Cellular response to transforming growth factor-beta1 and basic fibroblast growth factor depends on release kinetics and extracellular matrix interactions

Bubble nucleation and dynamics in acoustic droplet vaporization: a review of concepts, applications, and new directions

The development of phase-shift droplets has broadened the scope of ultrasound-based biomedical applications. When subjected to sufficient acoustic pressures, the perfluorocarbon phase in phase-shift droplets undergoes a phase-transition to a gaseous state. This phenomenon, termed acoustic droplet vaporization (ADV), has been the subject of substantial research over the last two decades with great progress made in design of phase-shift droplets, fundamental physics of bubble nucleation and dynamics, and applications. Here, we review experimental approaches, carried out via high-speed microscopy, as well as theoretical models that have been proposed to study the fundamental physics of ADV including vapor nucleation and ADV-induced bubble dynamics. In addition, we highlight new developments of ADV in tissue regeneration, which is a relatively recently exploited application. We conclude this review with future opportunities of ADV for advanced applications such as in situ microrheology and pressure estimation.

Multi-time scale characterization of acoustic droplet vaporization and payload release of phase-shift emulsions using high-speed microscopy

Acoustic droplet vaporization (ADV) is the phase-transitioning of perfluorocarbon emulsions, termed phase-shift emulsions, into bubbles using focused ultrasound. ADV has been utilized in many biomedical applications. For localized drug release, phase-shift emulsions with a bioactive payload can be incorporated within a hydrogel to yield an acoustically-responsive scaffold (ARS). The dynamics of ADV and associated drug release within hydrogels are not well understood. Additionally, emulsions used in ARSs often contain high molecular weight perfluorocarbons, which is unique relative to other ADV applications. In this study, we used ultra-high-speed brightfield and fluorescence microscopy, at frame rates up to 30 million and 0.5 million frames per second, respectively, to elucidate ADV dynamics and payload release kinetics in fibrin-based ARSs containing phase-shift emulsions with three different perfluorocarbons: perfluoropentane (PFP), perfluorohexane (PFH), and perfluorooctane (PFO). At an ultrasound excitation frequency of 2.5 MHz, the maximum expansion ratio, defined as the maximum bubble diameter during ADV normalized by the initial emulsion diameter, was 4.3 ± 0.8, 4.1 ± 0.6, and 3.6 ± 0.4, for PFP, PFH, PFO emulsions, respectively. ADV yielded stable bubble formation in PFP and PFH emulsions, though the bubble growth rate post-ADV was three orders of magnitudes slower in the latter emulsion. Comparatively, ADV generated bubbles in PFO emulsions underwent repeated vaporization/recondensation or fragmentation. Different ADV-generated bubble dynamics resulted in distinct release kinetics in phase-shift emulsions carrying fluorescently-labeled payloads. The results provide physical insight enabling the modulation of bubble dynamics with ADV and hence release kinetics, which can be used for both diagnostic and therapeutic applications of ultrasound.

Contribution of tetrodotoxin-resistant persistent Na+ currents to the excitability of C-type dural afferent neurons in rats

BACKGROUND

Growing evidence supports the important role of persistent sodium currents (I_NaP) in the neuronal excitability of various central neurons. However, the role of tetrodotoxin-resistant (TTX-R) Na⁺ channel-mediated I_NaP in the neuronal excitability of nociceptive neurons remains poorly understood.

METHODS

We investigated the functional role of TTX-R I_NaP in the excitability of C-type nociceptive dural afferent neurons, which was identified using a fluorescent dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchloride (DiI), and a whole-cell patch-clamp technique.

RESULTS

TTX-R I_NaP were found in most DiI-positive neurons, but their density was proportional to neuronal size. Although the voltage dependence of TTX-R Na⁺ channels did not differ among DiI-positive neurons, the extent of the onset of slow inactivation, recovery from inactivation, and use-dependent inhibition of these channels was highly correlated with neuronal size and, to a great extent, the density of TTX-R I_NaP. In the presence of TTX, treatment with a specific I_NaP inhibitor, riluzole, substantially decreased the number of action potentials generated by depolarizing current injection, suggesting that TTX-R I_NaP are related to the excitability of dural afferent neurons. In animals treated chronically with inflammatory mediators, the density of TTX-R I_NaP was significantly increased, and it was difficult to inactivate TTX-R Na⁺ channels.

CONCLUSIONS

TTX-R I_NaP apparently contributes to the differential properties of TTX-R Na⁺ channels and neuronal excitability. Consequently, the selective modulation of TTX-R I_NaP could be, at least in part, a new approach for the treatment of migraine headaches.

Development of Neuronal Guidance Fibers for Stimulating Electrodes: Basic Construction and Delivery of a Growth Factor

State-of-the-art treatment for sensorineural hearing loss is based on electrical stimulation of residual spiral ganglion neurons (SGNs) with cochlear implants (CIs). Due to the anatomical gap between the electrode contacts of the CI and the residual afferent fibers of the SGNs, spatial spreading of the stimulation signal hampers focused neuronal stimulation. Also, the efficiency of a CI is limited because SGNs degenerate over time due to loss of trophic support. A promising option to close the anatomical gap is to install fibers as artificial nerve guidance structures on the surface of the implant and install on these fibers drug delivery systems releasing neuroprotective agents. Here, we describe the first steps in this direction. In the present study, suture yarns made of biodegradable polymers (polyglycolide/poly-ε-caprolactone) serve as the basic fiber material. In addition to the unmodified fiber, also fibers modified with amine groups were employed. Cell culture investigations with NIH 3T3 fibroblasts attested good cytocompatibility to both types of fibers. The fibers were then coated with the extracellular matrix component heparan sulfate (HS) as a biomimetic of the extracellular matrix. HS is known to bind, stabilize, modulate, and sustainably release growth factors. Here, we loaded the HS-carrying fibers with the brain-derived neurotrophic factor (BDNF) which is known to act neuroprotectively. Release of this neurotrophic factor from the fibers was followed over a period of 110 days. Cell culture investigations with spiral ganglion cells, using the supernatants from the release studies, showed that the BDNF delivered from the fibers drastically increased the survival rate of SGNs in vitro. Thus, biodegradable polymer fibers with attached HS and loaded with BDNF are suitable for the protection and support of SGNs. Moreover, they present a promising base material for the further development towards a future neuronal guiding scaffold.

Cell Cycle Synchronization of Primary Articular Chondrocytes Enhances Chondrogenesis

OBJECTIVE

Although tissue engineering is a promising option for articular cartilage repair, it has been challenging to generate functional cartilaginous tissue. While the synthetic response of chondrocytes can be influenced by various means, most approaches treat chondrocytes as a homogeneous population that would respond similarly. However, isolated cells heterogeneously progress through the cell cycle, which can affect macromolecular biosynthesis. As it is possible to synchronize cells within discrete cell cycle phases, the purpose of this study was to investigate the effects of cell cycle synchronization on the chondrogenic potential of primary articular chondrocytes.

DESIGN

Different methods of cell synchronization (serum starvation, thymidine, nocodazole, aphidicolin, and RO-3306) were tested for their ability to synchronize primary articular chondrocytes during the process of cell isolation. Cells (unsynchronized and synchronized) were then encapsulated in alginate gels, cultured for 4 weeks, and analyzed for their structural and biochemical properties.

