Smart biomaterials: From 3D printing to 4D bioprinting.

This century is blessed with enhanced medical facilities on the grounds of the development of smart biomaterials. The rise of the four-dimensional (4D) bioprinting technology is a shining example. Using inert biomaterials as the bioinks for the three-dimensional (3D) printing process, static objects that might not be able to mimic the dynamic nature of tissues would be fabricated; by contrast, 4D bioprinting can be used for the fabrication of stimuli-responsive cell-laden structures that can evolve with time and enable engineered tissues to undergo morphological changes in a pre-planned way. For all the aptitude of 4D bioprinting technology in tissue engineering, it is imperative to select suitable stimuli-responsive biomaterials with cell-supporting functionalities and responsiveness; as a result, in this article, recent advances and challenges in smart biomaterials for 4D bioprinting are briefly discussed. An overview perspective concerning the latest developments in 4D-bioprinting is also provided.

Biodegradable Magnesium Biomaterials-Road to the Clinic.

In recent decades, we have witnessed radical changes in the use of permanent biomaterials. The intrinsic ability of magnesium (Mg) and its alloys to degrade without releasing toxic degradation products has led to a vast range of applications in the biomedical field, including cardiovascular stents, musculoskeletal, and orthopedic applications. With the use of biodegradable Mg biomaterials, patients would not suffer second surgery and surgical pain anymore. Be that as it may, the main drawbacks of these biomaterials are the high corrosion rate and unexpected degradation in physiological environments. Since biodegradable Mg-based implants are expected to show controllable degradation and match the requirements of specific applications, various techniques, such as designing a magnesium alloy and modifying the surface characteristics, are employed to tailor the degradation rate. In this paper, some fundamentals and particular aspects of magnesium degradation in physiological environments are summarized, and approaches to control the degradation behavior of Mg-based biomaterials are presented.

Biodegradable magnesium-based biomaterials: An overview of challenges and opportunities.

As promising biodegradable materials with nontoxic degradation products, magnesium (Mg) and its alloys have received more and more attention in the biomedical field very recently. Having excellent biocompatibility and unique mechanical properties, magnesium-based alloys currently cover a broad range of applications in the biomedical field. The use of Mg-based biomedical devices eliminates the need for biomaterial removal surgery after the healing process and reduces adverse effects induced by the implantation of permanent biomaterials. However, the high corrosion rate of Mg-based implants leads to unexpected degradation, structural failure, hydrogen evolution, alkalization, and cytotoxicity. To overcome these limitations, alloying Mg with suitable alloying elements and surface treatment come highly recommended. In this area, open questions remain on the behavior of Mg-based biomaterials in the human body and the effects of different factors that have resulted in these challenges. In addition to that, many techniques are yet to be verified to turn these challenges into opportunities. Accordingly, this article aims to review major challenges and opportunities for Mg-based biomaterials to minimize the challenges for the development of novel biomaterials made of Mg and its alloys.