Articles (Review & Research)

4D printing involves the creation of dynamic structures that can change their properties, shape, or functionality over time in response to specific external stimuli like temperature, pH, humidity, and light. By combining the capacity of 3D printing to produce complex architectures with the realm of smart materials, 4D printing enables the design and manufacturing of objects capable of interacting with their environment. Despite its potential, the field of 4D printing is predominantly reliant on synthetic responsive materials, with limited advancements towards more eco-friendly alternatives. Additionally, while many 4D structures draw inspiration from nature, the integration of bio-based or biodegradable materials remains relatively uncommon. Aiming to draw the 4D printing community's attention to the need for sustainable smart materials, this review highlights the use of natural materials in 4D printing as alternatives to conventional synthetic ones. First, an introduction to 4D printing technology and its foundational elements is provided. Next, the natural materials that have been printed are detailed, including wood, natural fibers (flax and ramie), cellulose, lignin, plant oils (limonene, linalool, and soybean oil), starch, alginate, agarose, silk, chitosan, keratin, gelatin, pollen, proteins (bovine serum albumin), and xanthan gum, along with their biocomposites rheological, mechanical, and responsive properties. Finally, current applications, challenges, and future perspectives for green materials in 4D printing are discussed, contributing to the advancement of this emergent research field.

Programmable materials are desirable for a variety of functional applications that range from biomedical devices, actuators and soft robots to adaptive surfaces and deployable structures. However, current smart materials are often designed to respond to single stimuli (like temperature, humidity, or light). Here, a novel multi-stimuli-responsive composite is fabricated using direct ink writing (DIW) to enable programmability in both space and time and computation of logic operations. The composite hydrogels consist of double-network matrices of poly(N-isopropylacrylamide) (PNIPAM) or poly(acrylic acid) (PAA) and sodium alginate (SA) and are reinforced by a high content of cellulose nanocrystals (CNC) (14 wt%) and nanofibers (CNF) (1 wt%). These composites exhibit a simultaneously tunable response to external stimuli, such as temperature, pH, and ion concentration, enabling precise control over their swelling and shrinking behavior, shape, and mechanical properties over time. Bilayer hydrogel actuators are designed to display bidirectional bending in response to various stimuli scenarios. Finally, to leverage the multi-responsiveness and programmability of this new composite, Boolean algebra concepts are used to design and execute NOT, YES, OR, and AND logic gates, paving the way for self-actuating materials with embodied logic.

Coastal infrastructure replaces complex and heterogeneous natural habitats with flat, two-dimensional concrete walls, reducing refuges against predation, which modifies the composition and identity of the dominant species in sessile communities. This modification in the community structure can also change the reproductive propagules available in plankton, affecting the recruitment dynamics in communities from natural habitats nearby. Here, we tested the combined effects of the habitat type (simple vs. complex with holes) and predation on the diversity, larval production, and structure of sessile communities from a recreational marina. Complex substrates showed a larger biomass and a greater abundance of solitary organisms, mainly ascidians and bivalves, that benefited from refuges. Barnacles and calcified encrusting bryozoans dominated simple, flat substrates. The difference in dominance affected the pool of larvae produced by the communities. After eight months, communities growing on flat substrates produced more barnacle larvae than those from complex substrates, where larvae of ascidians were more abundant. However, this difference disappeared after 18 months of community development. The difference in the pool of larvae between simple and complex substrates did not affect the structure of the community on flat substrates nearby, which was determined by the predation regime. In the studied region, communities in artificial environments are under intense predation control, suppressing eventual recruitment differences in communities developing in flat substrates. Large interventions that modify habitat topography, creating refuges in the subtidal zone, can change the dynamic of the sessile communities in artificial habitats and, consequently, the larval supply in the vicinities. However, differences in larval supply will only translate in distinct sessile communities when the scale of intervention encompasses large areas, and other processes do not buffer the differences in recruitment.

Biomimetics enables the use of nature as a source of inspiration for the elaboration of high-performance materials. In this scenario, the development of bioinspired composites emerges as a promising proposal, capable of generating technological innovation in numerous areas of engineering, considering the exceptional mechanical performance of materials of this kind. That said, this review article characterizes the design principles and fundamental parameters for bioinspired composites design. In addition, the main challenges to be overcome in the development of bioinspired materials are discussed, with the presentation of some experimental studies that lead to the practical application of such principles. Future applications for this class of materials are also highlighted.

