Derivation and performance of an entirely autologous injectable hydrogel delivery system for cell-based therapies

Biomaterial-induced conversion of quiescent cardiomyocytes into pacemaker cells in rats

Pacemaker cells can be differentiated from stem cells or transdifferentiated from quiescent mature cardiac cells via genetic manipulation. Here we show that the exposure of rat quiescent ventricular cardiomyocytes to a silk-fibroin hydrogel activates the direct conversion of the quiescent cardiomyocytes to pacemaker cardiomyocytes by inducing the ectopic expression of the vascular endothelial cell-adhesion glycoprotein cadherin. The silk-fibroin-induced pacemaker cells exhibited functional and morphological features of genuine sinoatrial-node cardiomyocytes in vitro, and pacemaker cells generated via the injection of silk fibroin in the left ventricles of rats functioned as a surrogate in situ sinoatrial node. Biomaterials with suitable surface structure, mechanics and biochemistry could facilitate the scalable production of biological pacemakers for human use.

Effects of Matrix Metalloproteinases on the Performance of Platelet Fibrin Gel Spiked With Cardiac Stem Cells in Heart Repair

Stem cells and biomaterials have been studied for therapeutic cardiac repair. Previous studies have shown the beneficial effects of platelet fibrin gel and cardiac stem cells when cotransplanted into rodent hearts with myocardial infarction (MI). We hypothesized that matrix metalloproteinases (MMPs) play an important role in such protection. Thus, the present study is designed to elucidate the effects of MMP inhibition on the therapeutic benefits of intramyocardial injection of platelet fibrin gel spiked with cardiac stem cells (cell-gel) in a rat model of acute MI. In vitro, broad-spectrum MMP inhibitor GM6001 undermines cell spreading and cardiomyocyte contraction. In a syngeneic rat model of myocardial infarction, MMP inhibition blunted the recruitment of endogenous cardiovascular cells into the injected biomaterials, therefore hindering de novo angiogenesis and cardiomyogenesis. Echocardiography and histology 3 weeks after treatment revealed that metalloproteinase inhibition diminished the functional and structural benefits of cell-gel in treating MI. Reduction of host angiogenesis, cardiomyocyte cycling, and MMP-2 activities was evident in animals treated with GM6001. Our findings suggest that MMPs play a critical role in the therapeutic benefits of platelet fibrin gel spiked with cardiac stem cells for treating MI.

SIGNIFICANCE

In this study, the effects of matrix metalloproteinase inhibition on the performance of platelet gel spiked with cardiac stem cells (cell-gel) for heart regeneration are explored. The results demonstrate that matrix metalloproteinases are required for cell-gel to exert its benefits in cardiac repair. Inhibition of matrix metalloproteinases reduces cell engraftment, host angiogenesis, and recruitment of endogenous cardiovascular cells in rats with heart attack.

Systemic inflammatory cytokine analysis to monitor biomaterial augmented tissue healing

PURPOSE

Hernias can be repaired by reinforcement of damaged fascia using biomaterials to provide stabilisation. Repair materials are usually porous, through which cells infiltrate, proliferate and secrete ECM. Their efficacy relies on good tissue integration and resolution of host defence mechanisms. Therefore, understanding the dynamics by which biomaterials interact with tissue will provide knowledge to advance prosthesis design. Furthermore, determining host response in real time would provide significant advantage both clinically and scientifically over the current terminal process of histology.

METHODS

3 materials comprising synthetic and composite (synthetic materials hybridised with a resorbable biologic component) meshes were implanted into a rat full-thickness abdominal wall excision model. Their efficacy was evaluated using histopathology whilst also monitoring systemic concentrations of cytokines associated with inflammation and wound healing to predict material outcome over 12 weeks.

RESULTS

The noncomposite material (polyester) and Material B (polypropylene mesh with oligocaprone film and polydioxanone glue) stimulated the largest degree of adhesion from the 3 materials tested, although after 28 days adhesions were stronger to Material B. Histologically, all 3 materials integrated well with abdominal musculature and infiltrated completely with cells.

CONCLUSIONS

Analysis of systemic inflammation biomarkers confirmed inflammation elicited by surgeries and meshes irrespective of their composition. However, at an early postoperative endpoint (i.e., 1 week), some biomarkers, namely, IL-18 and RANTES, appeared to discriminate the noncomposite mesh from the composite materials, although in this study all materials successfully repaired the defects without recurrence or external indicators of postoperative chronic pain.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

Characterisation and comparison of the host response of 6 tissue-based surgical implants in a subcutaneous in vivo rat model

BACKGROUND

Hernia repair often involves fascial augmentation using biologic prostheses. Small processing changes during preparation modulate host tissue response, which influence material efficacy and longevity. In this pilot study, a rat model was used to determine the specific influence of tissue origin, decellularisation treatment and 1,6-hexamethylene diisocyanate (HMDI) cross-linking.