RESULTS

The double-thymidine method yielded the highest level of cell purity, with cells synchronized in S phase. While the cells started to lose synchronization after 24 hours, tissue constructs developed from initially S phase synchronized cells had significantly higher glycosaminoglycan and collagen II amounts than those developed using unsynchronized cells.

CONCLUSIONS

Initial synchronization led to long-term changes in cartilaginous tissue formation. This effect was postulated to be due to the rapid auto-induction of TGF-βs by actively dividing S phase cells, thereby stimulating chondrogenesis. Cell synchronization methods may also be applied in conjunction with redifferentiation methods to improve the chondrogenic potential of dedifferentiated or diseased chondrocytes.

LPCGF and EDTA conditioning of the root surface promotes the adhesion, growth, migration and differentiation of periodontal ligament cells

BACKGROUND

Liquid-phase concentrated growth factor (LPCGF), a new-generation platelet concentrate, may potently stimulate human periodontal ligament (PDL) cells. This study assessed the effectiveness of ethylenediaminetetraacetic acid (EDTA) and/or LPCGF on periodontally diseased root surfaces through their effects on PDL cells.

METHODS

Dentin blocks prepared from periodontal teeth were divided into four groups and treated as follows: group I, scaling and root planning (SRP); group II, SRP + EDTA; group III, SRP + LPCGF; and group IV, SRP+EDTA + LPCGF. PDL cells were cultured on dentin blocks, and LPCGF-induced biological effects were evaluated by migration and cell adhesion/proliferation assays. Furthermore, PDL cell differentiation was assessed by real-time polymerase chain reaction (PCR).

RESULTS

Significantly more adherent cells were observed in the EDTA, LPCGF and combination treatment groups than in the control group. Root conditioning with EDTA and/or LPCGF enhanced cell proliferation and migration more than SRP did. Compared with the control group, the combined treatment group exhibited significant upregulation of cell differentiation-related genes. Electron microscopy of the tooth surface revealed removal of the smear layer and exposed dentin holes in the EDTA-treated group but not in the control group.

CONCLUSION

EDTA and LPCGF application to periodontitis-affected root surfaces forms a surface suitable for cell attachment, growth, migration and differentiation. Thus, LPCGF is promising in clinical periodontics applications. Further studies to support these results are necessary.

Engineering Approaches to Study Cellular Decision Making

In their native environment, cells are immersed in a complex milieu of biochemical and biophysical cues. These cues may include growth factors, the extracellular matrix, cell-cell contacts, stiffness, and topography, and they are responsible for regulating cellular behaviors such as adhesion, proliferation, migration, apoptosis, and differentiation. The decision-making process used to convert these extracellular inputs into actions is highly complex and sensitive to changes both in the type of individual cue (e.g., growth factor dose/level, timing) and in how these individual cues are combined (e.g., homotypic/heterotypic combinations). In this review, we highlight recent advances in the development of engineering-based approaches to study the cellular decision-making process. Specifically, we discuss the use of biomaterial platforms that enable controlled and tailored delivery of individual and combined cues, as well as the application of computational modeling to analyses of the complex cellular decision-making networks.

The influence of tissue microenvironment on stem cell-based cartilage repair

Mesenchymal stem/progenitor cells and induced pluripotent stem cells have become viable cell sources for prospective cell-based cartilage engineering and tissue repair. The development and function of stem cells are influenced by the tissue microenvironment. Specifically, the local tissue microenvironment can dictate how stem cells integrate into the existing tissue matrix and how successfully they can restore function to the damaged area in question. This review focuses on the microenvironmental features of articular cartilage and how they influence stem cell-based cartilage tissue repair. Also discussed are current tissue-engineering strategies used in combination with cell-based therapies, all of which are designed to mimic the natural properties of cartilage tissue in order to achieve a better healing response.

Stem cells display a donor dependent response to escalating levels of growth factor release from extracellular matrix-derived scaffolds

Numerous growth factor delivery systems have been developed for tissue engineering. However, little is known about how the dose of a specific protein will influence tissue regeneration, or how different patients will respond to altered levels of growth factor presentation. The objective of the present study was to assess stem cell chondrogenesis within extracellular-matrix (ECM)-derived scaffolds loaded with escalating levels of transforming growth factor (TGF)-β3. It was also sought to determine if stem cells display a donor-dependent response to different doses of TGF-β3, from low (5 ng) to high (200 ng), released from such scaffolds. It was found that ECM-derived scaffolds possess the capacity to bind and release increasing amounts of TGF-β3, with between 60% and 75% of this growth factor released into the media over the first 12 days of culture. After seeding these scaffolds with human infrapatellar fat pad-derived stem cells (FPSCs), it was found that cartilage-specific ECM accumulation was greatest for the higher levels of growth factor loading. Importantly, soak-loading cartilage ECM-derived scaffolds with high levels of TGF-β3 always resulted in at least comparable levels of chondrogenesis to controls where this growth factor was continuously added to the culture media. Similar results were observed for FPSCs from all donors, although the absolute level of secreted matrix did vary from donor to donor. Therefore, while no single growth factor release profile will be optimal for all patients, the results of this study suggest that the combination of a highly porous cartilage ECM-derived scaffold coupled with appropriate levels of TGF-β3 can consistently drive chondrogenesis of adult stem cells. Copyright © 2016 John Wiley & Sons, Ltd.

Neutrophil Elastase-Generated Fragment of Vascular Endothelial Growth Factor-A Stimulates Macrophage and Endothelial Progenitor Cell Migration

Elastase released from neutrophils as part of the innate immune system has been implicated in chronic diseases such as emphysema and cardiovascular disease. We have previously shown that neutrophil elastase targets vascular endothelial growth factor-A (VEGF) for partial degradation to generate a fragment of VEGF (VEGFf) that has distinct activities. Namely, VEGFf binds to VEGF receptor 1 but not to VEGF receptor 2 and shows altered signaling compared to intact VEGF. In the present study we investigated the chemotactic function of VEGF and VEGFf released from cells by neutrophil elastase. We found that endothelial cells migrated in response to intact VEGF but not VEGFf whereas RAW 264.7 macrophages/monocytes and embryonic endothelial progenitor cells were stimulated to migrate by either VEGF or VEGFf. To investigate the role of elastase-mediated release of VEGF from cells/extracellular matrices, a co-culture system was established. High or low VEGF producing cells were co-cultured with macrophages, endothelial or endothelial progenitor cells and treated with neutrophil elastase. Elastase treatment stimulated macrophage and endothelial progenitor cell migration with the response being greater with the high VEGF expressing cells. However, elastase treatment led to decreased endothelial cell migration due to VEGF cleavage to VEGF fragment. These findings suggest that the tissue response to NE-mediated injury might involve the generation of diffusible VEGF fragments that stimulate inflammatory cell recruitment.

