Clinical Applications of Injectable Biomaterials

Bottlebrush Pastes as a Platform for Solvent-Free, Injectable, and Shape-Persistent Materials with Tissue-Mimetic Viscoelasticity

Architecturally hindered crystallization of bottlebrush graft copolymers offers a reaction- and solvent-free pathway for creating injectable elastomers with tissue-mimetic softness. Currently, injectable materials involve solvents and chemical reactions, leading to uncontrolled swelling, leaching of unreacted moieties, and side reactions with tissue. To address this issue, bottlebrush copolymers with a poly(ethylene glycol) (PEG) amorphous block and crystallizable poly(lactic acid) (PLA) grafted chains (A-g-B) were synthesized, with grafted chains of controlled length arranged along the backbone at controlled spacing. The densely grafted PEG brush is leveraged to architecturally control both the rate and degree of crystallization of PLA grafts, offering tunability of mechanical properties as a function of architecture and time in a single-component solvent-free system covering a broad range of aggregation states comprising fluid-, paste-, and elastomer-like behaviors with modulus ranging from 1 to 50 kPa. The PLA-g-PEG pastes are particularly interesting, as they combine solvent-free injectability and time-controlled formation of shape-persistent elastomers at constant temperature. This molecular paste platform may advance reconstructive surgery, drug depots, and tissue engineering.

Advances in Injectable Polymeric Biomaterials and Their Contemporary Medical Practices

Injectable biomaterials have been engineered to operate within the human body, offering versatile solutions for minimally invasive therapies and meeting several stringent requirements such as biocompatibility, biodegradability, low viscosity for ease of injection, mechanical strength, rapid gelation postinjection, controlled release of therapeutic agents, hydrophobicity/hydrophilicity balance, stability under physiological conditions, and the ability to be sterilized. Their adaptability and performance in diverse clinical settings make them invaluable for modern medical treatments. This article reviews recent advancements in the design, synthesis, and characterization of injectable polymeric biomaterials, providing insights into their emerging applications. We discuss a broad spectrum of these materials, including natural, synthetic, hybrid, and composite types, that are being applied in targeted drug delivery, cell and protein transport, regenerative medicine, tissue adhesives, injectable implants, bioimaging, diagnostics, and 3D bioprinting. Ultimately, the review highlights the critical role of injectable polymeric biomaterials in shaping the future of medical treatments and improving patient outcomes across a wide range of therapeutic and diagnostic applications.

Bioactivity and in vitro immunological studies of xenogeneic decellularized extracellular matrix scaffolds for implantable applications

Decellularized scaffolds retain the main bioactive substances of the extracellular matrix, which can better promote cell proliferation and matrix reconstruction at the defect site, and have great potential for morphological and functional restoration in patients with tissue defects. Due to the safety of the material source of allogeneic decellularized scaffolds, there is a great limitation in their clinical application, so the preparation and evaluation of xenodermal acellular scaffolds have attracted much attention. In terms of skin tissue structure and function, porcine skin has a high degree of similarity to human skin and has the advantages of sufficient quantity and no ethical issues. However, there is a risk of immune rejection after xenodermal acellular scaffold transplantation. To address the above problems, this paper focuses on porcine dermal decellularized scaffolds prepared using two common decellularization preparation methods and compares the decellularization efficiency, retention of active components of the extracellular matrix, structural characterization of the decellularized scaffolds, and the effect of porcine dermal decellularized scaffolds on mouse Raw264.7 macrophages, so as to make a functional evaluation of the active components and immune effects of porcine dermal decellularized scaffolds, and to provide a reference for filling trauma-induced defects in humans.

Injectable and adhesive hydrogels for dealing with wounds

INTRODUCTION

The development of wound dressing materials that combine healing properties, ability to self-repair the material damages, skin-friendly adhesive nature, and competent mechanical properties have surpassing functional importance in healthcare. Due to their specificity, hydrogels have been recognized as a new gateway in biological materials to treat dysfunctional tissues. The design and creation of injectable hydrogel-based scaffolds have extensively progressed in recent years to improve their therapeutic efficacy and to pave the way for their easy minimally invasive administration. Hence, injectable hydrogel biomaterials have been prepared to eventually translate into minimally invasive therapy and pose a lasting effect on regenerative medicine.

AREAS COVERED

This review highlights the recent development of adhesive and injectable hydrogels that have applications in wound healing and wound dressing. Such hydrogel materials are not only expected to improve therapeutic outcomes but also to facilitate the easy surgical process in both wound healing and dressing.

EXPERT OPINION

Wound healing seems to be an appealing approach for treating countless life-threatening disorders. With the average increase of life expectancy in human societies, an increase in demand for injectable skin replacements and drug delivery carriers for chronic wound healing is expected.

