Growth Factor Release Profiles Research Articles

Arrhenius-model-based degradable oligourethane hydrogels for controlled growth factor release.

Biodegradable hydrogels are growing in demand to enable the delivery of biomolecules (e.g. growth factors) for regenerative medicine. This research investigated the resorption of an oligourethane/polyacrylic acid hydrogel, a biodegradable hydrogel which supports tissue regeneration. The Arrhenius model was used to characterize the resorption of the polymeric gels in relevant in vitro conditions, and the Flory-Rehner equation was used to correlate the volumetric swelling ratio with the extent of degradation. The study found that the swelling rate of the hydrogel follows the Arrhenius model at elevated temperatures, estimating degradation time in saline solution at 37°C to be between 5 and 13 months, serving as a preliminary approximation of degradation in vivo. The degradation products had low cytotoxicity towards endothelial cells, and the hydrogel supported stromal cell proliferation. Additionally, the hydrogels were able to release growth factors and maintain the biomolecules' bioactivity towards cell proliferation. The study of the vascular endothelial growth factor (VEGF) release from the hydrogel used a diffusion process model, showing that the electrostatic attraction between VEGF and the anionic hydrogel allowed for controlled and sustained VEGF release over three weeks. In a rat subcutaneous implant model, a selected hydrogel with desired degradation rates exhibited minimal foreign body response and supported M2a macrophage phenotype, and vascularization. The low M1 and high M2a macrophage phenotypes within the implants were associated with tissue integration. This research supports the use of oligourethane/polyacrylic acid hydrogels as a promising material for delivering growth factors and supporting tissue regeneration. STATEMENT OF SIGNIFICANCE: There is a need for degradable elastomeric hydrogels that can support the formation of soft tissues and minimize long-term foreign body responses. An Arrhenius model was used to estimate the relative breakdown of hydrogels, in-vitro. The results demonstrate that hydrogels made from a combination of poly(acrylic acid) and oligo-urethane diacrylates can be designed to resorb over defined periods ranging from months to years depending on the chemical formulation prescribed by the model. The hydrogel formulations also provided for different release profiles of growth factors, relevant to tissue regeneration. In-vivo, these hydrogels had minimal inflammatory effects and showed evidence of integration into the surrounding tissue. The hydrogel approach can help the field design a broader range of biomaterials for tissue regeneration.

Fast stress relaxing gellan gum that enhances the microenvironment and secreting function of bone mesenchymal stem cells

This study shows tunable stress relaxing gellan gum (GG) hydrogel for enhanced cell growth and regenerative medicine. The molecular weight and physical crosslinking density of GG were tuned and characterized with physicochemical analysis and mechanical tests. The result showed that a decrease in the molecular weight of the GG correlated with a decline in the mechanical properties but faster stress relaxing character. We also discovered that human-derived bone marrow stem cells (hBMSC) showed active viability, proliferation, and remodeling in the fast stress relaxing GG hydrogel. In particular, hBMSC showed an enhanced release profile of growth factors and exosomes (Exo) in the fast stress relaxing GG hydrogel. The secretome obtained from hBMSC embedded in hydrogel exhibited similar cytotoxicity and wound healing properties to that of secretome extracted from hBMSC cultured in a tissue culture plate (TCP) a standard culture condition. Thus, this work demonstrates the potential of fast stress relaxing GG hydrogels for medical application.

Increased local concentrations of growth factors from leucocyte‐ and platelet‐rich fibrin do not translate into improved alveolar ridge preservation: An intra‐individual mechanistic randomized controlled trial