Engineered Microtissues Formed by Schiff Base Crosslinking Restore the Chondrogenic Potential of Aged Mesenchymal Stem Cells

A universal method for reproducibly directing stem cell differentiation remains a major challenge for clinical applications involving cell-based therapies. The standard approach for chondrogenic induction by micromass pellet culture is highly susceptible to interdonor variability. A novel method for the fabrication of condensation-like engineered microtissues (EMTs) that utilizes hydrophilic polysaccharides to induce cell aggregation is reported here. Chondrogenesis of mesenchymal stem cells (MSCs) in EMTs is significantly enhanced compared to micromass pellets made by centrifugation measured by type II collagen gene expression, dimethylmethylene blue assay, and histology. MSCs from aged donors that fail to differentiate in pellet culture are successfully induced to synthesize cartilage-specific matrix in EMTs under identical media conditions. Furthermore, the EMT polysaccharides support the loading and release of the chondroinduction factor transforming growth factor β3 (TGF-β3). TGF-β-loaded EMTs (EMT(+TGF) ) facilitate cartilaginous tissue formation during culture in media not supplemented with the growth factor. The clinical potential of this approach is demonstrated in an explant defect model where EMT(+TGF) from aged MSCs synthesize de novo tissue containing sulfated glycosaminoglycans and type II collagen in situ.

IGF-1 release kinetics from chitosan microparticles fabricated using environmentally benign conditions

The main objective of this study is to maximize growth factor encapsulation efficiency into microparticles. The novelty of this study is to maximize the encapsulated growth factors into microparticles by minimizing the use of organic solvents and using relatively low temperatures. The microparticles were fabricated using chitosan biopolymer as a base polymer and cross-linked with tripolyphosphate (TPP). Insulin like-growth factor-1 (IGF-1) was encapsulated into microparticles to study release kinetics and bioactivity. In order to authenticate the harms of using organic solvents like hexane and acetone during microparticle preparation, IGF-1 encapsulated microparticles prepared by the emulsification and coacervation methods were compared. The microparticles fabricated by emulsification method have shown a significant decrease (p<0.05) in IGF-1 encapsulation efficiency, and cumulative release during the two-week period. The biocompatibility of chitosan microparticles and the bioactivity of the released IGF-1 were determined in vitro by live/dead viability assay. The mineralization data observed with von Kossa assay, was supported by mRNA expression levels of osterix and runx2, which are transcription factors necessary for osteoblasts differentiation. Real time RT-PCR data showed an increased expression of runx2 and a decreased expression of osterix over time, indicating differentiating osteoblasts. Chitosan microparticles prepared in optimum environmental conditions are a promising controlled delivery system for cells to attach, proliferate, differentiate and mineralize, thereby acting as a suitable bone repairing material.

Pilot safety study of perivascular injection of tissue-engineered allogeneic aortic endothelial cells in patients undergoing minimally invasive peripheral revascularization

OBJECTIVE

Restenosis is a limitation of endovascular interventions performed in the superficial femoral artery (SFA). Preclinical studies have demonstrated that the perivascular delivery of tissue-engineered allogeneic aortic endothelial cells (PVS-10200) reduced stenosis in porcine models of SFA revascularization. The purpose of this study was to investigate the safety and feasibility of percutaneous PVS-10200 delivery after angioplasty and stenting in the SFA of patients with peripheral artery disease.

METHODS

In this phase I open-label trial, 21 patients (average lesion length of 10.10 ± 2.36 cm and ≥70% stenosis) were treated with PVS-10200: 11 in a low-dose cohort (cohort A) and 10 in a high-dose cohort (cohort B). The primary objective was to demonstrate the safety (incidence of major adverse events) of PVS-10200 within 4 weeks after surgery. Secondary end points included assessments of resting ankle-brachial index (ABI) in the treated leg, Fontaine class, and time to target lesion revascularization (TLR).

RESULTS

No patient had a major adverse event within 4 weeks. One patient required a limb amputation at 30 weeks. At 48 weeks, cohort A and cohort B patients maintained a 37% and 62% increase in ABI compared with baseline, respectively; 70% of cohort A and 78% of cohort B improved by ≥1 Fontaine classification stage, and the TLR rate was 39% for cohort A and 20% for cohort B.

CONCLUSIONS

Percutaneous local delivery of PVS-10200 is a well-tolerated and novel therapeutic approach that may be a suitable treatment for patients after endovascular intervention of the SFA. Larger randomized trials are needed to determine if PVS-10200 can improve ABI and reduce TLR rates.

Transforming growth factor Beta-releasing scaffolds for cartilage tissue engineering

The maintenance of a critical threshold concentration of transforming growth factor beta (TGF-β) for a given period of time is crucial for the onset and maintenance of chondrogenesis. Thus, the development of scaffolds that provide temporal and/or spatial control of TGF-β bioavailability has appeal as a mechanism to induce the chondrogenesis of stem cells in vitro and in vivo for articular cartilage repair. In the past decade, many types of scaffolds have been designed to advance this goal: hydrogels based on polysaccharides, hyaluronic acid, and alginate; protein-based hydrogels such as fibrin, gelatin, and collagens; biopolymeric gels and synthetic polymers; and solid and hybrid composite (hydrogel/solid) scaffolds. In this study, we review the progress in developing strategies to deliver TGF-β from scaffolds with the aim of enhancing chondrogenesis. In the future, such scaffolds could prove critical for tissue engineering cartilage, both in vitro and in vivo.

Local delivery of small and large biomolecules in craniomaxillofacial bone

Current state of the art reconstruction of bony defects in the craniomaxillofacial (CMF) area involves transplantation of autogenous or allogenous bone grafts. However, the inherent drawbacks of this approach strongly urge clinicians and researchers to explore alternative treatment options. Currently, a wide interest exists in local delivery of biomolecules from synthetic biomaterials for CMF bone regeneration, in which small biomolecules are rapidly emerging in recent years as an interesting adjunct for upgrading the clinical treatment of CMF bone regeneration under compromised healing conditions. This review highlights recent advances in the local delivery small and large biomolecules for the clinical treatment of CMF bone defects. Further, it provides a perspective on the efficacy of biomolecule delivery in CMF bone regeneration by reviewing presently available reports of pre-clinical studies using various animal models.

Ultrasound-guided percutaneous delivery of tissue-engineered endothelial cells to the adventitia of stented arteries controls the response to vascular injury in a porcine model

OBJECTIVE

High restenosis rates are a limitation of peripheral vascular interventions. Previous studies have shown that surgical implantation of a tissue-engineered endothelium onto the adventitia surface of injured vessels regulates vascular repair. In the present study, we developed a particulate formulation of tissue-engineered endothelium and a method to deliver the formulation perivascular to injured blood vessels using a percutaneous, minimally invasive technique.

METHODS

Stainless steel stents were implanted in 18 balloon-injured femoral arteries of nine domestic swine, followed by ultrasound-guided percutaneous perivascular injection of gelatin particles containing cultured allogeneic porcine aortic endothelial cells (PAE). Controls received injections of empty particles (matrix) or no perivascular injection (sham) after stent deployment. Animals were sacrificed after 90 days.

