Combinatorial
Chemistry & High Throughput Screening
ISSN: 1386-2073
Combinatorial Chemistry &
High Throughput Screening
Volume 12, Number 6, July 2009
Contents
Combinatorial and High Throughput Screening of Cell
Response to Biomaterials (Part 1)
Guest Editor: Carl G. Simon Jr.
Editorial Pp. 543
Review Articles
Cell Interactions with Biomaterials Gradients and Arrays Pp.
544-553
Carl G. Simon Jr., Yanyin Yang, Vinoy Thomas,
Shauna M. Dorsey and Abby W. Morgan
[Abstract] [Purchase
Article] [PMID:
19601752 PubMed - indexed for MEDLINE]
High Throughput Optimization of Stem
Cell Microenvironments Pp. 554-561
Fan Yang, Ying Mei, Robert Langer and Daniel G. Anderson
[Abstract] [Purchase
Article] [PMID:
19601753 PubMed - indexed for MEDLINE]
Combinatorial Approaches to Controlling
Cell Behaviour and Tissue Formation in 3D via Rapid-Prototyping
and Smart Scaffold Design Pp. 562-579
Tim B.F. Woodfield, Lorenzo Moroni and
Jos Malda
[Abstract] [Purchase
Article] [PMID:
19601754 PubMed - indexed for MEDLINE]
Assays for Eukaryotic Cell Chemotaxis
Pp. 580-588
Zac Pujic, Duncan Mortimer, Julia Feldner and Geoffrey
J. Goodhill
[Abstract] [Purchase
Article] [PMID:
19601755 PubMed - indexed for MEDLINE]
Biomimetic Stratified Scaffold Design
for Ligament-to-Bone Interface Tissue Engineering Pp.
589-597
Helen H. Lu and Jeffrey P. Spalazzi
[Abstract] [Purchase
Article] [PMID:
19601756 PubMed - indexed for MEDLINE]
Original Research Articles
Haptotactic Gradients for Directed Cell Migration: Stimulation
and Inhibition Using Soluble Factors Pp. 598-603
Jason T. Smith, Donghwan H. Kim and
William M. Reichert
[Abstract] [Purchase
Article] [PMID:
19601757 PubMed - indexed for MEDLINE]
Inkjet Printing of Growth Factor Concentration
Gradients and Combinatorial Arrays Immobilized on Biologically-Relevant
Substrates Pp. 604-618
Eric D. Miller, Julie A. Phillippi, Gregory W.
Fisher, Phil G. Campbell, Lynn M. Walker and Lee
E. Weiss
[Abstract] [Purchase
Article] [PMID:
19601758 PubMed - indexed for MEDLINE]
Quantification of Cell Response to Polymeric Composites Using
a Two-Dimensional Gradient Platform Pp. 619-625
Nancy J. Lin, Haiqing Hu, Lipin Sung and
Sheng Lin-Gibson
[Abstract] [Purchase
Article] [PMID:
19601759 PubMed - indexed for MEDLINE]
Local Histogram Analysis: Detecting Cell-Microstructure
Interactions on Combinatorial Biomaterial Libraries Pp.
626-633
Jing Su and J. Carson Meredith
[Abstract]
[Purchase
Article] [PMID:
19601760 PubMed - indexed for MEDLINE]
Abstracts
[Back to top]
[Purchase
Article] [PMID:
19601751 PubMed - indexed for MEDLINE]
Editorial:
Despite significant investment in tissue engineering
research, few successful products have come to market. Hence,
there is a need to accelerate tissue engineering research.
One approach to accelerating development is combinatorial
and high throughput (CHT) screening. Combinatorial approaches
are utilized extensively for pharmaceutical research and their
application to biomaterials development is growing. This special
issue is a collection of primary research articles and reviews
that highlight the state of the art in this exciting and burgeoning
field of research.
The basic premise of combinatorial and high throughput biomaterials
research is the development of methods for rapidly screening
cell response to libraries of biomaterials. Just as combinatorial
libraries of candidate drug compounds are screened for therapeutic
effects using in vitro cell culture, combinatorial
libraries of biomaterials can be screened for their ability
to positively influence cells. Typically, miniaturized specimens
of biomaterials are fabricated in the form of gradients or
arrays such that many biomaterials, compositions and material
properties are present in each specimen or library. Cells
are then seeded onto the library specimens and responses such
as adhesion, morphology, proliferation, migration and differentiation
are assessed.
