Three-dimensional (3D) bioprinting, known as a promising technology for bioartificial organ manufacturing, has provided unprecedented versatility to manipulate cells and other biomaterials with precise control their locations in space. Over the last decade, a number of 3D bioprinting technologies have been explored. Natural polymers have played a central role in supporting the cellular and biomolecular activities before, during and after the 3D bioprinting processes. These polymers have been widely used as effective cell-loading hydrogels for homogeneous/heterogeneous tissue/organ formation, hierarchical vascular/neural/lymphatic network construction, as well as multiple biological/biochemial/physiological/biomedical/pathological functionality realization. This review aims to cover recent progress in natural polymers for bioartificial organ 3D bioprinting. It is structured as introducing the important properties of 3D printable natural polymers, successful models of 3D tissue/organ construction and typical technologies for bioartificial organ 3D bioprinting.

An organ manufacturing technique was developed that enables the formation of cell/extracellular matrix (ECM) complexes for in vitro or in vivo growth. In this study, a three-dimensional (3D) structure composed of hepatocytes and gelatin/alginate hydrogel was made using a cell assembler-I apparatus to thoroughly control cell assembling. Hepatocytes and ECM were constructed into 10 X 10 X 3mm³ structures according to a designed pattern. The embedded hepatocytes remained viable and performed biological functions in the construct for more than 12 days. This 3D structure has the potential to be used as a precursor for tissue or organ regeneration. This technology offers the potential for high-throughput production of artificial human tissues and organs.

Brain tissue engineering has now emerged as one of the most promising treatments for the traumatic brain injury. In this article, two groups of three-dimensional (3D) hydrogel structures composed of gelatin and gelatin/hyaluronan have been formed using our 3D cell assembly technique for in vivo study in rats, in order to investigate their effects in reparation of injury in the central nervous system (CNS). The structures were implanted into cortical defects created in rat brains, and their abilities to improve the brain tissue reconstruction were then evaluated. After 4, 8, 10, and 13 weeks of implantation, sections of brains were processed with NISSL staining for observing the immigration of host neural cells into the implanted materials and the degradation property of the materials. The results showed that simplex gelatin and gelatin/hyaluronan (20:1) with 3D structures both have good biocompatibility with brain tissue while gelatin/hyaluronan has a better contiguity with the surrounding tissue. Through our primary study, it seems that 3D gelatin/hyaluronan structures may be useful in brain tissue repair.

Presently, there is a recognized and imperative need for bioartificial organs. The technological advances in transgenosis, tissue engineering, and rapid prototyping have led to the development of spatially complex tissues. An ideal artificial organ should provide nutrient transport system, mechanical stable architecture, and synergetic multicellular organization in one construct. The multinozzle rapid prototyping technique simultaneously assembles vascular systems including hierarchical multicellular structures in an automated and reproducible manner and offers an effective way for treating organ failures. In this article, a brief overview of the recent trends and outstanding challenges in organ manufacturing is provided. From the viewpoint of disciplinary crossing, integration, and development, future directions in the coming years were pointed out.

A new technique for preparing double-layer polyurethane (PU)–collagen nerve conduits for peripheral nerve repair via a double-nozzle, low-temperature, deposition manufacturing (DLDM) system has been developed. The DLDM system is based on a digital prototyping approach, and uses a combination of thermally induced phase separation and freeze-drying. With this system, two kinds of biomaterials with different properties can be combined to produce scaffold structures with good biocompatibility in the inner layer and with the desired mechanical strength protruded by the outer. The forming precision is high, the wall thickness can be controlled, and a tight connection between the two layers can be achieved. The effects of changing the processing parameters and the material temperature on the structure of the scaffolds have been investigated. Additionally, the effect of material concentration on the mechanical strength and hydrophilic properties of the scaffolds has also been studied. Ideal peripheral nerve repair conduits, comprising an outer microporous layer of PU and internal oriented filaments of collagen, have been manufactured through optimizing the processing parameters and the biomaterial concentrations.