RESULTS

Angiographic analysis revealed a significantly greater lumen diameter in the stented segments of arteries treated with PAE/matrix (4.72 ± 0.12 mm) compared with matrix (4.01 ± 0.20 mm) or sham (4.03 ± 0.16 mm) controls (P < .05). Similarly, histologic analysis revealed that PAE/matrix-treated arteries had the greatest lumen area (20.4 ± 0.7 mm(2); P < .05) compared with controls (16.1 ± 0.9 mm(2) and 17.1 ± 1.0 mm(2) for sham and matrix controls, respectively) and the smallest intimal area (3.3 ± 0.4 mm(2); P < .05) compared with controls (6.2 ± 0.5 mm(2) and 4.4 ± 0.5 mm(2) for sham and matrix controls, respectively). Overall, PAE-treated arteries had a 33% to 50% decrease in percent occlusion (P < .05) compared with controls. Histopathological analysis revealed fewer leukocytes present in the intima in the PAE/matrix group compared with control groups, suggesting that the biological effects were in part due to inhibition of the inflammatory phase of the vascular response to injury.

CONCLUSIONS

Minimally invasive, perivascular delivery of PAE/matrix to stented arteries was performed safely using ultrasound-guided percutaneous injections and significantly decreased stenosis. Application at the time of or subsequent to peripheral interventions may decrease clinical restenosis rates.

Eotaxin and FGF enhance signaling through an extracellular signal-related kinase (ERK)-dependent pathway in the pathogenesis of Eosinophilic esophagitis

Background

Eosinophilic esophagitis (EoE) is characterized by the inflammation of the esophagus and the infiltration of eosinophils into the esophagus, leading to symptoms such as dysphagia and stricture formation. Systemic immune indicators like eotaxin and fibroblast growth factor were evaluated for possible synergistic pathological effects. Moreover, blood cells, local tissue, and plasma from EoE and control subjects were studied to determine if the localized disease was associated with a systemic effect that correlated with presence of EoE disease.

Method

Real-time polymerase chain reaction from peripheral blood mononuclear cells (PBMC), immunohistochemistry from local esophageal biopsies, fluid assays on plasma, and fluorescence-activated cell sorting on peripheral blood cells from subjects were used to study the systemic immune indicators in newly diagnosed EoE (n = 35), treated EoE (n = 9), Gastroesophageal reflux disease (GERD) (n = 8), ulcerative colitis (n = 5), Crohn's disease (n = 5), and healthy controls (n = 8).

Result

Of the transcripts tested for possible immune indicators, we found extracellular signal-regulated kinase (ERK), Bcl-2, bFGF (basic fibroblast growth factor), and eotaxin levels were highly upregulated in PBMC and associated with disease presence of EoE. Increased FGF detected by immunohistochemistry in esophageal tissues and in PBMC was correlated with low levels of pro-apoptotic factors (Fas, Caspase 8) in PBMC from EoE subjects. Plasma-derived bFGF was shown to be the most elevated and most specific in EoE subjects in comparison to healthy controls and disease control subjects.

Conclusion

We describe for the first time a possible mechanism by which increased FGF is associated with inhibiting apoptosis in local esophageal tissues of EoE subjects as compared to controls. Eotaxin and FGF signaling pathways share activation through the ERK pathway; together, they could act to increase eosinophil activation and prolong the half-life of eosinophils in local tissues of the esophagus in EoE subjects.

Hypromellose films for the delivery of growth factors for wound healing

Hypromellose was investigated as a carrier for extending topical growth factor delivery to wounds. Films of hypromellose (E4M, K4M and E10M) containing a model protein horseradish peroxidase (1 % w/w HRP, MW 40 000) were cast from aqueous solutions and dried at 37°C. In-vitro release was determined using Franz-type diffusion cells and films were mounted directly into the Franz cell or cast onto a wound dressing (Melolin) backing. There was an initial burst release then an extended release over 5 h. The Melolin backing significantly reduced the burst but not the extended release rates (P &lt; 0.05). Release of HRP was also determined from 7% w/v hypromellose gels and was significantly lower for E10M than E4M, suggesting that, once hydrated, the E10M hypromellose provides the greatest resistance to HRP release. The release profile of basic fibroblast growth factor from Melolin-backed films made from E4M hypromellose was not significantly different at any time point to that of HRP release from the same formulation. Hypromellose may be incorporated into a wound dressing such as Melolin to provide a prolonged release of an incorporated protein active.

Vascular growth factor binding kinetics to the endothelial cell basement membrane, with a kinetics-based correction for substrate binding

Vascular growth factors, including vascular endothelial growth factor and fibroblast growth factor-2, bind to heparan sulfate proteoglycans in the basement membrane. While this binding, storage, and release system provides a critical model for controlled drug release devices, basement membrane-growth factor binding kinetics have not been fully established. We modified endothelial cell-growth factor binding kinetics protocols for the basement membrane. The basement membrane showed low affinity for fibroblast growth factor-2 (K d = 185.8 nM), with a slow off rate (k off = 0.00338 min(-1)). However, results were confounded by growth factor binding to tissue culture polystyrene in a manner strikingly similar to basement membrane. Since substrate binding could not be blocked, a binding kinetics based correction technique was developed to account for polystyrene growth factor binding. This method was validated by conducting binding kinetics experiments on bacteriologic plates that exhibit little growth factor binding. This novel method will improve our understanding of cell and protein interaction with the basement membrane in health and disease. They can also further be applied to develop biomimetic drug delivery systems.

Mild immobilization of diverse macromolecular bioactive agents onto multifunctional fibrous membranes prepared by coaxial electrospinning

Coaxial electrospinning was proved to be a facile method to produce multifunctional fibrous matrices which could essentially emulate certain features of native extracellular matrix. In order to further confer capability of immobilizing diverse macromolecular bioactive agents to the fibers, composite membranes composed of cationized gelatin-coated polycaprolactone (PCL) fibers were prepared by coaxial electrospinning. Gelatin was cationized by derivation with N,N-dimethylethylenediamine. The cationized gelatin (CG) was used as a shell material for constructing a core-shell fibrous membrane. PCL formed the core section of the core-shell fibers thereby improving the mechanical properties of nanofibrous CG hydrogel. The outer CG layer was crosslinked by exposing the membranes in glutaraldehyde vapor. The adsorption behaviors of FITC-labeled bovine serum albumin (FITC-BSA) or FITC-heparin onto the fibers were investigated. The core-shell fibers could effectively immobilize the two types of agents under mild conditions. The adsorption amount could reach about 12 microg of BSA per mg of membrane and 23 microg mg(-1) for heparin. Furthermore, vascular endothelial growth factor (VEGF) could be conveniently impregnated into the fibers through specific interactions with the adsorbed heparin in the outer CG layer. Sustained release of bioactive VEGF could be achieved for more than 15 days.

Vascular regeneration by local growth factor release is self-limited by microvascular clearance

BACKGROUND

The challenge of angiogenesis science is that stable sustained vascular regeneration in humans has not been realized despite promising preclinical findings. We hypothesized that angiogenic therapies powerfully self-regulate by dynamically altering tissue characteristics. Induced neocapillaries increase drug clearance and limit tissue retention and subsequent angiogenesis even in the face of sustained delivery.

