Gas-Foamed Scaffold Gradients for Combinatorial Screening in 3D

Development of a Workflow to Engineer Tailored Microparticles Via Inkjet Printing

PURPOSE

New drug development and delivery approaches result in an ever-increasing demand for tailored microparticles with defined sizes and structures. Inkjet printing technologies could be promising new processes to engineer particles with defined characteristics, as they are created to precisely deliver liquid droplets with high uniformity.

METHODS

D-mannitol was used as a model compound alone or co-processed with the pore former agent ammonium bicarbonate, and the polymer polyethylene glycol 200. Firstly, a drop shape analyzer was used to characterize and understand ink/substrate interactions, evaporation, and solidification kinetics. Consequently, the process was transferred to a laboratory-scale inkjet printer and the resulting particles collected, characterized and compared to others obtained via an industrial standard technique.

RESULTS

The droplet shape analysis allowed to understand how 3D structures are formed and helped define the formulation and process parameters for inkjet printing. By adjusting the drop number and process waveform, spherical particles with a mean size of approximately 100 µm were obtained. The addition of pore former and polymer allowed to tailor the crystallization kinetics, resulting in particles with a different surface (i.e., spike-like surface) and bulk (e.g. porous and non-porous) structure.

CONCLUSION

The workflow described enabled the production of 3D structures via inkjet printing, demonstrating that this technique can be a promising approach to engineer microparticles.

3D-printed gelatin methacrylate (GelMA)/silanated silica scaffold assisted by two-stage cooling system for hard tissue regeneration

Among many biomaterials, gelatin methacrylate (GelMA), a photocurable protein, has been widely used in 3D bioprinting process owing to its excellent cellular responses, biocompatibility and biodegradability. However, GelMA still shows a low processability due to the severe temperature dependence of viscosity. To overcome this obstacle, we propose a two-stage temperature control system to effectively control the viscosity of GelMA. To optimize the process conditions, we evaluated the temperature of the cooling system (jacket and stage). Using the established system, three GelMA scaffolds were fabricated in which different concentrations (0, 3 and 10 wt%) of silanated silica particles were embedded. To evaluate the performances of the prepared scaffolds suitable for hard tissue regeneration, we analyzed the physical (viscoelasticity, surface roughness, compressive modulus and wettability) and biological (human mesenchymal stem cells growth, western blotting and osteogenic differentiation) properties. Consequently, the composite scaffold with greater silica contents (10 wt%) showed enhanced physical and biological performances including mechanical strength, cell initial attachment, cell proliferation and osteogenic differentiation compared with those of the controls. Our results indicate that the GelMA/silanated silica composite scaffold can be potentially used for hard tissue regeneration.

Combination of electrospinning with other techniques for the fabrication of 3D polymeric and composite nanofibrous scaffolds with improved cellular interactions

The development of three-dimensional (3D) scaffolds with physical and chemical topological cues at the macro-, micro-, and nanometer scale is urgently needed for successful tissue engineering applications. 3D scaffolds can be manufactured by a wide variety of techniques. Electrospinning technology has emerged as a powerful manufacturing technique to produce non-woven nanofibrous scaffolds with very interesting features for tissue engineering products. However, electrospun scaffolds have some inherent limitations that compromise the regeneration of thick and complex tissues. By integrating electrospinning and other fabrication technologies, multifunctional 3D fibrous assemblies with micro/nanotopographical features can be created. The proper combination of techniques leads to materials with nano and macro-structure, allowing an improvement in the biological performance of tissue-engineered constructs. In this review, we focus on the most relevant strategies to produce electrospun polymer/composite scaffolds with 3D architecture. A detailed description of procedures involving physical and chemical agents to create structures with large pores and 3D fiber assemblies is introduced. Finally, characterization and biological assays including in vitro and in vivo studies of structures intended for the regeneration of functional tissues are briefly presented and discussed.

Gradient platform for combinatorial screening of thermoset polymers for biomedical applications

The goal of this work was to design a device for rapid screening of crosslinked thermoset polymers. This gradient curing platform is capable of yielding a library of polyesters with systematically varying mechanical and physicochemical properties and the resultant cellular response. A library of poly(xylitolsebacate) polyesters was prepared in this device by differential curing to yield a gradient polymer. The resultant polymer exhibits a gradient in the storage modulus (1 to 5 MPa), wettability (70° < water contact angle < 110°), degree of crosslinking, degradation rate (3-25% in 7 days), drug release and biological response (ability to support stem cell proliferation and differentiation) from one end of the polymer to the other. Primary human mesenchymal stem cells were cultured to assess the cellular response in vitro. Maximal stem cell proliferation and osteogenesis was observed on the highly crosslinked polyester segments that provide high stiffness, are hydrophobic and are slow degrading as compared to the lower cured counterparts. Under in vivo conditions, this material showed differential response across the gradient without displaying significant concerns for inflammation or infection. This gradient curing device is capable of ascertaining suitable curing conditions to obtain appropriate polymers for application specific requirements. This gradient platform was further used to identify optimal processing parameters to prepare three-dimensional tissue scaffolds such as electrospun fiber mats and porous foams. Thus, this versatile combinatorial platform is well suited for rapid screening of thermoset polymers for biomedical applications.

