Current treatment modalities for soft tissue augmentation which use autologous grafting and commercially available fillers present a number of challenges and limitations, such as donor site morbidity and volume loss over time. Adipose tissue engineering technology may provide an attractive alternative. This study investigated the feasibility of a degradable alginate hydrogel system with commercially available cryopreserved human adipose stem cells (hADSCs) to engineer adipose tissue. hADSCs were differentiated into adipogenic cells, and encapsulated in alginate hydrogels made susceptible to hydrolysis by partial periodate oxidation of the polymer chains. Cell laden gels were subcutaneously injected into the chest wall of male nude mice, and a cell suspension without alginate served as control. After 10 weeks, specimens were harvested and analyzed morphologically, histologically, and with immunoblotting of tissue extractions. Newly generated tissues were semitransparent and soft in all experimental mice, grossly resembling adipose tissue. Analysis using confocal live imaging, immunohistochemisty and western blot analysis revealed that the newly generated tissue was adipose tissue. This study demonstrates that degradable, injectable alginate hydrogels provide a suitable delivery vehicle for preconditioned cryopreserved hADSCs to engineer adipose tissue.
AIMS: Endurance training may be associated with arrhythmogenic cardiac remodelling of the right ventricle (RV). We examined whether myocardial dysfunction following intense endurance exercise affects the RV more than the left ventricle (LV) and whether cumulative exposure to endurance competition influences cardiac remodelling (including fibrosis) in well-trained athletes.
METHODS AND RESULTS: Forty athletes were studied at baseline, immediately following an endurance race (3-11 h duration) and 1-week post-race. Evaluation included cardiac troponin (cTnI), B-type natriuretic peptide, and echocardiography [including three-dimensional volumes, ejection fraction (EF), and systolic strain rate]. Delayed gadolinium enhancement (DGE) on cardiac magnetic resonance imaging (CMR) was assessed as a marker of myocardial fibrosis. Relative to baseline, RV volumes increased and all functional measures decreased post-race, whereas LV volumes reduced and function was preserved. B-type natriuretic peptide (13.1 ± 14.0 vs. 25.4 ± 21.4 ng/L, P = 0.003) and cTnI (0.01 ± .03 vs. 0.14 ± .17 μg/L, P < 0.0001) increased post-race and correlated with reductions in RVEF (r = 0.52, P = 0.001 and r = 0.49, P = 0.002, respectively), but not LVEF. Right ventricular ejection fraction decreased with increasing race duration (r = -0.501, P < 0.0001) and VO(2)max (r = -0.359, P = 0.011). Right ventricular function mostly recovered by 1 week. On CMR, DGE localized to the interventricular septum was identified in 5 of 39 athletes who had greater cumulative exercise exposure and lower RVEF (47.1 ± 5.9 vs. 51.1 ± 3.7%, P = 0.042) than those with normal CMR.
CONCLUSION: Intense endurance exercise causes acute dysfunction of the RV, but not the LV. Although short-term recovery appears complete, chronic structural changes and reduced RV function are evident in some of the most practiced athletes, the long-term clinical significance of which warrants further study.
Lymph node stromal cells (LNSCs) closely regulate immunity and self-tolerance, yet key aspects of their biology remain poorly elucidated. Here, comparative transcriptomic analyses of mouse LNSC subsets demonstrated the expression of important immune mediators, growth factors and previously unknown structural components. Pairwise analyses of ligands and cognate receptors across hematopoietic and stromal subsets suggested a complex web of crosstalk. Fibroblastic reticular cells (FRCs) showed enrichment for higher expression of genes relevant to cytokine signaling, relative to their expression in skin and thymic fibroblasts. LNSCs from inflamed lymph nodes upregulated expression of genes encoding chemokines and molecules involved in the acute-phase response and the antigen-processing and antigen-presentation machinery. Poorly studied podoplanin (gp38)-negative CD31(-) LNSCs showed similarities to FRCs but lacked expression of interleukin 7 (IL-7) and were identified as myofibroblastic pericytes that expressed integrin α(7). Together our data comprehensively describe the transcriptional characteristics of LNSC subsets.