METHODS AND RESULTS

We quantified how capillary flow clears fibroblast growth factor after local epicardial delivery. Fibroblast growth factor spatial loading was significantly reduced with intact coronary perfusion. Penetration and retention decreased with transendothelial permeability, a trend diametrically opposite to intravascular delivery, in which factor delivery depends on vascular leak, but consistent with a continuum model of drug transport in perfused tissues. Model predictions of fibroblast growth factor sensitivity to manipulations of its diffusivity and transendothelial permeability were validated by conjugation to sucrose octasulfate. Induction of neocapillaries adds pharmacokinetic complexity. Sustained local fibroblast growth factor delivery in vivo produced a burst of neovascularization in ischemic myocardium but was followed by drug washout and a 5-fold decrease in fibroblast growth factor penetration depth.

CONCLUSIONS

The very efficacy of proangiogenic compounds enhances their clearance and abrogates their pharmacological benefit. This self-limiting property of angiogenesis may explain the failures of promising proangiogenic therapies.

Role of connective tissue growth factor and its interaction with basic fibroblast growth factor and macrophage chemoattractant protein-1 in skin fibrosis

Activation of the immune system and abnormal growth of skin fibroblasts cause systemic sclerosis. Growth factors have various biological activities, including mediation of immune reactions. The growth factor family includes basic fibroblast growth factor (bFGF), transforming growth factor-beta (TGF-beta), and connective tissue growth factor (CTGF). CTGF, an important downstream mediator of TGF-beta in fibrosis, has been suggested to play a specific role in fibrotic disorders. We have directed our attention to the role of CTGF in sustaining skin fibrosis. To better understand its effects in vivo, we established an animal model of skin fibrosis induced by exogenous application of growth factors. In this model, bFGF transiently induced subcutaneous fibrosis. Simultaneous injection of bFGF and CTGF increased skin fibrosis compared with a single injection of bFGF. Serial injections of bFGF for 3 days followed by CTGF for 4 days, or of CTGF followed by bFGF, did not cause skin fibrosis but simultaneous injections increased macrophage chemoattractant protein-1 (MCP-1) mRNA expression levels. To further define the mechanisms of skin fibrosis in vivo, bFGF and CTGF were injected simultaneously into MCP-1 knockout mice, resulting in decreased collagen levels in granulation tissues on day 8. The number of inflammatory cells, such as mast cells, macrophages and lymphocytes, was significantly decreased in MCP-1 knockout mice compared with wild-type mice. These results suggest that bFGF induces collagen production by stimulating skin fibroblasts and CTGF cooperates with bFGF. Our results indicate that the induction of MCP-1 is necessary for infiltration of inflammatory cells.

Controlled release of bioactive transforming growth factor beta-1 from fibrin gels in vitro

This study analyzed the ability of fibrin gels to deliver added recombinant transforming growth factor beta-1 (TGF-beta1) in a controlled manner and biologically active form. First, the effects of the amount of TGF-beta1 on the release kinetics were analyzed using a single fibrin gel formulation (fibrinogen complex (FC) at 25 mg/mL, thrombin at 2 IU/mL). Then, the effects of FC and thrombin concentrations were analyzed. Finally, to test the biological activity of the released TGF-beta1 from the gels, medium supernatants taken from gels at day 3 were used as culture medium for human mesenchymal stem cell (HMSC) monolayers. Cell proliferation was analyzed after staining with calcein dye, and changes in cell morphology were observed under fluorescence microscopy at days 1, 4, and 7. At day 7, HMSC chondrogenic differentiation was assessed by Alcian Blue staining and osteogenic differentiation by alkaline phosphatase activity and Alizarin Red staining. Results showed that TGF-beta1 added to fibrin gels was gradually released from the gels and increased with the amount of TGF-beta1 initially seeded, with a total of approximately 50% of the initial amount released by day 10 (with gels containing 25 mg/mL of FC and 2 IU/mL of thrombin). The release was lower with increasing FC concentrations, suggesting a binding affinity of TGF-beta1 with the FC component. Varying the thrombin concentration had a lesser effect. HMSC monolayers cultured with medium supernatants collected from gels at day 3 and containing released TGF-beta1 showed a change in morphology (squared to polygonal), lower cell proliferation, positive Alcian Blue staining but low levels of osteogenic differentiation markers. These results demonstrated that released TGF-beta1 was still bioactive and tended to induce mainly chondrogenic differentiation of the HMSC. Overall, the present study demonstrated that fibrin gels could be used as a carrier matrix for controlled release of bioactive TGF-beta1 by adjusting the concentrations of FC and thrombin in the gels.

The pericyte: cellular regulator of microvascular blood flow

The vascular system - through its development, response to injury, and remodeling during disease - constitutes one of the key organ systems sustaining normal human physiology; conversely, its dysregulation also underlies multiple pathophysiologic processes. Regulation of vascular endothelial cell function requires the integration of complex signals via multiple cell types, including arterial smooth muscle, capillary and post-capillary pericytes, and other perivascular cells such as glial and immune cells. Here, we focus on the pericyte and its roles in microvascular remodeling, reviewing current concepts in microvascular pathophysiology and offering new insights into the specific roles that pericyte-dependent signaling pathways may play in modulating endothelial growth and microvascular tone during pathologic angiogenesis and essential hypertension.

Solvent-Free Protein Encapsulation within Biodegradable Polymer Foams

Microporous poly(D,L-lactide-co-glycolide) matrices containing encapsulated proteins were fabricated in a solvent-free manner. Microporous foam was generated by saturating a mixture of polymer and protein particles in supercritical carbon dioxide (SC-CO2), dispersing the protein particles in the polymer melt followed by a rapid evaporation of the CO2 phase. The release rates of protein encapsulated within porous poly(lactide-co-glycolide)(PLGA) constructs produced in SC-CO2 were measured in vitro. Although a substantial amount of protein was released within the first 48 h, results indicated that protein may be dispersed throughout the polymer phase and released over 3 weeks using this solvent-free technique. Basic fibroblast growth factor (bFGF), known to promote angiogenesis in vivo, was encapsulated within the polymer matrix. In addition, retention of biological activity was measured for bFGF encapsulated within PLGA foams. Encapsulated bFGF was released from the porous constructs for up to 10 days in vitro with little loss of biological activity.

Critical factors in the design of growth factor releasing scaffolds for cartilage tissue engineering

BACKGROUND

Trauma or degenerative diseases of the joints are common clinical problems resulting in high morbidity. Although various orthopedic treatments have been developed and evaluated, the low repair capacities of articular cartilage renders functional results unsatisfactory in the long term. Over the last decade, a different approach (tissue engineering) has emerged that aims not only to repair impaired cartilage, but also to fully regenerate it, by combining cells, biomaterials mimicking extracellular matrix (scaffolds) and regulatory signals. The latter is of high importance as growth factors have the potency to induce, support or enhance the growth and differentiation of various cell types towards the chondrogenic lineage. Therefore, the controlled release of different growth factors from scaffolds appears to have great potential to orchestrate tissue repair effectively.

OBJECTIVE

This review aims to highlight considerations and limitations of the design, materials and processing methods available to create scaffolds, in relation to the suitability to incorporate and release growth factors in a safe and defined manner. Furthermore, the current state of the art of signalling molecules release from scaffolds and the impact on cartilage regeneration in vitro and in vivo is reported and critically discussed.

