Computational sensitivity investigation of hydrogel injection characteristics for myocardial support

Injectable Hydrogels: A Paradigm Tailored with Design, Characterization, and Multifaceted Approaches

Biomaterials denoting self-healing and versatile structural integrity are highly curious in the biomedicine segment. The injectable and/or printable 3D printing technology is explored in a few decades back, which can alter their dimensions temporarily under shear stress, showing potential healing/recovery tendency with patient-specific intervention toward the development of personalized medicine. Thus, self-healing injectable hydrogels (IHs) are stunning toward developing a paradigm for tissue regeneration. This review comprises the designing of IHs, rheological characterization and stability, several benchmark consequences for self-healing IHs, their translation into tissue regeneration of specific types, applications of IHs in biomedical such as anticancer and immunomodulation, wound healing and tissue/bone regeneration, antimicrobial potentials, drugs, gene and vaccine delivery, ocular delivery, 3D printing, cosmeceuticals, and photothermal therapy as well as in other allied avenues like agriculture, aerospace, electronic/electrical industries, coating approaches, patents associated with therapeutic/nontherapeutic avenues, and numerous futuristic challenges and solutions.

In silico Mechanics of Stem Cells Intramyocardially Transplanted with a Biomaterial Injectate for Treatment of Myocardial Infarction

PURPOSE

Biomaterial and stem cell delivery are promising approaches to treating myocardial infarction. However, the mechanical and biochemical mechanisms underlying the therapeutic benefits require further clarification. This study aimed to assess the deformation of stem cells injected with the biomaterial into the infarcted heart.

METHODS

A microstructural finite element model of a mid-wall infarcted myocardial region was developed from ex vivo microcomputed tomography data of a rat heart with left ventricular infarct and intramyocardial biomaterial injectate. Nine cells were numerically seeded in the injectate of the microstructural model. The microstructural and a previously developed biventricular finite element model of the same rat heart were used to quantify the deformation of the cells during a cardiac cycle for a biomaterial elastic modulus (Einj) ranging between 4.1 and 405,900 kPa.

RESULTS

The transplanted cells' deformation was largest for Einj = 7.4 kPa, matching that of the cells, and decreased for an increase and decrease in Einj. The cell deformation was more sensitive to Einj changes for softer (Einj ≤ 738 kPa) than stiffer biomaterials.

CONCLUSIONS

Combining the microstructural and biventricular finite element models enables quantifying micromechanics of transplanted cells in the heart. The approach offers a broader scope for in silico investigations of biomaterial and cell therapies for myocardial infarction and other cardiac pathologies.

Research progress on hydrogel-based drug therapy in melanoma immunotherapy

Melanoma is one of the most aggressive skin tumors, and conventional treatment modalities are not effective in treating advanced melanoma. Although immunotherapy is an effective treatment for melanoma, it has disadvantages, such as a poor response rate and serious systemic immune-related toxic side effects. The main solution to this problem is the use of biological materials such as hydrogels to reduce these side effects and amplify the immune killing effect against tumor cells. Hydrogels have great advantages as local slow-release drug carriers, including the ability to deliver antitumor drugs directly to the tumor site, enhance the local drug concentration in tumor tissue, reduce systemic drug distribution and exhibit good degradability. Despite these advantages, there has been limited research on the application of hydrogels in melanoma treatment. Therefore, this article provides a comprehensive review of the potential application of hydrogels in melanoma immunotherapy. Hydrogels can serve as carriers for sustained drug delivery, enabling the targeted and localized delivery of drugs with minimal systemic side effects. This approach has the potential to improve the efficacy of immunotherapy for melanoma. Thus, the use of hydrogels as drug delivery vehicles for melanoma immunotherapy has great potential and warrants further exploration. [BMB Reports 2024; 57(2): 71-78].