Leucocyte- and platelet-rich fibrin (L-PRF) has been tested for enhancing alveolar ridge preservation (ARP), but little is known about the local release profile of growth factors (GF), and the clinical equipoise related to its efficacy remains. This study compared the patterns of GF release, early soft tissue healing, and alveolar ridge resorption following unassisted healing and L-PRF application in non-molar extraction sockets. Atraumatic tooth extraction of two hopeless teeth per patient was followed by unassisted healing or L-PRF placement to fill the socket in 18 systemically healthy, non-smoking subjects. This intra-individual trial was powered to assess changes in horizontal alveolar ridge dimensions 1 mm below the crest of alveolar bone. GF concentrations in wound fluid were assessed with a multiplex assay at 6, 24, 72, and 168 h. Early healing was evaluated with the wound healing index and changes in soft tissue volumes on serial digital scans. Hard tissue changes were measured on superimposed CBCT images after 5months of healing. L-PRF resulted in higher GF concentrations in wound fluid (WF) than in the control, but no differences in release patterns or time of peak were observed. No inter-group differences in early healing parameters were observed. Alveolar bone resorption was observed in both groups. No significant inter-group differences were observed in hard tissue healing 1, 3, or 5 mm apical to the original bone crest or in the ability to digitally plan a prosthetically guided implant with or without bone augmentation. L-PRF increased the GF concentrations in WF of extraction sockets without shifting the pattern observed in unassisted healing, while the increased delivery did not translate into clinical benefits in early wound healing or ARP. The current findings question the assumption that increased local concentrations of GF by L-PRF translate into improved clinical outcomes. Additional definitive studies are needed to establish the benefits of L-PRF in ARP (ClinicalTrials.gov NCT03985033).

In Vitro and Ex Vivo Kinetic Release Profile of Growth Factors and Cytokines from Leucocyte- and Platelet-Rich Fibrin (L-PRF) Preparations.

L-PRF is an autologous blood-derived biomaterial (ABDB) capable of releasing biologically active agents to promote healing. Little is known about its release profile of growth factors (GFs), cytokines, and MMPs. This study reported the in vitro and ex vivo release kinetics of GFs, cytokines, and MMPs from L-PRF at 6, 24, 72, and 168 h. The in vitro release rates of PDGF, TGF-β1, EGF, FGF-2, VEGF, and MMPs decreased over time with different rates, while those of IL-1β, IL-6, TNF-α, IL-8, and IL-10 were low at 6 h and then increased rapidly for up to 24 h and subsequently decreased. Of note, the release rates of the GFs followed first-order kinetics both in vitro and ex vivo. Higher rates of release were found ex vivo, suggesting that significant amounts of GFs were produced by the local cells within the wound. In addition, the half-life times of GFs locally produced in the wound, including PDGF-AA, PDGF-AB/BB, and VEGF, were significantly extended (p < 0.05). This work demonstrates that L-PRF can sustain the release of GFs and cytokines for up to 7 days, and it shows that the former can activate cells to produce additional mediators and amplify the communication network for optimizing the wound environment, thereby enhancing healing.

Dual Delivery of BMP2 and IGF1 Through Injectable Hydrogel Promotes Cranial Bone Defect Healing.

Critical-sized cranial bone defect remains a great clinical challenge. With advantages in regenerative medicine, injectable hydrogels incorporated with bioactive molecules show great potential in promoting cranial bone repair. Recently, we developed a dual delivery system by sequential release of bone morphogenetic protein 2 (BMP2) followed by insulin-like growth factor 1 (IGF1) in microparticles (MPs), and an injectable alginate/collagen (alg/col)-based hydrogel. In this study, we aim to evaluate the effect of dual delivery of BMP2 and IGF1 in MPs through the injectable hydrogel in critical-sized cranial bone defect healing. The gelatin MPs loaded with BMP2 and poly(lactic-co-glycolic acid)-poly(ethylene glycol)-carboxyl (PLGA-PEG-COOH) MPs loaded with IGF1 were prepared, respectively. The encapsulation efficiency and release profile of growth factors in MPs were measured. A cranial defect model was applied to evaluate the efficacy of the dual delivery system in bone regeneration. Adult Sprague Dawley rats were subjected to osteotomy to make an ⌀8-mm cranial defect. The injectable hydrogel containing MPs loaded with BMP2 (2 μg), IGF1 (2 μg), or a combination of BMP2 (1 μg) and IGF1 (1 μg) were injected to the defect site. New bone formation was evaluated by microcomputed tomography, histological analysis, and immunohistochemistry after 4 or 8 weeks. Data showed that dual delivery of the low-dose BMP2 and IGF1 in MPs through alg/col-based hydrogel successfully restored cranial bone as early as 4 weeks after implantation, whose effect was comparable to the single delivery of high-dose BMP2 in MPs. In conclusion, this study suggests that dual delivery of BMP2 and IGF1 in MPs in alg/col-based hydrogel achieves early bone regeneration in critical-sized bone defect, with advantage in reducing the dose of BMP2. Impact Statement Sequential release of bone morphogenetic protein 2 (BMP2) followed by insulin-like growth factor 1 (IGF1) in two different microparticles promotes critical-sized bone defect healing. This dual delivery system reduces the dose of BMP2 by supplementing IGF1, which may diminish the potential side effects of BMP2.

