Hydrogel tissue expanders for stomatology. Part I. Methacrylate-based polymers

Applications of Hydrogels in Drug Delivery for Oral and Maxillofacial Diseases

Oral and maxillofacial diseases have an important impact on local function, facial appearance, and general health. As a multifunctional platform, hydrogels are widely used in the biomedical field due to their excellent physicochemical properties. In recent years, a large number of studies have been conducted to adapt hydrogels to the complex oral and maxillofacial environment by modulating their pore size, swelling, degradability, stimulus-response properties, etc. Meanwhile, many studies have attempted to use hydrogels as drug delivery carriers to load drugs, cytokines, and stem cells for antibacterial, anticancer, and tissue regeneration applications in oral and maxillofacial regions. This paper reviews the application and research progress of hydrogel-based drug delivery systems in the treatment of oral and maxillofacial diseases such as caries, endodontic diseases, periodontal diseases, maxillofacial bone diseases, mucosal diseases, oral cancer, etc. The characteristics and applications of hydrogels and drug-delivery systems employed for the treatment of different diseases are discussed in order to provide a reference for further research on hydrogel drug-delivery systems in the future.

Self-swelling tissue expander for soft tissue reconstruction in the craniofacial region: An in vitro and in vivo evaluation

BACKGROUND

Craniofacial soft-tissue defects mostly have an impact on the treatment of various oral diseases. Tissue expander is an important technique for tissue reconstruction, especially for soft tissues in reconstructive surgery.

OBJECTIVE

This research aimed to develop a new self-swelling tissue expander, namely hydrogel, for soft tissue reconstruction in craniofacial region.

METHODS

In vitro, the chemical and physical characteristics of hydrogel were evaluated by SEM, swelling rate, mechanical testing, EDS, and FT-IR. In vivo, the craniofacial implant model of SD rats were divided into group A as control, group B with hydrogels for 1 week expansion, group C for 2 weeks and group D for 4 weeks (n = 5), and the effects were analyzed by HE staining, histological and radiographic evaluation.

RESULTS

The in vitro results suggested that dry hydrogel possessed a uniform surface with micropores, the surface of post-swelling hydrogel formed three-dimensional meshwork. Within 24 hours, hydrogels expanded markedly, then slowed down. The mechanical property of hydrogels with longer expansion was better, whose main elements were carbon and oxygen. FT-IR also verified its molecular structure. In vivo, the wounds of rats recovered well, hydrogels could be removed as one whole piece with original shape and examined by radiographic evaluation, besides, the expanded skin and developed fibrous capsule formed surrounding hydrogels.

CONCLUSION

The new expander was designed successfully with good chemical and physical characteristics, and could be applied in an animal model to help tissue reconstruction.

Tissue Expansion Improves the Outcome and Predictability for Alveolar Bone Augmentation: Prospective, Multicenter, Randomized Controlled Trial

Objectives: The purpose of this study was to evaluate the effectiveness of the intraoral use of subperiosteally placed self-inflating tissue expanders for subsequent bone augmentation and implant integrity. Material and methods: A prospective, multicenter, randomized controlled trial was performed on patients requiring alveolar bone graft for dental implant insertion. Patients were assigned to three groups: tissue expansion and tunneling graft (TET group), tissue expansion and conventional bone graft (TEG), and control group without tissue expansion. Dimensional changes of soft tissue and radiographic vertical bone gain, retention, and peri-implant marginal bone changes were evaluated and secondary outcomes; clinical complications and thickness changes of expanded overlying tissue were assessed. Results: Among 75 patients screened, a total of 57 patients were included in the final analysis. Most patients showed uneventful soft tissue expansion without any inflammatory sign or symptoms. Ultrasonographic measurements of overlying gingiva revealed no thinning after tissue expansion (p > 0.05). Mean soft vertical and horizontal tissue measurements at the end of its expansion were 5.62 and 6.03 mm, respectively. Significantly higher vertical bone gain was shown in the TEG (5.71 ± 1.99 mm) compared with that in the control patients (4.32 ± 0.97 mm; p < 0.05). Hard tissue retention— measured by bone resorption after 6 months—showed that control group showed higher amount of vertical (2.06 ± 1.00 mm) and horizontal bone resorption (1.69 ± 0.81 mm) compared to that of the TEG group (p < 0.05). Conclusion: The self-inflating tissue expander effectively augmented soft tissue volume and both conventional bone graft and tunneling techniques confirmed their effectiveness in bone augmentation. With greater amount of bone gain and better 6 month hard tissue integrity, the TEG group compared to the control group—without tissue expansion—showed that the combined modality of tissue expander use and guided bone regeneration (GBR) technique may improve the outcome and predictability of hard tissue augmentation.

Hydrogel Tissue Expanders for Stomatology. Part II. Poly(styrene-maleic anhydride) Hydrogels

Self-inflating soft tissue expanders represent a valuable modality in reconstructive surgery. For this purpose, particularly synthetic hydrogels that increase their volume by swelling in aqueous environment are used. The current challenge in the field is to deliver a material with a suitable protracted swelling response, ideally with an induction period (for sutured wound healing) followed by a linear increase in volume lasting several days for required tissue reconstruction. Here, we report on synthesis, swelling, thermal, mechanical and biological properties of novel hydrogel tissue expanders based on poly(styrene-alt-maleic anhydride) copolymers covalently crosslinked with p-divinylbenzene. The hydrogels exerted hydrolysis-driven swelling response with induction period over the first two days with minimal volume change and gradual volume growth within 30 days in buffered saline solution. Their final swollen volume reached more than 14 times the dry volume with little dependence on the crosslinker content. The mechanical coherence of samples during swelling and in their fully swollen state was excellent, the compression modulus of elasticity being between 750 and 850 kPa. In vitro cell culture experiments and in vivo evaluation in mice models showed excellent biocompatibility and suitable swelling responses meeting thus the application requirements as soft tissue expanders.

Assessment and prevention of cartilage degeneration surrounding a focal chondral defect in the porcine model

Focal defects in articular cartilage are unable to self-repair and, if left untreated, are a leading risk factor for osteoarthritis. This study examined cartilage degeneration surrounding a defect and then assessed whether infilling the defect prevents degeneration. We created a focal chondral defect in porcine osteochondral explants and cultured them ex vivo with and without dynamic compressive loading to decouple the role of loading. When compared to a defect in a porcine knee four weeks post-injury, this model captured loss in sulfated glycosaminoglycans (sGAGs) along the defect's edge that was observed in vivo, but this loss was not load dependent. Loading, however, reduced the indentation modulus of the surrounding cartilage. After infilling with in situ polymerized hydrogels that were soft (100 kPa) or stiff (1 MPa) and which produced swelling pressures of 13 and 310 kPa, respectively, sGAG loss was reduced. This reduction correlated with increased hydrogel stiffness and swelling pressure, but was not affected by loading. This ex vivo model recapitulates sGAG loss surrounding a defect and, when infilled with a mechanically supportive hydrogel, degeneration is minimized.