Alginate is a biomaterial that has found numerous applications in biomedical science and engineering due to its favorable properties, including biocompatibility and ease of gelation. Alginate hydrogels have been particularly attractive in wound healing, drug delivery, and tissue engineering applications to date, as these gels retain structural similarity to the extracellular matrices in tissues and can be manipulated to play several critical roles. This review will provide a comprehensive overview of general properties of alginate and its hydrogels, their biomedical applications, and suggest new perspectives for future studies with these polymers.
Complications in treatment of large bone defects using bone grafting still remain. Our understanding of the endogenous bone regeneration cascade has inspired the exploration of a wide variety of growth factors (GFs) in an effort to mimic the natural signaling that controls bone healing. Biomaterial-based delivery of single exogenous GFs has shown therapeutic efficacy, and this likely relates to its ability to recruit and promote replication of cells involved in tissue development and the healing process. However, as the natural bone healing cascade involves the action of multiple factors, each acting in a specific spatiotemporal pattern, strategies aiming to mimic the critical aspects of this process will likely benefit from the usage of multiple therapeutic agents. This article reviews the current status of approaches to deliver single GFs, as well as ongoing efforts to develop sophisticated delivery platforms to deliver multiple lineage-directing morphogens (multiple GFs) during bone healing.
Hydrogels are used as scaffolds for tissue engineering, vehicles for drug delivery, actuators for optics and fluidics, and model extracellular matrices for biological studies. The scope of hydrogel applications, however, is often severely limited by their mechanical behaviour. Most hydrogels do not exhibit high stretchability; for example, an alginate hydrogel ruptures when stretched to about 1.2 times its original length. Some synthetic elastic hydrogels have achieved stretches in the range 10-20, but these values are markedly reduced in samples containing notches. Most hydrogels are brittle, with fracture energies of about 10 J m(-2) (ref. 8), as compared with ∼1,000 J m(-2) for cartilage and ∼10,000 J m(-2) for natural rubbers. Intense efforts are devoted to synthesizing hydrogels with improved mechanical properties; certain synthetic gels have reached fracture energies of 100-1,000 J m(-2) (refs 11, 14, 17). Here we report the synthesis of hydrogels from polymers forming ionically and covalently crosslinked networks. Although such gels contain ∼90% water, they can be stretched beyond 20 times their initial length, and have fracture energies of ∼9,000 J m(-2). Even for samples containing notches, a stretch of 17 is demonstrated. We attribute the gels' toughness to the synergy of two mechanisms: crack bridging by the network of covalent crosslinks, and hysteresis by unzipping the network of ionic crosslinks. Furthermore, the network of covalent crosslinks preserves the memory of the initial state, so that much of the large deformation is removed on unloading. The unzipped ionic crosslinks cause internal damage, which heals by re-zipping. These gels may serve as model systems to explore mechanisms of deformation and energy dissipation, and expand the scope of hydrogel applications.
Injectable biomaterials are increasingly being explored to minimize risks and complications associated with surgical implantation. We describe a strategy for delivery via conventional needle-syringe injection of large preformed macroporous scaffolds with well-defined properties. Injectable 3D scaffolds, in the form of elastic sponge-like matrices, were prepared by environmentally friendly cryotropic gelation of a naturally sourced polymer. Cryogels with shape-memory properties may be molded to a variety of shapes and sizes, and may be optionally loaded with therapeutic agents or cells. These scaffolds have the capability to withstand reversible deformations at over 90% strain level, and a rapid volumetric recovery allows the structurally defined scaffolds to be injected through a small-bore needle with nearly complete geometric restoration once delivered. These gels demonstrated long-term release of biomolecules in vivo. Furthermore, cryogels impregnated with bioluminescent reporter cells provided enhanced survival, higher local retention, and extended engraftment of transplanted cells at the injection site compared with a standard injection technique. These injectable scaffolds show great promise for various biomedical applications, including cell therapies.
