Gas Permeability of Mold during Freezing Process Alters the Pore Distribution of Gelatin Sponge and Its Bone-Forming Ability.

Xiaoyu Han,Kazuki Imura,Kazuyo Yamamoto,Tomonari Tanaka,Kazushi Yoshikawa,Yoshiya Hashimoto,Yoshitomo Honda

doi:10.3390/ma13214705

Abstract

Freeze-drying, also known as lyophilization, is widely used in the preparation of porous biomaterials. Nevertheless, limited information is known regarding the effect of gas permeability on molds to obtain porous materials. We demonstrated that the different levels of gas permeability of molds remarkably altered the pore distribution of prepared gelatin sponges and distinct bone formation at critical-sized bone defects of the rat calvaria. Three types of molds were prepared: silicon tube (ST), which has high gas permeability; ST covered with polyvinylidene chloride (PVDC) film, which has low gas permeability, at the lateral side (STPL); and ST covered with PVDC at both the lateral and bottom sides (STPLB). The cross sections or curved surfaces of the sponges were evaluated using scanning electron microscopy and quantitative image analysis. The gelatin sponge prepared using ST mold demonstrated wider pore size and spatial distribution and larger average pore diameter (149.2 µm) compared with that prepared using STPL and STPLB. The sponges using ST demonstrated significantly poor bone formation and bone mineral density after 3 weeks. The results suggest that the gas permeability of molds critically alters the pore size and spatial pore distribution of prepared sponges during the freeze-drying process, which probably causes distinct bone formation.

Highlights

Three-dimensional porous materials have been widely used in various fields, such as regenerative medicine, as scaffolds [1], cell-seeding materials [2,3], or drug carriers [4]
Three different types of molds were used to alter the gas permeability in molds: (1) silicon tube with high permeability (ST); (2) ST covered with polyvinylidene chloride (PVDC), which has less permeability than ST, at the lateral side (STPL); and (3) ST covered with PVDC at the lateral and bottom sides (STPLB)
This study demonstrated that pore size and spatial pore distribution are altered by the gas permeability of molds

Summary

Introduction

Three-dimensional porous materials have been widely used in various fields, such as regenerative medicine, as scaffolds [1], cell-seeding materials [2,3], or drug carriers [4]. Suitable porous structures of such materials contribute to the efficient supply of oxygen and nutrients [5], which significantly influence cell activity, such as vascular and cell ingrowth [6], and cellular differentiation [7,8], resulting in sufficient tissue regeneration [6]. A further detailed examination of the freeze-drying technique may be required to verify its effect on pore distribution in prepared porous materials.

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Conclusion