📚 Experimental Design: Investigating the Composition of the Skeleton | 实验设计：探究骨骼的组成
The human skeleton provides support, protection, and movement. Understanding its composition is key to grasping how bones maintain strength and flexibility. This experimental design guides you through a classic investigation into the roles of two main bone components: organic collagen fibres and inorganic calcium phosphate. By selectively removing each component, we can observe the resulting changes in bone properties.
人体骨骼提供支撑、保护和运动功能。了解其组成是掌握骨骼如何保持强度和柔韧性的关键。本实验设计将引导您进行一项经典研究，探究两种主要骨骼成分的作用：有机胶原纤维和无机磷酸钙。通过依次去除每种成分，我们可以观察骨骼性质的变化。
1. Background: The Dual Nature of Bone | 背景：骨骼的双重属性
Bone is not a uniform, static tissue; it is a composite biomaterial with two main fractions: an organic matrix (primarily type I collagen) and inorganic mineral crystals (mainly hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂). The collagen provides tensile strength and flexibility, while the mineral gives compressive strength and rigidity. Without collagen, bone becomes brittle; without minerals, bone becomes overly flexible.
骨骼并非均一的静态组织，而是一种复合材料，包含两个主要部分：有机基质（主要是I型胶原蛋白）和无机矿物晶体（主要是羟磷灰石，Ca₁₀(PO₄)₆(OH)₂）。胶原蛋白提供抗拉强度和柔韧性，而矿物质赋予抗压强度和刚性。没有胶原蛋白，骨头会变脆；没有矿物质，骨头会过于柔软。
This reciprocal relationship was elegantly demonstrated by early anatomists through simple demineralisation and deproteinisation experiments. Such experiments remain a cornerstone in secondary biology curricula to illustrate structure–function relationships.
这种相互关系被早期解剖学家通过简单的脱矿和脱蛋白实验优雅地展示出来。这些实验至今仍是中学生物课程中说明结构—功能关系的基石。
2. Aims and Hypothesis | 实验目的与假设
The main aim is to determine the individual contributions of the organic and inorganic components to the mechanical properties of bone. A secondary aim is to practice controlled experimental design and safety protocols.
主要目的是确定有机和无机成分对骨骼力学性质的单独作用。次要目的是练习受控实验设计和安全规程。
We hypothesise that: (1) treating bone with a mild acid will remove mineral salts, leaving it flexible and bendable; (2) heating bone will destroy organic matter, leaving it brittle and easily fragmented.
我们假设：（1）用弱酸处理骨头会去除矿物盐，使其变得柔韧可弯曲；（2）加热骨头会破坏有机物质，使其变脆易碎。
3. Materials and Equipment | 材料与设备
Careful selection of materials ensures reproducible results. Below is a list of items required for the investigation.
仔细选择材料可确保结果的可重复性。以下是本次探究所需的物品清单。
| Material | Purpose |
|---|---|
| Fresh chicken leg or wing bones (cleaned, with meat removed) × 4 | Test specimens; use similar size for fair comparison |
| White vinegar (5% acetic acid) or dilute HCl (0.1 M) – approx. 200 mL | To demineralise bones |
| Bunsen burner, tongs, heat-proof mat | To burn off organic matter |
| Beakers (250 mL) × 3, forceps, glass rod | For soaking and handling |
| Digital balance, ruler, camera or notebook | To record mass and dimensions |
| Safety goggles, lab coat, gloves | Personal protective equipment |
Note: Chicken bones are preferred because they are readily available and contain both compact and spongy bone regions. Avoid using cooked bones, as heating has already altered their properties.
注意：优先选用鸡骨头，因为它们容易获得，且含有密质骨和松质骨区域。请勿使用煮熟的骨头，因为加热已改变其性质。
4. Procedure A: Acid Demineralisation | 步骤A：酸脱矿
This procedure removes the inorganic calcium salts while leaving the collagen matrix intact.
该步骤去除无机钙盐，同时保留完整的胶原蛋白基质。
1. Label two beakers as 'Acid-treated' and 'Control (water)'. Place one cleaned bone in the acid-treated beaker and another bone in water. Ensure the bones are fully submerged. Add approximately 100 mL of vinegar to the acid beaker and tap water to the control.
1. 将两个烧杯分别标记为“酸处理”和“对照（水）”。将一根清洗干净的骨头放入酸处理烧杯，另一根放入水中。确保骨头完全浸没。在酸烧杯中加入约100毫升醋，在对照烧杯中加入自来水。
2. Cover the beakers with cling film to prevent evaporation and leave at room temperature for 48–72 hours. Change the vinegar every 24 hours to maintain acid concentration.
2. 用保鲜膜盖住烧杯以防蒸发，在室温下静置48–72小时。每24小时更换一次醋以保持酸浓度。
3. After the incubation period, use forceps to remove the bones. Rinse them gently in water. Record visual changes and test mechanical properties by trying to bend the bone gently. Compare with the control.
3. 浸泡结束后，用镊子取出骨头。在水中轻轻冲洗。记录视觉变化，并通过尝试轻轻弯曲骨头来测试机械性能。与对照骨比较。
Expected result: The acid-treated bone will become highly flexible and may even be tied into a loose knot, whereas the control bone remains rigid.
预期结果：酸处理的骨头会变得非常柔韧，甚至可以打一个松结，而对照骨保持坚硬。
5. Procedure B: Heat Deproteinisation | 步骤B：加热脱蛋白
This step removes organic collagen, leaving behind the brittle mineral framework.
该步骤去除有机胶原蛋白，留下脆性矿物质骨架。
1. Take a third cleaned bone and place it on a heat-proof mat. Using tongs, hold the bone over a Bunsen burner flame or use a kiln/oven at 400°C for 2 hours (if a fume cupboard is available). Heat until all organic material is charred and the bone turns white/ashy.
1. 取第三根清洗干净的骨头，放在防火垫上。用坩埚钳夹住骨头，在本生灯火焰上加热，或在有通风橱的条件下使用400°C烤箱加热2小时。加热至所有有机物炭化，骨头变为白色或灰状。
2. Allow the bone to cool completely on the heat-proof mat. Do not touch with bare hands. Observe its appearance: the shape may be preserved, but the bone will be extremely fragile.
2. 让骨头在防火垫上完全冷却。请勿徒手触摸。观察其外观：形状可能保留，但骨头将极为易碎。
3. Gently press the bone with forceps. It should crumble easily into powder. Compare this brittleness to the flexibility of the acid-treated bone and the normal control.
3. 用镊子轻轻按压骨头。它应易碎成粉末。将此脆性与酸处理骨的柔韧性和正常对照骨进行比较。
6. Quantitative Observations and Data Collection | 定量观察与数据收集
For a more rigorous investigation, record measurements before and after treatments.
为了更严谨的探究，请在处理前后记录测量数据。
2 = slightly flexible, 3 = very flexible/bendable). Take photographs to document changes.
创建一个表格来记录：骨质量（克）、长度（厘米）、中点直径（厘米），以及定性柔韧度评分（例如，1 = 僵硬，2 = 稍柔韧，3 = 非常柔韧/可弯曲）。拍照记录变化。
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