Enhancing the Functionality of Trabecular Allografts Through Polymeric Coating for Factor Loading

Event Abstract Back to Event Molecularly regulated release of growth factors from programmable hydrogels for angiogenesis Yong Wang1*, Nan Zhao1, Xiaolong Zhang1*, Li-Juan Duan2* and Guo-Hua Fong2* 1 Penn State University, Department of Biomedical Engineering, United States 2 UConn Health Center, Center for Vascular Biology, United States Introduction: Vascularization is important to treatment of ischemic diseases and survival of tissue-engineered constructs[1]. Delivery of growth factors is a promising strategy for vascularization. However, polymeric systems for growth factor delivery face several challenges including denaturation of growth factors, difficulty of controlling growth factor release kinetics, and/or lack of macroporous structures for cell growth[2]. The purpose of this work was to demonstrate that oligonucleotide aptamers and macroporous hydrogels could be used to develop a multifunctional biomaterial with great potential of overcoming all of these challenges. Materials and Methods: The multifunctional hydrogel was synthesized in a cylindrical mold with free radical polymerization and gas formation[3]. The key components in the pregel solution were oligonucleotide aptamers and acrylated gelatin that were incorporated into the hydrogel during the polymerization. The incorporation efficiency was determined by protein and oligonucleotide staining assays. The hydrogel was thoroughly washed to remove unreacted monomers and immersed in solution with VEGF and PDGF-BB for growth factor sequestration. The kinetics of growth factor release was examined using ELISA. The bioactivity of released or retained growth factors was measured using the standard HUVEC tube formation assay. To demonstrate directly the ability of this new hydrogel in promoting angiogenesis, the hydrogels with growth factors were subcutaneously implanted into a mouse model. The hydrogels were collected and analyzed after 4-week implantation. Endothelial cell surface biomarker CD31 was stained to examine populated vascular lumens in the hydrogels and tissues adjacent to the hydrogels. Results and Discussion: Macroporous hydrogels were successfully synthesized with free radical polymerization coupled with gas formation. The SEM images show that macroporous structures had an average pore diameter of 50 microns (Figure 1a). Both aptamers and gelatin were efficiently incorporated into the hydrogel network. Importantly, growth factors could be rapidly sequestered into the hydrogel network. When the superporous hydrogels were immersed into release media, aptamers effectively reduced the burst release effect and prolonged the growth factor release with desired kinetics. Moreover, the released and retained growth factors maintained high bioactivity (Figure 1b). For instance, at the end of two weeks, VEGF could maintain ~50% bioactivity that is much higher than the data reported in the literature. The animal studies showed that the multifunctional hydrogel stimulated angiogenesis much more effectively than the control hydrogels without aptamers (Figure 1c). Conclusions: Aptamer-functionalized hydrogels are a promising multifunctional biomaterial for controlled growth factor release. They hold great potential to stimulate vascularization for treatment of ischemic diseases or enhance survival of tissue-engineered constructs. U.S. NSF CAREER program under award number DMR-1332351; the National Heart, Lung, and Blood Institute of the NIH under award number R01HL122311

Protein growth factors have demonstrated great potential for tissue repair, but their inherent instability and large size prevents meaningful presentation to biologically protected nervous tissue. Here, we create a nanofibrous network from a self-assembling peptide (SAP) hydrogel to carry and stabilize the growth factors. We significantly reduced growth factor degradation to increase their lifespan by over 40 times. To control the temporal release profile we covalently attached polysaccharide chitosan molecules to the growth factor to increase its interactions with the hydrogel nanofibers and achieved a 4 h delay, demonstrating the potential of this method to provide temporally controlled growth factor delivery. We also describe release rate based analysis to examine the growth factor delivery in more detail than standard cumulative release profiles allow and show that the chitosan attachment method provided a more consistent release profile with a 60% reduction in fluctuations. To prove the potential of this system as a complex growth factor delivery platform we demonstrate for the first time temporally distinct release of multiple growth factors from a single tissue specific SAP hydrogel: a significant goal in regenerative medicine.

Dual release of growth factor from nanocomposite fibrous scaffold promotes vascularisation and bone regeneration in rat critical sized calvarial defect

Nanoparticle-Coated Sutures Providing Sustained Growth Factor Delivery to Improve the Healing Strengths of Injured Tendons

How does the pathophysiological context influence delivery of bone growth factors?

The purposes of this study were: to review studies of growth factors in cutaneous wounds of animals with diabetes to identify those factors with altered gene expression and content compared with nondiabetic animals; and to explore which deficiencies of growth factors in diabetic wounds may or may not be improved by laser irradiation. Wound healing is compromised in diabetes. Decreased production and/or increased destruction of growth factors may be responsible. Laser irradiation can increase the gene expression and release of certain growth factors by cells. Research articles investigating growth factor expression in wounds of nondiabetic and diabetic mice and rats published through September 2011 were retrieved from library sources, PubMed databases, reference lists of articles, and searches of relevant journals. Vascular endothelial growth factor (VEGF), placental growth factor (PlGF), keratinocyte growth factor (KGF), fibroblast growth factor 1 (FGF-1), FGF-2, insulin-like growth factor 1 (IGF-1), IGF-2, transforming growth factor beta (TGF-β), and nerve growth factor (NGF) had decreased gene expression and content in early phases of healing for diabetic wounds. Gene expression of KGF, IGF-1, and IGF-2 was delayed, whereas that of FGF-1 and FGF-2 occurred earlier, in diabetic compared with nondiabetic wounds. Growth factor administration combined with laser irradiation may provide an effective therapy to maximize healing of diabetic wounds.