Standardized Platelet-Rich Fibrin (PRF) from canine and feline origin: An analysis on its secretome pattern and architectural structure.

Platelet-rich fibrin (PRF) has been incorporated in surgical procedures to promote tissue and bone healing, particularly in human medicine. The rationale for the use of platelet-based products stems from the fact that platelets, after being activated, release growth factors (GFs) and other active molecules such as cytokines, that modulate inflammation and tissue repair. Although PRF has been advanced as a therapeutic treatment for veterinary use, namely in canine and feline patients (following human medicine developments), to our knowledge a full characterization of PRF therapeutic effectors has never been performed. Herein, we studied the biological properties and release profile of GFs and other cytokines throughout ten days in in vitro culture conditions, in order to investigate the potential therapeutic ability of PRF for canine and feline practice. A protocol for obtaining PRF from whole blood without anti-coagulant from both species was optimized, originating large and homogenous PRF clots. Then, PRF clots obtained from four dogs and four cats were incubated in culture medium to assess the temporal release of platelet-derived growth factor-BB (PDGF-BB), vascular endothelial factor-A (VEGF-A), transforming growth factor β-1 (TGF-β1), and interleukin-8 (IL-8). Furthermore, morphological characterization of PRF clots, fresh and after 10days of incubation, was performed by histology and high-resolution field emission electron scanning microscopy. In standard culture conditions, PRF clots from both species released PDGF-BB, TGF- β1 and VEGF-A, in a sustained manner, up to day 10. Moreover, PRF presents an initial burst release of IL-8, a mediator of inflammatory response which plays a key role in neutrophil recruitment and degranulation. Overall, our findings show that PRF clots may be an efficient therapeutic strategy in canine and feline clinical practice, accelerating the local healing mechanism, through the sustained delivery of signalling molecules involved in the healing cascade.

An Injectable Multifunctional Dual-Phase Bead-Reinforced Gelatin Matrix Permissive of Mesenchymal Stem Cell Infiltration for Musculoskeletal Soft Tissue Repair.

This study develops a novel strategy for regenerative therapy of musculoskeletal soft tissue defects using a dual-phase multifunctional injectable gelatin-hydroxyphenyl propionic acid (Gtn-HPA) composite. The dual-phase gel consists of stiff, degradation-resistant, ≈2-mm diameter spherical beads made from 8 wt% Gtn-HPA in a 2 wt% Gtn-HPA matrix. The results of a 3D migration assay show that both the cell number and migration distance in the dual-phase gel system are comparable with the 2 wt% mono-phase Gtn-HPA, but notably significantly higher than for 8 wt% mono-phase Gtn-HPA (into which few cells migrated). The results also show that the dual phase gel system has degradation resistance and a prolonged growth factor release profile comparable with 8 wt% mono-phase Gtn-HPA. In addition, the compressive modulus of the 2 wt% dual-phase gel system incorporating the 8 wt% bead phase is nearly four-fold higher than the 2wt% mono-phase gel (5.3 ± 0.4 kPa versus 1.5 ± 0.06 kPa). This novel injectable dual-phase Gtn-HPA composite thus combines the advantages of low-concentration Gtn-HPA (cell migration) with high-concentration Gtn-HPA (stiffness, degradation resistance, slower chemical release kinetics) to facilitate effective reparative/regenerative processes in musculoskeletal soft tissue.

