The use of 3D printing for rapid tooling and manufacturing has promised to produce components with complex geometries according to computer designs. Due to the intrinsically limited mechanical properties and functionalities of printed pure polymer parts, there is a critical need to develop printable polymer composites with high performance. 3D printing offers many advantages in the fabrication of composites, including high precision, cost effective and customized geometry. This article gives an overview on 3D printing techniques of polymer composite materials and the properties and performance of 3D printed composite parts as well as their potential applications in the fields of biomedical, electronics and aerospace engineering. Common 3D printing techniques such as fused deposition modeling, selective laser sintering, inkjet 3D printing, stereolithography, and 3D plotting are introduced. The formation methodology and the performance of particle-, fiber- and nanomaterial-reinforced polymer composites are emphasized. Finally, important limitations are identified to motivate the future research of 3D printing.

3D printing of polymer matrix composites: A review and prospective

BACKGROUND Hydrogels are formed through the cross-linking of hydrophilic polymer chains within an aqueous microenvironment. The gelation can be achieved through a variety of mechanisms, spanning physical entanglement of polymer chains, electrostatic interactions, and covalent chemical cross-linking. The water-rich nature of hydrogels makes them broadly applicable to many areas, including tissue engineering, drug delivery, soft electronics, and actuators. Conventional hydrogels usually possess limited mechanical strength and are prone to permanent breakage. The lack of desired dynamic cues and structural complexity within the hydrogels has further limited their functions. Broadened applications of hydrogels, however, require advanced engineering of parameters such as mechanics and spatiotemporal presentation of active or bioactive moieties, as well as manipulation of multiscale shape, structure, and architecture. ADVANCES Hydrogels with substantially improved physicochemical properties have been enabled by rational design at the molecular level and control over multiscale architecture. For example, formulations that combine permanent polymer networks with reversibly bonding chains for energy dissipation show strong toughness and stretchability. Similar strategies may also substantially enhance the bonding affinity of hydrogels at interfaces with solids by covalently anchoring the polymer networks of tough hydrogels onto solid surfaces. Shear-thinning hydrogels that feature reversible bonds impart a fluidic nature upon application of shear forces and return back to their gel states once the forces are released. Self-healing hydrogels based on nanomaterial hybridization, electrostatic interactions, and slide-ring configurations exhibit excellent abilities in spontaneously healing themselves after damages. Additionally, harnessing techniques that can dynamically and precisely configure hydrogels have resulted in flexibility to regulate their architecture, activity, and functionality. Dynamic modulations of polymer chain physics and chemistry can lead to temporal alteration of hydrogel structures in a programmed manner. Three-dimensional printing enables architectural control of hydrogels at high precision, with a potential to further integrate elements that enable change of hydrogel configurations along prescribed paths. OUTLOOK We envision the continuation of innovation in new bioorthogonal chemistries for making hydrogels, enabling their fabrication in the presence of biological species without impairing cellular or biomolecule functions. We also foresee opportunities in the further development of more sophisticated fabrication methods that allow better-controlled hydrogel architecture across multiple length scales. In addition, technologies that precisely regulate the physicochemical properties of hydrogels in spatiotemporally controlled manners are crucial in controlling their dynamics, such as degradation and dynamic presentation of biomolecules. We believe that the fabrication of hydrogels should be coupled with end applications in a feedback loop in order to achieve optimal designs through iterations. In the end, it is the combination of multiscale constituents and complementary strategies that will enable new applications of this important class of materials.

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Advances in engineering hydrogels

Bone tissue engineering using 3D printing

Injectable hydrogels with biodegradability have in situ formability which in vitro/in vivo allows an effective and homogeneous encapsulation of drugs/cells, and convenient in vivo surgical operation in a minimally invasive way, causing smaller scar size and less pain for patients. Therefore, they have found a variety of biomedical applications, such as drug delivery, cell encapsulation, and tissue engineering. This critical review systematically summarizes the recent progresses on biodegradable and injectable hydrogels fabricated from natural polymers (chitosan, hyaluronic acid, alginates, gelatin, heparin, chondroitin sulfate, etc.) and biodegradable synthetic polymers (polypeptides, polyesters, polyphosphazenes, etc.). The review includes the novel naturally based hydrogels with high potential for biomedical applications developed in the past five years which integrate the excellent biocompatibility of natural polymers/synthetic polypeptides with structural controllability via chemical modification. The gelation and biodegradation which are two key factors to affect the cell fate or drug delivery are highlighted. A brief outlook on the future of injectable and biodegradable hydrogels is also presented (326 references).

