Polymeric biomaterials for regeneration applications

Abstract

One of the biggest threats to human health is the loss of tissues and organs. Every year, injuries and trauma result in the suffering and deaths of millions of people. According to the WHO, injuries and trauma claim the lives of 4.4 million people globally each year, accounting for nearly 8% of all deaths. In the process of researching ways to repair injured tissues, scientists have come up with the innovative concept of tissue regeneration, which integrates the principles from biology, engineering, medicine, and materials science to develop in vitro substitutes that can be implanted into the body to restore or enhance biological function. Successful tissue regeneration is hindered by bacterial infections, biofilm formation, and excessive bleeding. Also, conventional methods used for tissue regeneration, such as allografts and autografts, suffer from limitations like donor tissue scarcity, morbidity, immune rejection, and disease transmission risks that pose major public health concerns. Despite advancements, challenges persist in tissue regeneration, which has prompted researchers to explore alternative approaches, and biomaterials have been used to restore damaged tissues. Biomaterials are synthetic or natural materials designed for biomedical applications and exhibit safe interaction with tissue, blood, and biological fluids, without harming the organism. Out of different biomaterials, polymeric biomaterials, such as hydrogels/gels and polymer-coated nanoparticles because of their unique properties and abilities, such as tunability, biocompatibility, degradability, and extracellular matrix (ECM)-mimicking properties, offer tailored solutions to tissue regeneration applications. Wound healing is a complex process, with chronic wounds affecting millions of people globally. Bacterial infection, excessive bleeding, and biofilm formation prolong the inflammatory phase of wound healing and contribute to the delayed healing with increased mortality rates. Bacterial skin infections impact around 150 million people globally, with antibiotic resistance contributing to 700,000 deaths annually. Additionally, blood loss from traumatic injuries accounts for over 30% of trauma-related deaths worldwide, further increasing the risk of infection and mortality. The current treatment approaches lack sufficient efficacy and inclusion of antibiotics elevates the risk of antibiotic resistance. To address these challenges, multifunctional wound dressings with antibacterial, antibiofilm, and rapid hemostatic properties are needed. Also, bone tissue regeneration is the process of restoration of lost or damaged bone caused by infection, surgery, or trauma through natural or engineered means. The Global Burden of Disease (GBD) study done in 2019 reported 178 million new bone fracture cases worldwide. Osteoporosis, which weakens bones by reducing bone mass, contributes to over 8.9 million fractures annually. Autografts and allografts continue to be the most popular therapy options for the treatment of bone defects, with over 2.2 million procedures performed worldwide annually. However, graft rejection, post-operative problems, and other constraints make these approaches less effective clinically. Thus, there is a need for alternative therapeutic interventions to address the unmet challenges in bone regeneration. This thesis deals with the development and evaluation of polymeric biomaterials for tissue regeneration, in particular, for wound healing and bone regeneration, and is structured into 5 chapters. Chapter 1: This chapter provides an overview of tissue regeneration, with a focus on wound healing and bone regeneration. It discusses the role of polymeric biomaterials in these applications, highlighting the challenges associated with their use in tissue regeneration. A thorough literature review identifies existing knowledge gaps, leading to the formulation of research hypotheses and the objectives of this thesis. The chapter also outlines the organization of the thesis, detailing its structure and the progression of research topics. Chapter 2: Impaired wound healing poses significant health concerns and also contributes to medical and financial burdens. Currently, available wound dressings, including creams, ointments, and gels suffer from limitations, such as narrow-spectrum activity, cytotoxicity, and ineffectiveness against biofilms. Addressing the limitations of current wound dressings, which often rely on antibiotics and thus, pose an increased risk of antimicrobial resistance, this chapter deals with the development of β-Ga2O3 nanoparticles loaded within an imine crosslinked hydrogel of quaternized chitosan and oxidized sodium alginate. This polymeric hydrogel targets iron-dependent pathways crucial for bacterial growth and