Toward the development of partially biodegradable and injectable thermoresponsive hydrogels for potential biomedical applications

Phase transition and potential biomedical applications of thermoresponsive compositions based on polysaccharides, proteins and DNA: A review

Smart thermoresponsive polymers have long attracted attention as materials of a great potential for biomedical applications, mainly for drug delivery, tissue engineering and wound dressing, with a special interest to injectable hydrogels. Poly-N-isopropylacrylamide (PNIPAM) is the most important synthetic thermoresponsive polymer due to its physiologically relevant transition temperature. However, the use of unmodified PNIPAM encounters such problems as low biodegradability, low drug loading capacity, slow response to thermal stimuli, and insufficient mechanical robustness. The use of natural polysaccharides and proteins in combinations with PNIPAM, in the form of grafted copolymers, IPNs, microgels and physical mixtures, is aimed at overcoming these drawbacks and creating dual-functional materials with both synthetic and natural polymers' properties. When developing such compositions, special attention should be paid to preserving their key property, thermoresponsiveness. Addition of hydrophobic and hydrophilic fragments to PNIPAM is known to affect its transition temperature. This review covers various classes of natural polymers - polysaccharides, fibrous and non-fibrous proteins, DNA - used in combination with PNIPAM for the prospective biomedical purposes, with a focus on their phase transition temperatures and its relation to the natural polymer's structure.

Stimuli-responsive hydrogels: smart state of-the-art platforms for cardiac tissue engineering

Biomedicine and tissue regeneration have made significant advancements recently, positively affecting the whole healthcare spectrum. This opened the way for them to develop their applications for revitalizing damaged tissues. Thus, their functionality will be restored. Cardiac tissue engineering (CTE) using curative procedures that combine biomolecules, biomimetic scaffolds, and cells plays a critical part in this path. Stimuli-responsive hydrogels (SRHs) are excellent three-dimensional (3D) biomaterials for tissue engineering (TE) and various biomedical applications. They can mimic the intrinsic tissues' physicochemical, mechanical, and biological characteristics in a variety of ways. They also provide for 3D setup, adequate aqueous conditions, and the mechanical consistency required for cell development. Furthermore, they function as competent delivery platforms for various biomolecules. Many natural and synthetic polymers were used to fabricate these intelligent platforms with innovative enhanced features and specialized capabilities that are appropriate for CTE applications. In the present review, different strategies employed for CTE were outlined. The light was shed on the limitations of the use of conventional hydrogels in CTE. Moreover, diverse types of SRHs, their characteristics, assembly and exploitation for CTE were discussed. To summarize, recent development in the construction of SRHs increases their potential to operate as intelligent, sophisticated systems in the reconstruction of degenerated cardiac tissues.

Designing Double-Layer Multi-Material Composite Patch Scaffold with Adhesion Resistance for Hernia Repair

Hernia repair mesh is associated with a number of complications, including adhesions and limited mobility, due to insufficient mechanical strength and non-resorbability. Among them, visceral adhesions are one of the most serious complications of patch repair. In this study, a degradable patch with an anti-adhesive layer was prepared for hernia repair by 3D printing and electrospinning techniques using polycaprolactone (PCL), polyvinyl alcohol (PVA), and soybean peptide (SP). The study into the physicochemical properties of the patch was found that it had adequate mechanical strength requirements (16 N cm^-1 ) and large elongation at break, which were superior than commercial polypropylene (PP) patches. In vivo and in vitro experiments showed that human umbilical vein endothelial cells (HUVECs) proliferated well on composite patches, and showed excellent biocompatibility with the host and little adhesion through a rat abdominal wall defect model. In conclusion, the results of this study show that composite patch can effectively reduce the occurrence of adhesions, while the addition of SP in the patch further enhances its biocompatibility. We believe that a regenerative biological patch with great potential in hernia repair provides a new strategy for the development of new biomimetic biodegradable patches. This article is protected by copyright. All rights reserved.

