Xiao Zheng Shu

Release of basic fibroblast growth factor from a crosslinked glycosaminoglycan hydrogel promotes wound healing

We describe synthetic extracellular matrix (sECM) hydrogel films composed of co‐crosslinked thiolated derivatives of chondroitin 6‐sulfate (CS) and heparin (HP) for controlled‐release delivery of basic fibroblast growth factor (bFGF) to full‐thickness wounds in genetically diabetic (db/db) mice. In this model for chronic wound repair, full‐thickness wounds were treated with CS, CS‐bFGF, or CS‐HP‐bFGF films. At 2 and 4 weeks postinjury, wound closure and formation of the new epidermis and dermis were determined. Both CS and CS‐HP hydrogel films accelerated wound repair, even without bFGF. Addition of bFGF to CS films showed partial dose‐dependent acceleration of wound repair. Importantly, addition of bFGF to co‐crosslinked CS‐HP sECM films showed a dramatic bFGF dose‐dependent acceleration of wound healing, as well as improved dermis formation and vascularization. Compared with 27% wound closure in 2 weeks in the controls, 89% wound closure was observed for mice treated with the CS‐HP‐bFGF films. The synthetic CS‐HP sECM films mimic the chemistry and biology of heparan sulfate proteoglycans, and may have clinical potential for topical delivery of growth factors to patients with compromised wound healing.

In vivo engineering of the vocal fold extracellular matrix with injectable hyaluronic acid hydrogels : Early effects on tissue repair and biomechanics in a rabbit model

Objectives: A prospective, controlled animal study was performed to determine whether the use of injectable, chemically modified hyaluronic acid (HA) derivatives at the time of intentional vocal fold resection might facilitate wound repair and preserve the unique viscoelastic properties of the vocal fold extracellular matrix. Methods: We performed bilateral vocal fold biopsies on 33 rabbits. Two groups of rabbits were unilaterally treated with 2 different HA derivatives — Carbylan-SX and HA-DTPH-PEGDA — at the time of resection. Saline was injected as a control into the contralateral fold. The animals were painlessly sacrificed 3 weeks after biopsy and injection. The outcomes measured included histologic fibrosis level, tissue HA level, and tissue viscosity and elasticity. Results: The Carbylan-SX—treated vocal folds were found to have significantly less fibrosis than the saline-treated controls. The levels of HA in the treated vocal folds were not significantly different from those in the controls at 3 weeks as measured by enzyme-linked immunosorbent assay. The Carbylan-SX—treated vocal folds had significantly improved biomechanical properties of elasticity and viscosity. The HA-DTPH-PEGDA injections yielded significantly improved viscosity, but not elasticity. Conclusions: Prophylactic in vivo manipulation of the extracellular matrix with an injectable Carbylan-SX hydrogel appears to induce vocal fold tissue regeneration to yield optimal tissue composition and biomechanical properties favorable for phonation.

Injectable synthetic extracellular matrices for tissue engineering and repair.

The development of novel biointeractive hydrogels for tissue engineering1, 2, 3, tissue repair, and release of drugs4 and growth factors5 has attracted considerable attention over the past decade. Our attention has focused on hydrogels based on the extracellular matrix (ECM), a heterogeneous collection of covalent and noncovalent molecular interactions comprised primary of proteins and glycosaminoglycans (GAGs)6. In the ECM, covalent interactions connect chondroitin sulfate (CS), heparan sulfate (HS) and other sulfated GAGs to core proteins forming proteoglycans (PGs). Noncovalent interactions include binding of link modules of PGs to hyaluronan (HA), electrostatic associations with ions, hydration of the polysaccharide chains, and triple helix formation to generate collagen fibrils.

Composition of hyaluronan affects wound healing in the rabbit maxillary sinus.