Nitric Oxide generating coating alters hematoma structure and soft tissue healing

IntroductionPeri-implantitis remains a major clinical problem due to the challenges in soft tissue integration on implants surfaces. During tissue healing processes, hematoma formation is the initial response to implant surfaces, which serves as a reservoir for growth factors and provides a natural scaffold for cell infiltration. However, little information is available regarding whether altering hematoma properties can benefit soft tissue healing and tissue integration. This study aims to modulate hematoma properties to create a friendly microenvironment for a strong soft tissue seal on implant surfaces. MethodsWe developed a polydopamine (PDAM) based coating capable of well-controlled nitric oxide (NO) generation by applying the copper (Cu) dose gradient. The incorporated copper with progressive raw concentrations of 10, 50 and 250µg/mL in the coating (PDAM@Cu coatings) served as a catalyst and reacted with endogenous NO donors in the blood. The resulting influence on clot structure and tissue healing microenvironment were analyzed along with its impact on the migration and proliferation of human gingival fibroblasts (HGFs). ResultsIt was noted that NO generation rates could be controlled using Cu from the coatings as a catalyst. As a result of this, the clot formation, structural properties, clot degradation, and growth factor release could be manipulated. Consequently, the NO generating surfaces of PDAM@Cu coating yielded a desired porous structure in clots and growth factor release profile, especially of platelet derived growth factors such as platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF). The NO generating surfaces of PDAM@Cu coating subsequently allowed increased migration and proliferation of HGFs. ConclusionIn this study, we developed a novel NO-generating strategy to regulate hematoma properties and growth factors release. The optimized coating could provide a favourable micro-environment for soft tissue healing and prompt cell migration and proliferation of HGFs. Therefore, PDAM surface modification with incorporation of Cu as a catalyst for NO generation could induce a functional implant surface for soft tissue integration.

Effects of Antiplatelet and Nonsteroidal Anti-inflammatory Medications on Platelet-Rich Plasma: A Systematic Review.

Background:Platelet-rich plasma (PRP) has wide applications in orthopaedic care. Its beneficial effects are attributed to the growth factor profile from the platelet secretome. In theory, these effects would be diminished by medications that inhibit platelet activation and/or the subsequent release of growth factors.Purpose:To determine whether commonly used antiplatelets, nonsteroidal anti-inflammatory drugs (NSAIDs), or anticoagulant medications affect platelet growth factor release in PRP.Study Design:Systematic review; Level of evidence, 2.Method:A systematic review of the literature related to antiplatelet, anti-inflammatory, and anticoagulant drugs was performed following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. We used the Downs and Black objective quality scoring system. The literature search consisted of PubMed and Cochrane Library databases. Search terms consisted of 1 item selected from “platelet-rich plasma,” “platelet-derived growth factor,” and “platelet-rich plasma AND growth factor” combined with 1 item from “antiplatelet,” “aspirin,” “anticoagulant,” and “NSAID.” Only studies published within the past 25 years were included.Results:A total of 15 studies met the inclusion criteria: 7 studies detected no significant decrease in growth factors or mitogenesis, whereas 6 detected a decrease with antiplatelet agents, 1 detected mixed results with an antiplatelet agent, and 1 had mixed results with an antiplatelet agent/vasodilator. In terms of PRP activation, all 3 studies assessing collagen, the 2 studies analyzing adenosine diphosphate alone, and the 1 study investigating arachidonic acid found a decrease in growth factor concentration.Conclusion:Antiplatelet medications may decrease the growth factor release profile in a cyclooxygenase 1– and cyclooxygenase 2–dependent manner. Eight of 15 studies found a decrease in growth factors or mitogenesis. However, more studies are needed to comprehensively understand antiplatelet effects on the PRP secretome.