Co-Delivery of Paclitaxel and shMCL-1 by Folic Acid-Modified Nonviral Vector to Overcome Cancer Chemotherapy Resistance

Acquired chemoresistance presents a major clinical impediment, which is an urgent problem to be solved. Interestingly, myeloma cell leukemia-1 (MCL-1) and folate receptor expression levels are higher in chemotherapy-resistant patients than in pretreatment patients. In this study, a multifunctional folic acid (FA)-targeting core-shell structure is presented for simultaneous delivery of shMCL-1 and paclitaxel (PTX). The transfection efficiency of shMCL-1 with the FA-targeting delivery system is higher than with a nontargeting delivery system in Skov3 and A2780T cells. The FA-targeting system significantly inhibits cell growth, blocks cell cycles, and promotes apoptosis of cancer cells in vitro. The mechanisms involved in inhibiting growth are related to Bcl-2/Bax and cdc2/Cyclin B1 pathways. An analysis of RNA sequencing suggests that shMCL-1 reverses chemoresistance through regulating genes such as regulator of chromosome condensation 2 (RCC2). The synergetic effect of shMCL-1 and PTX effectively inhibits tumor growth in both PTX-resistant and normal cancer models by inducing tumor apoptosis, inhibiting proliferation, and limiting tumor angiogenesis. The study results indicate that a FA-targeting delivery system combining shMCL-1 with PTX can simultaneously target tumor sites and restore the sensitivity of chemotherapy-resistant cancer to PTX. These findings have important implications for patients with normal or PTX-resistant cancer.

Beyond Color: The New Carbon Ink

For thousands of years, carbon ink has been used as a black color pigment for writing and painting purposes. However, recent discoveries of nanocarbon materials, including fullerenes, carbon nanotubes, graphene, and their various derivative forms, together with the advances in large-scale synthesis, are enabling a whole new generation of carbon inks that can serve as an intrinsically programmable materials platform for developing advanced functionalities far beyond color. The marriage between these multifunctional nanocarbon inks with modern printing technologies is facilitating and even transforming many applications, including flexible electronics, wearable and implantable sensors, actuators, and autonomous robotics. This review examines recent progress in the reborn field of carbon inks, highlighting their programmability and multifunctionality for applications in flexible electronics and stimuli-responsive devices. Current challenges and opportunities will also be discussed from a materials science perspective towards the advancement of carbon ink for new applications beyond color.

Cardiac Stem Cell-Loaded Delivery Systems: A New Challenge for Myocardial Tissue Regeneration

Cardiovascular disease (CVD) remains the leading cause of death in Western countries. Post-myocardial infarction heart failure can be considered a degenerative disease where myocyte loss outweighs any regenerative potential. In this scenario, regenerative biology and tissue engineering can provide effective solutions to repair the infarcted failing heart. The main strategies involve the use of stem and progenitor cells to regenerate/repair lost and dysfunctional tissue, administrated as a suspension or encapsulated in specific delivery systems. Several studies demonstrated that effectiveness of direct injection of cardiac stem cells (CSCs) is limited in humans by the hostile cardiac microenvironment and poor cell engraftment; therefore, the use of injectable hydrogel or pre-formed patches have been strongly advocated to obtain a better integration between delivered stem cells and host myocardial tissue. Several approaches were used to refine these types of constructs, trying to obtain an optimized functional scaffold. Despite the promising features of these stem cells’ delivery systems, few have reached the clinical practice. In this review, we summarize the advantages, and the novelty but also the current limitations of engineered patches and injectable hydrogels for tissue regenerative purposes, offering a perspective of how we believe tissue engineering should evolve to obtain the optimal delivery system applicable to the everyday clinical scenario.

Drug-loaded and Blue-ray Filtered Hydrogel as a Potential Intraocular Lens for Cataract Treatment

Background:

Indomethacin (IND) is a class of non-steroidal, anti-inflammatory drugs, which is used to treat various kinds of ocular inflammation, and has been reported to prevent posterior capsule opacification (PCO) by inhibiting the mitosis and collagen synthesis of human lens epithelial cells (LECs). In addition, the specific absorption spectrum of indomethacin shows the effect of absorbing short-wavelength blue-violet light.

Objective:

We prepared an indomethacin-loaded hydrogel as a potential intraocular lens (IOLs) material to prevent endophthalmitis, PCO and filter harmful blue light.

Methods:

Indomethacin prodrugs (HEMA-IND) (HI) were prepared by esterification of indomethacin and 2-hydroxyethyl methacrylate (HEMA), and poly (HEMA-co-MAA-co-MMA-co- HI) (HAMI) hydrogels were prepared by free-radical polymerization of 2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), methacrylic acid (MAA) and HI. The physical and chemical properties of obtained hydrogel were detected, including optical, morphology, thermomechanical and surface properties, equilibrium water content, drug release behaviors and cytotoxicity.

Results:

HAMI hydrogels can filter harmful short-wavelength blue light and show other necessary properties like visible light transparency, glass transition temperatures, mechanical strength, and biocompatibility for making intraocular lenses. Meanwhile, MAA increases the hydrophilicity of the hydrogels, resulting in a lower water contact angle and controllable drug release from the hydrogels.