METHODS

Materials (1 cm2) were implanted subcutaneously into 6-week-old Wistar rats (4 materials per animal, n=6/material per time point) for 2, 5, 7, 14 and 28 days. Histologic processing was carried out after resin infiltration, observing classical histopathology and pathologic indexing. Materials comprised 6 tissue-based grafts covering both experimental and commercial porcine decellularised dermal and small intestinal submucosal materials.

RESULTS

Subcutaneous delivery of biologics demonstrated material-specific inflammatory/host responses. Controlled variations of the PermacolTM manufacturing process showed sodium dodecyl sulfate (SDS) was the most proinflammatory decellularisation reagent, and HMDI cross-linking had no effect on host response. All materials remained recoverable after 28 days, although SurgisisTM had partially resorbed.

CONCLUSION

Differences in host responses exist between biologic implants for hernia repair in this rat model. It is postulated that these modifications are induced during processing and may have an effect on the clinical outcome of hernia repair.

Paracrine effect of mesenchymal stem cells derived from human adipose tissue in bone regeneration

Mesenchymal stem cell (MSC) transplantation has proved to be a promising strategy in cell therapy and regenerative medicine. Although their mechanism of action is not completely clear, it has been suggested that their therapeutic activity may be mediated by a paracrine effect. The main goal of this study was to evaluate by radiographic, morphometric and histological analysis the ability of mesenchymal stem cells derived from human adipose tissue (Ad-MSC) and their conditioned medium (CM), to repair surgical bone lesions using an in vivo model (rabbit mandibles). The results demonstrated that both, Ad-MSC and CM, induce bone regeneration in surgically created lesions in rabbit's jaws, suggesting that Ad-MSC improve the process of bone regeneration mainly by releasing paracrine factors. The evidence of the paracrine effect of MSC on bone regeneration has a major impact on regenerative medicine, and the use of their CM can address some issues and difficulties related to cell transplants. In particular, CM can be easily stored and transported, and is easier to handle by medical personnel during clinical procedures.

The in vivo evaluation of tissue-based biomaterials in a rat full-thickness abdominal wall defect model

Hernias are defects in which an anatomical fascia is breached resulting in ectopic positioning of an organ into an orifice which routinely does not contain it. Intervention often involves repositioning translocated organs and repair of damaged fascia using exogenous grafts. Despite hernia prevalence, repairs can still fail due to postoperative complications, such as chronic pain and decreased mobility. This study compared repair capacities and characterized the foreign body response elicited by a number of hernia repair grafts to deduce their bulk inflammatory properties while also concluding the point in their fabrication when these are inferred. Materials derived from human dermis (Alloderm(®) ), porcine dermis (Permacol™, patch A, patch D and Strattice(®) ), porcine small-intestinal submucosa (Surgisis™) and a synthetic (multifilament Surgipro™) were implanted into a rat full-thickness abdominal wall excision model, incubated for up to 2 years and characterized histopathologically. Surgisis™ resorbed the fastest of the materials tested (1-3 months) resulting in a mechanically stable parietal peritoneum. Decellularization using sodium dodecyl sulfate (patch A) stimulated a large early inflammatory response which ultimately may have contributed to increased resorption of porcine dermal matrix however the remaining materials typically persisted throughout the 2-year incubation. Cross-linking porcine dermis using 1,6-hexamethylene disocyanate (vs. an identical noncross-linked counterpart) showed no difference in cell recruitment or material integration over 2 years. Typically Strattice(®) and Alloderm(®) recruited larger early populations of cells than Permacol™; however, over extended periods of time in vivo this response normalized.

Evaluation of six synthetic surgical meshes implanted subcutaneously in a rat model

The long-term efficacy and mechanical integrity of implanted materials is largely determined by early host response. Therefore, implanting materials with well-characterized tissue responses provides the greatest chance of 'one-hit' surgical successes, without repeated interventions to replace, repair or remove non-compliant biomaterials. Six synthetic meshes were implanted subcutaneously in a rat model to deduce and quantify modulations in host response, based on material fabrication variables. The materials consisted of knitting variations of polypropylene (PP), polyethyleneterephthalate (PET) and polyglycolic acid (PGA) yarns and were implanted for 2, 5, 7, 14 and 28 days before fixation and both semi- and fully quantitative histopathology. In a subcutaneous niche, material weight did not influence foreign body response. PET stimulated earlier inflammation than PP and PGA, which normalized over 28 days. Multifilament meshes recruited foreign body giant cells, which were largely absent from monofilaments. Using CD68, PGA was demonstrated to be the greatest leukocyte-activating polymer at a number of the time points analysed. This research therefore highlights that underlying polymer composition may be more over-arching in deciding the inflammatory properties of surgical meshes, based on increased macrophagic responses to PGA vs alternative base polymers of comparable weights and porosities. Copyright © 2013 John Wiley & Sons, Ltd.