Incorporating platelet-rich plasma into coaxial electrospun nanofibers for bone tissue engineering

Platelet-rich plasma (PRP) is used in therapy for bone tissue repair because an abundance of osteogenesis-related growth factors can be released from the concentrated platelets. However, its clinical use is limited because growth factors, temporally released from PRP, are degraded rapidly. This study aimed to incorporate PRP-derived growth factors into SF/PCL/PVA nanofibers by coaxial electrospinning to determine the release profiles of growth factors and how the presence of these growth factors enhances the osteogenic abilities of the nanofibers. Scaffolds containing different ratios of PRP and PVA were prepared and characterized. We then quantified the release of growth factors from the nanofibers over time, and evaluated the proliferation, migration and osteogenic differentiation of MSCs. The in vivo osteogenic capacity of the PRP-containing core-shell NFS was also evaluated by transplanting the PRP/MSCs/CS/β-TCP compounds into the skin on the back of nude mice and by treating cranial defects of C57BL/6 mice. The results of such treatments were analyzed by immunofluorescent staining, μ computed tomography (μCT), and histological observation. The results show that coaxial nanofibers with a PRP-5% PVA solution ratio of 7:1 contained a relatively high amount of PRP and exhibited a more uniform distribution of fiber diameters. The bioactivity of the scaffolds was enhanced due to the increased proliferation and migration of bone marrow mesenchymal stem cells (BMSCs). When the cells were inoculated and cultured on the PRP-loaded nanofibrous mats, the expression of collagen type II also increased. Furthermore, new bone formation was also promoted by PRP-NFS after 8 weeks of implantation. In conclusion, this study shows that the incorporation of PRP had positive effects on the bioactivity and osteogenic ability of coaxial nanofibrous mats. Such nanofibrous mats may prove beneficial in various applications of bone tissue engineering.

Growth-Factor-Releasing Polyelectrolyte Multilayer Films to Control the Cell Culture Environment.

Polyelectrolyte multilayers (PEMs) are of great interest as cell culture surfaces because of their ability to modify topography and surface energy and release biologically relevant molecules such as growth factors. In this work, fibroblast growth factor 2 (FGF2) was adsorbed directly onto polystyrene, plasma-treated polystyrene, and glass surfaces with a poly(methacrylic acid) and poly-l-histidine PEM assembled above it. Up to 14 ng/cm2 of FGF2 could be released from plasma-treated polystyrene surfaces over the course of 7 days with an FGF2 solution concentration of 100 μg/mL applied during the adsorption process. This release rate could be modulated by adjusting the adsorption concentration, decreasing to as low as 2 ng/cm2 total release over 7 days using a 12.5 μg/mL FGF2 solution. The surface energy and roughness could also be regulated using the adsorbed PEM. These properties were found to be substrate- and first-layer-dependent, supporting current theories of PEM assembly. When released, FGF2 from the PEMs was found to significantly enhance fibroblast proliferation as compared to culture conditions without FGF2. The results showed that growth factor release profiles and surface properties are easily controllable through modification of the PEM assembly steps and that these strategies can be effectively applied to common cell culture surfaces to control the cell fate.

ID: 1059 Biomimetic release of growth factor from porous beads for enhanced bone regeneration

Three dimensional scaffolds which allow sustained release of bioactive molecules have been considered as an essential component for enhanced bone regeneration. In recent years, combination system of various bioactive molecules has been extensively investigated to reconstruct more sophisticated bone regeneration. It is well-known that if the certain bioactive molecules with appropriate dose and stimulation periods are applied to bone defect, the physiological processes in bone regeneration may be accelerated. However, many studies were not concerned stimulation periods of bioactive molecules occurred in body during new bone formation because of absence of proper release system for the bioactive molecules. In this study, we selected three bioactive molecules (PDGF-BB, VEGF, BMP-2) which widely used for effective bone healing, and developed a porous bead with leaf-stacked structure which can allow controlled release of growth factors by concentration and composition of Pluronics. The morphology, each growth factor release profiles, migration (boyden chamber assay), angiogenic differentiation (tube formation, ICC, and RT-PCR), osteogenic differentiation (ALP activity, calcium deposition, alizarin/ALP staining, ICC, and RT-PCR) of human periosteum-derived cells and new bone formation of rat calvarial defect model by controlled release of growth factors were estimated

Generating favorable growth factor and protease release profiles to enable extracellular matrix accumulation within an in vitro tissue engineering environment.