Control of the post-infarct immune microenvironment through biotherapeutic and biomaterial-based approaches

Ischemic heart failure (IHF) is a leading cause of morbidity and mortality worldwide, for which heart transplantation remains the only definitive treatment. IHF manifests from myocardial infarction (MI) that initiates tissue remodeling processes, mediated by mechanical changes in the tissue (loss of contractility, softening of the myocardium) that are interdependent with cellular mechanisms (cardiomyocyte death, inflammatory response). The early remodeling phase is characterized by robust inflammation that is necessary for tissue debridement and the initiation of repair processes. While later transition toward an immunoregenerative function is desirable, functional reorientation from an inflammatory to reparatory environment is often lacking, trapping the heart in a chronically inflamed state that perpetuates cardiomyocyte death, ventricular dilatation, excess fibrosis, and progressive IHF. Therapies can redirect the immune microenvironment, including biotherapeutic and biomaterial-based approaches. In this review, we outline these existing approaches, with a particular focus on the immunomodulatory effects of therapeutics (small molecule drugs, biomolecules, and cell or cell-derived products). Cardioprotective strategies, often focusing on immunosuppression, have shown promise in pre-clinical and clinical trials. However, immunoregenerative therapies are emerging that often benefit from exacerbating early inflammation. Biomaterials can be used to enhance these therapies as a result of their intrinsic immunomodulatory properties, parallel mechanisms of action (e.g., mechanical restraint), or by enabling cell or tissue-targeted delivery. We further discuss translatability and the continued progress of technologies and procedures that contribute to the bench-to-bedside development of these critically needed treatments.

Effect of biomaterial stiffness on cardiac mechanics in a biventricular infarcted rat heart model with microstructural representation of in situ intramyocardial injectate

Intramyocardial delivery of biomaterials is a promising concept for treating myocardial infarction. The delivered biomaterial provides mechanical support and attenuates wall thinning and elevated wall stress in the infarct region. This study aimed at developing a biventricular finite element model of an infarcted rat heart with a microstructural representation of an in situ biomaterial injectate, and a parametric investigation of the effect of the injectate stiffness on the cardiac mechanics. A three-dimensional subject-specific biventricular finite element model of a rat heart with left ventricular infarct and microstructurally dispersed biomaterial delivered 1 week after infarct induction was developed from ex vivo microcomputed tomography data. The volumetric mesh density varied between 303 mm-3 in the myocardium and 3852 mm-3 in the injectate region due to the microstructural intramyocardial dispersion. Parametric simulations were conducted with the injectate's elastic modulus varying from 4.1 to 405,900 kPa, and myocardial and injectate strains were recorded. With increasing injectate stiffness, the end-diastolic median myocardial fibre and cross-fibre strain decreased in magnitude from 3.6% to 1.1% and from -6.0% to -2.9%, respectively. At end-systole, the myocardial fibre and cross-fibre strain decreased in magnitude from -20.4% to -11.8% and from 6.5% to 4.6%, respectively. In the injectate, the maximum and minimum principal strains decreased in magnitude from 5.4% to 0.001% and from -5.4% to -0.001%, respectively, at end-diastole and from 38.5% to 0.06% and from -39.0% to -0.06%, respectively, at end-systole. With the microstructural injectate geometry, the developed subject-specific cardiac finite element model offers potential for extension to cellular injectates and in silico studies of mechanotransduction and therapeutic signalling in the infarcted heart with an infarct animal model extensively used in preclinical research.

Self-Healing Injectable Hydrogels for Tissue Regeneration

Biomaterials with the ability to self-heal and recover their structural integrity offer many advantages for applications in biomedicine. The past decade has witnessed the rapid emergence of a new class of self-healing biomaterials commonly termed injectable, or printable in the context of 3D printing. These self-healing injectable biomaterials, mostly hydrogels and other soft condensed matter based on reversible chemistry, are able to temporarily fluidize under shear stress and subsequently recover their original mechanical properties. Self-healing injectable hydrogels offer distinct advantages compared to traditional biomaterials. Most notably, they can be administered in a locally targeted and minimally invasive manner through a narrow syringe without the need for invasive surgery. Their moldability allows for a patient-specific intervention and shows great prospects for personalized medicine. Injected hydrogels can facilitate tissue regeneration in multiple ways owing to their viscoelastic and diffusive nature, ranging from simple mechanical support, spatiotemporally controlled delivery of cells or therapeutics, to local recruitment and modulation of host cells to promote tissue regeneration. Consequently, self-healing injectable hydrogels have been at the forefront of many cutting-edge tissue regeneration strategies. This study provides a critical review of the current state of self-healing injectable hydrogels for tissue regeneration. As key challenges toward further maturation of this exciting research field, we identify (i) the trade-off between the self-healing and injectability of hydrogels vs their physical stability, (ii) the lack of consensus on rheological characterization and quantitative benchmarks for self-healing injectable hydrogels, particularly regarding the capillary flow in syringes, and (iii) practical limitations regarding translation toward therapeutically effective formulations for regeneration of specific tissues. Hence, here we (i) review chemical and physical design strategies for self-healing injectable hydrogels, (ii) provide a practical guide for their rheological analysis, and (iii) showcase their applicability for regeneration of various tissues and 3D printing of complex tissues and organoids.