Conclusion:

In summary, HAMI hydrogels show a great potential as IOL biomaterials that can maintain the sustained release of indomethacin and filter harmful blue light after cataract surgery.

Lay Summary:

People with cataract surgery can be at high risk of postoperative complications, such as PCO and postoperative endophthalmitis. Moreover, early IOLs allowed all ultraviolet (UV) and visible light to pass through retina without restriction, thus to damage the retina and the retinal pigment epithelium, which may lead to retinopathy and age-related macular degeneration (AMD). Herein, we sought to design and prepare a kind of IOLs loaded with indomethacin to mitigate those postoperative complications and filter harmful blue light to improve the treatment prognosis.

Intra-myocardial Delivery of a Novel Thermosensitive Hydrogel Inhibits Post-infarct Heart Failure After Degradation in Rat

Whether intra-myocardial delivery of hydrogel can prevent post-infarct heart failure (HF) in a long follow-up period, especially after it is degraded, remains unclear. In this study, Dex-PCL-HEMA/PNIPAAm (DPHP) hydrogel was delivered into peri-infarct myocardium of rat when coronary artery was ligated, while PBS was employed as control. Twelve weeks later, compared with control, left ventricle remodeling was attenuated and cardiac function was preserved; serum brain natriuretic peptide, cardiac aldosterone, and pulmonary congestion were suppressed in hydrogel group. Pro-fibrogenic mRNA increased in infarct area while decreased in remote zone, as well as hypertrophic mRNA. These data proves DPHP hydrogel suppresses ventricular remodeling and HF by promoting fibrotic healing in infarct area and inhibiting reactive fibrosis and hypertrophy in remote zone. Timely intra-myocardial hydrogel implantation is an effective strategy to inhibit post-infarct cardiac remodeling and have a long-term beneficial effect even after it has been biodegraded.

Extravascular gelation shrinkage-derived internal stress enables tumor starvation therapy with suppressed metastasis and recurrence

Despite the efficacy of current starvation therapies, they are often associated with some intrinsic drawbacks such as poor persistence, facile tumor metastasis and recurrence. Herein, we establish an extravascular gelation shrinkage-derived internal stress strategy for squeezing and narrowing blood vessels, occluding blood & nutrition supply, reducing vascular density, inducing hypoxia and apoptosis and eventually realizing starvation therapy of malignancies. To this end, a biocompatible composite hydrogel consisting of gold nanorods (GNRs) and thermal-sensitive hydrogel mixture was engineered, wherein GRNs can strengthen the structural property of hydrogel mixture and enable robust gelation shrinkage-induced internal stresses. Systematic experiments demonstrate that this starvation therapy can suppress the growths of PANC-1 pancreatic cancer and 4T1 breast cancer. More significantly, this starvation strategy can suppress tumor metastasis and tumor recurrence via reducing vascular density and blood supply and occluding tumor migration passages, which thus provides a promising avenue to comprehensive cancer therapy.

A thermo-sensitive, injectable and biodegradable in situ hydrogel as a potential formulation for uveitis treatment

The thermo-sensitive hydrogels with high drug loading rate achieved sustained drug release over 2 weeks. Histopathological examination of retina confirmed the excellent biocompatibility and effective anti-inflammatory property of the hydrogel.

Thermoresponsive polysaccharides and their thermoreversible physical hydrogel networks

Thermoresponsive polymers have been used extensively for various applications including food additives, pharmaceutical formulations, therapeutic delivery, cosmetics and environmental remediation, to mention a few. Many thermoresponsive polymers have the ability to form physical hydrogel networks in response to temperature changes, which are particularly useful for emerging biomedical applications, including cell therapies, drug delivery systems, tissue engineering, wound healing and 3D bioprinting. In particular, the use of polysaccharides with thermoresponsive properties has been of interest due to their wide availability, versatile functionality, biodegradability, and in many cases, inherent biocompatibility. Naturally thermoresponsive polysaccharides include agarose, carrageenans and gellan gum, which exhibit upper critical solution temperatures, transitioning from a solution to a gel state upon cooling. Arguably, this limits their use in biomedical applications, particularly for cell encapsulation as they require raised temperatures to maintain a solution state that may be detrimental to living systems. Conversely, significant progress has been made over recent years to develop synthetically modified polysaccharides, which tend to exhibit lower critical solution temperatures, transitioning from a solution to a gel state upon warming. Of particular interest are thermoresponsive polysaccharides with a lower critical solution temperature in between room temperature and physiological temperature, as their solutions can conveniently be manipulated at room temperature before gelling upon warming to physiological temperature, which makes them ideal candidates for many biological applications. Therefore, this review provides an introduction to the different types of thermoresponsive polysaccharides that have been developed, their resulting hydrogels and properties, and the exciting applications that have emerged as a result of these properties.

