The demand for new biomaterials in several biomedical applications, such as regenerative engineering and drug delivery, has increased over the past two decades due to emerging technological advances in biomedicine. Degradable polymeric biomaterials continue to play a significant role as scaffolding materials and drug devices. Polyphosphazene platform is a subject of broad interest, as it presents an avenue for attaining versatile polymeric materials with excellent structure and property tunability, and high functional diversity. Macromolecular substitution enables the facile attachment of different organic groups and drug molecules to the polyphosphazene backbone for the development of a broad class of materials. These materials are more biocompatible than traditional biomaterials, mixable with other clinically relevant polymers to obtain new materials and exhibit unique erosion with near-neutral degradation products. Hence, polyphosphazene represents the next generation of biomaterials. In this review, the authors systematically discuss the synthetic design, structure-property relationships, and the promising potentials of polyphosphazenes in regenerative engineering and drug delivery.

In the pursuit of continuous improvement in the area of biomaterial design, blends of mixed-substituent polyphosphazenes and poly(lactic acid−glycolic acid) (PLGA) were prepared, and their morphology of phase distributions for the first time was studied. The degradation mechanism and osteocompatibility of the blends were also evaluated for their use as regenerative materials. Poly-[(ethylphenylalanato) 25 (glycine ethylglycinato) 75 phosphazene] (PNEPAGEG) and poly[(glycine ethylglycinato) 75 (phenylphenoxy) 25 phosphazene] (PNGEGPhPh) were blended with PLGA at various weight ratios to yield different blends, namely

Although numerous conventional organic polymers have been utilized in biomedical applications, a few numbers of them have had expected and desired success for essential medical use such as scaffolding materials for regenerative engineering, controlled drug delivery systems, and surgical sutures (Ogueri, Jafari, Ivirico, & Laurencin, 2019). This is because most organic polymers (with few exceptions) lack the design flexibility and property tunability as materials scientist and engineers often focus on harnessing and optimizing the physicochemical properties of polymers during design, scale-up, and commercialization (Ogueri, Ivirico, Nair, Allcock,

The polyphosphazene backbone provides a versatile platform to explore numerous synthesis and structure-property relationships for many technological applications. In this study, a new class of polyphosphazene semiconducting materials was synthesized via macromolecular substitution, which integrates a P N backbone with thiophene-based side groups. The synthesized thiophene-based polymers were subjected to chemical oxidation (oxidative coupling) to optimize their optoelectronic properties through side-chain chemistry. Both the spectroscopic and electronic analyses revealed that optical and electronic properties, as well as glass transition temperatures could be modulated by chemical oxidation of the polymers. The suitability of the polymers as potential semiconductors was further evaluated using their steady-state fluorescence quenching behavior in the presence of four different dopants (PC70BM, PC60BM, F4TCNQ, and TCNQ). It was found that the addition of dopant as a quencher to the polymer solutions does not form a complex in the ground state, and its excited state shows an efficient decrease in fluorescence intensity without altering the shape and peak position of the fluorescence band. The overall results demonstrate that the utilization of chemical oxidation via side-chain chemistry of polyphosphazenes offers an adaptable toolbox that can be used to make new and potentially useful polymeric semiconductors for applications in organic electronics.

In an effort to understand the biological capability of polyphosphazene-based polymers, three-dimensional biomimetic bone scaffolds were fabricated using the blends of poly­[(glycine ethylglycinato)75(phenylphenoxy)25]­phosphazene (PNGEGPhPh) and poly­(lactic-co-glycolic acid) (PLGA), and an in vivo evaluation was performed in a rabbit critical-sized bone defect model. The matrices constructed from PNGEGPhPh–PLGA blends were surgically implanted into 15 mm critical-sized radial defects of the rabbits as structural templates for bone tissue regeneration. PLGA, which is the most commonly used synthetic bone graft substitute, was used as a control in this study. Radiological and histological analyses demonstrated that PNGEGPhPh–PLGA blends exhibited favorable in vivo biocompatibility and osteoconductivity, as the newly designed matrices allowed new bone formation to occur without adverse immunoreactions. The X-ray images of the blends showed higher levels of radiodensity than that of the pristine PLGA, indicating higher rates of new bone formation and regeneration. Micro-computed tomography quantification revealed that new bone volume fractions were significantly higher for the PNGEGPhPh–PLGA blends than for the PLGA controls after 4 weeks. The new bone volume increased linearly with increasing time points, with the new tissues observed throughout the defect area for the blend and only at the implant site’s extremes for the PLGA control. Histologically, the polyphosphazene system appeared to show tissue responses and bone ingrowths superior to PLGA. By the end of the study, the defects with PNGEGPhPh–PLGA scaffolds exhibited evidence of effective bone tissue ingrowth and minimal inflammatory responses. Thus, polyphosphazene-containing biomaterials have excellent translational potential for use in bone regenerative engineering applications.