Instead of responding to soluble factors as is characteristic
in drug screening, the cells in a biomaterials screen are
responding to the properties of their adhesive biomaterial
substrate. The chemical and physical properties of a material
will strongly influence cell response. It is also important
to keep in mind that cells rarely interact directly with a
biomaterial. Proteins present in blood in vivo or
serum in vitro immediately adsorb onto most materials.
Thus, cell response to a biomaterial is strongly influenced
(and some would say dominated) by the species, amount and
conformation of proteins that adsorb onto a biomaterial.
Advances in combinatorial screening of biomaterials are being
made at all levels including biomaterials synthesis, library
fabrication, cell screening and data analysis; and articles
that focus on each of these levels have been contributed to
this special issue. In addition to their applications in screening,
biomaterial gradients also have potential applications as
functional materials. A scaffold with a gradient in properties
could serve as a template for the generation of a graded tissue.
Gradients in composition and properties are common at the
boundaries of most tissues and the need for “interface
tissue engineering” is well-recognized. I hope you enjoy
the articles in this special issue. It will be exciting to
see where the innovators in this field will take us next.
All articles and reviews in this special issue were peer-reviewed
by 2 referees according to the journal’s standard editorial
policies. I would like to thank all of the contributors and
reviewers who helped make this issue possible. I would also
like to thank Richard van Breemen (Editor-in-Chief), Samina
Khan, Sadaf Zehra, as well as the entire staff at Combinatorial
Chemistry and High Throughput Screening for their assistance
in putting this issue together.
Carl G. Simon Jr.
(Guest Editor)
Polymers Division
National Institute of Standards and Technology
Gaithersburg
MD 20899
USA
E-mail: carl.simon@nist.gov
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[Purchase Article] [PMID:
19601752 PubMed - indexed for MEDLINE]
Cell Interactions with Biomaterials Gradients and Arrays
Carl G. Simon Jr., Yanyin Yang, Vinoy Thomas,
Shauna M. Dorsey and Abby W. Morgan
Gradients and arrays have become very useful to the fields
of tissue engineering and biomaterials. Both gradients and
arrays make efficient platforms for screening cell response
to biomaterials. Graded biomaterials also have functional
applications and make useful substrates for fundamental studies
of cell phenomena such as migration. This article will review
the use of gradients and arrays in tissue engineering and
biomaterials research, with a focus on cellular and biologic
responses.
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[Purchase Article] [PMID:
19601753 PubMed - indexed for MEDLINE]
High Throughput Optimization of Stem Cell Microenvironments
Fan Yang, Ying Mei, Robert Langer and Daniel
G. Anderson
Stem cells have great potential as cell sources for regenerative
medicine due to both their self-renewal and multi-lineage
differentiation capacity. Despite advances in the field of
stem cell biology, major challenges remain before stem cells
can be widely used for therapeutic purposes. One challenge
is to develop reproducible methods to control stem cell growth
and differentiation. The niche in which stem cells reside
is a complex, multi-factorial environment. In contrast to
using cells alone, biomaterials can provide initial structural
support, and allow cells to adhere, proliferate and differentiate
in a three-dimensional environment. Researchers have incorporated
signals into the biomaterials that can promote desired cell
functions in a spatially and temporally controlled manner.
Despite progress in biomaterial design and methods to modulate
cellular behavior, many of the complex signal networks that
regulate cell-material interactions remain unclear. Due to
the vast numbers of material properties to be explored and
the complexity of cell-surface interactions, it is often difficult
to optimize stem cell microenvironments using conventional,
iterative approaches. To address these challenges, high throughput
screening of combinatorial libraries has emerged as a novel
approach to achieve rapid screening with reduced materials
and costs. In this review, we discuss recent research in the
area of high throughput approaches for characterization and
optimization of cellular interactions with their microenvironments.
In contrast to conventional approaches, screening combinatorial
libraries can result in the discovery of unexpected material
solutions to these complex problems.
[Back to top]
[Purchase Article] [PMID:
19601754 PubMed - indexed for MEDLINE]
Combinatorial Approaches to Controlling Cell Behaviour and
Tissue Formation in 3D via Rapid-Prototyping and Smart Scaffold
Design
Tim B.F. Woodfield, Lorenzo Moroni and
Jos Malda
The understanding of fundamental phenomena involved in
tissue engineering and regenerative medicine is continuously
growing and leads to the demand for three-dimensional (3D)
models that better represent tissue architecture and direct
cells into the proper lineage for specific tissue repair.