Background Hyaluronan (HA) is a ubiquitous component of the extracellular matrix. HA and its derivatives have been used in the sinuses to reduce scarring and possibly promote wound healing. However, in recent animal studies, HA esters exhibited inflammatory effects. Mitomycin C (MMC) is another potential antiscarring treatment. This study prospectively evaluated the effects of three different HA constructs on wound healing in the rabbit maxillary sinus: (i) a novel cross-linked HA hydrogel, (ii) the cross-linked HA gel containing covalently bound MMC, and (iii) a commercially available woven HA ester (Merogel). Methods Ostia were created with a 4-mm otologic drill in the maxillary sinuses of 15 New Zealand white rabbits with one side randomly chosen for treatment. After 14 or 21 days the size of the maxillary ostia were recorded and the tissue was examined under light microscopy. Results Sinuses treated with the novel HA and HA-MMC hydrogels showed an increased ostial diameter compared with untreated controls. Woven HA ester–treated sinuses showed no improvement, with a trend toward a smaller ostium than controls. Histological examination showed that woven HA ester tended to cause increased fibrosis and granulomatous inflammation, and heterophilia was slightly increased in the HA hydrogel-treated sinuses. Blinded observation noted foamy macrophages surrounding the residual woven HA ester in each specimen while no similar reaction was noted near the residual HA or HA-MMC hydrogels. Conclusion This study suggests that the degree of ostial narrowing, inflammation, and fibrosis depends on the formulation of the HA used. Minimal, if any, additional benefit is seen with addition of MMC to the HA hydrogel in this pilot study.

Effect of Gelatin on Heparin Regulation of Cytokine Release from Hyaluronan-Based Hydrogels

The hypothesis that incorporation of small amounts (0.3% w/w) of modified heparin in thiol-modified hyaluronan or HA and gelatin hydrogels would regulate release of cytokine growth factors (GFs) from those gels has been investigated in vitro. In addition, the physiologic response to gel implantation has been evaluated in vivo. Tests were performed with 6 GFs: basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), angiopoietin-1 (Ang-1), keratinocyte growth factor, platelet-derived growth factor-AA (PDGF), and transforming growth factor-β 1. Release profiles for all 6 over several weeks were well fit by first order exponential kinetics (R2 > 0.9 for all cases). The most remarkable result of the experiment was a dramatic variation in the total mass ultimately released, which varied from as much as 90.2% of the initial load for bFGF to as little as 1.8% for PDGF, a 45-fold difference. Furthermore, gels containing either VEGF of Ang-1 produced twice the vascularization response in vivo as gels not containing a growth factor. Thus, those GFs maintained strong physiologic effectiveness.

Chapter 22 – Therapeutic Biomaterials from Chemically Modified Hyaluronan

This chapter explores the chemical modification of hyaluronan and the potential uses of these biomaterials in tissue engineering and drug delivery. Most chemical modification strategies target the carboxyl and hydroxyl groups of the sugar moieties. First, the basic chemistry of these modifications is reviewed. Then, the uses of these and other reactions to produce biomedically useful hyaluronan-derived materials are explored. Hyaluronan is a nonsulfated glycosaminoglycan present in all connective tissues as a major constituent of the extracellular matrix (ECM). Due to its unique physicochemical properties and distinctive biological functions, this polyanionic polymer is an attractive building block for new biocompatible and biodegradable materials in drug delivery, tissue engineering, and viscosupplementation. However, the poor biomechanical properties of this soluble, natural polymer and its rapid degradation in vivo preclude many direct clinical applications. Therefore, to obtain materials that are more mechanically and chemically robust, a variety of chemical modification strategies have been explored to produce insoluble or gel-like hyaluronan materials. These hyaluronan derivatives have physicochemical properties that may significantly differ from the native polymer. Most derivatives are biocompatible and biodegradable and retain the pharmacological and therapeutic properties of native hyaluronan.