The additive manufacturing of titanium into porous geometries offers a means to generate low-stiffness endosseous implants with a greater surface area available for osseointegration. In this work, selective laser melting was used to produce gyroid-based scaffolds with a uniform pore size of 300 μm or functionally graded pore size from 600 μm to 300 μm. Initial in vitro assessment with Saos-2 cells showed favourable cell proliferation at pore sizes of 300 and 600 μm. Following implantation into rabbit tibiae, early histological observations at four weeks indicated some residual inflammation alongside neovessel infiltration into the scaffold interior and some early apposition of mineralized bone tissue. At twelve weeks, both scaffolds were filled with a mixture of adipocyte-rich marrow, micro-capillaries, and mineralized bone tissue. X-ray microcomputed tomography showed a higher bone volume fraction (BV/TV) and percentage of bone-implant contact (BIC) in the implants with 300 μm pores than in the functionally graded specimens. In functionally graded specimens, localized BV/TV measurement was observed to be higher in the innermost region containing smaller pores (estimated at 300–400 μm) than in larger pores at the implant exterior. The unit cell topology of the porous implant was also observed to guide the direction of bone ingrowth by conducting along the implant struts. These results suggest that in vivo experimentation is necessary alongside parametric optimization of functionally graded porous implants to predict short-term and long-term bone apposition.

Large quantities of carbon dioxide (CO2) are emitted to the atmosphere during the traditional burning brick process, taking part in the construction industry affectations. This paper presents an alternative way that faces environmental issues by using low-Impact materials in construction; for this purpose, it is proposed the formulation of an admixture for the fabrication of unfired clay bricks. Three different clay-base formulations were developed to analyze their behavior underwater, plasticity, and drying time to determinate the best one to get an unfired brick. The sample with the better performance underwater was tested to water absorption and compressive strength tests. Results show that it is possible to obtain an unfired clay-based material utilizing low environmental impact admixtures to elaborate construction bricks. Finally, a Life Cycle Analysis assessment was conducted to determine CO2 emissions when utilizing the propossed formulation.

The idea of transferring vital drugs through nanotubes in the human body has attracted the attention of many researchers in the field of nanomedicine. Accordingly, the main objective of this article is to investigate the forced vibration response of two hybrid smart carbon nanotubes connected using springs and conveying a nanofluid, with each one including either a piezoelectric or electrorheological fluid layer. To this aim, a slip boundary condition along with a Knudsen number is employed to address the vibration behavior of smart hybrid sandwich nanotubes acted upon by a moving sinusoidal load, while equations are derived with the aid of the Timoshenko beam model and nonlocal strain gradient theory. The former theory is complemented with hardening and softening material effects which can greatly enhance the precision of the results. Furthermore, Hamilton’s principle is implemented to obtain the equations of motion. Regarding the time response of the structure, a combination of modal analysis and the Laplace transform is applied. The accuracy of the developed procedure is verified through a set of comparisons of static deflection (as a result of a point load) and vibration frequencies. In addition, the impact of a number of parameters ranging from nanoparticle velocity to material length scale is investigated.

3D printing permits the construction of objects by layer-by-layer deposition of material, resulting in precise control of the dimensions and properties of complex printed structures. Although 3D printing fabricates inanimate objects, the emerging technology of 4D printing allows for animated structures that change their shape, function, or properties over time when exposed to specific external stimuli after fabrication. Among the materials used in 4D printing, hydrogels have attracted growing interest due to the availability of various smart hydrogels. The reversible shape-morphing in 4D printed hydrogel structures is driven by a stress mismatch arising from
the different swelling degrees in the parts of the structure upon application of a stimulus. This review provides the state-of-the-art of 4D printing of hydrogels from the materials perspective. First, the main 3D printing technologies employed are briefly depicted, and, for each one, the required physico-chemical properties of the precursor material. Then, the hydrogels that have been printed are described, including stimuli-responsive hydrogels, non-responsive hydrogels that are sensitive to solvent absorption/ desorption, and multimaterial structures that are totally hydrogel-based. Finally, the current and future applications of this technology are presented, and the requisites and avenues of improvement in terms of material properties are discussed.

With recent advances in the field of 3D printing, new prosthetic features have been developed to provide accessibility to patients. However, the mechanisms employed for its performance still need to be better explored. In this article, a study is proposed on the angular variation between the joints of a human finger and a design solution based on soft robotics, in order to guide studies on prosthetic solutions.

This paper presents some results of an ongoing interdisciplinary research about models and prototypes of biomimetic devices via installations and the focus of this paper is to outline this research role in architectural purposes as it perpasses the cultural and heritage contexts by being a way of understanding and living in the world as well as taking place in the world as devices or environments that pass on to future generation to use, learn from and be inspired by.

Sustainable energy performance: Bio-inspiration from thermoregulation of the termite mounds

This research reflects on the possibility of architecture eco-­‐sustainable development from the point of view of energy, space and environmental heritage, based on the constructive process of some species of social wasps ( Hymenoptera) and termites ( Isoptera)

Para a pesquisa em andamento, estão sendo desenvolvidas, através do uso de metodologias apropriadas de design, sistemas CAD/CAE e elaboração de protótipos, embalagens para cosméticos com formas e funcionalidades inspiradas na natureza, com a incorporação de materiais biodegradáveis, obtendo um produto capaz de atender aos requisitos de design e sustentabilidade.

O presente trabalho, que mostra resultados preliminares de pesquisa em andamento, consiste no estudo de materiais hidrogéis e suas possibilidades de aplicação por meio de impressão 4D, descrevendo os principais fatores relacionados a este método e as propriedades do hidrogel que justificam seu uso neste contexto