based on poly(ε-caprolactone) (PCL) offer unique advantages as a regenerative treatment strategy for critical-sized bone defects. In particular, a conformal fit may be achieved following exposure to warm saline, thereby improving osseointegration and regeneration. Advancing the clinical translation of these SMP scaffolds requires establishment of efficacy not only in non-loading models, but also load-bearing or load-sharing models. Thus, the present study evaluated the biocompatibility and bone regeneration potential of SMP scaffolds in a rabbit distal femoral condyle model. Two distinct SMP scaffold compositions were evaluated, a "PCL-only" scaffold formed from PCL-diacrylate (PCL-DA) and a semi-interpenetrating network (semi-IPN) formed from PCL-DA and poly(L-lactic acid) (PCL:PLLA). Semi-IPN PCL:PLLA scaffolds possess greater rigidity and faster rates of degradation versus PCL scaffolds. In vivo biocompatibility was assessed with a rat subcutaneous implantation model, whereas osseointegration was assessed with a 4 mm × 8 mm rabbit distal femoral condyle defect model. Both types of SMP scaffolds exhibited excellent biocompatibility marked by infiltration with fibrous tissue and a minimal inflammatory response. When implanted in the rabbit distal femur, both SMP scaffolds supported bone ingrowth. Collectively, these results demonstrate that the SMP scaffolds are biocompatible and integrate with adjacent host osseous tissues when implanted in vivo in a load-sharing environment. This study provides key proof-of-concept data necessary to proceed with large animal translational studies and clinical trials in human subjects.

Stimuli-responsive hydrogels for bone tissue engineering

The treatment of bone defects remains a great clinical challenge. With the development of science and technology, bone tissue engineering technology has emerged, which can mimic the structure and function of natural bone tissues and create solutions for repairing or replacing human bone tissues based on biocompatible materials, cells and bioactive factors. Hydrogels are favoured by researchers due to their high water content, degradability and good biocompatibility. This paper describes the hydrogel sources, roles and applications. According to the different types of stimuli, hydrogels are classified into three categories: physical, chemical and biochemical responses, and the applications of different stimuli-responsive hydrogels in bone tissue engineering are summarised. Stimuli-responsive hydrogels can form a semi-solid with good adhesion based on different physiological environments, which can carry a variety of bone-enhancing bioactive factors, drugs and cells, and have a long retention time in the local area, which is conducive to a long period of controlled release; they can also form a scaffold for constructing tissue repair, which can jointly promote the repair of bone injury sites. However, it also has many defects, such as poor biocompatibility, immunogenicity and mechanical stability. Further studies are still needed in the future to facilitate its clinical translation.

Three-Dimensional-Printed Spherical Hollow Structural Scaffolds for Guiding Critical-Sized Bone Regeneration

The treatment of bone tissue defects continues to be a complex medical issue. Recently, three-dimensional (3D)-printed scaffold technology for bone tissue engineering (BTE) has emerged as an important therapeutic approach for bone defect repair. Despite the potential of BTE scaffolds to contribute to long-term bone reconstruction, there are certain challenges associated with it including the impediment of bone growth within the scaffolds and vascular infiltration. These difficulties can be resolved by using scaffold structural modification strategies that can effectively guide bone regeneration. This study involved the preparation of biphasic calcium phosphate spherical hollow structural scaffolds (SHSS) with varying pore sizes using 3D printing (photopolymerized via digital light processing). The chemical compositions, microscopic morphologies, mechanical properties, biocompatibilities, osteogenic properties, and impact on repairing critical-sized bone defects of SHSS were assessed through characterization analyses, in vitro cytological assays, and in vivo biological experiments. The results revealed the biomimetic properties of SHSS and their favorable biocompatibility. The scaffolds stimulated cell adhesion, proliferation, differentiation, and migration and facilitated the expression of osteogenic genes and proteins, including Col-1, OCN, and OPN. Furthermore, they could effectively repair a critical-sized bone defect in a rabbit femoral condyle by establishing an osteogenic platform and guiding bone regeneration in the defect region. This innovative strategy presents a novel therapeutic approach for assessing critical-sized bone defects.

Achieving outstanding mechanical/bonding performances by epoxy nanocomposite as concrete-steel rebar adhesive using silane modification of nano SiO2

Anchoring steel rebar in concrete structures is a common method in the building and construction industry. This research focuses on improving the mechanical/bonding properties of the prepared epoxy nanocomposite adhesive using surface treatment of SiO₂ nano fillers by glycidoxypropyltrimethoxysilane (GPTMS). For this purpose, the nano silica particles were silanized via a facile sol-gel method at silane concentrations of 1, 5, 10 and 20X (i.e. X is stoichiometric silane concentration). The nanoparticles were characterized carefully by FTIR, TGA, XRD and XPS techniques. It was found that the highest GPTMS grafting ratio was obtained at silane concentration of 10X. The pure and silanized nanoparticles were added to a two-pack epoxy resin and were compared for tensile and compressive properties. It was found that surface modification of nano silica caused improvement in the strength, modulus, compressive strength and compressive modulus by 56, 81, 200 and 66% compared to the pristine epoxy adhesive and also 70, 20, 17 and 21% compared to the pure nano silica containing adhesive. It also caused 40 and 25% improvement in the pullout strength, 33 and 18% enhancement in the pullout displacement and 130 and 50% in adhesion energy compared to the pristine and raw silica-containing adhesives, respectively.

Smart Hydrogels for Bone Reconstruction via Modulating the Microenvironment

Rapid and effective repair of injured or diseased bone defects remains a major challenge due to shortages of implants. Smart hydrogels that respond to internal and external stimuli to achieve therapeutic actions in a spatially and temporally controlled manner have recently attracted much attention for bone therapy and regeneration. These hydrogels can be modified by introducing responsive moieties or embedding nanoparticles to increase their capacity for bone repair. Under specific stimuli, smart hydrogels can achieve variable, programmable, and controllable changes on demand to modulate the microenvironment for promoting bone healing. In this review, we highlight the advantages of smart hydrogels and summarize their materials, gelation methods, and properties. Then, we overview the recent advances in developing hydrogels that respond to biochemical signals, electromagnetic energy, and physical stimuli, including single, dual, and multiple types of stimuli, to enable physiological and pathological bone repair by modulating the microenvironment. Then, we discuss the current challenges and future perspectives regarding the clinical translation of smart hydrogels.

3D Printing in Regenerative Medicine: Technologies and Resources Utilized

Over the past ten years, the use of additive manufacturing techniques, also known as "3D printing", has steadily increased in a variety of scientific fields. There are a number of inherent advantages to these fabrication methods over conventional manufacturing due to the way that they work, which is based on the layer-by-layer material-deposition principle. These benefits include the accurate attribution of complex, pre-designed shapes, as well as the use of a variety of innovative raw materials. Its main advantage is the ability to fabricate custom shapes with an interior lattice network connecting them and a porous surface that traditional manufacturing techniques cannot adequately attribute. Such structures are being used for direct implantation into the human body in the biomedical field in areas such as bio-printing, where this potential is being heavily utilized. The fabricated items must be made of biomaterials with the proper mechanical properties, as well as biomaterials that exhibit characteristics such as biocompatibility, bioresorbability, and biodegradability, in order to meet the strict requirements that such procedures impose. The most significant biomaterials used in these techniques are listed in this work, but their advantages and disadvantages are also discussed in relation to the aforementioned properties that are crucial to their use.