Cell encapsulation in sub-mm sized gel modules using replica molding

Laser-assisted cell printing: principle, physical parameters versus cell fate and perspectives in tissue engineering

We describe the physical parameters involved in laser-assisted cell printing and present evidence that this technology is coming of age. Finally we discuss how this high-throughput, high-resolution technique may help in reproducing local cell microenvironments, and thereby create functional tissue-engineered 3D constructs.

Monodisperse cell-encapsulating peptide microgel beads for 3D cell culture

This paper describes a method to produce monodisperse cell-encapsulating microgel beads composed of a self-assembling peptide gel for three-dimensional (3D) cell culture. We used a 3D microfluidic axisymmetric flow-focusing device with an external gelation method. The finely powdered salts were dispersed into a continuous phase, and the salts induced the gelation when in contact with the peptide solution. Over 93% of the cells survived after the encapsulation, and the cells migrated and grew within the gels. Applications of our cell-encapsulating beads include bead-based cell assays in drug testing and engineering tissue constructs.

Microfabrication of homogenous, asymmetric cell-laden hydrogel capsules

Cell encapsulation has been broadly investigated as a technology to provide immunoprotection for transplanted endocrine cells. Here we develop a new fabrication method that allows for rapid, homogenous microencapsulation of insulin-secreting cells with varying microscale geometries and asymmetrically modified surfaces. Micromolding systems were developed using polypropylene mesh, and the material/surface properties associated with efficient encapsulation were identified. Cells encapsulated using these methods maintain desirable viability and preserve their ability to proliferate and secrete insulin in a glucose-responsive manner. This new cell encapsulation approach enables a practical route to an inexpensive and convenient process for the generation of cell-laden microcapsules without requiring any specialized equipment or microfabrication process.

A novel 3-D model for cell culture and tissue engineering

A novel method of making microcapsules in a macrocapsule is demonstrated as a 3-D culture system in this article. Mouse embryonic stem (mES) cells as model cells were used in the 3-D culture space, and the cell viability and histological observation were conducted. Furthermore, Oct4 gene expression was evaluated for the undifferentiated status of mES cells in this 3-D model. The results showed that mES cells can grow in this 3-D model and retain their normal viability and morphology. This 3-D model allows mES cells to stay in the undifferentiated state better than 2-D culture systems. This work demonstrates a new 3-D tissue model which can provide an in vivo like microenvironment for non-differentiated mES cells with good immunoisolation. This approach may bridge the gap between traditional 2-D cell culture and animal models.

In vitro microscale systems for systematic drug toxicity study

After administration, drugs go through a complex, dynamic process of absorption, distribution, metabolism and excretion. The resulting time-dependent concentration, termed pharmacokinetics (PK), is critical to the pharmacological response from patients. An in vitro system that can test the dynamics of drug effects in a more systematic way would save time and costs in drug development. Integration of microfabrication and cell culture techniques has resulted in 'cells-on-a-chip' technology, which is showing promise for high-throughput drug screening in physiologically relevant manner. In this review, we summarize current research efforts which ultimately lead to in vitro systems for testing drug's effect in PK-based manner. In particular, we highlight the contribution of microscale systems towards this goal. We envision that the 'cells-on-a-chip' technology will serve as a valuable link between in vitro and in vivo studies, reducing the demand for animal studies, and making clinical trials more effective.

Image-guided tissue engineering

Replication of anatomic shape is a significant challenge in developing implants for regenerative medicine. This has lead to significant interest in using medical imaging techniques such as magnetic resonance imaging and computed tomography to design tissue engineered constructs. Implementation of medical imaging and computer aided design in combination with technologies for rapid prototyping of living implants enables the generation of highly reproducible constructs with spatial resolution up to 25 microm. In this paper, we review the medical imaging modalities available and a paradigm for choosing a particular imaging technique. We also present fabrication techniques and methodologies for producing cellular engineered constructs. Finally, we comment on future challenges involved with image guided tissue engineering and efforts to generate engineered constructs ready for implantation.

Modular Tissue Engineering: Engineering Biological Tissues from the Bottom Up

Tissue engineering creates biological tissues that aim to improve the function of diseased or damaged tissues. To enhance the function of engineered tissues there is a need to generate structures that mimic the intricate architecture and complexity of native organs and tissues. With the desire to create more complex tissues with features such as developed and functional microvasculature, cell binding motifs and tissue specific morphology, tissue engineering techniques are beginning to focus on building modular microtissues with repeated functional units. The emerging field known as modular tissue engineering focuses on fabricating tissue building blocks with specific microarchitectural features and using these modular units to engineer biological tissues from the bottom up. In this review we will examine the promise and shortcomings of "bottom-up" approaches to creating engineered biological tissues. Specifically, we will survey the current techniques for controlling cell aggregation, proliferation and extracellular matrix deposition, as well as approaches to generating shape-controlled tissue modules. We will then highlight techniques utilized to create macroscale engineered biological tissues from modular microscale units.