Transcript Controlled release

Manifestation of Novel Social Challenges of the
European Union
in the Teaching Material of
Medical Biotechnology Master’s Programmes
at the University of Pécs and at the University
of Debrecen
Identification number: TÁMOP-4.1.2-08/1/A-2009-0011
Manifestation of Novel Social Challenges of the
European Union
in the Teaching Material of
Medical Biotechnology Master’s Programmes
at the University of Pécs and at the University
of Debrecen
Identification number: TÁMOP-4.1.2-08/1/A-2009-0011
Dr. Judit Pongrácz
Three dimensional tissue cultures and
tissue engineering – Lecture 13
CONTROLLED RELEASE
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Controlled drug delivery
from scaffolds
• Drug release upon matrix degradation
• Drug release upon diffusion
• Long-term maintenance of effective
local concentration
• Localized effects ensured
• Limited systemic effects
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Ideal scaffold
• 3-dimensional and well defined
microstructure
• Interconnected pore network
• Mechanical properties similar to those
of natural tissues
• Biocompatible and bio-resorbable
• Controllable degradation and
resorption
• Local sequestration and controlled
delivery of specific bioactive factors
• Thus enhancing and guideing the
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ECM mimicry as a guide for
scaffold design
• ECM is the natural medium where cells
proliferate, differentiate and migrate
• ECM is a highly organized dynamic
biomolecular environment where motifs
governing cell behaviours are
continuously generated and sequestered
• Motifs are locally released according
to cellular stimuli
• Relase occurs on-demand upon
degradation of the adhesion sites
binding them to the ECM
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Growth factors and the ECM
• Growth factors (GFs) are locally
stored by ECM
• Storage in insoluble/latent forms
• Specific binding with
glycosaminoglycans (e.g. heparins)
• Elicit biological activity once
released
• ECM binding provides concentration
gradient important in morphogenesis
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Mimic the function of ECM
• Future generations of TE scaffolds
need to have extended functionality
and bioactivity
• Synthetic bio-inspired ECM should
broadcast specific cellular events
• The ability of controlled release of
multiple bioactive molecules will
allow the control of cellular
behaviour and successful regeneration
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Interspersed signals
• Hydrogels (either natural or synthetic)
have been succesfully used for
controlled release of bioactive protein
compounds
• Molecules were simply mixed with the
polymer and were entrapped upon gelation
• Natural (collagen, fibrin, hyaluronan)
and synthetic (PEG-based, peptide-based)
hydrogels have been used
• Release characteristic may modulated
with crosslinking agents
• Solid-state scaffolds: fabrication
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Immobilized signals
• Modification of polymer scaffolds to
interact with signaling molecules:
immobilization
• Prolonged diffusion out of the scaffold
platform
• Reversible or irreversible binding to the
polymer.
• Released upon degradation of a linking
tether or the matrix itself
• Determinants of the amount of bound signal
and release profile:
– The number of binding sites
– Affinity of the signal for sites
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Signal delivery from cells
• Inclusion of nucleic acids (NA)
encoding the desired protein
• NA are introduced into target cells,
which then produce the desired
proteins
• Antisense oligos can be used to return
abnormal gene expression to a certain
state
• Synthetic polymers containing adhesion
sites (RGD) proved to be more
effective in delivering the plasmid
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Protein delivery systems
(DS) in TE
• DS must prevent the protein from
inactivation or degradation
• Fine-tuning of the release rate can be
achieved by modulating the
composition, shape, and architecture
of the platform
• Continous and pulsatile delivery
• Biodegradable and non-degradable
platforms
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Non-biodegradable systems
Ethylene-vinyl acetate copolymers (EVAc) and
silicones:
• Mass transport through polymer chains or
pores is the only rate-limiting step
• Possible application in cell encapsulation
preventing them to interact with the immune
system
Time
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Biodegradable systems
• PLGA is a very versatile and widely used
system
• Poly-ortho esters are newly in the centre of
interest (no heating or solvents, injectable
polymers)
• Polyanhydrides usually undergo surface
erosion which has a favorable kinetics
Time
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Controlled release profiles in
biodegradable systems
Amount of drug released
Protein or small
molecule drug
Corresponding
rate
dc(t)/dt
Release rate
t
t
Typical release
profile
Corresponding
rate
Release rate
t
Toxic dose
ceff(t)
Bulk erosion
Typical release
profile
dc(t)/dt
Protein or small
molecule drug
Amount of drug released
Surface erosion
t
t
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On-off drug delivery
systems
• Pulsatile mode of protein and peptide
release
• Rapid and transient release of a certain
amount of drug molecules within a short
time-period immediately after a predetermined off-release interval
• Classified into “programmed” and “triggered”
delivery systems (DS):