Transiently thermoresponsive polymers and their applications in biomedicine

The focus of this review is on the class of transiently thermoresponsive polymers. These polymers are thermoresponsive, but gradually lose this property upon chemical transformation - often a hydrolysis reaction - in the polymer side chain or backbone. An overview of the different approaches used for the design of these polymers along with their physicochemical properties is given. Their amphiphilic properties and degradability into fully soluble compounds make this class of responsive polymers attractive for drug delivery and tissue engineering applications. Examples of these are also provided in this review.

Injectable hydrogels for delivering biotherapeutic molecules

To date, numerous delivery systems based on either organic or inorganic material have been developed to achieve efficient and sustained delivery of therapeutics. Hydrogels, which are three dimensional networks of crosslinked hydrophilic polymers, have a significant role in solving the clinical and pharmacological limitations of present systems because of their biocompatibility, ease of preparation and unique physical properties such as a tunable porous nature and affinity for biological fluids. Development of an in situ forming injectable hydrogel system has allowed excellent spatial and temporal control, unlike systemically administered therapeutics. Injectable hydrogel systems can offset difficulties with conventional hydrogel-based drug delivery systems in the clinic by forming a drug/gene delivery or cell-growing depot in the body with a single injection, thereby enabling patient compliance and comfort. Carbohydrate polymers are widely used for the synthesis of injectable in situ-forming hydrogels because of ready availability, presence of modifiable functional groups, biocompatibility and other physiochemical properties. In this review, we discuss different aspects of injectable hydrogels, such as bulk hydrogels/macrogels, microgels, and nanogels derived from natural polymers, and their importance in the delivery of therapeutics such as genes, drugs, cells or other biomolecules and how these revolutionary systems can complement existing therapeutic delivery systems.

Intramyocardial delivery of bFGF with a biodegradable and thermosensitive hydrogel improves angiogenesis and cardio-protection in infarcted myocardium

Basic fibroblast growth factor (bFGF), a known angiogenic factor, may provide a potential strategy for the treatment of myocardial infarction (MI), but it is limited by a relatively short half-life. Dex-PCL-HEMA/PNIPAAm hydrogel provides a reservoir for the controlled release of growth factors. The aim of the current study was to evaluate the effects of bFGF incorporated into a Dex-PCL-HEMA/PNIPAAm hydrogel on angiogenesis and cardiac health in a rat model of acute MI, induced by coronary artery ligation. Phosphate-buffered solution (PBS group), Dex-PCL-HEMA/PNIPAAm hydrogel (Gel group), bFGF in phosphate-buffered solution (bFGF group) or bFGF in hydrogel (Gel + bFGF group) was injected into a peri-infarcted area of cardiac tissue immediately following MI. On day 30 post-surgery, cardiac function was assessed by echocardiography, apoptosis index by terminal deoxynucleotidyl transferase dUTP nick-end labeling assessment and vascular development by immunohistochemical staining. The findings demonstrated that injection of bFGF along with hydrogel induced angiogenesis, reduced collagen content, MI area and cell apoptosis and improved cardiac function compared with the injection of either bFGF or hydrogel alone. bFGF incorporated with Dex-PCL-HEMA/PNIPAAm hydrogel injection induces angiogenesis, attenuates cardiac remodeling and improves cardiac function following MI.

Artificial Cardiac Muscle with or without the Use of Scaffolds

During the past several decades, major advances and improvements now promote better treatment options for cardiovascular diseases. However, these diseases still remain the single leading cause of death worldwide. The rapid development of cardiac tissue engineering has provided the opportunity to potentially restore the contractile function and retain the pumping feature of injured hearts. This conception of cardiac tissue engineering can enable researchers to produce autologous and functional biomaterials which represents a promising technique to benefit patients with cardiovascular diseases. Such an approach will ultimately reshape existing heart transplantation protocols. Notable efforts are accelerating the development of cardiac tissue engineering, particularly to create larger tissue with enhanced functionality. Decellularized scaffolds, polymer synthetics fibrous matrix, and natural materials are used to build robust cardiac tissue scaffolds to imitate the morphological and physiological patterns of natural tissue. This ultimately helps cells to implant properly to obtain endogenous biological capacity. However, newer designs such as the hydrogel scaffold-free matrix can increase the applicability of artificial tissue to engineering strategies. In this review, we summarize all the methods to produce artificial cardiac tissue using scaffold and scaffold-free technology, their advantages and disadvantages, and their relevance to clinical practice.