The clinical potential of short interfering RNA (siRNA) based therapeutics remains hindered by the challenge of delivering enough siRNA into the cytoplasm to yield a clinically relevant effect. Although much research has focused on optimizing delivery vehicles for this class of molecules, considerably less is known about the microenvironmental influences on the response of target cells to siRNA. The substrate to which cells adhere is one component of the microenvironment that can modulate cellular behavior. Here, we tested the hypothesis that modulating the properties of cellular adhesion substrates can alter siRNA efficacy. Specifically, cationic lipid complexed siRNA particles were applied to U251 cells seeded on alginate hydrogel surfaces with systematic variation in elastic modulus and integrin ligand arginine-glycine-aspartate (RGD) peptide density. These experiments revealed no change in siRNA-mediated eGFP knockdown over the elastic modulus range tested (53-133 kPa). However, an eightfold increase in RGD content of the alginate growth substrate resulted in an increase in siRNA knockdown efficacy from 25 ± 12% to 52 ± 10%, a more than twofold increase in silencing. Our results identify control of the cell-adhesion substrate interaction as a modulator of siRNA protein silencing efficacy.
Many biological processes, including angiogenesis, involve intercellular feedback and temporal coordination, but inference of these relations is often drowned in low sample sizes or noisy population data. To address this issue, a methodology was developed to statistically study spatial lateral inhibition and temporal synchronization in one specific biological process, endothelial sprouting mediated by Notch signaling. Notch plays an essential role in the development of organized vasculature, but the effects of Notch on the temporal characteristics of angiogenesis are not well understood. Results from this study showed that Notch lateral inhibition operates at distances less than 31 μm. Furthermore, combining time lapse microscopy with an intraclass correlation model typically used to analyze family data showed intrinsic temporal synchronization among endothelial sprouts originating from the same microcarrier. Such synchronization was reduced with Notch inhibitors, but was enhanced with the addition of Notch ligands. These results indicate that Notch plays a critical role in the temporal regulation of angiogenesis, as well as spatial control, and this method of analysis will be of significant utility in studies of a variety of other biological processes.
Poly(ethylene) glycol is commonly used to stabilize gold nanoparticles (GNPs). In this study, we evaluated the ability of cysteine-functionalized alginate-derived polymers to both provide colloidal stability to GNPs and avoid recognition and sequestration by the body's defense system. These polymers contain multiple reactive chemical groups (hydroxyl and carboxyl groups) that could allow for ready functionalization with, for example, cell-targeting ligands and therapeutic drugs. We report here that alginate-coupled GNPs demonstrate enhanced stability in comparison with bare citrate-coated GNPs and a similar lack of interaction with proteins in vitro and long in vivo circulation as PEG-coated GNPs.
Porous biomaterials have been widely used as scaffolds in tissue engineering and cell-based therapies. The release of biological agents from conventional porous scaffolds is typically governed by molecular diffusion, material degradation, and cell migration, which do not allow for dynamic external regulation. We present a new active porous scaffold that can be remotely controlled by a magnetic field to deliver various biological agents on demand. The active porous scaffold, in the form of a macroporous ferrogel, gives a large deformation and volume change of over 70% under a moderate magnetic field. The deformation and volume variation allows a new mechanism to trigger and enhance the release of various drugs including mitoxantrone, plasmid DNA, and a chemokine from the scaffold. The porous scaffold can also act as a depot of various cells, whose release can be controlled by external magnetic fields.
The treatment of challenging fractures and large osseous defects presents a formidable problem for orthopaedic surgeons. Tissue engineering/regenerative medicine approaches seek to solve this problem by delivering osteogenic signals within scaffolding biomaterials. In this study, we introduce a hybrid growth factor delivery system that consists of an electrospun nanofiber mesh tube for guiding bone regeneration combined with peptide-modified alginate hydrogel injected inside the tube for sustained growth factor release. We tested the ability of this system to deliver recombinant bone morphogenetic protein-2 (rhBMP-2) for the repair of critically-sized segmental bone defects in a rat model. Longitudinal μ-CT analysis and torsional testing provided quantitative assessment of bone regeneration. Our results indicate that the hybrid delivery system resulted in consistent bony bridging of the challenging bone defects. However, in the absence of rhBMP-2, the use of nanofiber mesh tube and alginate did not result in substantial bone formation. Perforations in the nanofiber mesh accelerated the rhBMP-2 mediated bone repair, and resulted in functional restoration of the regenerated bone. μ-CT based angiography indicated that perforations did not significantly affect the revascularization of defects, suggesting that some other interaction with the tissue surrounding the defect such as improved infiltration of osteoprogenitor cells contributed to the observed differences in repair. Overall, our results indicate that the hybrid alginate/nanofiber mesh system is a promising growth factor delivery strategy for the repair of challenging bone injuries.