The innate oxygen dependant immune pathway as a sensitive parameter to predict the performance of biological graft materials

Clinical performance of a biomaterial is decided early after implantation as leukocytes interrogate the graft throughout acute inflammation. High degrees of leukocyte activation lead to poor material/patient compliance, accelerated degeneration and graft rejection. A number reactive oxygen species (ROS) are released by leukocytes throughout their interaction with a material, which can be used as a sensitive measure of leukocyte activation. The aim of this study was to compare leukocyte activation by commercially available biologic surgical materials and define the extent manufacturing variables influence down-stream ROS response. Chemiluminescence assays were performed using modifications to a commercially available kit (Knight Scientific, UK). Whole blood was obtained from 4 healthy human adults at 7 day intervals for 4 weeks, combined with Adjuvant K, Pholasin (a highly sensitive ROS excitable photoprotein) and biomaterial, and incubated for 60 min with continuous chemiluminescent measurements. Leukocyte ROS inducers fMLP and PMA were added as controls. Xeno- and allogeneic dermal and small intestinal submucosal (SIS) derived biomaterials were produced commercially (Surgisis Biodesign™, Alloderm(®), Strattice(®)Firm & Pliable & Permacol™) or fabricated in house to induce variations in decellularisation and cross-linking. Statistics were performed using Waller-Duncan post hoc ranking. Materials demonstrated significant differences in leukocyte activation as a function of decellularisation reagent and tissue origin. The data demonstrated SIS was significantly more pro-inflammatory than dermis. Additionally it was deduced that SDS during decellularisation induced pro-inflammatory changes to dermal materials. Furthermore, it was possible to conclude inter-patient variation in leukocyte response. The in vitro findings were validated in vivo which confirmed the chemiluminescence observations, highlighting the potential for translation of this technique as a routine component of pre-surgical evaluation to maximise foreign body compliance.

A feeder-free, human plasma-derived hydrogel for maintenance of a human embryonic stem cell phenotype in vitro

Background

Human embryonic stem cells (hESCs) represent a tremendous resource for cell therapies and the study of human development; however to maintain their undifferentiated state in vitro they routinely require the use of mouse embryonic fibroblast (MEF) feeder-layers and exogenous protein media supplementation.

Results

These well established requirements can be overcome and in this study, it will be demonstrated that phenotypic stability of hESCs can be maintained using a novel, human plasma protein-based hydrogel as an extracellular culture matrix without the use of feeder cell co-culture. hESCs were resuspended in human platelet poor plasma (PPP), which was gelled by the addition of calcium containing DMEM-based hESC culture medium. Phenotypic and genomic expression of the pluripotency markers OCT4, NANOG and SOX2 were measured using immunohistochemistry and qRT-PCR respectively. Typical hESC morphology was demonstrated throughout in vitro culture and both viability and phenotypic stability were maintained throughout extended culture, up to 25 passages.

Conclusions

PPP-derived hydrogel has demonstrated to be an efficacious alternative to MEF co-culture with its hydrophilicity allowing for this substrate to be delivered via minimally invasive procedures in a liquid phase with polymerization ensuing in situ. Together this provides a novel technique for the study of this unique group of stem cells in either 2D or 3D both in vitro and in vivo.

Intramyocardial injection of platelet gel promotes endogenous repair and augments cardiac function in rats with myocardial infarction

OBJECTIVES

This study sought to explore the therapeutic potential of platelet gel for the treatment of myocardial infarction.

BACKGROUND

Cardiac dysfunction after acute myocardial infarction is a major cause of heart failure. Current therapy relies on prompt reperfusion and blockage of secondary maladaptive pathways by small molecules. Platelet gels are biomaterials rich in cytokines and growth factors, which can be manufactured in an autologous manner and are effective in various models of wound healing. However, the potential utility of platelet gel in cardiac regeneration has yet to be tested.

METHODS

Platelet gel was derived from syngeneic rats and its morphology, biocompatibility, secretion of beneficial factors, and in vivo degradation profile were characterized.

RESULTS

After delivery into infarcted rat hearts, the gel was efficiently infiltrated by cardiomyocytes and endothelial cells. Gel-treated hearts exhibited enhanced tissue protection, greater recruitment of endogenous regeneration, higher capillary density, and less compensatory myocyte hypertrophy. The cardiac function of control-injected animals deteriorated over the 6-week time course, while that of platelet gel-injected animals did not. In addition, the gel did not exacerbate inflammation in the heart.