Injectable and 3D Bioprinted Polysaccharide Hydrogels: From Cartilage to Osteochondral Tissue Engineering

Biomechanical performance of functional cartilage is executed by the exclusive anisotropic composition and spatially varying intricate architecture in articulating ends of diarthrodial joint. Osteochondral tissue constituting the articulating ends comprise superfical soft cartilage over hard subchondral bone sandwiching interfacial soft-hard tissue. The shock-absorbent, lubricating property of cartilage and mechanical stability of subchondral bone regions are rendered by extended chemical structure of glycosaminoglycans and mineral deposition, respectively. Extracellular matrix glycosaminoglycans analogous polysaccharides are major class of hydrogels investigated for restoration of functional cartilage. Recently, injectable hydrogels have gained momentum as it offers patient compliance, tunable mechanical properties, cell deliverability, and facile administration at physiological condition with long-term functionality and hyaline cartilage construction. Interestingly, facile modifiable functional groups in carbohydrate polymers impart tailorability of desired physicochemical properties and versatile injectable chemistry for the development of highly potent biomimetic in situ forming scaffold. The scaffold design strategies have also evolved from single component to bi- or multilayered and graded constructs with osteogenic properties for deep subchondral regeneration. This review highlights the significance of polysaccharide structure-based functions in engineering cartilage tissue, injectable chemistries, strategies for combining analogous matrices with cells/stem cells and biomolecules and multicomponent approaches for osteochondral mimetic constructs. Further, the rheology and precise spatiotemporal positioning of cells in hydrogel bioink for rapid prototyping of complex three-dimensional anisotropic cartilage have also been discussed.

A Review of Injectable Polymeric Hydrogel Systems for Application in Bone Tissue Engineering

Biodegradable, stimuli-responsive polymers are essential platforms in the field of drug delivery and injectable biomaterials for application of bone tissue engineering. Various thermo-responsive hydrogels display water-based homogenous properties to encapsulate, manipulate and transfer its contents to the surrounding tissue, in the least invasive manner. The success of bioengineered injectable tissue modified delivery systems depends significantly on their chemical, physical and biological properties. Irrespective of shape and defect geometry, injectable therapy has an unparalleled advantage in which intricate therapy sites can be effortlessly targeted with minimally invasive procedures. Using material testing, it was found that properties of stimuli-responsive hydrogel systems enhance cellular responses and cell distribution at any site prior to the transitional phase leading to gelation. The substantially hydrated nature allows significant simulation of the extracellular matrix (ECM), due to its similar structural properties. Significant current research strategies have been identified and reported to date by various institutions, with particular attention to thermo-responsive hydrogel delivery systems, and their pertinent focus for bone tissue engineering. Research on future perspective studies which have been proposed for evaluation, have also been reported in this review, directing considerable attention to the modification of delivering natural and synthetic polymers, to improve their biocompatibility and mechanical properties.

Injectable and Thermosensitive Hydrogel Containing Liraglutide as a Long-Acting Antidiabetic System

Diabetes, a global epidemic, has become a serious threat to public health. The present study is aimed at constructing an injectable thermosensitive PEG-polyester hydrogel formulation of liraglutide (Lira), a "smart" antidiabetic polypeptide, in the long-acting treatment of type 2 diabetes mellitus. A total of three thermosensitive poly(ε-caprolactone-co-glycolic acid)-poly(ethylene glycol)-poly(ε-caprolactone-co-glycolic acid) (PCGA-PEG-PCGA) triblock copolymers with similar molecular weights but different ε-caprolactone-to-glycolide (CL-to-GA) ratios were synthesized. The polymer aqueous solutions exhibited free-flowing sols at room temperature and formed in situ hydrogels at body temperature. While the different bulk morphologies, stabilities of aqueous solutions, and the varying in vivo persistence time of hydrogels in ICR mice were found among the three copolymers, all of the Lira-loaded gel formulations exhibited a sustained drug release manner in vitro regardless of CL-to-GA ratios. The specimen with a powder form in the bulk state, a stable aqueous solution before heating, and an appropriate degradation rate in vivo was selected as the optimal carrier to evaluate the in vivo efficacy. A single injection of the optimal gel formulation showed a remarkable hypoglycemic efficacy up to 1 week in diabetic db/db mice. Furthermore, three successive administrations of this gel formulation within one month significantly lowered glycosylated hemoglobin and protected islets of db/db mice. As a result, a promising once-weekly delivery system of Lira was developed, which not only afforded long-term glycemic control but also significantly improved patient compliance.

