Transcript NSF Grantees Meeting 12/4/07

NIRT: Self-Assembled Nanohydrogels for
Differential Cell Adhesion and Infection Control
Matthew Libera, Woo Lee, Mercedes McKay, Svetlana Sukhishvili, Hongjun Wang
Stevens Institute of Technology, Hoboken, New Jersey 07030
Project Overview
Infection: A Major Mode of Orthopaedic Implant Failure
Infection occurs in approximately 0.5 – 5% of all hip and knee replacements.
It is a catastrophic problem, because bacteria that colonize an implant surface develop
into biofilms where they are as much as 10,000 times more resistant to antibiotics than
planktonic bacteria. The most effective therapy is to remove an infected implant, cure
the infection, and then pursue a subsequent revision surgery. The consequences to
patient well being and medical cost in this situation are compellingly significant.
At its core, implant infection is a biomaterials problem. While surfaces have
been developed which repel bacterial adhesion – e.g. PEGylated surfaces – these also
repel the eukaryotic cells necessary for the development of a healthy implant-tissue
interface. Instead, surfaces are needed that are differentially adhesive, i.e. that it
promote eukaryotic (e.g. osteoblast) adhesion and proliferation while simultaneously
repelling bacteria. This is a fundamental biomaterials problem that remains unsolved.
BGS
$.4, 5%
 Hips
Bacterial biofilms form complex and
hierarchically structured communities
which are as much as 10kx more resistant
to antibiotics than planktonic bacterial.
0.3 - 1%
Knees
1 - 4%
Fixation devices
~1 m
Cell-Interactive
nanohydrogels
hierarchically structured
on the surface of a
macroscopically beaded
surface of a modern
orthopaedic implant.
> 15%
e.g. Intramedullary trauma rods
~2 mm
Infection by
Staphylococcal Biofilms
This project explores a new mechanism to create differentially adhesive
surfaces. The key idea rests in the fact that important staphylococcal bacterial cells are
significantly smaller (~ 600-900 nm dia)
Global Orthopaedic Markets (2005)
than eukaryotic cells (~5-50 μm dia).
Furthermore, the cell walls of these grampositive bacteria are less able to conform to
a substrate than are eukaryotic cell walls. We
hypothesize that heterostructures of nanosized
hydrogels self assembled in 2D over micrometer
length scales will allow focal contact formation
and subsequent osteoblast adhesion but prevent
bacterial adhesion.
Biologics
$1.0, 23%
Infection Rates
Differentially Adhesive Surfaces Repulsive to Bacteria but Attractive to Eukaryotic Cells
attachment
• S. aureus (40%)
Polysaccharide
secretion
Maturation
and biofilm
growth
Release of
planktonic
progeny
~350 m
The biofilm cycle
• S. epidermis (20%)
adapted from Sauer, Genome Biology, 2003)
osteoblast
5 m
Hips
$4.0, 9%
S. aureus
Spinal
$4.0, 24%
substrate
Knees
$5.0, 16%
Trauma
$3.0, 14%
Extremities
$0.4, 11%
Sports Medicine
$1.0, 9%
Arthroscopy
$1.0, 8%
Bone Cement
$0.3, 7%
S. epi
polycation primer layer
5 m
Actin filaments (green) and
vinculin containing focal
adhesions (red) in fibroblasts
S. epidermidis
9 hr culture on glass
Ancillary
$2.0, 10%
self-assembled
nanohydrogels
repulsive
adhesive
Source: Merrill Lynch
Courtesy of G. Grobe
DePuy Orthopaedics
Nanohydrogel Synthesis and Surface Self Assembly
- - - - --- - -+
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-- -- --
-- -- -- --- +
+
+
+
Self-Assembled Nanohydrogels
Reduce S. epidermidis Adhesion
PEGDA/AA
Multiplexed Microfluidic Methods
to Assess Differential Cell Adhesion
PL Primer
Biological Framework of
3-D Microscale Environment
+
0.04
Host Defense Mechanism
0.01
Self-Assembled Nanohydrogel Surface
0
in
e
GOAL: Develop, integrate and pilot two new
educational modules that introduce forwardlooking ideas of nanotechnology to high
school chemistry and biology curricula.
ly
s
D
A
G
PE
D
A/
Controlling nanoparticle adhesion
via controlled surface chemistry
S. epidermidis
The Stevens Center for Innovation in Engineering and
Science Education (CIESE), working with the Stevens
NIRT Team, Stryker Orthopaedics and high-school
teachers from New Jersey school districts, will:
0.02
G
SEM Images of emulsionpolymerized PEG nanohydrogels
on a silicon substrate
Osteoblast
0.03
AA
200 nm
Preconditioning
Therapeutic Delivery
0.05
PE
- Control of electrostatic
interactions between
nanohydrogels & substrate
0.06
Po
ly
- Selective functionalization
of cell-adhesive ligands
S. epi area fraction
10 m
- Emulsion polymerization
of PEGDA
Outreach and Broader Impact
A surface modified by< 6% coverage
of poly(PEG-co acrylic acid)
nanohydrogels reduces S. epi
adhesion by a factor of more than 3
relative to a PL-treated surface.
• Expose students to nanotechnology-based research
• Demonstrate the societal relevance
• Enhance/modernize biology & chemistry curricula
• Create a real-world context for basic-science concepts
Tool Functions
• Microfluidic Multiplexing
• Nontransparent Biomaterial
• In-situ Imaging
+
Particle density #/
m2
500 nm
5.0
+ +
+
+
4.0
+
3.0
+
2.0
0.2
0.4
0.6
0.8
PAH thickness (nm)
1.0
At high pH, PAH polycationic films
have higher charge, more
conformational loops, and hence are
thicker than those deposited at lower
pH. Thicker films provide more
adhesion sites for negatively charged
Ag nanoparticles
200x30 m channel
with 4 embedded microvalves
Osteoblast
Seeded in
800x200 m
Channel
5 mm
800 m
S. epidermidis
Cultured in
100x100 mm
Channel
100 m
CIESE has nearly 20 years of K-12 curriculum and professional
development expertise in STEM education, and has impacted
over 20,000 educators worldwide