Emerging growth factor delivery hydrogel system for wound healing

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

Biomaterials based growth factor delivery for brain regeneration after injury

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.

Design of a composite biomaterial system for tissue engineering applications

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

Wound healing and tissue regeneration are orchestrated by the cellular microenvironment, e.g. the extracellular matrix (ECM). Including ECM components inbiomaterials is a promising approach for improving regenerative processes, e.g. wound healing in skin. Thisreview addresses recent findings for enhanced epidermal-dermal regenerative processes oncollagen (coll)/glycosaminoglycan (GAG)-based matrices containing sulfated GAG (sGAG) in simple and complex invitro models. These matrices comprise 2D-coatings, electrospun nanofibrous scaffolds, and photo-crosslinked acrylated hyaluronan (HA-AC)/coll-based hydrogels. They demonstrated to regulate keratinocyteand fibroblast migration and growth, to stimulate melanogenesis in melanocytes from the outer root sheath (ORS) of hair follicles and to enhance the epithelial differentiation of human mesenchymal stem cells (hMSC). The matrices' suitability for delivery of relevant growth factors, like heparin-binding epidermal growth factor like growth factor (HB-EGF), further highlights their potential as bioinspired, functional microenvironments for enhancing skin regeneration.

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

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

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.

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

Allografts are commonly used as an alternative to autografts for bone defect repair, but in some instances suffer from reduced host incorporation that can lead to complications 5 and 10 years post-implantation. We have previously demonstrated that using a thin polymeric coating along the outer surfaces of cortical bone can improve the biofunctionality of devitalized bone allografts by permitting the upload and delivery of growth factors from the thin coating. Here, we expand on our previous work to develop a methodology to coat porous trabecular allografts with a similar polymer coating with careful attention to maintaining an open pore network within the allograft and establishing the effect of varying the polymer solution viscosity on coating extent and thickness. Results indicate that varying the polymer solution viscosity by changing the polymer to solvent ratio used to coat the samples allows for variations in coating thickness and extent of surface area coverage, each perhaps allowing for greater control over growth factor loading and release concentration and kinetics. Further, we develop a dynamic coating method that produces a continuous and consistent coating throughout the pore structure vs. the previously used static method that resulted in a discontinuous coating throughout the pore network. The work demonstrated here provides important techniques for varying the payload of polymer-coated, factor-loaded trabecular allografts which would provide another tool to the orthopedic surgeon when healing large-scale defects with trabecular allograft. Large scale bone defects are traditionally treated with either autografts or allografts. Allografts suffer from poor incorporation in part due to the processing undertaken to render them safe to transplant from one individual to another. We sought to add back some of the biological functionality that is removed in this processing by loading growth factors into a very thin polymeric coating that we apply to the surface of the allograft. Our results indicate a thin, continuous polymeric coating throughout the trabecular allograft, with the amount of this coating varying as we vary the concentration of this polymer solution prior to coating. Future studies will evaluate the ability of this varied concentration of polymer coating to permit the delivery of varying amounts of growth factors, imparting a greater degree of control over the amount of growth factor delivered from the coated allografts.

Sustained delivery of growth factors, proteins, drugs and other biologically active molecules is necessary for tissue engineering applications. Electrospun fibers are attractive tissue engineering scaffolds as they partially mimic the topography of the extracellular matrix (ECM). However, they do not provide continuous nourishment to the tissue. In search of a biomimetic scaffold for salivary gland tissue regeneration, we previously developed a blend nanofiber scaffold composed of the protein elastin and the synthetic polymer polylactic-co-glycolic acid (PLGA). The nanofiber scaffold promoted in vivo-like salivary epithelial cell tissue organization and apicobasal polarization. However, in order to enhance the salivary cell proliferation and biomimetic character of the scaffold, sustained growth factor delivery is needed. The composite nanofiber scaffold was optimized to act as a growth factor delivery system using epidermal growth factor (EGF) as a model protein. The nanofiber/EGF hybrid nanofibers were synthesized by double emulsion electrospinning where EGF is emulsified within a water/oil/water (w/o/w) double emulsion system. Successful incorporation of EGF was confirmed using Raman spectroscopy. EGF release profile was characterized using enzyme-linked immunosorbent assay (ELIZA) of the EGF content. Double emulsion electrospinning resulted in slower release of EGF. We demonstrated the potential of the proposed double emulsion electrospun nanofiber scaffold for the delivery of growth factors and/or drugs for tissue engineering and pharmaceutical applications.