Stem cells and injectable hydrogels: Synergistic therapeutics in myocardial repair

One of the major problems in the treatment of cardiovascular diseases is the inability of myocardium to self-regenerate. Current therapies are unable to restore the heart's function after myocardial infarction. Myocardial tissue engineering is potentially a key approach to regenerate damaged heart muscle. Myocardial patches are applied surgically, whereas injectable hydrogels provide effective minimally invasive approaches to recover functional myocardium. These hydrogels are easily administered and can be either cell free or loaded with bioactive agents and/or cardiac stem cells, which may apply paracrine effects. The aim of this review is to investigate the advantages and disadvantages of injectable stem cell-laden hydrogels and highlight their potential applications for myocardium repair.

Biodegradable, thermoresponsive PNIPAM-based hydrogel scaffolds for the sustained release of levofloxacin

The cumulative release of LVF-loaded TBHs exhibited a thermo-induced slow sustained drug release and a reduction-induced fast release.

Using carbohydrate-based biomaterials as scaffolds to control human stem cell fate

This review describes the current state and applications of several important and extensively studied natural polysaccharide and glycoprotein scaffolds that can control the stem cell fate.

pH dependent thermoresponsive behavior of acrylamide–acrylonitrile UCST-type copolymers in aqueous media

pH-dependent UCST-transitions and influence of sacrificial additives on the thermoresponsivity of acrylamide- acrylonitrile copolymers is shown.

Effective Bone Regeneration Using Thermosensitive Poly(N-Isopropylacrylamide) Grafted Gelatin as Injectable Carrier for Bone Mesenchymal Stem Cells

In this study, thermosensitive poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto gelatin via atom transfer radical polymerization (ATRP). The chemical structure of PNIPAAm-grafted gelatin (Gel-PNIPAAm) was confirmed by XPS, ATR-IR, and (1)H NMR characterizations. Gel-PNIPAAm aqueous solution exhibited sol-to-gel transformation at physiological temperature, and was studied as injectable hydrogel for bone defect regeneration in a cranial model. The hydrogel was biocompatible and demonstrated the ability to enhance bone regeneration in comparison with the untreated group (control). With the incorporation of rat bone mesenchymal stem cells (BMSCs) into the hydrogel, the bone regeneration rate was further significantly enhanced. As indicated by micro-CT, histological (H&E and Masson) and immunohistochemical (osteocalcin and osteopontin) staining, newly formed woven bone tissue was clearly detected at 12 weeks postimplantation in the hydrogel/BMSCs treated group, showing indistinguishable boundary with surrounding host bone tissues. The results suggested that the thermosensitive Gel-PNIPAAm hydrogel was an excellent injectable delivery vehicle of BMSCs for in vivo bone defect regeneration.

Intramyocardial delivery of VEGF165 via a novel biodegradable hydrogel induces angiogenesis and improves cardiac function after rat myocardial infarction

Vascular endothelial growth factor (VEGF), an independent mitogen, has been reported to induce angiogenesis and thus attenuates the damage induced by myocardial infarction (MI). VEGF165 is the most abundant and predominant isoform of VEGF. This study investigates whether this effect could be strengthened by local intramyocardial injection of VEGF165 along with a novel biodegradable Dex-PCL-HEMA/PNIPAAm hydrogel and ascertains its possible mechanism of action. Rat models of myocardial infarction were induced by coronary artery ligation. Phosphate-buffered saline (PBS group), Dex-PCL-HEMA/PNIPAAm hydrogel (Gel group), phosphate-buffered saline containing VEGF165 (VP group), and hydrogel containing VEGF165 (VPG group) were injected into a peri-infarcted area of cardiac tissue immediately after myocardial infarction, respectively. The sham group was thoracic but without myocardial infarction. The injection of VEGF165 along with a hydrogel induced angiogenesis, reduced collagen content and MI area, inhibited cell apoptosis, increased the level of VEGF165 protein and the expression of flk-1 and flt-1, and improved cardiac function compared with the injection of either alone after MI in rats. The results suggest that injection of VEGF165 along with a hydrogel acquires more cardioprotective effects than either alone in rat with MI by sustained release of VEGF165, then may enhance the feedback between VEGF and its receptors flk-1 and flt-1.

Supramolecular association of 2D alumino-siloxane aquagel building blocks to 3D porous cages and its efficacy for topical and injectable delivery of fluconazole, an antifungal drug

A fascinating 2D architecture of an alumino-siloxane gel self-assembled into a well-defined 3D porous aquagel cage. It is identified to be an excellently mechanically stable, injectable and non-cytotoxic medium for drug delivery applications.

