Bone tissue engineering (BTE) is a rapidly growing field aiming to create a biofunctional tissue that can integrate and degrade in vivo to treat diseased or damaged tissue. It has become evident that scaffold fabrication techniques are very important in dictating the final structural, mechanical properties, and biological response of the implanted biomaterials. A comprehensive review of the current accomplishments on scaffold fabrication techniques, their structure, and function properties for BTE is provided herein. Different types of biomaterials ranging from inorganic biomaterials to natural and synthetic polymers and related composites for scaffold processing are presented. Emergent scaffolding techniques such as electrospinning, freeze-drying, bioprinting, and decellularization are also discussed. Strategies to improve vascularization potential and immunomodulation, which is considered a grand challenge in BTE scaffolding, are also presented.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adfm.202010609

Scaffold fabrication technologies and structure/function properties in bone tissue engineering

The ability to model CNS tissues in vitro for in vivo transplantation has the potential to be of critical importance in a variety of medical conditions such as spinal cord injury, traumatic brain injury, stroke, and degenerative neurologic disease. Our approach to generating functional CNS tissue constructs relies on a “multiprong” combination of sophisticated 3D bioprinting and cell culture expertise. Here, as an example for utilizing novel 3D neurobioprinting, we have devised a method to model the cytoarchitecture of spinal cord tissue.

Supporting data for 3D Printed Stem-Cell Derived Neural Progenitors Generate Spinal Cord Scaffolds

Bone defect caused by trauma, tumor, infection, and other reasons is a thorny problem that needs to be solved in orthopedic clinic. Customized bone repair biomaterials and their fabrication still need to be explored. Three-dimensional (3D) printing is a high-speed fabrication process for bone tissue biomaterials, which paves the way of solving clinical bone defect problems in a new way. In this study, the fused deposition modeling (FDM) technology was used to prepare the composite scaffolds of polylactic acid (PLA) and nano-hydroxyapatite (n-HA). The composite scaffold was optimized by material characterization, mechanical property test, and in vitro bone marrow mesenchymal stem cells biocompatibility test. Finally, a rabbit model was established to evaluate the osteogenic ability of PLA/n-HA scaffolds in vivo. The results showed that the PLA/n-HA composites proposed in this study were highly printable, and the printed scaffold showed tunable mechanical strength accompanied by the proportion of n-HA components. The biocompatibility and osteogenic induction properties were proved better than that of the pure PLA scaffold. This composite scaffold of PLA and n-HA provides a promising strategy for the repair of large bone defects.

3D printing of PLA/n-HA composite scaffolds with customized mechanical properties and biological functions for bone tissue engineering

4D printing of shape memory polymer composites: A review on fabrication techniques, applications, and future perspectives

Recent advances in 3D-printed polylactide and polycaprolactone-based biomaterials for tissue engineering applications.

Over the last decade, 3D bioprinting has received immense attention from research communities for developing functional tissues. Thanks to the complexity of tissues, various bioprinting methods have been exploited to figure out the challenges of tissue fabrication, in which hydrogels are widely adopted as a bioink in cell printing technologies based on the extrusion principle. Thus far, there is a wealth of literature proposing the crucial parameters of extrusion-based bioprinting of hydrogel biomaterials (e.g., hydrogel properties, printing conditions, and tissue scaffold design) toward enhancing performance. Despite the growing research in this field, numerous challenges that hinder advanced applications still exist. Herein, the most recently reported hydrogel-based bioprinted scaffolds, i.e., skin, bone, cartilage, vascular, neural, and muscular (including skeletal, cardiac, and smooth) scaffolds, are systematically discussed with an emphasis on the advanced fabrication techniques from the tissue engineering perspective. The methods covered include multiple-dispenser, coaxial, and hybrid 3D bioprinting. The present work is a unique study to figure out the opportunities of the novel techniques to fabricate complicated constructs with structural and functional heterogeneity. Finally, the principal challenges of current studies and a vision of future research are presented.

/pdf/recent-progress-in-extrusion-3d-bioprinting-of-hydrogel-h2upbumxyq.pdf

Recent progress in extrusion 3D bioprinting of hydrogel biomaterials for tissue regeneration: a comprehensive review with focus on advanced fabrication techniques

Nature’s materials have evolved over time to be able to respond to environmental stimuli by generating complex structures that can change their functions in response to distance, time, and direction of stimuli. A number of technical efforts are currently being made to improve printing resolution, shape fidelity, and printing speed to mimic the structural design of natural materials with three-dimensional printing. Unfortunately, this technology is limited by the fact that printed objects are static and cannot be reshaped dynamically in response to stimuli. In recent years, several smart materials have been developed that can undergo dynamic morphing in response to a stimulus, thus resolving this issue. Four-dimensional (4D) printing refers to a manufacturing process involving additive manufacturing, smart materials, and specific geometries. It has become an essential technology for biomedical engineering and has the potential to create a wide range of useful biomedical products. This paper will discuss the concept of 4D bioprinting and the recent developments in smart materials, which can be actuated by different stimuli and be exploited to develop biomimetic materials and structures, with significant implications for pharmaceutics and biomedical research, as well as prospects for the future.

4D printing: a cutting-edge platform for biomedical applications

In this research, the fracture behavior of brittle specimens weakened by V-shaped notches with end holes (VO-notches) is studied. First, an experimental investigation is conducted to evaluate the effect of VO-notches on fracture behavior. To this end, VO-notched samples of PMMA are made and exposed to pure opening mode loading, pure tearing mode loading, and some combinations of these two loading types. As part of this study, samples with end-hole radii of 1, 2, and 4 mm are prepared to determine the effect of the notch end-hole size on the fracture resistance. Second, two well-known stress-based criteria, namely the maximum tangential stress (MTS) criterion and the mean stress (MS) criterion, are developed for VO-shaped notches subjected to mixed-mode I/III loading, also determining the associated fracture limit curves. A comparison between the theoretical and the experimental critical conditions indicates that the resulting VO-MTS and VO-MS criteria predict the fracture resistance of VO-notched samples with about 92% and 90% accuracy, respectively, confirming their capacity to estimate fracture conditions.

/pdf/vo-notches-subjected-to-tension-torsion-loading-experimental-17kd78kx.pdf

Mohsen Askari

Papers

Recent progress in extrusion 3D bioprinting of hydrogel biomaterials for tissue regeneration: a comprehensive review with focus on advanced fabrication techniques

4D printing: a cutting-edge platform for biomedical applications

VO-Notches Subjected to Tension–Torsion Loading: Experimental and Theoretical Fracture Study on Polymeric Samples