Porous 3D scaffolds are used in tissue engineering as templates
to allow cell attachment and tissue formation. Scaffold design
plays a central role in guiding cells to synthesize and maintain
new tissues. While a number of techniques have been developed
and are now in use for high-throughput screening of combinatorial
factors involved in biotechnology in two-dimensions, high-throughput
screening in 3D is still in its infancy. There is a broad
interest in developing similar techniques to assess which
variables are critical in designing 3D scaffolds to achieve
proper and lasting tissue regeneration. We describe, herein,
a number of studies adopting smart scaffold design and in
vitro and in vivo analysis as the basis for
3D model systems for evaluating combinatorial factors influencing
cell differentiation and tissue formation.
[Back to top]
[Purchase Article] [PMID:
19601755 PubMed - indexed for MEDLINE]
Assays for Eukaryotic Cell Chemotaxis
Zac Pujic, Duncan Mortimer, Julia Feldner and Geoffrey
J. Goodhill
IChemotaxis is essential for many biological processes. Much
of our understanding of the mechanisms underlying chemotaxis
is based on a variety of in vitro assays. We review
these assays, dividing them into groups depending on the process
used to generate the gradient. We describe how each method
works, its strengths and limitations, and provide some information
about the kinds of cells that have been studied with each
assay.
[Back to top]
[Purchase Article] [PMID:
19601756 PubMed - indexed for MEDLINE]
Biomimetic Stratified Scaffold Design for Ligament-to-Bone
Interface Tissue Engineering
Helen H. Lu and Jeffrey P.
Spalazzi
The emphasis in the field of orthopaedic tissue engineering
is on imparting biomimetic functionality to tissue engineered
bone or soft tissue grafts and enabling their translation
to the clinic. A significant challenge in achieving extended
graft functionality is engineering the biological fixation
of these grafts with each other as well as with the host environment.
Biological fixation will require re-establishment of the structure-function
relationship inherent at the native soft tissue-to-bone interface
on these tissue engineered grafts. To this end, strategic
biomimicry must be incorporated into advanced scaffold design.
To facilitate integration between distinct tissue types (e.g.,
bone with soft tissues such as cartilage, ligament, or tendon),
a stratified or multi-phasic scaffold with distinct yet continuous
tissue regions is required to pre-engineer the interface between
bone and soft tissues. Using the ACL-to-bone interface as
a model system, this review outlines the strategies for stratified
scaffold design for interface tissue engineering, focusing
on identifying the relevant design parameters derived from
an understanding of the structure-function relationship inherent
at the soft-to-hard tissue interface. The design approach
centers on first addressing the challenge of soft tissue-to-bone
integration ex vivo, and then subsequently focusing
on the relatively less difficult task of bone-to-bone integration
in vivo. In addition, we will review stratified scaffold
design aimed at exercising spatial control over heterotypic
cellular interactions, which are critical for facilitating
the formation and maintenance of distinct yet continuous multi-tissue
regions. Finally, potential challenges and future directions
in this emerging area of advanced scaffold design will be
discussed.
[Back to top]
[Purchase Article] [PMID:
19601757 PubMed - indexed for MEDLINE]
Haptotactic Gradients for Directed Cell Migration: Stimulation
and Inhibition Using Soluble Factors
Jason T. Smith, Donghwan H. Kim and
William M. Reichert
A recently developed technique for the measurement of
cell migration on surface bound gradients was used to assay
the behavior of microvascular endothelial cells on a range
of fibronectin gradient slopes in the presence of soluble
promoters and inhibitors of chemotaxis. Directional microvascular
endothelial cell migration was shown to increase with increasing
gradient slope with no significant change in cellular persistence
time or random cell speed. Uniformly distributed soluble chemotactic
factor in the hMEC growth media enhanced directional migration.
The addition of migration-inhibiting LY294002 eliminated the
directional component of cell migration at a 5 μM
dosing. These experiments broaden the understanding of the
directional nature of cell motion and present a reliable system
for the quantitative study of cell migration in complex conditions
in vitro.
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[Purchase Article] [PMID:
19601758 PubMed - indexed for MEDLINE]
Inkjet Printing of Growth Factor Concentration Gradients and
Combinatorial Arrays Immobilized on Biologically-Relevant
Substrates
Eric D. Miller, Julie A. Phillippi, Gregory W.
