Silk Sponge Research Articles

223: Progesterone inhibits cervical tissue formation in a 3D culture system in a dose-dependent fashion

3D culture system in a dose-dependent fashion Michael House, Serkalem Tadesse, Errol Norwitz, David Kaplan Tufts Medical Center, Maternal Fetal Medicine, Boston, MA, Tufts University, Biomedical Engineering, Medford, MA, Yale University, Obstetrics and Gynecology, New Haven, CT OBJECTIVE: Progesterone supplementation can prevent preterm birth in some women with cervical shortening, suggesting that progesterone may directly affect remodeling of cervical tissue. A previously described 3D culture system was used to test progesterone effects on cervical tissue synthesis. STUDY DESIGN: Fibroblasts were obtained from cervical biopsies of non-pregnant premenopausal women undergoing hysterectomy for benign disease. Fibroblasts from passage 5 were seeded on silk sponge scaffolds and cultured in spinner flasks using previously validated culture system (House, Tissue Eng Part A, 2012). Culture media included DMEM 5% charcoal-stripped FBS estradiol 10-8M. Five progesterone conditions were used: 0 (vehicle), 10-9M, 10-8M, 10-7M and 10-7M 10-6M mifepristone. Scaffolds were cultured for 4 weeks and assayed for collagen production (hydroxyproline), histology and immunohistochemistry (IHC). Cervical-like tissue was assayed for estrogen and progesterone receptors using IHC and western blot. Experiments were repeated in triplicate with cells from 3 different women. RESULTS: Cervical cells reliably synthesized cervical-like tissue in 3D. Both progesterone and estrogen receptors were documented by IHC and western blot. A dose-dependent inhibitory effect of progesterone was observed. The highest progesterone concentration (10-7M) was associated with the least amount of collagen synthesis. Collagen synthesis increased progressively as progesterone concentration decreased (p .01). This effect was abrogated by mifepristone (p .05). Differences in tissue morphology on histology and IHC correlated with collagen synthesis. CONCLUSION: Progesterone inhibited the synthesis of cervical-like tissue in 3D culture from cervical fibroblasts in a dose-dependent manner. This effect was abrogated by mifepristone, a progesterone receptor antagonist. This hormonally-responsive in vitro culture system could be used to study the mechanism of progesterone effects on the cervix. 224 Role of (pro)rennin and its receptor in pathogenesis of preeclampsia: a rat model and human patients studies Kelsey Kelso, Russell Fothergill, Steven Allen, Richard Jones, Thomas Kuehl, Mohammad Uddin Scott & White Memorial Hospital / Texas AM placental (pro)renin for NP:152 79 and PreE:302 42 ng/g tissue). In addition to serving as a source of (pro)renin, the placenta is also a site for signaling as ERK1/2 phosphorylation is greater (p 0.05) in placental tissue of preE rats. CONCLUSION: Together with the upregulation of ERK1/2 phosphorylation in placenta of the rat model, there is now evidence of (pro)renin and its receptor associated novel RAS activation to play a role in preE pathogenesis through (pro)renin receptor-mediated detrimental cellular signaling at the placental boundary. This offers an opportunity for interventional treatments with signal inhibitors.

Small‐Diameter Silk Vascular Grafts (3 mm Diameter) with a Double‐Raschel Knitted Silk Tube Coated with Silk Fibroin Sponge

Small-diameter (less than 6 mm in diameter) vascular grafts are highly desirable due to the large demand for surgical revascularization; however, there are no available artificial grafts. Vascular grafts of 1.5 mm diameter prepared by our group with silk fibroin fiber have been proved to be excellent grafts with remarkably high patency and remodeling, based on rat implantation experiment (Enomoto et al., 2010). In this study, a silk fibroin vascular graft with 3 mm diameter which can be used for the coronary arteries or lower extremity arteries is prepared with a double-raschel knitted Bombyx mori silk fiber tube coated with B. mori silk fibroin sponge. Here the silk sponge is prepared from an aqueous solution of the silk fibroin and poly(ethylene) glycol diglycidyl ether as porogen. Sufficient strength, proper elasticity, and protection from loose ends in the implantation process are obtained for the silk fibroin graft; low water permeability and relatively large compliance are also attained. These excellent physical properties make silk fibroin grafts suitable to be implanted in a canine model.