Design of a composite biomaterial system for tissue engineering applications

Biomaterials based growth factor delivery for brain regeneration after injury

Emerging growth factor delivery hydrogel system for wound healing

Spatially-directed cell migration in acoustically-responsive scaffolds through the controlled delivery of basic fibroblast growth factor

Regenerating large bone defects requires a multifaceted approach combining optimal scaffold designs with appropriate growth factor delivery. Supraphysiological doses of recombinant human bone morphogenetic protein 2 (rhBMP2), typically used for the regeneration of large bone defects clinically in conjunction with an acellular collagen sponge (ACS), have resulted in many complications. In this study, we develop a hydroxyapatite/collagen I (HA/Col) scaffold to improve the mechanical properties of the HA scaffolds, while maintaining open connected porosity. Varying rhBMP2 dosages were then delivered from a collagenous periosteal membrane and paired with HA or HA/Col scaffolds to treat critical-sized (15 mm) diaphyseal radial defect in New Zealand white rabbits. The groups examined were ACS +76 μg rhBMP2 (clinically used INFUSE dosage), HA +76 μg rhBMP2, HA +15 μg rhBMP2, HA/Col +15 μg rhBMP2, and HA/Col +15 μg rhBMP2 + bone marrow-derived stromal cells (bMSCs). After 8 weeks of implantation, all regenerated bones were evaluated using microcomputed tomography, histology, histomorphometry, and torsional testing. It was observed that the bone volume regenerated in the HA/Col +15 μg rhBMP2 group was significantly higher than that in the groups with 76 μg rhBMP2. The same scaffold and growth factor combination resulted in the highest bone mineral density of the regenerated bone, and the most bone apposition on the scaffold surface. Both the HA and HA/Col scaffolds paired with 15 μg rhBMP2 had sustained ingrowth of the mineralization front after 2 weeks compared to the groups with 76 μg rhBMP2, which had far greater mineralization in the first 2 weeks after implantation. Complete bridging of the defect site and no significant difference in torsional strength, stiffness, or angle at failure were observed across all groups. No benefit of additional bMSC seeding was observed on any of the quantified metrics, while bone-implant apposition was reduced in the cell-seeded group. This study demonstrated that the controlled spatial delivery of rhBMP2 at the periosteum at significantly lower doses can be used as a strategy to improve bone regeneration around space maintaining scaffolds. Tweet Inside-out or outside-in: growth factors delivered from the outside of porous mineral-collagen scaffolds, maintain strength and regrow bone better in a rabbit study. Twitter handle for senior author (@Guda_Lab) and sponsoring institution (@UTSA) Impact Statement This study provides insights on bone regeneration in the presence of spatially controlled delivery of recombinant human bone morphogenetic protein 2 (rhBMP2) from porous hydroxyapatite scaffolds coated with collagen I films. Using critical-sized defects created in the radial diaphysis of skeletally mature New Zealand White rabbits, microcomputed tomography and histomorphometry indicated significantly higher bone regeneration, bone mineral density, and bone-implant contact, as well as sustained regeneration over longer durations with lower dosage of rhBMP2 delivered periosteally.

Controlled release of nerve growth factor from a heparin-containing fibrin-based cell ingrowth matrix

Growth factor delivery using extracellular matrix-mimicking substrates for musculoskeletal tissue engineering and repair

Introduction Traditionally tissue engineering entails the seeding and culturing of differentiated somatic cells onto biodegradable scaffolds, with subsequent implantation of the cell–scaffold constructs into the defective or damaged sites to regenerate tissues [1]. In this approach, the scaffold acts as a three-dimensional (3D) framework to provide physical support and accommodate cell growth and deposition of extracellular matrices, and its biodegradability allows the scaffold material to be resorbed in pace with new tissue formation. Despite some encouraging successes in clinical trials [2, 3], two key limitations with this approach include the limited source of exogenous donor cells and the lack of adequate vascularity to maintain vitality of the newly regenerated tissues. To address these limitations, current advanced tissue engineering techniques gear toward harnessing a biomimetic scaffold that provides a synthetic regenerative microenvironment to support natural tissue regeneration and angiogenesis [4]. In addition to providing physical support, the ideal biomimetic scaffold would preferably also deliver bioactive factors, which instruct endogenous stem cell recruitment and differentiation three-dimensionally and in a controlled manner [5] (Figure 20.1). Various bioactive factors, including growth factors [6–8], nucleic acids [9], and integrin-binding ligands [10], have successfully been delivered or presented on biodegradable scaffolds. Among these, growth factors are the most important soluble signals in the natural regenerative microenvironment, being actively involved in stem cell recruitment, proliferation, and differentiation, angiogenesis, and tissue morphogenesis. Although they are potent, growth factors are expensive and have short half-lives in vivo. Therefore, scaffolds with controlled-release capacity are desired in order to preserve growth factor bioactivity and to prolong their function at therapeutic levels over an extended time period. However, there remain significant challenges in delivering growth factors effectively from scaffolds, including the need to preserve the bioactivity of growth factors during the possibly harsh incorporation process, the control of their release over an extended period during tissue regeneration, and the need for release to be restricted locally so as to avoid toxic or unwanted systemic side effects. Additionally, each individual delivery strategy is related, and sometimes restricted, to the type of scaffold utilized.

Release of Growth Factors into Root Canal by Irrigations in Regenerative Endodontics