Bringing hydrogel-based craniofacial therapies to the clinic

This review explores the evolution of the use of hydrogels for craniofacial soft tissue engineering, ranging in complexity from acellular injectable fillers to fabricated, cell-laden constructs with complex compositions and architectures. Addressing both in situ and ex vivo approaches, tissue restoration secondary to trauma or tumor resection is discussed. Beginning with relatively simple epithelia of oral mucosa and gingiva, then moving to more functional units like vocal cords or soft tissues with multilayer branched structures, such as salivary glands, various approaches are presented toward the design of function-driven architectures, inspired by native tissue organization. Multiple tissue replacement paradigms are presented here, including the application of hydrogels as structural materials and as delivery platforms for cells and/or therapeutics. A practical hierarchy is proposed for hydrogel systems in craniofacial applications, based on their material and cellular complexity, spatial order, and biological cargo(s). This hierarchy reflects the regulatory complexity dictated by the Food and Drug Administration (FDA) in the United States prior to commercialization of these systems for use in humans. The wide array of available biofabrication methods, ranging from simple syringe extrusion of a biomaterial to light-based spatial patterning for complex architectures, is considered within the history of FDA-approved commercial therapies. Lastly, the review assesses the impact of these regulatory pathways on the translational potential of promising pre-clinical technologies for craniofacial applications. STATEMENT OF SIGNIFICANCE: While many commercially available hydrogel-based products are in use for the craniofacial region, most are simple formulations that either are applied topically or injected into tissue for aesthetic purposes. The academic literature previews many exciting applications that harness the versatility of hydrogels for craniofacial soft tissue engineering. One of the most exciting developments in the field is the emergence of advanced biofabrication methods to design complex hydrogel systems that can promote the functional or structural repair of tissues. To date, no clinically available hydrogel-based therapy takes full advantage of current pre-clinical advances. This review surveys the increasing complexity of the current landscape of available clinical therapies and presents a framework for future expanded use of hydrogels with an eye toward translatability and U.S. regulatory approval for craniofacial applications.

Optimal timing and frequency of bone marrow soup therapy for functional restoration of salivary glands injured by single-dose or fractionated irradiation

Injections of bone marrow (BM) cell extract, known as 'BM soup', were previously reported to mitigate ionizing radiation (IR) injury to salivary glands (SGs). However, the optimal starting time and frequency to maintain BM soup therapeutic efficacy remains unknown. This study tested the optimal starting time and frequency of BM soup injections in mice radiated with either a single dose or a fractionated dose. First, BM soup treatment was started at 1, 3 or 7 weeks post-IR; positive (non-IR) and negative (IR) control mice received injections of saline (vehicle control). Second, BM soup-treated mice received injections at different frequencies (1, 2, 3 and 5 weekly injections). Third, a 'fractionated-dose radiation' model to injure mouse SGs was developed (5 Gy × 5 days) and compared with the single high dose radiation model. All mice (n = 65) were followed for 16 weeks post-IR. The results showed that starting injections of BM soup between 1 and 3 weeks mitigated the effect of IR-induced injury to SGs and improved the restoration of salivary function. Although the therapeutic effect of BM soup lessens after 8 weeks, it can be sustained by increasing the frequency of weekly injections. Moreover, both single-dose and fractionated-dose radiation models are efficient and comparable in inducing SG injury and BM soup treatments are effective in restoring salivary function in both radiation models. In conclusion, starting injections of BM soup within 3 weeks post-radiation, with 5 weekly injections, maintains 90-100% of saliva flow in radiated mice.