METHODS

The strict aspects of biomaterials, scaffolds and growth factor release from scaffolds for cartilage tissue engineering applications are considered.

CONCLUSION

Engineering defined scaffolds that deliver growth factors in a controlled way is a task seldom attained. If growth factor delivery appears to be beneficial overall, the optimal delivery conditions for cartilage reconstruction should be more thoroughly investigated.

Controlled drug delivery in tissue engineering

The concept of tissue and cell guidance is rapidly evolving as more information regarding the effect of the microenvironment on cellular function and tissue morphogenesis become available. These disclosures have lead to a tremendous advancement in the design of a new generation of multifunctional biomaterials able to mimic the molecular regulatory characteristics and the three-dimensional architecture of the native extracellular matrix. Micro- and nano-structured scaffolds able to sequester and deliver in a highly specific manner biomolecular moieties have already been proved to be effective in bone repairing, in guiding functional angiogenesis and in controlling stem cell differentiation. Although these platforms represent a first attempt to mimic the complex temporal and spatial microenvironment presented in vivo, an increased symbiosis of material engineering, drug delivery technology and cell and molecular biology may ultimately lead to biomaterials that encode the necessary signals to guide and control developmental process in tissue- and organ-specific differentiation and morphogenesis.

Adventitial endothelial implants reduce matrix metalloproteinase-2 expression and increase luminal diameter in porcine arteriovenous grafts

OBJECTIVE

Vascular access dysfunction is a major problem in hemodialysis patients. Only 50% of arteriovenous grafts (AVGs) will remain patent 1 year after surgery. AVGs frequently develop stenoses and occlusions at the venous anastomoses in the venous outflow tract. Lumen diameter is not only determined by intimal thickening but is also influenced by remodeling of the vessel wall. Vascular remodeling requires degradation and reorganization of the extracellular matrix by the degradation enzymes, matrix metalloproteinases (MMPs). In this study, we aimed to provide further insight into the mechanism of endothelial regulation of vascular remodeling and luminal narrowing in AVGs.

METHODS

End-to-side carotid artery-jugular vein polytetrafluoroethylene grafts were created in 20 domestic swine. The anastomoses and outflow vein were treated with Gelfoam matrices (Pfizer, New York, NY) containing allogeneic porcine aortic endothelial (PAE, n = 10) cells or control matrices without cells (n = 10), and the biologic responses to PAE implants were investigated 3 and 28 days postoperatively. Angiograms before euthanasia were compared with baseline angiograms. Tissue sections were stained with hematoxylin and eosin, Verhoeff elastin, and antibodies specific to MMP-9 and MMP-2 and underwent histopathologic, morphometric and immunohistochemical analysis.

RESULTS

Veins treated with PAE cell implants had a 2.8-fold increase in venous lumen diameter compared with baseline (P < .05), a 2.3-fold increase in lumen diameter compared with control, and an 81% decrease in stenosis (P < .05) compared with control at 28 days. The increase in lumen diameter by angiographic analysis correlated with morphometric analysis of tissue sections. PAE implants increased the venous lumen area 2.3-fold (P < .05), decreased venous luminal occlusion 66%, and increased positive venous remodeling 1.9-fold (P < .05) compared with control at 28 days. PAE cell implants reduced MMP-2 expression and neovascularization at 3 and 28 days and adventitial fibrosis at 28 days, suggesting a role of the implants in controlling the affects of medial and adventitial cells in the response to vascular injury.

CONCLUSIONS

These results demonstrate that the adventitial application of endothelial implants significantly reduced MMP-2 expression within the venous wall, and increased venous lumen diameter and positive remodeling in a porcine arteriovenous graft model. Adventitial endothelial implants may be useful in decreasing luminal narrowing in a clinical setting.

Hydrogels as Extracellular Matrices for Skeletal Tissue Engineering: State-of-the-Art and Novel Application in Organ Printing

Organ printing, a novel approach in tissue engineering, applies layered computer-driven deposition of cells and gels to create complex 3-dimensional cell-laden structures. It shows great promise in regenerative medicine, because it may help to solve the problem of limited donor grafts for tissue and organ repair. The technique enables anatomical cell arrangement using incorporation of cells and growth factors at predefined locations in the printed hydrogel scaffolds. This way, 3-dimensional biological structures, such as blood vessels, are already constructed. Organ printing is developing fast, and there are exciting new possibilities in this area. Hydrogels are highly hydrated polymer networks used as scaffolding materials in organ printing. These hydrogel matrices are natural or synthetic polymers that provide a supportive environment for cells to attach to and proliferate and differentiate in. Successful cell embedding requires hydrogels that are complemented with biomimetic and extracellular matrix components, to provide biological cues to elicit specific cellular responses and direct new tissue formation. This review surveys the use of hydrogels in organ printing and provides an evaluation of the recent advances in the development of hydrogels that are promising for use in skeletal regenerative medicine. Special emphasis is put on survival, proliferation and differentiation of skeletal connective tissue cells inside various hydrogel matrices.

Release rate controls biological activity of nerve growth factor released from fibrin matrices containing affinity‐based delivery systems

Previously, combinatorial techniques were used to identify peptide sequences exhibiting high, medium, and low affinity for heparin. Bidomain peptides were synthesized containing a transglutaminase sequence for one domain and one of the heparin-affinity sequences for the other domain. A delivery system was made consisting of bi-domain peptides, heparin, and nerve growth factor (NGF), which binds to heparin with moderate affinity. The goal of this research was to determine whether peptide affinity for heparin and the molar ratio of peptide to heparin affected the release rate of NGF from the delivery system and the biological activity of NGF released. This study also explored whether peptide affinity modulated biological activity independent of release rate. Mathematically modeling the delivery system confirmed that release could be controlled by both peptide affinity and molar ratio of peptide to heparin. Experimentally, the rate of NGF release from the delivery system was found to be affected by peptide affinity and molar ratio. The delivery system presented biologically active NGF as assayed by embryonic chick dorsal root ganglia (DRGs) neurite extension, where extension was similar to or increased for DRGs grown in fibrin matrices containing the delivery system compared to DRGs grown with NGF in the culture media. Furthermore, by modulating the molar ratio of peptide to heparin in the delivery system, similar release rates of NGF were obtained for different affinity peptides and these conditions promoted similar levels of neurite extension, demonstrating that release rate appears to be the main mechanism controlling the biological activity of released NGF.

Growth Factors in the Tear Film: Role in Tissue Maintenance, Wound Healing, and Ocular Pathology

Numerous biologically active growth factors are secreted by the lacrimal gland and distributed via the tears over the ocular surface, where they affect cellular proliferation, migration, differentiation, and survival. The role of growth factors and their receptors in maintenance of tissue homeostasis and wound healing continues to be elucidated, and the effect of growth factor imbalances in ocular surface diseases is just beginning to be understood. For instance, in eyes with ocular surface diseases, including conjunctivitis, corneal erosion, keratitis, and corneal ulcers, epidermal growth factor release rates have been shown to be significantly lower than in normal eyes during reflex tearing. Future research into the mechanisms of dry eye disease will focus on reasons for decreased tear and growth factor production in the neuronal reflex loop or the acinar lacrimal gland cells. Animal models to test therapeutic approaches must be developed.