PURPOSE: The prognosis for glioma patients is poor, and development of new treatments is critical. Previously, we engineered polymer-based vaccines that control GM-CSF, CpG-oligonucleotide, and tumor-lysate presentation to regulate immune cell trafficking and activation, which promoted potent immune responses against peripheral tumors. Here, we extend the use of this system to glioma.
METHODS: Rats were challenged with an intracranial injection of glioma cells followed (1 week) by administration of the polymeric vaccine (containing GM-CSF, CpG, and tumor-lysate) in the tumor bed. Control rats were treated with blank matrices, matrices with GM-CSF and CpG, or intra-tumoral bolus injections of GM-CSF, CpG, and tumor lysate. Rats were monitored for survival and tested for neurological function.
RESULTS: Survival studies confirmed a benefit of the polymeric vaccine as 90% of vaccinated rats survived for > 100 days. Control rats exhibited minimal benefit. Motor tests revealed that vaccination protected against the loss of forelimb use produced by glioma growth. Histological analysis quantitatively confirmed a robust and rapid reduction in tumor size. Long-term immunity was confirmed when 67% of survivors also survived a second glioma challenge.
CONCLUSIONS: These studies extend previous reports regarding this approach to tumor therapy and justify further development for glioma treatment.
PURPOSE: There is evolving evidence that intense exercise may place a disproportionate load on the right ventricle (RV) when compared with the left ventricle (LV) of the heart. Using a novel method of estimating end-systolic wall stress (ES-σ), we compared the RV and LV during exercise and assessed whether this influenced chronic ventricular remodeling in athletes.
METHODS: For this study, 39 endurance athletes (EA) and 14 nonathletes (NA) underwent resting cardiac magnetic resonance (CMR), maximal oxygen uptake (VO2), and exercise echocardiography studies. LV and RV end-systolic wall stress (ES-σ) were calculated using the Laplace relation (ES-σ = Pr/(2h)). Ventricular size and wall thickness were determined by CMR; invasive and Doppler echo estimates were used to measure systemic and pulmonary ventricular pressures, respectively; and stroke volume was quantified by Doppler echocardiography and used to calculate changes in ventricular geometry during exercise.
RESULTS: In EA, compared with NA, resting CMR measures showed greater RV than LV remodeling. The ratios RV ESV/LV ESV (1.40 ± 0.23 vs 1.26 ± 0.12, P = 0.007) and RV mass/LV mass (0.29 ± 0.04 vs 0.25 ± 0.03, P = 0.012) were greater in EA than in NA. RVES-σ was lower at rest than LVES-σ (143 ± 44 vs 252 ± 49 kdyn · cm, P < 0.001) but increased more with strenuous exercise (125% vs 14%, P < 0.001), resulting in similar peak exercise ES-σ (321 ± 106 vs 286 ± 77 kdyn · cm, P = 0.058). Peak exercise RVES-σ was greater in EA than in NA (340 ± 107 vs 266 ± 82 kdyn · cm, P = 0.028), whereas RVES-σ at matched absolute workloads did not differ (P = 0.79).
CONCLUSIONS: Exercise induces a relative increase in RVES-σ which exceeds LVES-σ. In athletes, greater RV enlargement and greater wall thickening may be a product of this disproportionate load excess.