Antibiotic‐Releasing Silk Biomaterials for Infection Prevention and Treatment

Effective treatment of infections in avascular and necrotic tissues can be challenging due to limited penetration into the target tissue and systemic toxicities. Controlled release polymer implants have the potential to achieve the high local concentrations needed while also minimizing systemic exposure. Silk biomaterials possess unique characteristics for antibiotic delivery including biocompatibility, tunable biodegradation, stabilizing effects, water-based processing and diverse material formats. We report on functional release of antibiotics spanning a range of chemical properties from different material formats of silk (films, microspheres, hydrogels, coatings). The release of penicillin and ampicillin from bulk-loaded silk films, drug-loaded silk microspheres suspended in silk hydrogels and bulk-loaded silk hydrogels was investigated and in vivo efficacy of ampicillin-releasing silk hydrogels was demonstrated in a murine infected wound model. Silk sponges with nanofilm coatings were loaded with gentamicin and cefazolin and release was sustained for 5 and 3 days, respectively. The capability of silk antibiotic carriers to sequester, stabilize and then release bioactive antibiotics represents a major advantage over implants and pumps based on liquid drug reservoirs where instability at room or body temperature is limiting. The present studies demonstrate that silk biomaterials represent a novel, customizable antibiotic platform for focal delivery of antibiotics using a range of material formats (injectable to implantable).

Enhanced osteoinductivity and osteoconductivity through hydroxyapatite coating of silk‐based tissue‐engineered ligament scaffold

Hybrid silk scaffolds combining knitted silk fibers and silk sponge have been recently developed for use as ligament-alone grafts. Incorporating an osteoinductive phase into the ends of a ligament scaffold may potentially generate an integrated "bone-ligament-bone" graft and improve graft osteointegration with host bone. To explore the possible application of hydroxyapatite (HA) coating in the fabrication of osteoinductive ends of silk-based scaffold, HA was coated on the hybrid silk scaffold and the effects to the bone-related cells were evaluated. HA could be coated in a uniform and controlled manner on the silk sponge, using an alternate soaking technology, with the amount deposited being dependent on the number of soaking cycles. HA coating also progressively reduced the hydrophobicity of silk surface (decreasing water contact angle from 87° to 42-76°, after 1-3 soaking cycles), making the HA-coated silk scaffold less favorable for initial cell attachments; but the attached cells showed viability and sustained proliferation on the HA-coated scaffold. As demonstrated by real-time polymerase chain reaction and alkaline phosphatase assay, the osteoinductivity of HA-coated silk scaffolds resulted in the osteogenic differentiation of bone marrow mesenchymal stem cells, and the osteoconductivity of HA-coated silk scaffolds supported osteoblasts growth and maintained the properties of mature osteoblasts. These properties of HA-coating demonstrated its possible application in fabricating osteoinductive ends of the silk-based ligament graft to potentially enhance graft-to-host bone integration.

Effects of supercooling and organic solvent on the formation of a silk sponge with porous 3-D structure, and its dynamical and structural characterization using solid-state NMR

Effects of supercooling and organic solvent on the formation of a silk sponge with porous 3-D structure, and its dynamical and structural characterization using solid-state NMR

Three-dimensional porous silk tumor constructs in the approximation of in vivo osteosarcoma physiology

The lack of good preclinical models has hampered anticancer drug discovery. Standard preclinical protocols require the growth of cells in high throughput two-dimensional (2D) culture systems. However, such in vitro drug testing methods yield drug efficacy results that differ greatly from animal models. Conversely, it is much more difficult and expensive to use animal models for large-scale molecular biology research. It is conceivable that three-dimensional (3D) growth may be responsible for some of these changes. Porous silk sponges were fabricated through freeze drying and seeded with 143.98.2 osteosarcoma cells. Molecular profiles were obtained by carrying out real-time polymerase chain reaction for angiogenic growth factors and proliferation markers for osteosarcoma cells grown under 2D, 3D, and SCID mouse xenograft conditions. The angiogenic factor expression profiles for cells grown in 2D differed greatly from the 3D silk scaffold model ( P < 0.05 for bFGF, HIF-1α, IL-8, and VEGF-A), whereas 3D tumor model profiles were found to be able to approximate that for the in vivo tumor better with no statistically different expression of HIF-1α and VEGF-A between the two. Immunohistochemistry staining for HIF-1α, VEGF-A, and VEGF receptor on osteosarcoma cells grown on the scaffolds validated the results obtained with the gene expression profiles. The results suggest that 3D tumor models could be used to bridge the gap between in vitro and in vivo tumor studies, and aid in the study of mechanisms activated during tumorigenesis for the development of novel targeted chemotherapy.