In this review, we analysed the role of stem cell and growth factor therapy on rotator cuff tendon repair. The injury to the rotator cuff tendons can be sustained in numerous ways and generally causes significant pain and disability to the affected individual. Following surgical repair of ruptured rotator cuff tendons re-rupture rates can be as high as 20-60%. In order to augment this repair process and to decrease the re-rupture rates tissue engineering methods can be used. These include the use of stem cells and growth factors. Mesenchymal stem cells are stem cells which can differentiate into a variety of connective tissue cell types and can therefore be utilised in repairing tendons. So far there has only been one human study using stem cells in rotator cuff tendon repair. This study has produced a positive result but consisted of only 14 patients and lacks a control group for comparison. Similar work has also been done using growth factors. Both individual and combination growth factor therapy have been used to improve rotator cuff tendon repair. However, the results so far have been disappointing with growth factors. For the purpose of future studies better techniques should be explored with regards to the delivery of stem cells and growth factors as well as the possibility of combining growth factor and stem cell therapy to improve repair rates.

Emerging advances in hydrogel-based therapeutic strategies for tissue regeneration

Foreword B. Swynghedauw. Preface P. Cummins. Introduction. 1. Growth factors: in vivo function and mechanism of action C.-H. Heldin, L. Claesson-Welsh, K. Miyazono, B. Westermark. Section one: Growth Factors in the Heart. 2. Fibroblast and transforming growth factors in the heart: a role for cardiac growth? P. Cummins, A.K. El Amrani, F. El Amrani. 3. Growth factors and the cardiac extra-cellular matrix L. Rappaport, J.L. Samuel. Section two: Growth Factors and the Cardiac Myocyte. 4. Transforming growth factor beta: Localisation and possible functional roles in cardiac myocytes A.B. Roberts, M.B. Sporn. 5. Basic fibroblast growth factor in cardiac myocytes: expression and effects E. Kardami, R.R. Padua, K.B.S. Pasumarthi, Lei Liu, B.W. Doble, S.E. Davey, P.A. Cattini. 6. Growth factor signal transduction in the cardiac myocyte: Functions of the serum response element M.D. Schneider, T. Brand, R.J. Schwartz, W.R. MacLellan. 7. Effects of growth factors on human cardiac myocytes B.I. Goldman, J. Wurzel. Section three: Growth Factors and Angiogenesis. 8. Growth factors and development of coronary collaterals H.H. Sharma, R. Zimmerman. 9. The role of growth factors in angiogenesis R.J. Schott, L.A. Morrow. Section four: Growth Factors and Atherosclerosis. 10. Atherosclerosis and platelet-derived growth factors G.A.A. Ferns, C. Rutherford. 11. Effects of transforming growth factor beta on vascular smooth muscle cell growth P.I. Weissberg, D.J. Grainger, J.C. Metcalfe. 12. Some aspectsof growth factor signal transduction in vascular smooth muscle cells A.C. Newby, N.P.J. Brindle. 13. Basic FGFs role in smooth muscle cell proliferation: A basis for molecular atherectomy W. Casscells, D.A. Lappi, A. Baird. Section five: Growth Factors and Cardiovascular Disease: Clinical and Therapeutic Implications. 14. Role of transforming growth factor b in cardioprotection of the ischemic-reperfused myocardium A.M. Lefer. 15. Platelet-derived growth factor release after angioplasty P. Macke Consigny. 16. Platelet-derived growth factor receptor activity induced by vascular injury G.E. Bilder. 17. Growth factors and hypertension: Implications of growth factor function in vascular remodelling A.K. El Amrani, F. El Amrani, P. Cummins. 18. Transforming growth factor b and carcinoid heart disease J. Waltenberger. Section six: Growth Factor Effects on the Myocardium. 19. Adrenergic stimulation and growth factor activity C.S. Long, P.C. Simpson. 20. Effects of transforming growth factor b on cardiac fibroblasts M. Eghbali. 21. Transforming growth factor b's and cardiac development R.J. Akhurst, M. Dickson, F.A. Millan. Index.