Anti-VEGF antibody delivered locally reduces bony bar formation following physeal injury in rats.

Physeal injuries can result in the formation of a "bony bar" which can lead to bone growth arrest and deformities in children. Vascular endothelial growth factor (VEGF) has been shown to play a role in bony bar formation, making it a potential target to inhibit bony repair tissue after physeal injury. The goal of this study was to investigate whether the local delivery of anti-VEGF antibody (α-VEGF; 7.5 µg) from alginate:chitosan hydrogels to the tibial physeal injury site in rats prevents bony bar formation. We tested the effects of quick or delayed delivery of α-VEGF using both 90:10 and 50:50 ratio alginate:chitosan hydrogels, respectively. Male and female 6-week-old Sprague-Dawley rats received a tibial physeal injury and the injured site injected with alginate-chitosan hydrogels: (1) 90:10 (Quick Release); (2) 90:10 + α-VEGF (Quick Release + α-VEGF); (3) 50:50 (Slow Release); (4) 50:50 + α-VEGF (Slow Release + α-VEGF); or (5) Untreated. At 2, 4, and 24 weeks postinjury, animals were euthanized and tibiae assessed for bony bar and vessel formation, repair tissue type, and limb lengthening. Our results indicate that Quick Release + α-VEGF reduced bony bar and vessel formation, while also increasing cartilage repair tissue. Further, the quick release of α-VEGF neither affected limb lengthening nor caused deleterious side-effects in the adjacent, uninjured physis. This α-VEGF treatment, which inhibits bony bar formation without interfering with normal bone elongation, could have positive implications for children suffering from physeal injuries.

In vivo degradation rate of alginate-chitosan hydrogels influences tissue repair following physeal injury.

The physis is a cartilaginous tissue in children's long bones that is responsible for bone elongation. Physeal injuries can heal with bony repair tissue known as a "bony bar," and this can cause growth deformities. Current treatments involve surgical resection of the bony bar and insertion of inert materials in hopes of preventing bony bar re-formation and preserving bone elongation. However, these materials frequently fail and the bony bar commonly returns. This study investigated alginate-chitosan hydrogels as interpositional materials to block bony bar formation in a rat model of physeal injury. Further, biomaterial properties such as substrate stiffness, permeability, and degradation rate were studied. Different ratio alginate:chitosan hydrogels with or without calcium cross-linking were tested for their inhibition of bony bar formation and restoration of the injured physis. Alginate:chitosan were mixed (a) 90:10 with calcium (90:10 + Ca); (b) 50:50 with calcium (50:50 + Ca); (c) 50:50 without calcium (50:50 - Ca); and (d) 50:50 made with irradiated alginate (IA) and without calcium. We found that repair tissue was determined primarily by the in vivo degradation rate of alginate-chitosan hydrogels. 90:10 + Ca had a slow degradation rate, prevented cellular infiltration, and produced the most bony bar tissue while having softer, more permeable material properties. IA had the fastest degradation, showed high cellular infiltration, and produced the most cartilage-like tissue while having stiffer, less permeable material properties. Our results suggest that the in vivo biomaterial degradation rate is a dynamic property that can be optimized to influence cell fate and tissue repair in physeal injuries.

Sustained delivery of anti-VEGF from injectable hydrogel systems provides a prolonged decrease of endothelial cell proliferation and angiogenesis in vitro.

Therapeutic antibodies are attractive treatment options for numerous diseases based on their ability to target and bind to specific proteins or antigens. Bevacizumab, an antiangiogenic antibody, has shown promise for multiple diseases, including various cancers and macular degeneration, where excessive VEGF secretion induces aberrant angiogenesis. In many cases local, sustained delivery of a therapeutic antibody would be preferable to maximize the therapeutic at the disease site, eliminate the need for repeated doses, and reduce systemic side effects. The biodegradable polysaccharides alginate and chitosan can electrostatically interact to form a polyelectrolyte complex (PEC), and have proved effective as a carrier for controlled release of antibodies. In this work, an alginate-chitosan PEC system was designed to produce targeted 30-day delivery of non-specific IgG and anti-VEGF antibodies. The release of anti-VEGF was slow relative to IgG release, suggesting that release rate is antibody specific and is based on the interactions of the PEC with charges present on the antibody surface. The anti-VEGF released from the PEC was shown to successfully inhibit VEGF-induced proliferation and angiogenesis in vitro throughout the 30-day test period.