Sufficient extracellular matrix accumulation within cardiovascular and connective tissue engineered constructs is a prerequisite for their appropriate function in vivo. This study established co-culture systems with tissue specific cells (vascular smooth muscle cells (VSMCs)) and defined ratios of immune cells (monocytes) to investigate extracellular matrix (ECM) generation and degradation processes, revealing important mechanisms underlying ECM turnover during vascular tissue regeneration/remodelling. A specific growth factor (IGF-1), as well as hydrolytic proteases (e.g. MMP2, MMP9, MMP13 and MMP14), were identified as playing important roles in these processes. ECM accumulation was found to be dependent on achieving a desired release profile of these ECM-promoting and ECM-degrading factors within the multi-cellular microenvironment. The findings enhance our understanding of ECM deposition and degradation during in vitro tissue engineering and would be applicable to the repair or regeneration of a variety of tissues.

Preparation and characterization of injectable chitosan–hyaluronic acid hydrogels for nerve growth factor sustained release

The usage of hollow nerve conduits shows inferior recovery effect on the repair of peripheral nerve defects. In this study, a biocompatible and biodegradable pH-induced injectable chitosan–hyaluronic acid hydrogel for nerve growth factor encapsulation and sustained release was developed as the fillers in the lumen of hollow nerve conduit to reform its microenvironment for peripheral nerve regeneration. The physicochemical properties of hydrogel were characterized by gelation time, Fourier transform infrared spectroscopy, scanning electron microscopy, compressive modulus, porosity, swelling ratio, and in vitro degradation. The in vitro nerve growth factor release profiles and cell evaluation were also investigated. The results show that the structure of chitosan–hyaluronic acid hydrogel is composed of interconnected channels with a controllable pore diameter ranging from 20 to 100 µm. The hydrogel can be degraded more than 70% within 8 weeks in vitro and is available for nerve growth factor sustained release. The chitosan–hyaluronic acid/nerve growth factor hydrogel is non-toxic and suitable for adhesion and proliferation of nerve cells and capable of maintaining nerve growth factor activity. Therefore, it could be a promising intraluminal filler of nerve conduits for peripheral nerve regeneration in neural tissue engineering.

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 (5ng) to high (200ng), 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 12days 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.

Novel Carriers for Growth Factors for Enhancing Spinal Fusion

Spinal fusion is a well-accepted surgical treatment for many spinal diseases; the costs amount to ~34 billion annually in the US alone, with significant increases projected due to an aging population. Non-unions are a notable complication of spinal fusion surgery. To promote bone regeneration, the FDA has approved rhBMP-2 with a rebsorbable collagen sponge as an alternative to the standard bone graft for spinal fusion. However, adverse events associated with supraphysiological doses, and burst release of rhBMP-2 is a recurring problem for clinicians. Formulations that help regulate the delivery and release profile of growth factors are needed to achieve consistent clinical outcomes. Numerous approaches have been tested, and some of them have shown promising results. Strategies tested for achieving this endeavor include: 1) optimization of cytokine kinetics, 2) combination of different growth factors, 3) utilization of osteoinductive and osteoconductive scaffolds, 4) incorporation of progenitor cells, 5) augmentation of biological activity with tropic bone factors, and, 6) reduction of the endogenous BMP antagonists. Disclosures: None

Agent-Based Modeling of Vascularization in Gradient Tissue Engineering Constructs

An agent-based model is developed to simulate the vascular growth in engineered biomaterials. This study investigates the influence of growth factor release rate on rapid and stable vascularization. Different growth factor release profiles are generated and tested using the agent-based model. The simulation results are verified with experimental studies. Effective release policies are identified; microsphere properties for promoting angiogenesis are suggested.

Biohybrid networks of selectively desulfated glycosaminoglycans for tunable growth factor delivery.