Matrix alteration and not residual sodium dodecyl sulfate cytotoxicity affects the cellular repopulation of a decellularized matrix

It has been suggested that residual cytotoxic sodium dodecyl sulfate (SDS) is responsible for the low levels of cell in-growth observed in SDS decellularized tissues. To determine whether this is the case, we used 2 washing methods to remove residual SDS and extensive biochemical, mechanical, and structural analyses to determine the effects of SDS-based decellularization on porcine anterior cruciate ligament (ACL) tissue and its propensity for cellular repopulation. The level of residual SDS in decellularized tissue was reduced using 2 different washing techniques (pH = 9 buffer, 75% ethanol). After washing in pH = 9 or 75% ethanol, residual SDS concentrations in decellularized tissues were found to be approximately 8 and 23 times less than reported SDS cytotoxic levels, respectively. It was found that SDS treatment significantly reduced glycosaminoglycan levels, increased collagen crimp amplitude and periodicity, and increased susceptibility of collagen to degradation by the gelatinase enzyme trypsin. The level of repopulation and viability of autologous ACL fibroblasts in the decellularized tissue after 28 days of culture were found to be the same regardless of the washing technique and resulting level of residual SDS in the tissue. This strongly indicates that alterations in tissue matrix biochemistry or structure from SDS treatment and not residual SDS cytotoxicity are responsible for the low cell re-population observed in SDS decellularized tissues.

Tailored release of TGF-β1 from porous scaffolds for cartilage tissue engineering

In view of cartilage tissue engineering, the possibility to prepare porous scaffolds releasing transforming growth factor-beta(1) (TGF-beta(1)) in a well controlled fashion was investigated by means of an emulsion-coating method. Poly(ether-ester) multiblock copolymers were used to prepare emulsions containing TGF-beta(1) which were subsequently applied onto prefabricated scaffolds. This approach resulted in defined porous structures (66%) with interconnected porosity, suitable to allow tissue ingrowth. The scaffolds were effectively associated with TGF-beta(1) and allowed to tailor precisely the release of the growth factor from 12 days to more than 50 days by varying the copolymer composition of the coating. An incomplete release was measured by ELISA, possibly linked to the rapid concentration decrease of the protein in solution. The released growth factor retained its biological activity as was assessed by a cell proliferation assay and by the ability of the released protein to induce chondrogenic differentiation of bone marrow-derived mesenchymal stem cells. However, exact bioactivity quantification was rendered difficult by the protein concentration decrease during storage. Therefore, this study confirms the interest of poly(ether-ester) multiblock copolymers for controlled release of growth factors, and indicates that emulsion-coated scaffolds are promising candidates for cartilage tissue engineering applications requiring precise TGF-beta(1) release rates.

Acellular biological tissues containing inherent glycosaminoglycans for loading basic fibroblast growth factor promote angiogenesis and tissue regeneration

It was found in our previous study that acellular tissues derived from bovine pericardia consist primarily of insoluble collagen, elastin, and tightly bound glycosaminoglycans (GAGs). It is speculated that the inherent GAGs in acellular tissues may serve as a reservoir for loading basic fibroblast growth factor (bFGF) and promote angiogenesis and tissue regeneration. This study was therefore designed to investigate effects of the content of GAGs in acellular bovine pericardia on the binding of bFGF and its release profile in vitro while its stimulation in angiogenesis and tissue regeneration in vivo were evaluated subcutaneously in a rat model. To control the content of GAGs, acellular tissues were treated additionally with hyaluronidase for 1 (Hase-D1), 3 (Hase-D3), or 5 days (Hase-D5). The in vitro results indicated that a higher content of GAGs in the acellular tissue resulted in an increase in bFGF binding and in a more gradual and sustained release of the growth factor. The in vivo results obtained at 1 week postoperatively showed that the density and the depth of neo-vessels infiltrated into the acellular tissue loaded with bFGF (acellular/bFGF) were significantly greater than the other test samples. At 1 month postoperatively, vascularized neo-connective tissues were found to fill the pores within each test sample, particularly for the acellular/bFGF tissue. These results suggested that the sustained release of bFGF from the acellular/ bFGF tissue continued to be effective in enhancing angiogenesis and generation of new tissues. In conclusion, the inherent GAGs present in acellular tissues may be used for binding and sustained release of bFGF to enhance angiogenesis and tissue regeneration.

Tissue-engineered valves with commissural alignment

We present a novel approach to producing bioartificial valves using the tissue-equivalent method of entrapping cells within a biopolymer gel and using a mold design that presents appropriate mechanical constraints to the cell-induced gel compaction to yield both the fibril alignment and the geometry of a native valve. Bileaflet valves were fabricated from bovine collagen and neonatal human dermal fibroblasts as proof of principle. The resultant valves possessed both commissure-tocommissure alignment of collagen fibers in the leaflets and circumferential alignment in the root. While this alignment was manifested in planar biaxial tensile mechanical properties, histology of the leaflets revealed an aligned collagen matrix but lacking other extracellular matrix (ECM) components present in the native valve. The apparent lack of ECM production by the fibroblasts after contracting and aligning the collagen fibrils is consistent with peak loads during biaxial testing being only approximately 10% of native leaflet values and a 0:1 coupling index that was only approximately 50% of native leaflet values despite exhibiting comparable values for the anisotropy index.

Effect of extraction protocols and epidermal growth factor on the cellular repopulation of decellularized anterior cruciate ligament allografts

We are developing a decellularized bone-anterior cruciate ligament (ACL)-bone allograft for treatment of ACL disruption in young or active patients. This study demonstrates the feasibility of seeding decellularized ACL tissue with primary ligament fibroblasts. Porcine ACLs were decellularized by one of three protocols, each differing only by the detergent/solvent used during the second wash (SDS, Triton-X, or TnBP). Porcine ACL fibroblasts were obtained by explant and seeded onto tissue samples of decellularized ACL. Culture conditions were varied to compare the relative effect of three different decellularization protocols on cellular repopulation. Culture condition variables included (1) the number of cells used for seeding, (2) the addition of epidermal growth factor (EGF), and (3) culture duration. Cellular ingrowth was assessed by metabolic activity (MTT assay), DNA quantification (Hoescht dye), and histology (H&E staining). Cell counting on histological sections demonstrated that Triton-X-and TnBP-treated ligaments were more receptive to cellular ingrowth than SDS-treated samples. The addition of EGF to culture medium did not significantly increase cellular ingrowth. Both the Triton-X and TnBP decellularization treatments provide suitable, naturally derived scaffolds for the ingrowth of primary ACL fibroblasts, and should be further investigated in the development of an allograft-derived bone-ACL-bone graft.

