materials Review Bioactivity and Biocompatibility Properties of Sustainable Wollastonite Bioceramics from Rice Husk Ash/Rice Straw Ash: A Review Hamisah Ismail and Hasmaliza Mohamad *   Citation: Ismail, H.; Mohamad, H. Bioactivity and Biocompatibility Properties of Sustainable Wollastonite Bioceramics from Rice Husk Ash/Rice Straw Ash: A Review. Materials 2021, 14, 5193. https:// doi.org/10.3390/ma14185193 Received: 9 June 2021 Accepted: 29 June 2021 Published: 10 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Nibong Tebal 14300, Penang, Malaysia; hamisahismail@usm.my * Correspondence: hasmaliza@usm.my Abstract: Recently, there has been an increase in interest in agricultural waste in scientific, technologi- cal, environmental, economic, and social contexts. The processing of rice husk ash/rice straw ash into biocompatible products—also known as biomaterials—used in biomedical implants is a technique that can enhance the value of agricultural waste. This method has effectively converted unprocessed agricultural waste into high-value products. Rice husk and straw are considered to be unwanted agricultural waste and are largely discarded because they pollute the environment. Because of the related components present in bone and teeth, this waste can produce wollastonite. Wollastonite is an excellent material for bone healing and implants, as well as tissue regeneration. The use of rice husk ash or rice straw ash in wollastonite production reduces the impact of agricultural waste on pollution and prompts the ensuing conversion of waste into a highly beneficial invention. The use of this agricultural waste in the fabrication of wollastonite using rice husk ash or rice straw ash was investigated in this paper. Wollastonite made from rice husk ash and rice straw ash has a fair chance of lowering the cost of bone and tooth repair and replacement, while having no environmental effects. Keywords: bioactivity; biocompatibility; wollastonite; rice husk ash; rice straw ash 1. Introduction Agricultural waste is any waste that was produced in accumulative concentrations because of various farming processes [1]. The effective use of agricultural waste mitigates environmental issues caused by reckless waste disposal. Agricultural waste management is a critical approach to environmental waste management. If some waste is abundant, it can significantly affect the ecosystem for humans, livestock, and plants [2]. The nature, amount, and types of waste produced in agriculture vary across countries. The quest for an efficient way to handle agricultural waste properly would enhance health quality and protect the environment. Waste can be reused, recycled, and guided into the manufacture of value-added goods for sustainable growth. This protects the environment on the one hand, and on the other creates a zero-waste standard to obtain value-added goods. The use of waste today is a priority for the achievement of sustainable development [3]. Rice husk or rice straw was used as a precursor for biomaterial, biomedical implants, and surgery applications, because agricultural waste of this type adds considerable value. Using agricultural waste to create value-added products has added a new dimension to producing biocompatible materials or biomaterials from agricultural waste. This is feasible because some of the waste contains active compounds that are needed for biomedical purposes. This is a modern medical procedure that is expected to be necessary. Most agricultural waste studies have focused primarily on its energy potential or use as func- tional renewable raw materials and an efficient chemical feedstock in producing valuable products, due to its abundance, low cost of availability, and renewability [4–11]. Microor- ganisms or their components carry out this conversion into valuable goods or energy Materials 2021, 14, 5193. https://doi.org/10.3390/ma14185193 https://www.mdpi.com/journal/materials