Enhanced Neovascularization Using Injectable and rhVEGF-Releasing Cryogel Microparticles

Cryogels are gel networks or scaffolds with a large porous structure; they can be tailored for injectability and for possessing a shape-memory ability. Herein, a growth factor-releasing cryogel microparticle (CMP) system is fabricated, and the therapeutic efficacy of recombinant human vascular endothelial growth factor (rhVEGF)-loaded CMP (V-CMP) for neovascularization is investigated. To prepare the cryogels, both methacrylated chitosan (Chi-MA) and methacrylated chondroitin sulfate (CS-MA) are used, and crosslinking using a radical crosslinking reaction is established. The physical, mechanical, and biological properties of the cryogels are analyzed by varying the amount of CS-MA used. The cryogels are then pulverized, and microsized CMPs are fabricated. CMPs dispersed in saline demonstrate a shear-thinning property, and can thus be extruded through a 23G needle. Additionally, V-CMP exhibit a sustained release profile of rhVEGF and enhance the in vitro proliferation of endothelial cells. Finally, neovascularization and effective tissue necrosis prevention are observed when V-CMPs are injected into a hindlimb ischemia mouse model. Thus, the injectable V-CMP system developed herein demonstrates a high potential utility in various tissue regeneration applications based on cell or growth factor delivery.

Preliminary assessment of an injectable extracellular matrix from decellularized bovine myocardial tissue

The goal of this study was to develop an injectable form of decellularized bovine myocardial tissue matrix which could retain high levels of functional ECM molecules, and could gel at physiological temperature. Dissected ventricular tissue was processed by a detergent-based protocol, lyophilized, enzymatically-digested, and neutralized to form the injectable myocardial matrix (IMM). Histochemical analysis, DNA quantification, and agarose gel electrophoresis demonstrated the efficiency of the applied protocol. Chemical, thermal, morphological, and rheological characterization; protein and sulfated glycosaminoglycan (sGAG) content analysis were performed, in vitro biological properties were evaluated. An in vivo histocompatibility and biodegradability study was performed. Histochemistry revealed complete removal of myocardial cells. DNA content analysis revealed a significant decrease (87%) in the nuclear material, while protein and sGAG contents were highly preserved following decellularization. Soluble IMM was capable of turning into gel form at ∼37 °C, indicating selfassembling property. In vitro findings showed the biomaterial was noncytotoxic, nonhemolytic, and supported the attachment and proliferation of mesenchymal stem cells. In vivo study demonstrated IMM was well-tolerated by rats receiving subcutaneous injection. This work demonstrates that the IMM from decellularized bovine myocardial tissue has the potential for use as a feasible regenerative biomaterial in prospective tissue engineering and regenerative medicine studies.

Magneto-sensitive decellularized bone matrix with or without low frequency-pulsed electromagnetic field exposure for the healing of a critical-size bone defect

Bioactive ECM-based materials mimic the complex composition and structure of natural tissues. Decellularized cancellous bone matrix (DBM) has potential for guiding new bone formation and accelerating the regeneration process. On the other hand, low frequency-pulsed electromagnetic field (LF-PEMF) has been shown to enhance the regeneration capacity of bone defects. The present study sought to explore the feasibility of using DBM and DBM/MNP, and LF-PEMF for treating critical-size bone defects. Firstly, decellularization protocol was optimized to obtain a bioactive DBM, then MNPs were incorporated. Later, the physical, chemical and biological properties of DBM and DBM/MNP were assessed in vitro. MNPs homogeneously distributed into the DBM were not found to be toxic to human osteoblast cultures. Finally, an in vivo study was carried out with DBM and DBM/MNP composites in a bilateral critical-size rat cranial defect model (n = 48) with or without LF-PEMF exposure for 45 and 90 days. The histomorphometric and radiographic evaluations revealed that, while the collagen (positive control) and Sham (negative control) groups showed high incidence of fibrous connective tissue together with low level of osteogenic activity, both the DBM and DBM/MNP-grafted groups significantly promoted new bone tissue formation and angiogenesis, by the appropriate use of LF-PEMF for 90 days.

Extracellular matrix grafts: From preparation to application (Review)

Recently, the increasing emergency of traffic accidents and the unsatisfactory outcome of surgical intervention are driving research to seek a novel technology to repair traumatic soft tissue injury. From this perspective, decellularized matrix grafts (ECM-G) including natural ECM materials, and their prepared hydrogels and bioscaffolds, have emerged as possible alternatives for tissue engineering and regenerative medicine. Over the past decades, several physical and chemical decellularization methods have been used extensively to deal with different tissues/organs in an attempt to carefully remove cellular antigens while maintaining the non-immunogenic ECM components. It is anticipated that when the decellularized biomaterials are seeded with cells in vitro or incorporated into irregularly shaped defects in vivo, they can provide the appropriate biomechanical and biochemical conditions for directing cell behavior and tissue remodeling. The aim of this review is to first summarize the characteristics of ECM-G and describe their major decellularization methods from different sources, followed by analysis of how the bioactive factors and undesired residual cellular compositions influence the biologic function and host tissue response following implantation. Lastly, we also provide an overview of the in vivoapplication of ECM-G in facilitating tissue repair and remodeling.