Degradable/cytocompatible and pH responsive amphiphilic conetwork gels based on agarose-graft copolymers and polycaprolactone

Amphiphilic conetwork gels based on graft copolymers of agarose and polycaprolactone exhibited desirable cytocompatibility/blood compatibility and pH responsive release of hydrophilic and hydrophobic drugs, and may be suitable for biomedical applications.

Evaluation of a thermoresponsive polycaprolactone scaffold for in vitro three-dimensional stem cell differentiation

Tissue engineering (TE) strategies aim at imitating the natural process of regeneration by using bioresorbable scaffolds that support cellular attachment, migration, proliferation, and differentiation. Based on the idea of combining a fully degradable polymer [poly(ɛ-caprolactone)] with a thermoresponsive polymer (polyethylene glycol methacrylate), a scaffold was developed, which liquefies below 20°C and solidifies at 37°C. In this study, this scaffold was evaluated for its ability to support C2C12 cells and human adipose-derived stem cells (ASCs) to generate an expandable three-dimensional (3D) construct for soft or bone TE. As a first step, biomaterial seeding was optimized and cellular attachment, survival, distribution, and persistence within the 3D material were characterized. C2C12 cells were differentiated toward the osteogenic as well as myogenic lineage, while ASCs were cultured in control, adipogenic, or osteogenic differentiation media. Differentiation was examined using quantitative real-time PCR for the expression of osteogenic, myogenic, and adipogenic markers and by enzyme activity and immunoassays. Both cell types attached and were found evenly distributed within the material. C2C12 cells and ASCs demonstrated the potential to differentiate in all tested lineages under 2D conditions. Under 3D osteogenic conditions for C2C12 cells, only osteocalcin expression (fold induction: 16.3±0.2) and alkaline phosphatase (ALP) activity (p<0.001) were increased compared with the control C2C12 cells. Three-dimensional osteogenic differentiation of ASC was limited and donor dependent. Only one donor showed an increase in the osteogenic markers osteocalcin (p=0.027) and osteopontin (p=0.038). In contrast, differentiation toward the myogenic or adipogenic lineage showed expression of specific markers in 3D, at least at the level of the 2D culture. In 3D culture, strong induction of myogenin (p<0.001) as well as myoD (p<0.001) was found in C2C12 cells. The adipogenic differentiation of one donor showed greater expression of peroxisome proliferative-activated receptor gamma (PPARγ) (p=0.004), fatty acid binding protein 4 (FABP4) (p=0.008), and adiponectin (p=0.045) in 3D compared with 2D culture. Leptin levels in the supernatant of the ASC cultures were elevated in the 3D cultures in both donors at day 14 and 21. In conclusion, the thermoresponsive scaffold was found suitable for 3D in vitro differentiation toward soft tissue.

Hydrogel based injectable scaffolds for cardiac tissue regeneration

Tissue engineering promises to be an effective strategy that can overcome the lacuna existing in the current pharmacological and interventional therapies and heart transplantation. Heart failure continues to be a major contributor to the morbidity and mortality across the globe. This may be attributed to the limited regeneration capacity after the adult cardiomyocytes are terminally differentiated or injured. Various strategies involving acellular scaffolds, stem cells, and combinations of stem cells, scaffolds and growth factors have been investigated for effective cardiac tissue regeneration. Recently, injectable hydrogels have emerged as a potential candidate among various categories of biomaterials for cardiac tissue regeneration due to improved patient compliance and facile administration via minimal invasive mode that treats complex infarction. This review discusses in detail on the advances made in the field of injectable materials for cardiac tissue engineering highlighting their merits over their preformed counterparts.

Control of hyperbranched structure of polycaprolactone/poly(ethylene glycol) polyurethane block copolymers by glycerol and their hydrogels for potential cell delivery

A series of biodegradable amphiphilic polyurethane block copolymers with hyperbranched structure were synthesized by copolymerizing poly(ε-caprolactone) (PCL) and poly(ethylene glycol) (PEG) together with glycerol. The copolymers were characterized, and their composition and branch length were varied with the feeding ratio between PCL, PEG, and glycerol used. Hydrogels were formed from these copolymers by swelling of water at low polymer concentrations. The hydrogels were thixotropic, and their dynamic viscoelastic properties were dependent on the copolymer composition, branch length, and polymer concentration. Hydrolytic degradation of the hydrogels was evaluated by mass loss and changes in molecular structures. The porous morphology of the hydrogels provided good permeability for gas and nutrition. Together with the tunable rheological properties, the hydrogels were found to be suitable for 3D living cell encapsulation and delivery. The morphology of the solid copolymers was semicrystalline, while the hydrogels were totally amorphous without crystallinity, providing a mild aqueous environment for living cells. When the encapsulated cells were recovered from the hydrogels followed by subculture, they showed good cell viability and proliferation ability. The results indicate that the hyperbranched copolymers hydrogels developed in this work may be promising candidates for potential injectable cell delivery application.