Multiscale simulations of left ventricular growth and remodeling

Cardiomyocytes can adapt their size, shape, and orientation in response to altered biomechanical or biochemical stimuli. The process by which the heart undergoes structural changes-affecting both geometry and material properties-in response to altered ventricular loading, altered hormonal levels, or mutant sarcomeric proteins is broadly known as cardiac growth and remodeling (G&R). Although it is likely that cardiac G&R initially occurs as an adaptive response of the heart to the underlying stimuli, prolonged pathological changes can lead to increased risk of atrial fibrillation, heart failure, and sudden death. During the past few decades, computational models have been extensively used to investigate the mechanisms of cardiac G&R, as a complement to experimental measurements. These models have provided an opportunity to quantitatively study the relationships between the underlying stimuli (primarily mechanical) and the adverse outcomes of cardiac G&R, i.e., alterations in ventricular size and function. State-of-the-art computational models have shown promise in predicting the progression of cardiac G&R. However, there are still limitations that need to be addressed in future works to advance the field. In this review, we first outline the current state of computational models of cardiac growth and myofiber remodeling. Then, we discuss the potential limitations of current models of cardiac G&R that need to be addressed before they can be utilized in clinical care. Finally, we briefly discuss the next feasible steps and future directions that could advance the field of cardiac G&R.

Biologics and their delivery systems: Trends in myocardial infarction

Cardiovascular disease is the leading cause of death around the world, in which myocardial infarction (MI) is a precipitating event. However, current therapies do not adequately address the multiple dysregulated systems following MI. Consequently, recent studies have developed novel biologic delivery systems to more effectively address these maladies. This review utilizes a scientometric summary of the recent literature to identify trends among biologic delivery systems designed to treat MI. Emphasis is placed on sustained or targeted release of biologics (e.g. growth factors, nucleic acids, stem cells, chemokines) from common delivery systems (e.g. microparticles, nanocarriers, injectable hydrogels, implantable patches). We also evaluate biologic delivery system trends in the entire regenerative medicine field to identify emerging approaches that may translate to the treatment of MI. Future developments include immune system targeting through soluble factor or chemokine delivery, and the development of advanced delivery systems that facilitate the synergistic delivery of biologics.

How hydrogel inclusions modulate the local mechanical response in early and fully formed post-infarcted myocardium

Expansion of myocardium after myocardial infarction (MI) has long been identified as the primary mechanism that drives adverse left ventricular (LV) remodeling towards heart failure and death. Direct injection of hydrogels into the myocardium to mechanically constrain the infarct has demonstrated promise in limiting its remodeling and expansion. Despite early successes, there remain open questions in the determination of optimal hydrogel therapies, key application characteristics for which include injected polymer volume, stiffness, and spatial placement. Addressing these questions is complicated by the substantial variations in infarct type and extent, as well as limited understanding of the underlying mechanisms. Herein, we present an investigation on how hydrogel inclusions affect the effective tissue-level stiffness and strain fields in myocardium using full three-dimensional (3D) finite element simulations at early and late post-MI time points. We calibrated our simulations to triaxial mechanical and structural measurements of cuboidal LV myocardial specimens of post-infarcted myocardium, 0 and 4 weeks post-MI, injected with a dual-crosslinking hyaluronic acid-based hydrogel. Simulations included multiple deformation modes that spanned the anticipated physiological range in order to assess the effects of variations in inclusion size, location, and modulus on tissue-level myocardial mechanics. We observed significant local stiffening in the hydrogel-injected specimens that was highly dependent on the volume and mechanical properties of the injected hydrogel. Simulations revealed that the primary effect of the injections under physiological loading was a reduction in myocardial strain. This result suggests that hydrogel injections reduce infarct expansion by limiting the peak strains over the cardiac cycle. Overall, our study indicated that modulation of local effective tissue stiffness and corresponding strain reduction are governed by the volume and stiffness of the hydrogel, but relatively insensitive to its transmural placement. These findings provide important insights into mechanisms for ameliorating post-MI remodeling, as well as guidance for the future design of post-MI therapies.