We previously engineered a macroporous, polymer-based vaccine that initially produces GM-CSF gradients to recruit local dendritic cells and subsequently presents CpG oligonucleotides, and tumor lysate to cell infiltrates to induce immune cell activation and immunity against tumor cells in peripheral tumor models. Here, we demonstrate that this system eradicates established intracranial glioma following implantation into brain tissue, whereas implantation in resection cavities obviates vaccine efficacy. Rats bearing seven-day old, intracranial glioma tumors were treated with PLG vaccines implanted into the tumor bed, resulting in retention of contralateral forelimb function (day 17) that is compromised by tumor formation in control animals, and 90% long-term survival (>100 days). Similar benefits were observed in animals receiving tumor resection plus vaccine implants into the adjacent parenchyma, but direct implantation of PLG vaccines into the resection cavity conferred no benefit. This dissociation of efficacy was likely related to GM-CSF distribution, as implantation of PLG vaccines within brain tissue produced significant GM-CSF gradients for prolonged periods, which was not detected after implantation in resection cavities. These studies demonstrate that PLG vaccine efficacy is correlated to GM-CSF gradient formation, which requires direct implantation into brain tissue, and justify further exploration of this approach for glioma treatment.
Osteogenic growth factors that promote endogenous repair mechanisms hold considerable potential for repairing challenging bone defects. The local delivery of one such growth factor, bone morphogenetic protein (BMP), has been successfully translated to clinical practice for spinal fusion and bone fractures. However, improvements are needed in the spatial and temporal control of BMP delivery to avoid the currently used supraphysiologic doses and the concomitant adverse effects. We have recently introduced a hybrid protein delivery system comprised of two parts: a perforated nanofibrous mesh that spatially confines the defect region and a functionalized alginate hydrogel that provides temporal growth factor release kinetics. Using this unique spatiotemporal delivery system, we previously demonstrated BMP-mediated functional restoration of challenging 8mm femoral defects in a rat model. In this study, we compared the efficacy of the hybrid system in repairing segmental bone defects to that of the current clinical standard, collagen sponge, at the same dose of recombinant human BMP-2. In addition, we investigated the specific role of the nanofibrous mesh tube on bone regeneration. Our results indicate that the hybrid delivery system significantly increased bone regeneration and improved biomechanical function compared to collagen sponge delivery. Furthermore, we observed that presence of the nanofiber mesh tube was essential to promote maximal mineralized matrix synthesis, prevent extra-anatomical mineralization, and guide an integrated pattern of bone formation. Together, these results suggest that spatiotemporal strategies for osteogenic protein delivery may enhance clinical outcomes by improving localized protein retention.
Oral Diseases (2011) 17, 241-251 The rapid advancement in basic biology knowledge, especially in the stem cell field, has created new opportunities to develop biomaterials capable of orchestrating the behavior of transplanted and host cells. Based on our current understanding of cellular differentiation, a conceptual framework for the use of materials to program cells in situ is presented, namely a domino vs a switchboard model, to highlight the use of single vs multiple cues in a controlled manner to modulate biological processes. Further, specific design principles of material systems to present soluble and insoluble cues that are capable of recruiting, programming and deploying host cells for various applications are presented. The evolution of biomaterials from simple inert substances used to fill defects, to the recent development of sophisticated material systems capable of programming cells in situ is providing a platform to translate our understanding of basic biological mechanisms to clinical care.
The identification and production of recombinant morphogens and growth factors that play key roles in tissue regeneration have generated much enthusiasm and numerous clinical trials, but the results of many of these trials have been largely disappointing. Interestingly, the trials that have shown benefit all contain a common denominator, the presence of a material carrier, suggesting strongly that spatio-temporal control over the location and bioactivity of factors after introduction into the body is crucial to achieve tangible therapeutic effect. Sophisticated materials systems that regulate the biological presentation of growth factors represent an attractive new generation of therapeutic agents for the treatment of a wide variety of diseases. This review provides an overview of growth factor delivery in tissue engineering. Certain fundamental issues and design strategies relevant to the material carriers that are being actively pursued to address specific technical objectives are discussed. Recent progress highlights the importance of materials science and engineering in growth factor delivery approaches to regenerative medicine.
Congrats to David and team on their recent publication in Nature Communications! Here, they utilized antigen presenting cell-mimetic scaffolds to tune CAR T-cell product functionality by controlling the precise level of stimulation during T-cell activation to accommodate individual differences in the donor cells. Check out the publication here: Enhancing CAR-T cell functionality in a patient-specific manner