Nucleation and growth of mineralized bone matrix on silk-hydroxyapatite composite scaffolds

We describe a composite hydroxyapatite (HA)–silk fibroin scaffold designed to induce and support the formation of mineralized bone matrix by human mesenchymal stem cells (hMSCs) in the absence of osteogenic growth factors. Porous three-dimensional silk scaffolds were extensively used in our previous work for bone tissue engineering and showed excellent biodegradability and biocompatibility. However, silk is not an osteogenic material and has a compressive stiffness significantly lower than that of native bone. In the present study, we explored the incorporation of silk sponge matrices with HA (bone mineral) micro-particles to generate highly osteogenic composite scaffolds capable of inducing the in vitro formation of tissue-engineered bone. Different amounts of HA were embedded in silk sponges at volume fractions of 0%, 1.6%, 3.1% and 4.6% to enhance the osteoconductive activity and mechanical properties of the scaffolds. The cultivation of hMSCs in the silk/HA composite scaffolds under perfusion conditions resulted in the formation of bone-like structures and an increase in the equilibrium Young’s modulus (up to 4-fold or 8-fold over 5 or 10 weeks of cultivation, respectively) in a manner that correlated with the initial HA content. The enhancement in mechanical properties was associated with the development of the structural connectivity of engineered bone matrix. Collectively, the data suggest two mechanisms by which the incorporated HA enhanced the formation of tissue engineered bone: through osteoconductivity of the material leading to increased bone matrix production, and by providing nucleation sites for new mineral resulting in the connectivity of trabecular-like architecture.

Ingrowth of human mesenchymal stem cells into porous silk particle reinforced silk composite scaffolds: An in vitro study

Silk fibroin protein is biodegradable and biocompatible, exhibiting excellent mechanical properties for various biomedical applications. However, porous three-dimensional (3-D) silk fibroin scaffolds, or silk sponges, usually fall short in matching the initial mechanical requirements for bone tissue engineering. In the present study, silk sponge matrices were reinforced with silk microparticles to generate protein–protein composite scaffolds with desirable mechanical properties for in vitro osteogenic tissue formation. It was found that increasing the silk microparticle loading led to a substantial increase in the scaffold compressive modulus from 0.3 MPa (non-reinforced) to 1.9 MPa for 1:2 (matrix:particle) reinforcement loading by dry mass. Biochemical, gene expression, and histological assays were employed to study the possible effects of increasing composite scaffold stiffness, due to microparticle reinforcement, on in vitro osteogenic differentiation of human mesenchymal stem cells (hMSCs). Increasing silk microparticle loading increased the osteogenic capability of hMSCs in the presence of bone morphogenic protein-2 (BMP-2) and other osteogenic factors in static culture for up to 6 weeks. The calcium adsorption increased dramatically with increasing loading, as observed from biochemical assays, histological staining, and microcomputer tomography (μCT) analysis. Specifically, calcium content in the scaffolds increased by 0.57, 0.71, and 1.27 mg (per μg of DNA) from 3 to 6 weeks for matrix to particle dry mass loading ratios of 1:0, 1:1, and 1:2, respectively. In addition, μCT imaging revealed that at 6 weeks, bone volume fraction increased from 0.78% for non-reinforced to 7.1% and 6.7% for 1:1 and 1:2 loading, respectively. Our results support the hypothesis that scaffold stiffness may strongly influence the 3-D in vitro differentiation capabilities of hMSCs, providing a means to improve osteogenic outcomes.

Small-diameter vascular grafts of Bombyx mori silk fibroin prepared by a combination of electrospinning and sponge coating

The present study aimed to produce small-diameter grafts made of a silk fibroin by electrospinning. In order to reinforce the electrospun silk fibroin graft (ES), the graft was coated with a silk sponge (ESSC). Physical properties such as a diameter of the electrospun silk fibers were influenced by a concentration of fibroin solution. Ultimate tensile strength (UTS) of the ESSC graft was improved compared to the ES graft. However, the ESSC graft was less compliant than the ES graft. Importantly, water permeability of the ESSC graft was within the range of which endothelialization was promoted in previous studies.

Anterior cruciate ligament regeneration using mesenchymal stem cells and silk scaffold in large animal model

Although in vivo studies in small animal model show the ligament regeneration by implanting mesenchymal stem cells (MSCs) and silk scaffold, large animal studies are still needed to evaluate the silk scaffold before starting a clinical trial. The aim of this study is to regenerate anterior cruciate ligament (ACL) in pig model. The micro-porous silk mesh was fabricated by incorporating silk sponges into knitted silk mesh with lyophilization. Then the scaffold was prepared by rolling the micro-porous silk mesh around a braided silk cord to produce a tightly wound shaft. In vitro study indicated that MSCs proliferated profusely on scaffold and differentiated into fibroblast-like cells by expressing collagen I, collagen III and tenascin-C genes in mRNA level. Then the MSCs-seeded scaffold was implanted in pig model to regenerate ACL. At 24 weeks postoperatively, the MSCs in regenerated ligament exhibited fibroblast morphology. The key ligament-specific extracellular matrix components were produced prominently and indirect ligament–bone insertion with three zones (bone, Sharpey's fibers and ligament) was observed. Although there was remarkable scaffold degradation, the maximum tensile load of regenerated ligament could be maintained after 24 weeks of implantation. In conclusion, the results imply that silk-based material has great potentials for clinical applications.