biofilm formation. The hydrogels exhibited multifaceted functionality, including broad-spectrum antibacterial properties, antioxidant potential, and antibiofilm activities. Moreover, hydrogels exhibited favorable interactions with platelets by promoting adhesion and thrombus formation, thereby positioning them as a preferred therapeutic option for efficient tissue regeneration in bacteria-infected wounds. Chapter 3: Harnessing the immunomodulatory properties of biomaterials represents a promising strategy for modulating macrophage polarization and creating a conducive environment for bone regeneration. This chapter reports the fabrication and evaluation of cobalt-doped biphasic calcium phosphate nanoparticles coated with acemannan for efficient bone regeneration. The immunomodulatory potential of acemannan and low doses of cobalt along with the osteogenic properties of biphasic calcium phosphate offer a promising solution for bone regeneration. The nanoparticles were cytocompatible and showed enhanced cell proliferation along with osteogenic differentiation as suggested by an increased ALP production and calcium deposition. They reduced the expression of M1 markers with enhanced expression of M2 markers as observed by RT-qPCR, ICC, and flow cytometry studies. The results suggest a strong potential of nanoparticles in modulating immune response and, thereby, facilitating efficient bone regeneration. Chapter 4: Bone regeneration in osteoporotic conditions has emerged as a major public health concern, particularly in elderly patients and postmenopausal women. There is a need of innovative therapeutic interventions for effective bone regeneration in osteoporotic conditions. To address this challenge, this chapter deals with the development of a phytoestrogen, genistein- loaded polymeric gel fabricated using ᴋ-carrageenan/quaternized dextran to target estrogen loss and enhanced reactive oxygen for bone regeneration in osteoporotic conditions. The presence of genistein endow the gel with excellent antioxidant properties and enhanced mineralization. Also, an upregulation of the expression of osteogenic markers, ALP, OCN, OPN, and RUNX 2 and downregulation in TRAP, an osteoclast differentiation marker, was observed after treatment with the gel. These findings provide evidence of the effectiveness of fabricated gel in suppressing osteoclast differentiation, while concurrently promoting osteoblast differentiation for accelerating bone regeneration in osteoporotic conditions. Chapter 5: This chapter provides the conclusions of the thesis, highlights the contributions made to the field of tissue regeneration, and discusses the future perspective of the thesis. The thesis presents significant research outcomes in the field of tissue regeneration, particularly in wound healing and bone regeneration. In bacteria-infected wounds, the imine crosslinked hydrogel loaded with β-Ga₂O₃ nanoparticles demonstrated not only broad-spectrum antibacterial and antibiofilm properties but also promoted platelet adhesion and showed strong hemostatic abilities, highlighting its potential for clinical applications. In bone regeneration, cobalt-doped biphasic calcium phosphate nanoparticles coated with acemannan effectively modulated macrophage polarization along with osteogenesis, fostering an immune environment conducive to healing. Additionally, the genistein-loaded polymeric gel effectively addressed the challenges of osteoporotic bone regeneration by exhibiting excellent ROS scavenging capabilities, suppressing osteoclast activity, and promoting osteoblast differentiation. To summarize, this thesis deals with the development of innovative multifunctional polymeric biomaterials that tackle key challenges in wound healing and bone regeneration through integrated antibacterial, immunomodulatory, and osteogenic properties. This thesis addresses critical challenges such as bacterial infections in wounds and impaired bone healing in osteoporotic conditions by developing innovative biomaterial-based solutions. These findings offer practical advancements for treating difficult clinical conditions while also contributing to the broader field of regenerative medicine. Future research should build on these insights by focusing on the development of multifunctional, smart biomaterials that not only target specific physiological challenges but also respond to environmental triggers such as pH, reactive oxygen species, or infections for controlled therapeutic release. Additionally, integrating bioactive molecules, or growth factors into these systems holds promise for enhancing tissue regeneration and immunomodulation. The incorporation of these strategies with advanced technologies like 3D bioprinting could further enable patient-specific treatments, pushing the boundaries of personalized and regenerative medicine.