Auxetic metamaterials are characterized by a negative Poisson ratio (NPR) and display an unexpected property of lateral expansion when stretched and densification when compressed. Auxetic properties can be achieved by designing special microstructures, hence their classification as metamaterials, and can be manufactured with varied raw materials and methods. Since work in this field began, auxetics have been considered for different biomedical applications, as some biological tissues have auxetic-like behaviour due to their lightweight structure and morphing properties, which makes auxetics ideal for interacting with the human body. This research study is developed with the aim of presenting an updated overview of auxetic metamaterials for biomedical devices. It stands out for providing a comprehensive view of medical applications for auxetics, including a focus on prosthetics, orthotics, ergonomic appliances, performance enhancement devices, in vitro medical devices for interacting with cells, and advanced medicinal clinical products, especially tissue engineering scaffolds with living cells. Innovative design and simulation approaches for the engineering of auxetic-based products are covered, and the relevant manufacturing technologies for prototyping and producing auxetics are analysed, taking into consideration those capable of processing biomaterials and enabling multi-scale and multi-material auxetics. An engineering design rational for auxetics-based medical devices is presented with integrative purposes. Finally, key research, development and expected technological breakthroughs are discussed.

The acceleration in advancements of smart materials and non-contact controlled devices in the field of 4D printing is facilitated by the use of magnetically responsive shape memory polymer (SMP) composites. This study is dedicated to the development of promising shape memory materials based on polylactic acid (PLA) and cobalt ferrite (CoFe₂O₄) nanoparticles. The activation of the shape memory effect (SME) in magnetic nanoparticle composites was achieved by applying a high-frequency alternating magnetic field (HFAMF). The PLA/CoFe₂O₄ composites exhibited a remarkable shape recovery ratio (>84%) and underwent rapid heating when exposed to HFAMF. The interaction of these composites with mouse adipose-derived mesenchymal stem cells demonstrated adequate cytocompatibility. The rapid magnetosensitive behavior and high shape recovery characteristics of PLA/CoFe₂O₄ composites make them promising candidates for biomedical applications.

The present work aimed to study the synergistic response of bioresorbable polylactide/bioactive wollastonite scaffolds towards mechanical stability, mesenchymal stromal cell colonization, and antibacterial activity in the physiological environment. Wollastonite was synthesized at 800 °C within 2 h by sol-gel combustion method. The surface area was found to be 1.51 m²/g, and Transmission Electron Microscopy (TEM) micrographs indicated the presence of porous structures. Fused deposition modeling was used to prepare 3D-printed polylactide/wollastonite and polylactide/hydroxyapatite scaffolds. Scanning Electron Microscopy (SEM) micrographs confirmed the interconnected porous structure and complex geometry of the scaffolds. The addition of wollastonite decreased the contact angle of the scaffolds. The mechanical testing of scaffolds examined by computational simulation, as well as machine testing, revealed their non-load-bearing capacity. The chemical constituent of the scaffolds was found to influence the attachment response of different cells on their surface. The incorporation of wollastonite effectively reduced live bacterial attachment, whereas the colonization of mesenchymal cells was improved. This observation confirms polylactide/wollastonite scaffold possesses both bactericidal as well as cytocompatible properties. Thus, the risk of peri-implant bacterial film formation can be prevented, and the biological fixation of the scaffold at the defect site can be enhanced by utilizing these composites.

Background. Patients with malignant bone and joint tumors often require reconstructive surgery for osteosynthesis or arthrodesis. The design of the implant can be realized by 3D printing using biodegradable materials with shape memory effect, which will facilitate operative access and reduce the risk of reoperation.Aim. The study aimed to evaluate the mechanical properties, biocompatibility and biological activity of polylactide (PLA) with hydroxyapatite (HA) and silicon dioxide (SiO2) produced by extrusion and 3D printing to identify prospects for the development of implants based on them for osteoreconstructive surgeries.Materials and methods. Materials based on PLA with the addition of 10, 15 and 20 % HA and SiO2 were obtained by extrusion. These materials were 3D-printed to produce samples that underwent a compression test. Their extracts obtained after incubation of the samples in fetal calf serum for 30 days were examined. Biocompatibility was assessed by the level of hemolysis and cytotoxicity of the extracts, as well as stimulation of oxidative stress. The effects of the extracts on cell adhesion and intensity of multipotent mesenchymal stromal cells colonization on the surface of both intact and biodegraded samples were studied separately.Results. The addition of HA and SiO2 to PLA did not significantly increase hemolysis and cytotoxicity compared to pure PLA. However, incubation with extracts of samples containing 20 % stimulated an increase in oxidative stress in leukocytes, and inhibited cell adhesion. Samples with 10 and 15 % HA maximally stimulated cell colonization on the sample surface.Conclusion. Materials based on PLA with 10 and 15 % HA combine high strength, biocompatibility, biodegradability and effective osteoconductivity, which makes them promising candidates for implants for osteoreconstruction and arthrodesis.

Background. Based on the results of evaluating the mechanical and strength characteristics and studying various aspects of biological activity, a composite material based on polylactide and hydroxyapatite (PLA/HA) is considered a promising component of shape-memory implants for osteoreconstructive surgeries. Aim. To evaluate the response of laboratory animals to the implantation of PLA/HA-based implant samples, as well as the potential for their use as a platform for the local administration of antibacterial agents. Materials and methods. Experimental samples were manufactured in the form of surgical staples from a PLA/HA composite material containing 15 % mass fraction of impurities by weight of hydroxyapatite in the form of 90 nm needle-shaped nanoparticles. To study biocompatibility and biodegradation in vivo, the staples were implanted subcutaneously in mice. After 50 days, the samples were removed, their weight changes were assessed, and histological tissue sections in the area of contact with the implants were examined. To explore the potential of using PLA/HA as a platform for local delivery of an antibacterial drug, 35 μg of an amoxicillin/clavulanic acid mixture was applied to the surface of the samples, followed by washing. The loaded samples were then placed on Mueller–Hinton agar seeded with Escherichia coli and Staphylococcus aureus. After 20 hours of incubation, the presence of zones of inhibition of colony formation around the samples and disks was assessed. Results. The shape memory effect was achieved by heating the samples, resulting in the closure of the initially open fixation clips. Although no significant change in sample weight was observed during their residence in the animals, histological examination of the surrounding tissue revealed signs of their initial biodegradation in vivo. No massive infiltration of tissue in the contact area by inflammatory cells, characteristic of an acute inflammatory response, was detected. However, isolated foreign body giant cells and isolated macrophages, lymphocytes, and neutrophils were observed in some samples. Microbiological studies demonstrated an inhibitory effect on the growth of E. coli and S. aureus colonies around the samples. Conclusion. The obtained results demonstrated the biocompatibility of PLA/HA with a hydroxyapatite content of 15 % mass fraction of impurities by weight, as its implantation did not induce an acute inflammatory reaction or rejection in experimental animals. Furthermore, it was demonstrated that products made from this material can be used as a platform for the local delivery of antibacterial agents.