3D Tissue Scaffolds

Our goal is to develop measurement tools and reference materials for physical and chemical characterization of 3D tissue scaffolds and their impact on cellular response. These tools will enable a better understanding cell-scaffold interactions, including identification of the relationships of cellular response on 2D surfaces to that in 3D scaffolds, and will facilitate improved design of future scaffold-based medical products.

We are leveraging non-invasive imaging techniques and combinatorial methods to develop improved characterization techniques for 3D tissue scaffolds and cell-scaffold interactions. Due to the complexity of testing in 3D, cell-material interactions are typically tested in 2D formats, even though it is widely accepted that 3D formats are more likely to yield a clinically relevant response. The methods we develop will both simplify characterization of cell-material interactions in 3D, and allow us to connect results from 2D systems to results in 3D scaffolds.

We have pioneered the first combinatorial methods for screening cell response to properties of 3D scaffolds; demonstrating methods for fabricating polymer scaffold libraries in the forms of both continuous gradients an discrete arrays. These combinatorial libraries contain scaffolds with variability over the full range of a particular variable, allowing complete characterization of cell response to that variable in relatively simple, compact experiments. Reference scaffolds we are developing will be used as calibration standards for the combinatorial libraries, as well as for industrial use in development of scaffolds-based medical products.

3D Scaffold Libraries: Previous combinatorial approaches for screening cell-material interactions have focused on planar (2D) surfaces or films. However, biomaterials are commonly used in 3D scaffolds and cells behave differently when cultured in a 3D environment. We successfully demonstrated the world’s first method for combinatorial screening of cell-material interactions in a 3D scaffold format. Our “combinatorial polymer scaffold library” approach was used to screen osteoblast function during culture in an array of scaffolds with different composition and properties. Examples of scaffold libraries are shown in the figure below where red dye was used to visualize changes in scaffold composition. Scaffold libraries can be fabricated as gradients (left) or arrays (right). In addition to testing for cell response, we have used the 3D scaffold libraries for characterization of scaffold physical properties in X-ray imaging. X-ray techniques enable non-invasive imaging of implants in vivo and in vitro. However, polymeric biomaterials must be spiked with radiopacifiers to improve contrast, which can adversely affect material properties and performance. We used 3D scaffold libraries to rapidly determine the minimal amount of contrast agent for reliable X-ray imaging. 
 

Links to Scaffold Library Fabrication YouTube Videos:

Reference 3D Tissue Scaffold: A reference scaffold is being developed with input from ASTM (F04.42.WK6507). The scaffolds were made by freeform fabrication since this approach offers the tightest control over scaffold structural morphology. Structure and permeability were characterized using microscopy, gravimetrics, μCT imaging and a permeameter. These well-characterized reference scaffolds will serve as standards during development of scaffolds-based products.

Links to Reference Scaffolds:

μCT Imaging Method Development: We have adapted X-ray micro-computed tomography (μCT) for measuring cell adhesion and proliferation in scaffolds. μCT has significant advantages over traditional optical microscopy in that it is an inherently 3D modality. In the image below, a confluent osteoblast cell layer adherent on the surface of a 3D polymer scaffold is shown. Staining was used to enhance cell contrast so that image contributions from polymer could be reliably removed, and only cells are visible in the image. This approach makes it possible to examine tissue formation within a scaffold without the tedium of serial sectioning and enables 3D visualization and quantification of cell migration into scaffolds.

Fluorescence micrograph (left) and μCT image (right) of 400K cells cultured 1 d on scaffold. Threshold for μCT image (right) was set so that 95% of the voxels shown are attributable to cells (not the scaffold).

• The US spends $35 billion annually (3% of healthcare costs) to care for the 100,000 patients with end stage organ failure waiting for organ transplants. Our measurement solutions will hasten development of engineered organ replacements, alleviating this burden.

• Reference tissue scaffolds has been developed in collaboration with ASTM (F04.42.WK6507) that will enable companies to reliably characterize physical properties of their scaffold-based products (RM 8395, RM8396, RM8397).

• We have developed the world’s first combinatorial method for screening cell response to 3D tissue scaffold properties.

• The National Institutes of Health support our work to develop combinatorial methods for screening cell-scaffold interactions at NIST (R21 EB006497-01) and in collaboration with the New Jersey Center for Biomaterials (RESBIO P41 EB 001046).

• We have organized a Special Issue on "Combinatorial and High-Throughput Screen of Cell Response to Biomaterials" for the journal Combinatorial Chemistry & High-Throughput Screening. The Issue is in press and will appear in early 2009. The Issue will have 5 reviews and 8 research articles contributed from leaders in the field.