Injectable and biodegradable hydrogels: gelation, biodegradation and biomedical applications

3D bioprinting for engineering complex tissues.

https://www.tpbin.com/Uploads/Subjects/52a6a915-a69b-492e-a7e1-4dceadf95df3.pdf

Influence of select extracellular matrix proteins on mesenchymal stem cell osteogenic commitment in three-dimensional contexts

Glaucoma is an optic neuropathy commonly associated with elevated intraocular pressure (IOP) resulting in progressive loss of retinal ganglion cells (RGCs) and optic nerve degeneration, leading to blindness. New therapeutic approaches that better preserve the visual field by promoting survival and health of RGCs are highly needed since RGC death occurs despite good IOP control in glaucoma patients. We have developed a novel approach to reliably induce chronic IOP elevation in mouse using a photopolymerizable biomatrix, hyaluronic acid glycidyl methacrylate. This is achieved by rapid in vivo crosslinking of the biomatrix at the iridocorneal angle by a flash of ultraviolet A (UVA) light to impede the aqueous outflow pathway with a controllable manner. Sustained IOP elevation was induced after a single manipulation and was maintained at ~45% above baseline for >4 weeks. Significant thinning of the inner retina and ~35% reduction in RGCs and axons was noted within one month of IOP elevation. Optic nerve degeneration showed positive correlation with cumulative IOP elevation. Activation of astrocytes and microglia appeared to be an early event in response to IOP elevation preceding detectable RGC and axon loss. Attenuated glial reactivity was noted at later stage where significant RGC/axon loss had occurred suggesting astrocytes and microglia may play different roles over the course of glaucomatous degeneration. This novel murine glaucoma model is reproducible and displays cellular changes that recapitulate several pathophysiological features of glaucoma.

A murine glaucoma model induced by rapid in vivo photopolymerization of hyaluronic acid glycidyl methacrylate.

A system and method for 3D microfabrication projects light capable of initiating photopolymerization toward a spatial light modulator that modulates light responsive to digital masks corresponding to layers of the structure. Projection optics focus the modulated light onto an optical plane within a photopolymerizable material supported on a stage. A computer controller causes the spatial light modulator to project a sequence of images corresponding to the digital masks while coordinating movement of the stage to move a position of the optical plane within the photopolymerizable material to sequentially project each image of the sequence to generate the structure by progressively photopolymerizing the photopolymerizable material.

Layerless bioprinting via dynamic optical projection and uses thereof

Despite a high incidence of calcific aortic valve disease in metabolic syndrome, there is little information about the fundamental metabolism of heart valves. Cell metabolism is a first responder t...

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2014.0852

Metabolic regulation of collagen gel contraction by porcine aortic valvular interstitial cells

A liver-mimetic device and method include a 3D polymer scaffold having a matrix of liver-like lobules with hepatic-functioning particles encapsulated within the lobules. In some embodiments, each liver-like lobule is hexagonal in structure and the matrix is in a honeycomb arrangement. In some embodiments, the hepatic-functioning particles are hepatic progenitor cells. In other embodiments, the hepatic-functioning particles are polymer nanoparticles adapted to capture pore-forming toxins.

Xin Qu

Papers

Influence of select extracellular matrix proteins on mesenchymal stem cell osteogenic commitment in three-dimensional contexts

A murine glaucoma model induced by rapid in vivo photopolymerization of hyaluronic acid glycidyl methacrylate.

Layerless bioprinting via dynamic optical projection and uses thereof

Metabolic regulation of collagen gel contraction by porcine aortic valvular interstitial cells

Liver-mimetic device and method for simulation of hepatic function using such device