Sulfation patterns of glycosaminoglycans (GAG) govern the electrostatic complexation of biomolecules and thus allow for modulating the release profiles of growth factors from GAG-based hydrogels. To explore options related to this, selectively desulfated heparin derivatives were prepared, thoroughly characterized, and covalently converted with star-shaped poly(ethylene glycol) into binary polymer networks. The impact of the GAG sulfation pattern on the network characteristics of the obtained hydrogels was theoretically evaluated by mean field methods and experimentally analyzed by rheometry and swelling measurements. Sulfation-dependent differences of reactivity and miscibility of the heparin derivatives were shown to determine network formation. A theory-based design concept for customizing growth factor affinity and physical characteristics was introduced and validated by quantifying the release of fibroblast growth factor 2 from a set of biohybrid gels. The resulting new class of cell-instructive polymer matrices with tunable GAG sulfation will be instrumental for multiple applications in biotechnology and medicine.

Bone Regeneration of Tibial Defects in Rats with Enzymatic Hydrogelation of Gelatin Derivative and Recombinant Human Platelet-Derived Growth Factor-BB Complex

To evaluate the capabilities of gelatin derivatives that incorporate phenolic hydroxyl groups (gelatin-Ph) as a delivery carrier with recombinant human platelet-derived growth factor-BB (rhPDGF-BB) for bone regeneration. The growth factor release profile from gelatin-Ph gel or atelocollagen was analyzed to evaluate the capability of gelatin-Ph as a carrier. The biocompatibility of gelatin-Ph (ie, the survival rates of the cells during gelation, and the morphology and proliferation of the cells) were investigated with rat bone marrow cells (RBMCs) in vitro. To evaluate the effect of the gelatin-Ph-rhPDGF-BB complex on bone formation, the complex was applied to bone defects in rat tibiae and undecalcified specimens were fabricated for histologic analysis. Scarce amounts of rhPDGF-BB from gelatin-Ph gel were detected during 30 days, but the addition of protease induced the release of rhPDGF-BB on day 31. No differences were observed in the survival rates of RBMCs during gelation and in the morphology and proliferation of RBMCs on the gel sheet between groups. Histological analyses demonstrated that the complex enhanced bone formation and mineralization at 2 and 4 weeks. These results suggest that gelatin-Ph gel can be an ideal delivery carrier, and the localized delivery of rhPDGF-BB in gelatin-Ph can contribute to bone formation.

Affinity-based growth factor delivery using biodegradable, photocrosslinked heparin-alginate hydrogels

Photocrosslinkable biomaterials are promising for tissue engineering applications due to their capacity to be injected and form hydrogels in situ in a minimally invasive manner. Our group recently reported on the development of photocrosslinked alginate hydrogels with controlled biodegradation rates, mechanical properties, and cell adhesive properties. In this study, we present an affinity-based growth factor delivery system by incorporating heparin into photocrosslinkable alginate hydrogels (HP-ALG), which allows for controlled, prolonged release of therapeutic proteins. Heparin modification had minimal effect on the biodegradation profiles, swelling ratios, and elastic moduli of the hydrogels in media. The release profiles of growth factors from this affinity-based platform were sustained for 3 weeks with no initial burst release, and the released growth factors retained their biological activity. Implantation of bone morphogenetic protein-2 (BMP-2)-loaded photocrosslinked alginate hydrogels induced moderate bone formation around the implant periphery. Importantly, BMP-2-loaded photocrosslinked HP-ALG hydrogels induced significantly more osteogenesis than BMP-2-loaded photocrosslinked unmodified alginate hydrogels, with 1.9-fold greater peripheral bone formation and 1.3-fold greater calcium content in the BMP-2-loaded photocrosslinked HP-ALG hydrogels compared to the BMP-2-loaded photocrosslinked unmodified alginate hydrogels after 8 weeks implantation. This sustained and controllable growth factor delivery system, with independently controllable physical and cell adhesive properties, may provide a powerful modality for a variety of therapeutic applications.