Delivery of basic fibroblast growth factor (bFGF) from photoresponsive hydrogel scaffolds

Exogenous growth factor therapy has shown a notable promise in accelerating the healing of acute and chronic wounds. However, their susceptibility to enzymatic degradation and short contact time with the wound bed warrant the use of sophisticated delivery vehicles that stabilize the encapsulated peptides and control their rate of release. Herein, we describe the synthesis of a nitrocinnamate-derived polyethylene glycol (PEG-NC) hydrogel system and study the release kinetics of basic fibroblast growth factor (bFGF) as a function of hydrogel properties. Long-wave ultraviolet irradiation (365 nm) was used to alter the physical properties of the gel scaffold (i.e. degree of swelling) and consequently control the release rates of the encapsulated bFGF. The degree of swelling (DS) decreased from 10.7 to 8 as the length of irradiation increased from 5 to 30 min. Similarly, the DS decreased from 17.5 to 11.5 by increasing the initial PEG-NC concentration from 10 to 30 w/v% while keeping the crosslinking irradiation at 10 min. Radiolabeled I(125) studies were used to monitor the release of bFGF from PEG-NC hydrogels with variable swellabilities. By increasing the length of irradiation from 2 to 10 min the rate of bFGF release from PEG-NC gel scaffolds was decreased by 29% due to the enhanced crosslinking density. The bFGF-releasing PEG-NC hydrogels were not cytotoxic to human neonatal fibroblast cells and the released growth factor maintained its activity and induced fibroblast proliferation and collagen production in vitro. The addition of heparin within the gel scaffolds further increased the growth factor's activity.

Effect of transforming growth factor-beta 1 (TGF-ß1) released from a scaffold on chondrogenesis in an osteochondral defect model in the rabbit

Articular cartilage repair might be stimulated by the controlled delivery of therapeutic factors. We tested the hypotheses whether TGF-ß1 can be released from a polymeric scaffold over a prolonged period of time in vitro and whether its transplantation modulates cartilage repair in vivo. Unloaded control or TGF-ß1 poly(ether-ester) copolymeric scaffolds were applied to osteochondral defects in the knee joints of rabbits. In vitro, a cumulative dose of 9 ng TGF-ß1 was released over 4 weeks. In vivo, there were no adverse effects on the synovial membrane. Defects treated with TGF-ß1 scaffolds showed no significant difference in individual parameters of chondrogenesis and in the average cartilage repair score after 3 weeks. There was a trend towards a smaller area (42.5 %) of the repair tissue that stained positive for safranin O in defects receiving TGF-ß1 scaffolds. The data indicate that TGF-ß1 is released from emulsion-coated scaffolds over a prolonged period of time in vitro and that application of these scaffolds does not significantly modulate cartilage repair after 3 weeks in vivo. Future studies need to address the importance of TGF-ß1 dose and release rate to modulate chondrogenesis.

Proliferation of Pulmonary Interstitial Fibroblasts Is Mediated by Transforming Growth Factor-β1-induced Release of Extracellular Fibroblast Growth Factor-2 and Phosphorylation of p38 MAPK and JNK

Idiopathic pulmonary fibrosis (IPF; a progressive lung disease) is characterized by parenchymal remodeling with enlarged air spaces called honeycomb cysts and palisades of fibroblasts called fibroblast foci. In IPF, lung epithelial cells covering honeycomb cysts and fibroblast foci aberrantly express the active conformation of the potent fibrogenic cytokine transforming growth factor-beta1 (TGF-beta1). Using explanted rat lung slices, we transfected alveolar epithelial cells with the retrovirus pMX containing a site-directed mutation in which Cys223 and Cys225 were substituted with serines, resulting in release of biologically active TGF-beta1 and fibroblast proliferation and remodeling that resembled IPF. Fibroblasts obtained from transfected explants and in culture for 6 weeks incorporated 6.59 +/- 1.55-fold more [3H]thymidine compared with control fibroblasts without transfection or fibroblasts obtained from transfected explants cultured with antibody to fibroblast growth factor-2 (FGF-2). Primary lung fibroblasts obtained from normal rat lungs cultured with TGF-beta1 expressed increased levels of phosphorylated p38 MAPK and JNK, but not ERK1/2. The presence of TGF-beta1 caused an immediate release of extracellular FGF-2 from primary pulmonary fibroblasts; and in the presence of anti-FGF-2 antibody, phosphorylated p38 MAPK and JNK were abrogated. TGF-beta inhibits cell proliferation by suppression of c-Myc and induction of p15INK46, p21CIP1, or p27KIP. Fibroblasts cultured with TGF-beta1 showed no regulation of c-Myc or induction of p15INK46, p21CIP1,or p27KIP. These findings suggest that pulmonary fibroblasts may not respond to the anti-proliferative effects of TGF-beta1, but proliferate in response to TGF-beta1 indirectly by the release of FGF-2, which induces phosphorylation of p38 MAPK and JNK.

Inductive tissue engineering with protein and DNA-releasing scaffolds

Cellular differentiation, organization, proliferation and apoptosis are determined by a combination of an intrinsic genetic program, matrix/substrate interactions, and extracellular cues received from the local microenvironment. These molecular cues come in the form of soluble (e.g. cytokines) and insoluble (e.g. ECM proteins) factors, as well as signals from surrounding cells that can promote specific cellular processes leading to tissue formation or regeneration. Recent developments in the field of tissue engineering have employed biomaterials to present these cues, providing powerful tools to investigate the cellular processes involved in tissue development, or to devise therapeutic strategies based on cell replacement or tissue regeneration. These inductive scaffolds utilize natural and/or synthetic biomaterials fabricated into three-dimensional structures. This review summarizes the use of scaffolds in the dual role of structural support for cell growth and vehicle for controlled release of tissue inductive factors, or DNA encoding for these factors. The confluence of molecular and cell biology, materials science and engineering provides the tools to create controllable microenvironments that mimic natural developmental processes and direct tissue formation for experimental and therapeutic applications.

Localized delivery of growth factors for bone repair

Delivery of growth factors for tissue (e.g. bone, cartilage) or cell repair (e.g. nerves) is about to gain important potential as a future therapeutic tool. Depending on the targeted cell type and its state of differentiation, growth factors can activate or regulate a variety of cellular functions. Therefore, strictly localized delivery regimens at well-defined kinetics appear to be logical prerequisites to assure safe and efficacious therapeutic use of such factors and avoid unwanted side effects and toxicity, a major hurdle in the clinical development of growth factor therapies so far. This review summarizes various approaches for localized growth factor delivery as focused on bone repair. Similar considerations may apply to other growth factors and therapeutic indications. Considering the vast number of preclinical studies reported in the area of growth factor-assisted bone repair, it surprises though that only two medical products for bone repair have so far been commercialized, both consisting of a collagen matrix impregnated with a bone morphogenetic protein. The marked diversity of the reported growth factors, delivery concepts and not yet standardized animal models adds to the complexity to learn from past preclinical studies presented in the literature. Nonetheless, it is now firmly established from the available information that the type, dose and delivery kinetics of growth factors all play a decisive role for the therapeutic success of any such approach. Very likely, all of these parameters have to be adapted and optimized for each animal model or clinical case. In the future, systems for localized growth factor delivery thus need to be designed in such a way that their modular components are readily adaptable to the individual pathology. To make such customized systems feasible, close cooperative networks of biomedical and biomaterials engineers, pharmaceutical scientists, chemists, biologists and clinicians need to be established.