Correction: Sustained delivery of anti-VEGF from injectable hydrogel systems provides a prolonged decrease of endothelial cell proliferation and angiogenesis in vitro.

[This corrects the article DOI: 10.1039/C7RA13014G.].

Cell-interactive alginate-chitosan biopolymer systems with tunable mechanics and antibody release rates.

This work investigates techniques to produce biocompatible hydrogels with tunable stiffness without the addition of crosslinking agents or altering cell binding sites. Alginate and water-soluble chitosan salts were used to form polyelectrolyte complexes (PECs), where the storage and loss moduli could be increased by raising gelation temperatures. The largest change, a 6.5-fold increase in storage modulus, occurred when the crosslinking temperature was increased from 37 to 50°C while using chitosan with chlorine counterions. Osteogenic MC3T3 cells were shown to have significantly higher proliferation on the stiffer PECs prepared at 50°C compared to 37°C. Gelation temperature showed minimal effect on antibody release, but the inclusion of CaSO4 provided a longer overall release where the rate was nearly linear for several weeks. However, CaSO4 inhibited the strengthening effect of increased gelation temperature. PECs containing glutamate counterions demonstrated an increase in stiffness with decreased chitosan content.

Comparative Study of Poly (ε-Caprolactone) and Poly(Lactic-co-Glycolic Acid) -Based Nanofiber Scaffolds for pH-Sensing.

PURPOSE: This study aims to develop biodegradable and biocompatible polymer-based nanofibers that continuously monitor pH within microenvironments of cultured cells in real-time. In the future, these fibers will provide a scaffold for tissue growth while simultaneously monitoring the extracellular environment. METHODS: Sensors to monitor pH were created by directly electrospinning the sensor components within a polymeric matrix. Specifically, the entire fiber structure is composed of the optical equivalent of an electrode, a pH-sensitive fluorophore, an ionic additive, a plasticizer, and a polymer to impart mechanical stability. The resulting poly(ε-caprolactone) (PCL) and poly(lactic-co-glycolic acid) (PLGA) based sensors were characterized by morphology, dynamic range, reversibility and stability. Since PCL-based nanofibers delivered the most desirable analytical response, this matrix was used for cellular studies. RESULTS: Electrospun nanofiber scaffolds (NFSs) were created directly out of optode material. The resulting NFS sensors respond to pH changes with a dynamic range centered at 7.8 ± 0.1 and 9.6 ± 0.2, for PCL and PLGA respectively. NFSs exhibited multiple cycles of reversibility with a lifetime of at least 15 days with preservation of response characteristics. By comparing the two NFSs, we found PCL-NFSs are more suitable for pH sensing due to their dynamic range and superior reversibility. CONCLUSION: The proposed sensing platform successfully exhibits a response to pH and compatibility with cultured cells. NSFs will be a useful tool for creating 3D cellular scaffolds that can monitor the cellular environment with applications in fields such as drug discovery and tissue engineering.

Controlled delivery of antibodies from injectable hydrogels.

Therapeutic antibodies are currently used for the treatment of various diseases, but large doses delivered systemically are typically required. Localized controlled delivery techniques would afford major benefits such as decreasing side effects and required doses. Injectable biopolymer systems are an attractive solution due to their minimally invasive potential for controlled release in a localized area. Here, alginate-chitosan hydrogels are demonstrated to provide controlled delivery of IgG model antibodies and also of Fab antibody fragments. Also, an alternate delivery system comprised of poly(lactic-co-glycolic acid) (PLGA) microspheres loaded with antibodies and encapsulated in alginate was shown to successfully provide another level of control over release. These biopolymer systems that offer controlled delivery for antibodies and antibody fragments will be promising for many applications in drug delivery and regenerative medicine.