Microneedle-mediated gene delivery for the treatment of ischemic myocardial disease

Cardiovascular disorders are still the primary cause of mortality worldwide. Although intramyocardial injection can effectively deliver agents to the myocardium, this approach is limited because of its restriction to needle-mediated injection and the minor retention of agents in the myocardium. Here, we engineered phase-transition microneedles (MNs) coated with adeno-associated virus (AAV) and achieved homogeneous distribution of AAV delivery. Bioluminescence imaging revealed the successful delivery and transfection of AAV-luciferase. AAV-green fluorescent protein-transfected cardiomyocytes were homogeneously distributed on postoperative day 28. AAV-vascular endothelial growth factor (VEGF)-loaded MNs improved heart function by enhancing VEGF expression, promoting functional angiogenesis, and activating the Akt signaling pathway. The results indicated the superiority of MNs over direct muscle injection. Consequently, MNs might emerge as a promising tool with great versatility for delivering various agents to treat ischemic myocardial disease.

Injectable Shear-Thinning Hydrogels Prevent Ischemic Mitral Regurgitation and Normalize Ventricular Flow Dynamics

Injectable hydrogels are known to attenuate left-ventricular (LV) remodeling following myocardial infarction (MI), dependent on material mechanical properties. The effect of hydrogel injection on ischemic mitral regurgitation (IMR) resultant from LV remodeling remains relatively unexplored. This study uses multiple imaging methods to evaluate the efficacy of injectable hydrogels with tunable modulus to prevent post-MI development of IMR. Posterolateral MI was induced in 20 sheep with subsequent epicardial injection of saline (control (MI); n = 7), soft hydrogel (guest-host crosslinking, modulus <1 kPa, n = 7), or stiff hydrogel (dual-crosslinking, modulus = 41.4 ± 4.3 kPa, n = 6) within the infarct region and 8-week follow-up. IMR and valve geometry were assessed by echocardiography. LV geometry (long-axis dimension, posterior chordae length) and ventricular flow dynamics were assessed by magnetic resonance imaging. IMR developed in MI controls at 8 weeks and was attenuated with hydrogel treatment (IMR grade for MI: 1.86 ± 0.69; guest-host crosslinking: 1.29 ± 1.11; dual-crosslinking: 0.50 ± 0.55, P = 0.02 vs MI). Tethering of the posterior leaflet increased in MI controls, but not with stiff hydrogel treatment. Across cohorts, IMR was correlated with changes in the long-axis dimension (Spearman R = 0.77) and posterior chordae length (Spearman R = 0.64). Intraventricular flow dynamics were highly disturbed in MI controls, but stiff hydrogel treatment normalized flow patterns and reduced the prevalence of large (≥2+ MR, >5 mL) regurgitant volumes. Injectable hydrogels attenuated subvalvular remodeling and leaflet tethering, preventing IMR development and normalizing LV flow dynamics. Hydrogels with a supraphysiological modulus yielded best outcomes.

Injectable and protease-degradable hydrogel for siRNA sequestration and triggered delivery to the heart

Injectable hydrogels have significant therapeutic potential for treatment of myocardial infarction (MI) through tissue bulking and local drug delivery, including the delivery of small interfering RNAs (siRNAs). As siRNA targets are identified as potential treatments for MI, hydrogels may bolster efficacy through local and sustained release. Here, we designed an injectable hydrogel to respond to local upregulation in proteolytic activity after MI to erode and release siRNA against MMP2 (siMMP2), a target implicated in deleterious remodeling. Specifically, hyaluronic acid (HA) was modified with hydrazides or aldehydes and mixed to form shear-thinning and self-healing hydrogels through dynamic hydrazone bonds and with peptide crosslinkers that degrade in response to protease activity. HA was further modified with β-cyclodextrin to sequester cholesterol-modified siRNA, limiting passive diffusion. Hydrogels eroded in response to proteases and released active siRNA that knocked down MMP2 in primary cardiac fibroblasts. In a rat model of MI, hydrogels delivering siMMP2 attenuated hydrogel erosion by ~46% at 4 weeks when compared to hydrogels delivering control siRNA, ultimately improving myocardial thickness in the infarct. Delivery of the siMMP2 hydrogel led to significant functional improvements, including increased ejection fraction (27%, 66%), stroke volume (32%, 120%), and cardiac output (20%, 128%) when compared to controls (% increase versus hydrogels with control siRNA, % increase versus saline injection alone). This report demonstrates the utility of biomaterial-based RNA delivery systems for cardiac applications.