In vivo study of anterior cruciate ligament regeneration using mesenchymal stem cells and silk scaffold

Although most in vitro studies indicate that silk is a suitable biomaterial for ligament tissue engineering, in vivo studies of implanted silk scaffolds for ligament reconstruction are still lacking. The objective of this study is to investigate anterior cruciate ligament (ACL) regeneration using mesenchymal stem cells (MSCs) and silk scaffold. The scaffold was fabricated by incorporating microporous silk sponges into knitted silk mesh, which mimicked the structures of ligament extracellular matrix (ECM). In vitro culture demonstrated that MSCs on scaffolds proliferated vigorously and produced abundant collagen. The transcription levels of ligament-specific genes also increased with time. Then MSCs/scaffold was implanted to regenerate ACL in vivo. After 24 weeks, histology observation showed that MSCs were distributed throughout the regenerated ligament and exhibited fibroblast morphology. The key ligament ECM components including collagen I, collagen III, and tenascin-C were produced prominently. Furthermore, direct ligament–bone insertion with typical four zones (bone, mineralized fibrocartilage, fibrocartilage, ligament) was reconstructed, which resembled the native structure of ACL–bone insertion. The tensile strength of regenerated ligament also met the mechanical requirements. Moreover, its histological grading score was significantly higher than that of control. In conclusion, the results imply that silk scaffold has great potentials in future clinical applications.

The interaction between a combined knitted silk scaffold and microporous silk sponge with human mesenchymal stem cells for ligament tissue engineering

Cell seeding on knitted scaffolds often require a gel system, which was found to be practically unsuitable for anterior cruciate ligament (ACL) reconstruction as the cell–gel composite often gets dislodged from the scaffold in the in vivo dynamic situations. In order to solve this problem, we fabricated this combined silk scaffold with weblike microporous silk sponges formed in the openings of a knitted silk scaffold and subsequently combined with adult human bone marrow-derived mesenchymal stem cells (hMSCs) for in vitro ligament tissue engineering. Human MSCs adhered and grew well on the combined silk scaffolds. Moreover, in comparison with the knitted silk scaffolds seeded with hMSCs in fibroin gel the cellular function was more actively exhibited on the combined silk scaffolds, as evident by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for ligament-related gene markers (e.g., type I, III collagen and tenascin-C), immunohistochemical and western blot evaluations of ligament-related extracellular matrix (ECM) components. While the knitted structure holds the microporous silk sponges together and provides the structural strength of the combined silk scaffold, the microporous structure of the silk sponges mimic the ECM which consequently promotes cell proliferation, function, and differentiation. This feature overcomes the limitation of knitted scaffold for ligament tissue engineering application.

Studies of Osteotropism on Both Sides of the Breast Cancer–Bone Interaction

While important advances have been made in the treatment of breast cancer (BrCa), little progress has been made in developing therapies for metastasis to bone, a complication that signals entry of the disease into an incurable phase. The process of identifying genes and gene signatures of BrCa associated with metastasis has begun. In contrast, knowledge of the contributions of bone to tumor-stroma interaction is still rudimentary. We are performing research designed to elucidate the mechanisms by which human BrCa metastasizes to bone (osteotropism). With evidence mounting that there is mutual recognition of BrCa and bone, we are investigating osteotropism from both sides of the tumor-stroma interface. We created a novel "all human" model in which human bone is transplanted into immunodeficient (NOD/SCID) mice. Human BrCa cells are injected into the mammary fat pad. Metastases later appear as metastases in the human bone, but not mouse skeleton. The model recapitulates the metastatic sequence occurring in patients. Using DNA microarrays, we plan to identify putative osteotropic genes expressed by metastatic BrCa cells. We will test the hypothesis that distinct "tool kits" are used by BrCa metastasizing to human bone. In addition, using human tissue-engineered bone, we are identifying components within bone stroma essential for metastasis, and osteotropism genes expressed by bone in response to the presence of BrCa. We recently demonstrated that tissue-engineered bone based on a silk sponge platform is a target for human BrCa metastasis, even in preference to the mouse skeleton.