Advances in biomaterials for adipose tissue reconstruction in plastic surgery

Adipose tissue reconstruction is an important technique for soft tissue defects caused by facial plastic surgery and trauma. Adipose tissue reconstruction can be repaired by fat transplantation and biomaterial filling, but there are some problems in fat transplantation, such as second operation and limited resources. The application of advanced artificial biomaterials is a promising strategy. In this paper, injectable biomaterials and three-dimensional (3D) tissue-engineered scaffold materials for adipose tissue reconstruction in plastic surgery are reviewed. Injectable biomaterials include natural biomaterials and artificial biomaterials, which generally have problems such as high absorptivity of fillers, repeated injection, and rejection. In recent years, the technology of new 3D tissue-engineering scaffold materials with adipose-derived stem cells (ADSCs) and porous scaffold as the core has made good progress in fat reconstruction, which is expected to solve the current problem of clinical adipose tissue reconstruction, and various biomaterials preparation technology and transformation research also provide the basis for clinical transformation of fat tissue reconstruction.

Filling the Gap: A Correlation between Objective and Subjective Measures of Injectability

Various injectable biomaterials are developed for the minimally invasive delivery of therapeutics. Typically, a mechanical tester is used to ascertain the force required to inject these biomaterials through a given syringe-needle system. However, currently there is no method to correlate the force measured in the laboratory to the perceived effort required to perform that injection by the end user. In this article, the injection force (F) for a variety of biomaterials, displaying a range of rheological properties, is compared with the effort scores from a 50 person panel study. The maximum injection force measured at crosshead speed 1 mm s^-1 is a good proxy for injection effort, with an R² of 0.89. This correlation leads to the following conclusions: participants can easily inject 5 mL of substance for F < 12 N; considerable effort is required to inject 5 mL for 12 N < F < 38 N; great effort is required and <5 mL can be injected for 38 N < F < 64 N; and materials are entirely non-injectable for F > 64 N. These values may be used by developers of injectable biomaterials to make decisions about formulations and needle sizes early in the translational process.

Macroporous elastic cryogels based on platelet lysate and oxidized dextran as tissue engineering scaffold: In vitro and in vivo evaluations

In this study, three-dimensional macroporous cryogels were developed from platelet lysate (PL) and different concentrations of oxidized dextran (OD; 0.5, 1, 2, 4%). Subsequently, PL/OD scaffolds were characterized for potential use in tissue engineering applications. The pore size and morphology of the resulting cryogels were visualized using scanning electron microscopy (SEM). The pore size distributions were determined using mercury intrusion porosimetry (MIP). In vitro hydrolytic degradation, water uptake, mechanical properties and hemocompatibility were investigated. Extraction test was carried out to evaluate potential in vitro toxic effects of the PL/OD. The in vitro adhesion, proliferation, chondrogenic differentiation, and extracellular matrix production of human adipose stem cells (hASCs) on PL/OD cryogels were evaluated. In vivo biodegradation of the cryogels was investigated at the subcutaneous dorsal site of rats. SEM and MIP results indicated that PL/OD had a macroporous pore structure with pore sizes ranging between 10 and 200 μm. The cryogels completely degraded within 90-240 days post-implantation, depending on OD concentration. Histochemical analysis revealed high levels of cell and tissue infiltration into the pores of PL/OD. In vitro cytotoxicity findings indicated that the extracts of PL/OD_0.5, PL/OD₁ and PL/OD₂ showed no cytotoxic effect, whereas that of PL/OD₄ exhibited a moderate cytotoxic effect on cell cultures. hASCs seeded on PL/OD₂ retained their viability and showed extensive spreading and filopodia formation after 7 days. PL/OD₂ also supported the chondrogenesis of hASCs in the presence of chondro-inductive factors. Given all the results, PL/OD could have potential as a scaffold for tissue engineering applications.

3D Bioprinting of Tissue Models with Customized Bioinks

The ordered assembly of multicellular structures mimicking native tissues has lately come into prominence for various applications of biomedicine. In this respect, three-dimensional bioprinting (3DP) of cells and other biologics through additive manufacturing techniques has brought the possibility to develop functional in vitro tissue models and perhaps creating de novo transplantable tissues or organs in time. Bioinks, which can be defined as the printable analogues of the extracellular matrix, represent the foremost component of 3DP. In this chapter, we attempt to elaborate the major classes of bioinks which are prevalently being evaluated for the 3DP of a wide range of tissue models.