Crosslinked hydrogels for tympanic membrane repair

PROBLEM: To provide a less expensive and more convenient protocol for the treatment of tympanic membrane perforations (TMPs). METHODS: Several materials were prepared and compared for TMP repair including Carbylan-SX, Gelatin-DTPH-PEGDA (GX), Carbylan-S/Gelatin-DTPH (Carbylan-GSX) (injectable and sponge), Gelfoam, Epifilm, and crosslinked thiolated chondroitin sulfate (CS-DTPH-PEGDA [CS-SX]). Hartley pigmented guinea pigs (Elm Hill) underwent bilateral myringotomy with 1 ear left as a control and the other treated with one of the previously mentioned materials. RESULTS: Carbylan-GSX (injectable and sponge), Gelfoam with saline, and CS-SX had the shortest time for TMP closure. Epifilm, Carbylan, and gelatin preparations resulted in closure rates similar to controls. CS-SX showed a marked inflammatory reaction compared with controls and other materials based on neutrophil, lymphocyte, epitheloid counts, and degree of fibrosis. CONCLUSIONS: This study shows the validity of Carbylan-GSX compared with Gelfoam as a material to promote TMP closure in an acute TMP guinea pig model.

Cross-linked hydrogels for middle ear packing.

Objective: To develop an ideal supportive packing material for ossiculoplasty, tympanoplasty, or other otologic procedures. Materials and Methods: Several materials, namely, Carbylan-SX (P-C; Sentrx Surgical, Inc., Salt Lake City, UT), Gelfoam (P-GF; Pharmacia & Upjohn, Kalamazoo, MI), and Merogel (P-MG; Medtronics, Inc., Minneapolis, MN), were prepared and then placed into a Hartley guinea pigs (Elm Hill, Chelmsford, MA) middle ear cavities through a large myringotomy incision. The contralateral ear underwent a large myringotomy without packing material being placed. Preoperative and posteroperative auditory brainstem response studies were performed using Intelligent Hearing system software. The animals were examined weekly. Two weeks after packing placement, the animals were killed, and the temporal bones were harvested. Whole temporal bone sectioning was performed to analyze the presence of implant, surrounding inflammation, presence of osteoneogenesis and fibrosis, or adhesions. Results: All the materials, except the P-MG, were easy to place into the middle ear cavity. The P-MG contains woven strands that are difficult to trim into the small sizes needed for placement. The P-MG group had a smaller average amount of implant present compared with the other groups at 2 weeks. The degree of osteoneogenesis was similar among the P-GF, P-C, and P-MG groups. The P-MG and P-C groups contained the lowest amount of fibrosis between the implant and surrounding middle ear structures. Conclusion: This study demonstrates promising results with P-C as a potential supportive packing material for otologic procedures. P-C compares favorably with P-MG and P-GF in a guinea pig model with respect to ease of placement and amount of fibrosis.

Structural variations in a single hyaluronan derivative significantly alter wound-healing effects in the rabbit maxillary sinus.

Background: Biomaterials based on hyaluronan (HA) are currently used after sinus surgery but have not been found to decrease scarring or enhance wound healing. Chemical composition of these modified HA molecules may impact their biological and clinical effects.

Cross-linked hyaluronan-coated stents in the prevention of airway stenosis.

OBJECTIVE: This project studies the use of airway stents coated with a cross-linked derivative of hyaluronan (HA) in a rabbit airway model of subglottic stenosis (SGS). STUDY DESIGN AND SETTING: An acute subglottic mucosal injury and airway stent placement design were used in a rabbit model. Thirty-six rabbits were randomized to 6 different study groups. Four groups had the subglottic mucosa denuded at the cricoid, and 2 groups received no injury. Airway stents coated with Carbylan-SX, a cross-linked derivative of HA, and controls were placed for 3 weeks. After sacrifice at 6 weeks, morphometric measurements of subglottic lumen were taken. RESULTS: In posttraumatic models, no significant differences were seen in airway area measures between groups (P = 0.86). In non-injury groups, a significant difference between Carbylan-SX versus non—HA-derivative-coated stents was seen (P = 0.05). CONCLUSION: In this model of acute subglottic mucosal injury, the HA-derivative—coated stent did not improve healing. However, in the absence of mucosal injury, the Carbylan-SX film—coated stent yielded significantly larger airway areas compared with a noncoated stent. SIGNIFICANCE: Stents or endotracheal tubes coated with a cross-linked derivative of HA may prevent stenosis in patients without airway injury but require long-term intubation or laryngotracheal stenting.