CONCLUSIONS

Intramyocardial injection of autologous platelet gel ameliorated cardiac dysfunction after myocardial infarction. The striking functional benefits, the simplicity of manufacturing, and the potentially autologous nature of this biomaterial provide impetus for further translation.

Improvement of neural stem cell survival in collagen hydrogels by incorporating laminin-derived cell adhesive polypeptides

Cell transplantation is a potential methodology for the treatment of Parkinson's disease. However, the therapeutic effect is limited by poor viability of transplanted cells. To overcome this problem, we hypothesized that a dual step approach, whereby providing an adhesive substrate for transplanted cells and, at the same time, by preventing the infiltration of activated microglia into the site of transplantation promotes the cell survival. To establish above conditions, attempts were made to prepare 3-D matrices using collagen hydrogels that incorporated integrin-binding polypeptides derived from laminin-1. Tandem combinations of laminin globular domains as well as a single globular domain 3 were prepared using recombinant DNA technology as a fusion with hexahistidine and bound to metal chelated surfaces to screen for the adhesion and proliferation of neural stem cells (NSCs). In addition, a small peptide derived from laminin γ1 chain was prepared and heterodimerized with the globular domain-containing chimeric proteins to evaluate for the enhancement of integrin-mediated cell adhesion. As a result, a heterodimer consisting of the globular domain 3 of the laminin α1 chain and the peptide from the laminin γ1 chain was selected as the best candidate among the polypeptides studied here for the incorporation into a collagen hydrogel. It was shown that the survival of NSCs was indeed promoted in the collagen hydrogel incorporating the heterodimer compared to the pure collagen hydrogel.

Transplantation of platelet gel spiked with cardiosphere-derived cells boosts structural and functional benefits relative to gel transplantation alone in rats with myocardial infarction

The emerging field of stem cell therapy and biomaterials has begun to provide promising strategies for the treatment of ischemic cardiomyopathy. Platelet gel and cardiosphere-derived cells (CDCs) are known to be beneficial when transplanted separately post-myocardial infarction (MI). We hypothesize that pre-seeding platelet gel with CDCs can enhance therapeutic efficacy. Platelet gel and CDCs were derived from venous blood and heart biopsies of syngeneic rats, respectively. In vitro, the viability, growth, and morphology of CDCs cultured in platelet gel were characterized. When delivered into infarcted rat hearts, platelet gel pre-seeded with CDCs was more efficiently populated with endogenous cardiomyocytes and endothelial cells than platelet gel alone. Recruitment of endogenous c-kit positive cells was enhanced in the hearts treated with gel with CDC. At 3 weeks, the hearts treated with CDC-seeded platelet gel exhibited the greatest attenuation of adverse left ventricular (LV) remodeling and the highest cardiac function (i.e., LV ejection fraction) as compared to hearts transplanted with Gel only or vehicle controls. Histological analysis revealed that, though some transplanted CDCs differentiated into cardiomyocytes and endothelial cells in the recipients' hearts, most of the incremental benefit arose from CDC-mediated endogenous repair. Pre-seeding platelet gel with CDCs enhanced the functional benefit of biomaterial therapy for treating myocardial infarction.

Injectable delivery system of 2-methoxyestradiol for breast cancer therapy using biodegradable thermosensitive poly(organophosphazene) hydrogel

2-Methoxyestradiol (2-ME) has been reported to have antiangiogenic and antitumor activity. Its biomedical application is limited due to its poor water solubility resulting in its low bioavailability. Poly(organophosphazenes) containing l-isoleucine ethyl ester, ethyl-2-(O-glycyl)lactate, and α-amino-ω-methoxy-poly(ethylene glycol) 550 were synthesized having M(W) of 35-38 kDa and polydispersity index of 2.38-2.73. Using a viscometer, the thermosensitivity useful for locally injectable drug delivery was verified. The aqueous polymer solution showed a sol state at a low temperature and transformed to a gel state at body temperature. The polymer solution (10 wt%) enhanced the solubility of 2-ME by about 10(4) times compared to that of phosphate buffered saline. 2-ME was released from the hydrogel mainly by diffusion, hydrophobic interaction, and surface erosion of the matrix. This release profile could be confirmed through an in vitro release test as a function of polymers and the concentration of 2-ME in hydrogels. By monitoring tumor volume and CD31 immunohistochemical staining in mouse orthotopic breast tumor (MDA-MB-231) model, it was found that the hydrogel containing a relatively low concentration (15 mg/kg) of 2-ME showed the improved antitumor and antiangiogenic activity relative to the original formulation. This research suggests that the developed formulation of poly(organophosphazenes) may have injectable carrier potentials for 2-ME and other lipophilic drugs.