Current status of three-dimensional printing inks for soft tissue regeneration

Recently, three-dimensional (3D) printing technologies have become an attractive manufacturing process, which is called additive manufacturing or rapid prototyping. A 3D printing system can design and fabricate 3D shapes and geometries resulting in custom 3D scaffolds in tissue engineering. In tissue regeneration and replacement, 3D printing systems have been frequently used with various biomaterials such as natural and synthetic polymers. In tissue engineering, soft tissue regeneration is very difficult because soft tissue has the properties of high elasticity, flexibility and viscosity which act as an obstacle when creating a 3D structure by stacking layer after layer of biomaterials compared to hard tissue regeneration. To overcome these limitations, many studies are trying to fabricate constructs with a very similar native micro-environmental property for a complex biofunctional scaffold with suitable biological and mechanical parameters by optimizing the biomaterials, for example, control the concentration and diversification of materials. In this review, we describe the characteristics of printing biomaterials such as hydrogel, synthetic polymer and composite type as well as recent advances in soft tissue regeneration. It is expected that 3D printed constructs will be able to replace as well as regenerate defective tissues or injured functional tissues and organs.

Research trends in biomimetic medical materials for tissue engineering: 3D bioprinting, surface modification, nano/micro-technology and clinical aspects in tissue engineering of cartilage and bone

This review discusses about biomimetic medical materials for tissue engineering of bone and cartilage, after previous scientific commentary of the invitation-based, Korea-China joint symposium on biomimetic medical materials, which was held in Seoul, Korea, from October 22 to 26, 2015. The contents of this review were evolved from the presentations of that symposium. Four topics of biomimetic medical materials were discussed from different research groups here: 1) 3D bioprinting medical materials, 2) nano/micro-technology, 3) surface modification of biomaterials for their interactions with cells and 4) clinical aspects of biomaterials for cartilage focusing on cells, scaffolds and cytokines.

Bone-tissue engineering: complex tunable structural and biological responses to injury, drug delivery, and cell-based therapies

Bone loss and failure of proper bone healing continues to be a significant medical condition in need of solutions that can be implemented successfully both in human and veterinary medicine. This is particularly true when large segmental defects are present, the bone has failed to return to normal form or function, or the healing process is extremely prolonged. Given the inherent complexity of bone tissue - its unique structural, mechanical, and compositional properties, as well as its ability to support various cells - it is difficult to find ideal candidate materials that could be used as the foundation for tissue regeneration from technological platforms. Recently, important developments have been made in the implementation of complex structures built both at the macro- and the nano-level that have been shown to positively impact bone formation and to have the ability to deliver active biological molecules (drugs, growth factors, proteins, cells) for controlled tissue regeneration and the prevention of infection. These materials are diverse, ranging from polymers to ceramics and various composites. This review presents developments in this area with a focus on the role of scaffold structure and chemistry on the biologic processes that influence bone physiology and regeneration.

Strontium eluting graphene hybrid nanoparticles augment osteogenesis in a 3D tissue scaffold

The objective of this work was to prepare hybrid nanoparticles of graphene sheets decorated with strontium metallic nanoparticles and demonstrate their advantages in bone tissue engineering. Strontium-decorated reduced graphene oxide (RGO_Sr) hybrid nanoparticles were synthesized by the facile reduction of graphene oxide and strontium nitrate. X-ray diffraction, transmission electron microscopy, and atomic force microscopy revealed that the hybrid particles were composed of RGO sheets decorated with 200-300 nm metallic strontium particles. Thermal gravimetric analysis further confirmed the composition of the hybrid particles as 22 wt% of strontium. Macroporous tissue scaffolds were prepared by incorporating RGO_Sr particles in poly(ε-caprolactone) (PCL). The PCL/RGO_Sr scaffolds were found to elute strontium ions in aqueous medium. Osteoblast proliferation and differentiation was significantly higher in the PCL scaffolds containing the RGO_Sr particles in contrast to neat PCL and PCL/RGO scaffolds. The increased biological activity can be attributed to the release of strontium ions from the hybrid nanoparticles. This study demonstrates that composites prepared using hybrid nanoparticles that elute strontium ions can be used to prepare multifunctional scaffolds with good mechanical and osteoinductive properties. These findings have important implications for designing the next generation of biomaterials for use in tissue regeneration.

Fabrication, characterisation and in vitro biological activities of a sulfuretin-supplemented nanofibrous composite scaffold for tissue engineering

A biocomposite consisting of PCL/BMP-2 and sulfuretin/alginate was proposed. Evaluation of in vitro cellular activities demonstrated that the sulfuretin can act as an outstanding biological component for enhancing bone tissue growth.

Cell-laden poly(ɛ-caprolactone)/alginate hybrid scaffolds fabricated by an aerosol cross-linking process for obtaining homogeneous cell distribution: fabrication, seeding efficiency, and cell proliferation and distribution

Generally, solid-freeform fabricated scaffolds show a controllable pore structure (pore size, porosity, pore connectivity, and permeability) and mechanical properties by using computer-aided techniques. Although the scaffolds can provide repeated and appropriate pore structures for tissue regeneration, they have a low biological activity, such as low cell-seeding efficiency and nonuniform cell density in the scaffold interior after a long culture period, due to a large pore size and completely open pores. Here we fabricated three different poly(ɛ-caprolactone) (PCL)/alginate scaffolds: (1) a rapid prototyped porous PCL scaffold coated with an alginate, (2) the same PCL scaffold coated with a mixture of alginate and cells, and (3) a multidispensed hybrid PCL/alginate scaffold embedded with cell-laden alginate struts. The three scaffolds had similar micropore structures (pore size = 430-580 μm, porosity = 62%-68%, square pore shape). Preosteoblast cells (MC3T3-E1) were used at the same cell density in each scaffold. By measuring cell-seeding efficiency, cell viability, and cell distribution after various periods of culturing, we sought to determine which scaffold was more appropriate for homogeneously regenerated tissues.