Fisher, Phil G. Campbell, Lynn M. Walker and
Lee E. Weiss
Current methods for engineering immobilized, ‘solid-phase’
growth factor patterns have not addressed the need for presentation
of the growth factors in a biologically-relevant context.
We developed an inkjet printing methodology for creating solid-phase
patterns of unmodified growth factors on native biological
material substrates. We demonstrate this approach by printing
gradients of fluorescently labeled bone morphogenetic protein-2
(BMP-2) and insulin-like growth factor-II (IGF-II) bio-inks
on fibrin-coated surfaces. Concentration gradients were created
by overprinting individual substrate locations using a dilute
bio-ink to modulate the surface concentration of deposited
growth factor. Persistence studies using fluorescently-labeled
BMP-2 verified that the gradients retained their shape for
up to 7 days. Desorption experiments performed with 125I-BMP-2
and 125I-IGF-II were used
to quantify the surface concentration of growth factor retained
on the substrate for up to 10 days in serum containing media
after rinsing of the unbound growth factor. The inkjet method
is programmable so the gradient shape can be easily modified
as demonstrated by printed linear gradients with varying slopes
and exponential gradients. In addition, the versatility of
this method enabled combinatorial arrays of multiple growth
factors to be created by printing overlapping patterns. The
overlapping printing method was used to create a combinatorial
square pattern array consisting of various surface concentrations
of BMP-2 and fibroblast growth factor-2 (FGF-2). C2C12 myogenic
precursor cells were seeded on the arrays and alkaline phosphatase
staining was performed to determine the effect of FGF-2 and
BMP-2 surface concentration on guiding C2C12 cells towards
an osteogenic lineage. These results demonstrate the utility
of inkjet printing for creating orthogonal growth factor gradients
to investigate how combinations of immobilized growth factors
influence cell fate.
[Back to top]
[Purchase Article] [PMID:
19601759 PubMed - indexed for MEDLINE]
Quantification of Cell Response to Polymeric Composites Using
a Two-Dimensional Gradient Platform
Nancy J. Lin, Haiqing Hu, Lipin Sung and
Sheng Lin-Gibson
A simple and straightforward screening process to assess
the toxicity and corresponding cell response of dental composites
would be useful prior to extensive in vitro or in
vivo characterization. To this end, gradient composite
samples were prepared with variations in filler content/type
and in degree of conversion (DC). The DC was determined using
near infrared spectroscopy (NIR), and the surface morphology
was evaluated by laser scanning confocal microscopy (LSCM).
RAW 264.7 macrophage-like cells were cultured directly on
the composite gradient samples, and cell viability, density,
and area were measured at 24 h. All three measures of cell
response varied as a function of material properties. For
instance, compositions with higher filler content had no reduction
in cell viability or cell density, even at low conversions
of 52%, whereas significant decreases in viability and density
were present when the filler content was 35% or below (by
mass). The overall results demonstrate the complexity of the
cell-material interactions, with properties including DC,
filler type, filler mass ratio, and surface morphology influencing
the cell response. The combinatorial approach described herein
enables simultaneous screening of multiple compositions and
material properties, providing a more thorough characterization
of cell response for the improved selection of biocompatible
composite formulations and processing conditions.
[Back to top]
[Purchase Article] [PMID:
19601760 PubMed - indexed for MEDLINE]
Local Histogram Analysis: Detecting Cell-Microstructure Interactions
on Combinatorial Biomaterial Libraries
Jing Su and J. Carson Meredith
Increasingly, combinatorial libraries are used to screen
large numbers of complex chemically- and physically-patterned
polymers against cell response. There is a strong need to
extract meaningful relationships between cell function and
material surface features from these experiments. A novel
high-throughput cell-material screening strategy, based upon
local cell-feature analysis (LCFA) was applied to screen osteoblast
proliferation behavior on combinatorial libraries of phase-separated
PLGA and PCL. Traditional factor importance analysis, which
uses summary statistical inference to identify significant
variables, indicated that one controlling material surface
feature was PCL diameter. However, the summary statistic analysis
was unable to uncover more subtle relationships. The LCFA
method, based on histograms of distances between cells and
microstructures, was able to identify non-linear, discrete
relationships between proliferation, PCL diameter, and cell-PCL
distance. LCFA provides an advantage in that a distribution
function is not assumed, but rather is developed from the
data. Using these results, we propose a model for classifying
the material-microstructure interactions, in which small PCL
islands far from the cell nucleus act as holders for attachment
and large islands close to cells act to shape the cell.
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