– Programmed-DS: the release is governed by
the inner mechanism of the device
– Triggered-DS: release is governed by
changes in the physiologic environment of
the device or by external stimuli
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Programmed and triggered
delivery systems
• Synthetic polymers can be engineered to be
applicable in programmed delivery
• Both surface and bulk-eroding systems may be
used
• Biggest interest in triggered delivery is
the glucose-sensitive insulin delivery
• The “intelligent” system consists of
immobilized glucose oxidase in a pHresponsive polymeric hydrogel
• In the gel, insulin is enclosed
• Upon glucose diffusion into the hydrogel,
glucose oxidase converts it into gluconic
acid
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Inclusion of drug molecules
into scaffolds
Poly-methyl-methacrylate (PMMA) beads with
antibiotics (mostly aminoglycosides):
• Orthopedic and trauma surgery
• Treatment of chronic osteomyelitis and/or
ulcers
• Bones and joints are „blind spots” of
systemic antibiotic therapy because the
limited blood supply
• PMMA beads release antibiotics gradually
• High local antibiotic concentration can be
achieved
• Limited systemic side effects
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Inclusion of bioactive
proteins into scaffolds
VEGF role in tissue vascularization:
•
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Cells in hypoxic tissues secrete VEGF
Endothelial cells express VEGFR
Stimulates endothel proliferation
Directs endothelial cell migration
Tissue vascularization is critical in
nutrition and oxigenization of
implanted TE constructs
• Controlled VEGF delivery is in the
focus of TE research
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VEGF supports TE tissue
vascularization
Controlled VEGF delivery
microparticles:
from alginate
• Bivalent cations mediate alginate
crosslinking
• VEGF encapsulation efficiency and
delivery ratio depends on the cation
species (Ca2+ or Zn2+)
• Zn2+-crosslinked particles proved to
be more toxic than Zn2+
• Mixture of Ca2+ and Zn2+ beads are the
most favorable
Support of tissue
differentiation with
bioactive proteins
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BMP-2:
• Key role in regulating osteoblast
differentiation
• Recombinant hBMP-2 is dissolved in
aquaeous solution of polyethyleneoxide (PEO)
• rhBMP-2 solution is then added to
scaffold material
• Scaffold materials include silk
fibroin, PCLA, PEG, PLGA, collagen,
etc.
Experimental results with
controlled drug delivery
scaffolds – VEGF
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• Half-life of VEGF is 50 min, therefore
controlled release is critical
• Controlled release is based on
electrostatic attractions between the
carrier (acidic gelatine, IEP=5.0) and
VEGF (IEP=8.6)
• Extent of gelatin cross-linking also
influences release
• Up to 90% of total VEGF vas released
within 30 days from sc. implants, 80%
within the first 5 days.
Clinical results with
controlled drug delivery
scaffolds – BMP-2
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• Use of BMP-2 filled collagen sponges
in spinal degenerative diseases to
enhance post-operative bone fusion.
• BMP-2 treated patients regain the
ability to self-care and mobility
faster, their pain scores are
significantly lower.
• Their mood and emotional control is
also significantly better than that of
control patients.
Manifestation of Novel Social Challenges of the
European Union
in the Teaching Material of
Medical Biotechnology Master’s Programmes
at the University of Pécs and at the University
of Debrecen
Identification number: TÁMOP-4.1.2-08/1/A-2009-0011
Dr. Judit Pongrácz
Three dimensional tissue cultures and
tissue engineering – Lecture 14
BIOSENSORS
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Definition
Biosensor is a device that transforms
or detects a biological signal and
transforms into a more easily
detectable one.
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Concept of an implantable
glucose sensor
Type I
Detector
(potentially a
mobile phone)
Signal
Glucose sensor
Implantable potentiostat
Type II
Glucose sensor
Insulin release
Signal
Signal
Insulin container
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Dexamethasone-loaded PLGA
Microspheres
10m
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Model of biosensor-tissue
interactions
Biosensor
Interphase
Tissue
Hydrogels + PEO
RBC
Sensor
Angiogenesis
WBC
Endothel
cell
Microsphere
for drug (TRM)
release
Angiogenic factor or other tissue response modifiers
Soluble proteins
Fibrin
Collagen
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The “intelligent” system
• Consists of immobilized glucose
oxidase in a pH-responsive polymeric
hydrogel, enclosing a saturated
insulin solution.
• As glucose diffuses into the hydrogel,
glucose oxidase catalyzes its
conversion to gluconic acid, thereby
lowering the pH in the
microenvironment of the membrane.
• Low pH causes swelling and insulin
release.
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Development of reliable
glucose biosensors require
1. Novel electrodes are required to decrease
invasiveness of the implantable glucose
biosensor
2. Bioactive coatings are necessary to
enhance the in vivo life of the implantable
glucose sensor
3. Biosensor coating using electrospinning
nanofibres need to be developed
4. Tissue responses are needed to be studied
further to optimize tissue responses to
biosensor signals
5. Angiogenesis around the glucose sensor
need to be increased to enhance detection