Physical properties of poly(N-isopropylacrylamide) hydrogel promote its effects on cardiac protection after myocardial infarction

OBJECTIVE

Studies have demonstrated the protective effects of biomaterials against myocardial infarction (MI), but the relationship between their physical characteristics and their function is incompletely understood. This study investigated such relationships for a hydrogel preparation.

METHODS

Two types of poly(N-isopropylacrylamide) (PNIPAAm) hydrogel with different degradation times (Gel A and Gel B) were synthesized. In vivo hydrogel formation and maintenance were observed and confirmed in mice. The solutions were also injected into the infarct area immediately after MI induction in rats.

RESULTS

PNIPAAm hydrogel exhibited a three-dimensional structure resembling native extracellular matrix (ECM). Compared with phosphate-buffered saline, Gel A and Gel B increased contractility of isolated infarcted myocardium, reduced collagen deposition, increased neovascularization, inhibited left ventricle expansion and improved cardiac function. Myocardial contractility was greater with Gel B than with Gel A.

CONCLUSIONS

Intramyocardial injection of PNIPAAm hydrogel provides structural support and some functional repair of damaged ECM, suggesting that it might be useful for cardiac tissue engineering.

Synthesis and fabrication of a degradable poly(N-isopropyl acrylamide) scaffold for tissue engineering applications

Biodegradable poly(N-isopropyl acrylamide) (polyNIPAM) hydrogels with controlled molecular weight of the parent polymer and its degradation products were synthesized by atom transfer radical polymerization in the presence of a polycaprolactone-based di-chlorinated macroinitiator and polycaprolactone dimethacrylate. The phase transition temperature, swelling, hydrolytic degradability, and mechanical properties at 25 and 37°C were explored. A cytocompatibility study showed good NIH3T3 cell response over 5 days culture on the surface of the hydrogels, demonstrated by a consistent increase in cell proliferation detected by an Alamar Blue assay. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] results suggested that the hydrogels and their degradation products in the concentration range of 1-25 mg/mL were not cytotoxic to NIH3T3 cells. A sphere-templating technique was utilized to fabricate biodegradable polyNIPAM scaffolds with monodisperse, pore size. Scaffolds with pore diameter of 48 ± 6 μm were loaded with A-10 smooth muscle cells and then warmed to 37°C entrapping cells in pores approximately 40 μm in diameter, a size we have found to be optimal for angiogenesis and biointegration. Due to their degradable nature, tunable molecular weight, highly interconnected morphology, thermally controlled monodisperse pore size, and temperature-induced volume expansion-contraction, the polyNIPAM-based scaffolds developed in this work will be valuable in tissue engineering.

Increased infarct wall thickness by a bio-inert material is insufficient to prevent negative left ventricular remodeling after myocardial infarction

BACKGROUND

Several injectable materials have been shown to preserve or improve cardiac function as well as prevent or slow left ventricular (LV) remodeling post-myocardial infarction (MI). However, it is unclear as to whether it is the structural support or the bioactivity of these polymers that lead to beneficial effects. Herein, we examine how passive structural enhancement of the LV wall by an increase in wall thickness affects cardiac function post-MI using a bio-inert, non-degradable synthetic polymer in an effort to better understand the mechanisms by which injectable materials affect LV remodeling.

METHODS AND RESULTS

Poly(ethylene glycol) (PEG) gels of storage modulus G' = 0.5±0.1 kPa were injected and polymerized in situ one week after total occlusion of the left coronary artery in female Sprague Dawley rats. The animals were imaged using magnetic resonance imaging (MRI) at 7±1 day(s) post-MI as a baseline and again post-injection 49±4 days after MI. Infarct wall thickness was statistically increased in PEG gel injected vs. control animals (p<0.01). However, animals in the polymer and control groups showed decreases in cardiac function in terms of end diastolic volume, end systolic volume and ejection fraction compared to baseline (p<0.01). The cellular response to injection was also similar in both groups.

CONCLUSION

The results of this study demonstrate that passive structural reinforcement alone was insufficient to prevent post-MI remodeling, suggesting that bioactivity and/or cell infiltration due to degradation of injectable materials are likely playing a key role in the preservation of cardiac function, thus providing a deeper understanding of the influencing properties of biomaterials necessary to prevent post-MI negative remodeling.